Tech & Links

Valve Train Geometry

Here are some useful technical articles and FAQ’s from some of our suppliers.

As cam profiles continue to get more aggressive and valve springs pressure increase, the importance of pushrod knowledge has never been more critical. Here are some answers to the most common questions that you might have for COMP Cams® tech support about pushrods.

Pushrod Length & Rocker Arm Geometry

A large number of variables are involved in determining the correct length pushrod for your application. Pushrod length is affected by any of the following:

• Block deck height
• Head deck height
• Head stud boss height
• Rocker arm brand/design
• Cam base circle size
• Lifter design/brand/pushrod seat height
• Valve stem length

Don’t assume anything when determining the right pushrod for your new engine. A pushrod that fits one engine may not necessarily work in another. Any number of items can be different on your engine, requiring you to use a different pushrod length. Following the steps below will streamline the pushrod selection process, ensuring that you get the right parts the first time.

1. Buy a checking pushrod.
Do not buy pushrods when you buy the cam, lifters and other valve train components. As much as we would like to sell you pushrods at this time, nobody can predict ahead of time what length a given engine needs, unless it is bone stock.

Instead, invest in a checking pushrod at this time. They are available in two different designs, with the more expensive of the two being easier to measure once you have it adjusted to the proper length for your valve train. Neither is particularly expensive if you consider time lost and freight costs when returning pushrods.

Other companies offer their own versions of pushrod length checking devices, funny little plastic things with complicated instructions to calculate the length. The main disadvantage with these is that you have to order the pushrods and receive them before you know if your calculations are correct. With a checking pushrod, you can actually rotate the motor over and check the rocker arm/valve tip relationship as you adjust the pushrod length. When you get the correct geometry, it is a simple matter then to measure the length and place an order. COMP Cams® carries a large number of various length and diameter pushrods so you get the correct length the first time.

2. Determine correct valve train geometry.
What is the correct length pushrod for your application? The one that produces correct valve train geometry. What is correct valve train geometry? When the rocker arm roller tip rolls from the intake side of the valve tip, across the center of the tip (at approximately mid-lift), to the exhaust side of the valve tip (at full lift) and back. See Diagram A.

3. Measure the resulting pushrod.
Measuring the length of a pushrod is a simple process. The most important thing to remember is that different manufacturers measure pushrods differently. Not all pushrods of a stated length will measure exactly the same. The three most common pushrod measurements are shown in Diagram B.

Theoretical Length: This assumes that the pushrod has no oil hole in the end of it. Therefore, the radius at either end is complete, which lengthens the pushrod approximately .017″ in the case of a 5/16″ pushrod with .100″ diameter oil holes, minimally chamfered.

Actual Length: This is what you would measure if you had a set of calipers large enough to measure over the oil holes at each end of the pushrod. This is the measurement that most people can relate to. Unfortunately, this measurement is affected not only by the diameter of the oil holes but also by the entrance chamfer for each oil hole.

Gauge Length: Although the most difficult to measure (it requires a special length checking gauge), this measurement is the most reliable. This is because the oil holes and their chamfers are eliminated from the measurement. The only problem is that not all companies use the same gauge diameter. COMP Cams® uses a .140″ gauge diameter. All Magnum and Hi-Tech™ Pushrods listed in this catalog are measured using this technique. See Diagram B on the following page.

4. Simple measurement techniques.
We realize that most people don’t have access to the special gauge required for these measurements or even a dial caliper large enough for most pushrods. We’ve developed two techniques to help you determine exact pushrod length so that the perfect valve train geometry is achieved in your engine.

Pushrod Measurement Techniques

Technique #1

This technique requires the use of a COMP Cams® Hi-Tech™ Pushrod Length Checker. These are marked with a standard length stamped in them. This number represents the gauge length of the part (.140″ gauge diameter) with the two halves screwed completely together. Extending the pushrod one rotation lengthens the gauge length .050″. For example, a pushrod stamped 7.800 and screwed apart one rotation would be 7.800″ + .050″ = 7.850″ gauge length. Therefore you would order the part number from the catalog that matches this gauge length, since gauge length is how they are listed.

Technique #2

This technique requires one of our Magnum Pushrod Length Checkers. Once fixed, you don’t need to have an expensive gauge or a pair of calipers to measure it. You just need a pushrod of a known length to compare it to (a standard). Then use a pair of common 6″ calipers to measure the difference between the standard and yours.

Here are a few final hints about pushrods in general. It is always a good idea to buy a few spares when purchasing a set of custom length pushrods, and stick them in your toolbox. If one ever fails at the track and you need a replacement, it would be nearly impossible to borrow one from a fellow racer.

Another hint involves cup end pushrods. Measuring them for length is especially difficult, no matter which technique above you choose to use. The size and shape of the cup end varies greatly from manufacturer to manufacturer, so measuring from the ball end to the cup end over the cup surface is a dangerous practice. The best strategy is to drop a 5/16″ diameter steel ball into the cup end, and do all measuring over this ball, subtracting the 5/16″ diameter (.3125″) to figure the length.

Valve Timing Tutorial
In an effort to simplify what actually happens inside an engine, COMP Cams® invites you to “take a walk” inside a typical engine, just like the one you might have in your car. We will discuss valve events, piston position, overlap and centerlines. Although we can not explain cam design in such a small space, we might be able to clear up some of the most misunderstood terms and make clearer what actually happens as the engine goes through its four-stroke cycle. We will graphically illustrate the relationship between all parts of the engine and try to help you understand how the camshaft affects the power of the engine. Put on your walking shoes, open your eyes and get ready for a good look inside this engine.

We begin with the piston all the way at the top with both valves closed. Just a few degrees ago the spark plug fired and the explosion and the expansion of the gasses is forcing the piston towards the bottom of the cylinder. This is the event that actually pushes the crankshaft around to create the power and is referred to as the “power stroke” (figure 1). Each “stroke” lasts one half crankshaft revolution or 180 crankshaft degrees. Since the camshaft turns at half of the speed of the crank, the power stroke only sees one fourth of a turn of the cam, or 90 camshaft degrees.

As we move closer to the bottom of the cylinder, a little before the piston reaches the bottom, the exhaust valve begins to open. By this time most of the charge has been burned and the cylinder pressure will begin to push this burnt mixture out into the exhaust port. After the piston passes the true bottom or Bottom Dead Center, it begins to rise back to the top. Now we have begun the exhaust stroke, another 180° in the cycle (figure 2). This forces the remainder of the mixture out of the chamber to make room for a fresh, clean charge of air-fuel mixture. While the piston is moving toward the top of the cylinder, the exhaust valve quickly opens, goes through maximum lift and begins to close.

Now something quite unique begins to take place. Just before the piston reaches the top, the intake valve begins to open and the exhaust valve is not yet fully closed. This doesn’t sound right, does it? Let’s try to figure out what is happening.

The exhaust stroke of the piston has pushed out just about all of the spent charge and as the piston approaches the top and the intake valve begins to open slowly, there begins a siphon or “scavenge” effect in the chamber. The rush of the gases out into the exhaust port will draw in the start of the intake charge. This is how the engine flushes out all of the used charge. Even some of the new gases escape into the exhaust. Once the piston passes through Top Dead Center and starts back down, the intake charge is being pulled in quickly so the exhaust valve must close at precisely the right point after the top to keep any burnt gas from reentering. This area around Top Dead Center with both valves open is referred to as “overlap”. This is one of the most critical moments in the running cycle, and all points must be positioned correctly with the Top Dead Center of the piston. We’ll look at this much more closely later.

We have now passed through overlap. The exhaust valve has closed just after the piston started down and the intake valve is opening very quickly. This is called the intake stroke (figure 3), where the engine “breathes” and fills itself with another charge of fresh air/fuel mixture. The intake valve reaches its maximum lift at some defined point (usually about 106 degrees) after top dead center. This is called the intake centerline, which refers to where the cam has been installed in the engine in relation to the crankshaft. This is commonly called “degreeing”. We will talk about this later also.

The piston again goes all the way to the bottom and as it starts up, the intake valve is rushing towards the seat. The closing point of the intake valve will determine where the cylinder actually begins to build pressure, as we are now into the compression stroke (figure 4). When the mixture has all been taken in and the valves are both closed, the piston begins to compress the mixture. This is where the engine can really build some power. Then, just prior to the top, the spark plug fires and we are ready to start all over again.

The engine cycle we have just observed is typical of all four- stroke engines. There are several things we have not discussed, such as lift, duration, opening and closing points, overlap, intake centerline and lobe separation angle. If you will refer to the valve timing diagram when we discuss these terms it might make things a lot easier to understand.

Most cams are rated by duration at some defined lift point. As slow as the valve opens and closes at the very beginning and end of its cycle, it would be impossible to find exactly where it begins to move. In the case illustrated, the rated duration is at .006″ tappet lift. In our plot, we use valve lift so we must multiply by the rocker arm ratio to find this lift. For example: .006″ x 1.5 =.009″. Instead of the original .006″ tappet lift, we now use .009″ valve lift. These opening and closing points are circled so that you can see them. If you count the number of degrees between these points you will arrive at the advertised duration, in this case 270 degrees of crank- shaft rotation. In this illustration this is the same for both the intake and the exhaust lobes, thus making this a single pattern cam. Some cam manufacturers rate their cams at .050″ lift. If we again multiply this by the rocker arm ratio, we get .075″. We can mark the diagram and read the duration at .050″ lift. This cam shows around 224 degrees, standard for this 270H cam. The lift is very simple to determine. You can simply read it from the axis going up. This is the lift at the valve as we said earlier. Sometimes you will hear lift referred to as “lobe lift”. This means the lift at the lobe or the valve lift divided by the rocker arm ratio. In this case, it would be .470″ divided by 1.5 or .313″ lobe lift. The lift is simply a straightforward measurement of the rise of the valve or lifter.

We touched on opening and closing points a little earlier, but now we want to consider them even further. We talked about when these points occur, and how they are measured. As you can see in figure 1, the valve begins to move very slowly then picks up speed as it approaches the top. It does the same closing, coming down quickly then slowing to a gentle stop. It’s kind of like driving your car. If you were to go from 0 to 60 mph in a fraction of a second and stop instantly, you can imagine what that would do to the car, not to mention the driver. It would be much too severe for any valve train to endure. You would bend pushrods, wear out cams, break springs and rockers, and lose all dynamic design. The cam would not run to the desired RPM level as you would have all these parts running into each other. As the valve approaches the seat, you also have to slow it down to keep the valve train from making any loud noises. If you slam the valve down onto the seat, you can expect some severe noise and a lot of worn and broken parts. So it is easy to see that you can only accelerate the valve a certain amount before you get into trouble. This is some- thing COMP Cams® has learned over the years-how far you can safely push this point.

Looking a bit further at the timing points, the first one we see on the diagram is the exhaust opening point. We have all noticed the different sounds of performance cams, with the distinct lopes or rough idle. This occurs when the exhaust valve opens earlier and lets the sound of combustion go out into the exhaust pipes. It may actually still be burning a little when it passes out of the engine, so this can be a very pronounced sound.

The next point on the graph is the intake opening. This begins the overlap phase, which is very critical to vacuum, throttle response, emissions and especially, gas mileage. The amount of overlap, or the area between the intake opening and the exhaust closing, and where it occurs, is one of the most critical points in the engine cycle. If the intake valve opens too early, it will push the new charge into the intake manifold. If it occurs too late, it will lean out the cylinder and greatly hinder the performance of the engine. If the exhaust valve closes too early it will trap some of the spent gases in the combustion chamber, and if it closes too late it will over-scavenge the chamber; taking out too much of the charge, again creating an artificially lean condition. If the overlap phase occurs too early, it will create an overly rich condition in the exhaust port, severely hurting the gas mileage. So, as you can see, everything about overlap is critical to the performance of the engine.

The last point in the cycle is the intake closing. This occurs slightly after Bottom Dead Center, and the quicker it closes, the more cylinder pressure the engine will develop. You have to be very careful, however, to make sure that you hold the valve open long enough to properly fill the chamber, but close it soon enough to yield maxi mum cylinder pressure. This is a very tricky point in the cycle of the camshaft.

The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the “lobe center” of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, is the position of the centerline, or peak lift point, of the intake lobe in relation to top dead center of the piston. This can be changed by “degreeing” the cam into the engine. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine. There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, COMP Cams® has produced a simple, comprehensive video (part #190) that will take you step-by-step through the process.

On these pages we have discussed theory but the video will show you how to actually get the job done. COMP Cams® has put a great deal of effort into the design and engineering of our camshafts. All of these points were considered in each and every cam listed in this catalog. What we intend to do here is show that camshaft design is not some “black art”, but rather a series of decisions and compromises based on the exact application of the cam. Only our many years of experience can say whether a certain combination of lobes will work, so you should trust the judgement of those who have engineered these combinations.

The Truth About Valve Springs

Valve springs are one of the most critical and most overlooked components in your engine. Proper selection of the valve spring begins with identifying the application and selecting all of the valve train components to achieve the engine builders’ goals.

The spring is selected to complement the system and must be matched with the entire valve train in order for the engine to reach its full potential. It does absolutely no good to install a cam that will rpm to 8000 if you do not have the correct springs. Improper selection of the wrong valve spring is one of the most common causes of engine failure. Other common causes are the incorrect installation and improper handling of the valve springs.

Selecting a Spring

1. Use only the valve springs that will give the correct spring pressure with the valve both on the seat and at maximum lift.

2. The outside diameter of the recommended valve spring may require that the spring pocket of the head be machined to a bigger size.

3. One of the easiest and sometimes most costly mistakes made in racing engines is not positively locating the spring. A valve spring that “dances” around on the cylinder head or retainer causes harmful harmonics and excessive wear. A spring that is forced onto a retainer is likely to fail at that coil. That is why we have such a large selection of steel and titanium retainers, hardened steel spring seat cups and I.D. locators to better match our springs. A spring that is contained properly at the retainer and the cylinder head will offer the longest possible service life.

Proper Spring Handling

1. Handle springs with care. Never place in a vise, grab with pliers or hit them with a hammer. This will damage the surface of the spring, which will cause a spring to fail.

2. When separating double or triple springs, use only a durable plastic object that cannot harm the shot-peened surface of the spring. Never use a tool or hard metal object like a screwdriver.

3. Valve springs are shipped with a rust preventative coating that should remain on the spring throughout engine assembly. Do not clean springs with acidic or evaporative cleaners. This causes rapid drying and promotes the formation of rust on the surface, which can cause catastrophic failures. Even a slight amount of corrosion can grow to be a problem.

4. When installing springs, use COMP Cams® Valve Train Assembly Spray (Part #106) to ease assembly and improve the life of the spring.

Checking Loads

1. COMP Cams® has matched each set of springs for load consistency. A variance of + or -10% is acceptable for new springs.

2. When checking the spring loads on a load tester (Part #5313) measure and note the thickness of the retainer where the outer spring sits. Assemble the retainer on the spring and place on the base of the spring checker.

3. Compress the spring to the desired installed height. This is the measurement between the top of the spring (on the bottom side of the retainer where the outer spring sits) and the bottom of the spring on the base.

* NOTE *
Since the retainer is installed in the spring when checking the spring loads, make certain that the thickness of the retainer is not included when calculating the installed height and is accounted for when compressing the spring. The spring load checker will show to be higher with the spring installed at the correct height.


1. Before installing the spring on the cylinder heads, check the installed spring height (Diagram A). This is the distance from the bottom of the retainer to the surface where the spring rests on the head. The valves, retainers and valve locks will be used in this step. First, install the valve in the guide, then install the retainer and valve locks. Pull the retainer tightly against the valve locks while holding the valve assembly steady.

Measure the distance between the spring seat and the outside step of the retainer using your height micrometer (Part #4928 or #4929) or a snap gauge and a pair of calipers. Repeat this procedure for all the valves and record your Information. After you have measured all the valves, find the shortest height. This will become the spring’s installed height on your heads. If your combination includes a dual or triple spring assembly, it will be necessary to allow for the inner steps of the retainer.

2. Once you have determined the shortest installed height, it will be necessary to use shims to obtain this height (±.020” is acceptable) on the remaining valves. These are available through our catalog or at any of
your local COMP Cams® dealers.

3. Before removing the retainers, measure the distance from the bottom of the retainer to the top of the valve seal (Diagram A). This distance must be greater than the lift of the valve. If not, the guide must be machined. This is a very common cause of early camshaft failure.

4. Once the valve springs have been installed, it is important to check for coil bind. This means that when the valve is fully open, there must be a minimum of .060” clearance between the coils of both the inner and outer springs. If this clearance does not exist, you must change either the retainer or the valve to gain more installed height, or change to a spring that will handle more lift or machine the spring seat for extra depth.

5. Always check for clearance between the retainer and the inside face of the rocker arm. This will be most evident while the valve is on the seat. Rocker arms are designed to clear specific spring diameters, so you should check to see that you have the proper rocker arm/retainer combination. This situation can also be the result of improper rocker geometry and may be corrected with different length pushrods or a different length valve.

6. To aid in the engine breaking process, spray the springs, rocker arms and pushrods with COMP Cams® Valve Train Assembly Spray (Part #106).

Breaking In a Spring

1. It is important for new springs to take a heat-set. Never abuse or run the engine at high rpm when the springs are new. Upon initial start-up, limit rpm to 1500 to 2000 until the temperature has reached operating levels. Shut off the engine and allow the springs to cool to room temperature. This usually will eliminate early breakage and prolong spring life. After the spring has been “broken-in”, it is common for it to lose a slight amount of pressure. Once this initial pressure loss occurs, the spring pressure should remain constant unless the engine is abused and the spring becomes overstressed. Then the springs must either be replaced or shimmed to the correct pressure.

Effect Of Changes In Cam Timing And Lobe Separation Angle

The following tables illustrate how variations in lobe separation angle and cam timing will effect the behavior of the engine in which the camshaft is installed.



– Begins Intake Event Sooner
– Open Intake Valve Sooner
– Builds More Low-End Torque
– Decrease Piston-Intake Valve Clearance
– Increase Piston-Exhaust Valve Clearance


– Delays Intake Closing Event
– Keeps Intake Valve Open Later
– Builds More High-RPM Power
– Increase Piston-Intake Valve Clearance
– Decrease Piston-Exhaust Valve Clearance


Tighten (smaller LSA number)

– Moves Torque to Lower RPM
– Increases Maximum Torque
– Narrow Power band
– Builds Higher Cylinder Pressure
– Increase Chance of Engine Knock
– Increase Cranking Compression
– Increase Effective Compression
– Idle Vacuum is Reduced
– Idle Quality Suffers
– Open Valve-Overlap Increases
– Closed Valve-Overlap Increases
– Natural EGR Effect Increases
– Decreases Piston-to-Valve Clearance

Widen (larger LSA number)

– Raise Torque to Higher RPM
– Reduces Maximum Torque
– Broadens Power Band
– Reduce Maximum Cylinder Pressure
– Decrease Chance of Engine Knock
– Decrease Cranking Compression
– Decrease Effective Compression
– Idle Vacuum is Increased
– Idle Quality Improves
– Open Valve-Overlap Decreases
– Closed Valve-Overlap Decreases
– Natural EGR Effect is Reduced
– Increases Piston-to-Valve Clearance


1) Max Lift or Nose
2) Flank
3) Opening Clearance Ramp
4) Closing Clearance Ramp
5) Base Circle
6) Exhaust Opening Timing Figure
7) Exhaust Closing Timing Figure
8) Intake Opening Timing Figure
9) Intake Closing Timing Figure
10) Intake to Exhaust Lobe Separation

Effects Of Changes In Cam Timing And Lobe Separation Angle

The following tables illustrate how variations in lobe separation angle and cam timing will effect the behaviour of the engine in which the camshaft is installed.



– Begins Intake Event Sooner
– Open Intake Valve Sooner
– Builds More Low-End Torque
– Decrease Piston-Intake Valve Clearance
– Increase Piston-Exhaust Valve Clearance


– Delays Intake Closing Event
– Keeps Intake Valve Open Later
– Builds More High-RPM Power
– Increase Piston-Intake Valve Clearance
– Decrease Piston-Exhaust Valve Clearance


Tighten (smaller LSA number)

– Moves Torque to Lower RPM
– Increases Maximum Torque
– Narrow Power band
– Builds Higher Cylinder Pressure
– Increase Chance of Engine Knock
– Increase Cranking Compression
– Increase Effective Compression
– Idle Vacuum is Reduced
– Idle Quality Suffers
– Open Valve-Overlap Increases
– Closed Valve-Overlap Increases
– Natural EGR Effect Increases
– Decreases Piston-to-Valve Clearance

Widen (larger LSA number)

– Raise Torque to Higher RPM
– Reduces Maximum Torque
– Broadens Power Band
– Reduce Maximum Cylinder Pressure
– Decrease Chance of Engine Knock
– Decrease Cranking Compression
– Decrease Effective Compression
– Idle Vacuum is Increased
– Idle Quality Improves
– Open Valve-Overlap Decreases
– Closed Valve-Overlap Decreases
– Natural EGR Effect is Reduced
– Increases Piston-to-Valve Clearance


1) Max Lift or Nose
2) Flank
3) Opening Clearance Ramp
4) Closing Clearance Ramp
5) Base Circle
6) Exhaust Opening Timing Figure
7) Exhaust Closing Timing Figure
8) Intake Opening Timing Figure
9) Intake Closing Timing Figure
10) Intake to Exhaust Lobe Separation

Cam Quest – Select the perfect camshaft

Racing Calculators

 Click on the link below to view different helpful calculators for all your racing needs

Formula for Calculating Speedometer Gears

The following formula will work for any GM, Ford or Chrysler vehicle and is very useful when there is no established baseline from which to work from such as replacing a transmission in a vehicle that was purchased without a drive line. The accompanying charts show what gears were manufactured for each type transmission. TCI® now stocks the most popular speedometer gears.

Note: Drive gear refers to the gear that is on the transmission output shaft. The driven gear is located in a removable housing usually in the tailhousing of the transmission. Be aware that some transmissions will have different driven gear housings depending on the tooth count of the driven gear.

Click on the link below to calculate your appropriate speed gear

Torque Convertors Explained
Torque converters are fluid-coupling devices that also act as a tq. multiplier during initial acceleration. 

1) Impeller Pump – The impeller pump is the outside half of the converter on the transmission side of the weld line. Inside the impeller pump is a series of longitudinal fins that drive the fluid around the outside diameter into the turbine because this component is welded to the cover, which is bolted to the flexplate. The size of the torque converter (and pump) and the number and shape of the fins all affect the characteristics of the converter. If long torque converter life is an objective, it is extremely important that the fins of the impeller pump are adequately reinforced against fatigue and the outside housing does not distort under stress.

2) Stator – The stator can be described as the “brain” of the torque converter, although it is not the sole determiner of converter function and characteristics. The stator, which changes fluid flow between the turbine and pump, is what makes a torque converter a torque converter (multiplier) and not strictly a fluid coupler. With the stator removed a converter will retain none of its torque multiplying effect.


– It must hold the stator perfectly still (locked in place) while the converter is in stall mode (slow relative turbine speed to the impeller pump speed).

– It must allow the stator to spin with the rest of the converter after the turbine speed approaches the pump speed. This allows for more efficient and less restrictive fluid flow. The sprag is a one-way mechanical clutch set between two races that fits inside the stator while the inner race splines onto the stator support of the transmission.

3) Turbine – The turbine rides within the cover and is attached to the drivetrain via a spline fit to the input shaft of the transmission. When the turbine moves, the car moves.

4) Cover – The cover (also referred to as the front) is the outside half of the housing toward the engine side from the weld line. The cover serves to attach the converter to the flexplate (engine) and contains the fluid. While the cover is not actively involved in the characteristics of performance, it is important that the cover remain rigid under stress (torsional and thrust stress as well as the tremendous hydraulic pressure generated by the torque converter internally).

Racing Oil 101

Today’s engine oils are not the same as they were even a few years ago.

Phosphorus and Zinc Reduction

  • Phosphorus degrades catalytic converters
  • Zinc & Phosphorus content unlimited before 1993
  • Phosphorus now limited to max 800 ppm (API SM / ILSAC GF-4)
  • Mandated for 10W-30 and lower – still occurring in higher grades
  • Diesel oils now limited to 1,200 ppm Phosphorus (Oct. 2006)

Increased Detergents

  • Exhaust Gas Recirculation Valves
  • Increased drain intervals – less waste oil

Lower Sulfur

  • Restricted Sulfur content


Detergent and dispersant additives “compete” against zinc in the engine because they are polar molecules as well. Detergents and dispersants clean the engine, but they don’t distinguish between sludge, varnish and zinc – they clean all three away.

Modern API certified oils contain higher levels of detergents and dispersants due to the exhaust gas recirculation (EGR) systems on passenger cars and diesel trucks. The “old school” theory on engine break-in was to run non-detergent oils, and this allowed for greater activation of the zinc additive in the oil.

Joe Gibbs Driven BR Break-In oils utilize the correct balance of anti-wear additives and detergents, so you don’t need to buy expensive additives to try to “fix” a low zinc (ZDDP) oil.


ZDP (aka Zinc) and Moly (MoS2) are polar molecules, so they are attracted to carbon steel surfaces where they react with heat, to create a sacrificial additive coating. The protective coating prevents metal to metal contact, which reduces friction and wear. Moly can withstand pressure up to 500,000 psi.

Detergent additives are also polar, so they “compete” against the Zinc and Moly.

Key Protection For:
Cams, Lifters, Push Rods, Wrist Pins, Distributor Gears, Bearings, Etc…


As Load Increases, Lubrication Moves From Full Film (Hydrodynamic) To Boundary Lubrication. Zinc Provides Boundary Lubrication.


The Right Oil

  • Proper viscosity and additives for operating temperature, RPM and load
  • There is no “magic molecule” that prevents engine failures
  • No amount of Zinc can fix bad geometry – lifters must spin

In The Right Place

  • The best oil sitting in the oil pan doesn’t help your camshaft
  • Oiling system design is critical to proper lubrication
  • Look into EDM hole lifters, piston oilers, valve spring oilers

In The Right Time

  • On time delivery is critical
  • Cold starts and Dry starts account for majority of engine wear – Multigrade oils dramatically reduce cold start wear

In The Right Amount

  • Proper oil flow is critical at all times
  • Oil is the lifeblood of an engine


A quart of oil contains 2 things:

Base Oil

Roughly 85% of what is in the bottle is base oil. Most base oils come from crude oil. There are 5 different classes of base oil based on purity and source material.

  • Crude
  • Distillation Gases
  • Vegetable oils and Animal fats

Additive Package

Roughly 15% of an oil is the additive package, but that 15% plays a
big role in performance.

  • Detergents
  • Anti-Wear (Zinc)
  • Friction Modifiers (Moly)
  • Viscosity Modifiers


Crude oil is fractioned by distillation into different “cuts” of oil and fuels. Engine oils come from the middle part of the tower, and are then refined by various methods to become base oil. The fraction of oil that becomes engine oil contains 3 families of molecules – Paraffins, Naphthas, and Aromatics.

Paraffins: Good VI, preferred molecule
Naphthas: Low VI
Aromatics: Very Volatile

Base Oil Choices

  • Group I, II & III are mineral oils (Crude Oil)
  • Group IV – PAO Synthetic (Distillation Gases)
  • Group V is everything else   (Animal fats and Vegetable oils)


The difference between synthetic and mineral oils are the structure of the molecules and the purity of the oil. Refined crude oil contains complex mixtures of different molecular structures and saturates (Nitrogen, Sulfur and Oxygen). There is no way to select only the best materials from this mixture. Thus mineral oils contain both the most suited materials and the least suited materials for an engine oil. Synthetic oils are man made, and have tailored molecular structures with predictable properties. Because of this, synthetics can have the best properties of a mineral oil without the un-desired materials. Synthetic oils have two unique advantages over mineral oils – lower traction coefficients and higher oxidation stability. This translates into improved energy efficiency – less friction – and longer drain intervals.


Oil is Not One Size Fits All

To achieve maximum lubricant performance, an oil must be formulated to meet the specific need of the application.

The choice of oil for any application should be guided by the following operating conditions:

  • Speed
  • Load
  • Temperature
  • Service Interval
  • Equipment Design
  • Operating Environment


Modern Engine Set-Ups

  • Low RPM (Low Load – Less Need For Anti-        Wear)
  • Overhead cams (No Flat Tappets or Push Rods – Less Need For Anti-Wear)
  • EGR Valves (More need for Detergents)
  • Extended Drain Intervals (increased detergents & acid neutralizers)
  • Modern engines built to use modern oils in order to achieve cleaner emissions

Race Engine Set-Ups

  • High RPM (High Load – More Need For Friction Modifiers)
  • Flat Tappet cams and Push-Rods – More Need For Anti-Wear
  • Short Drain Intervals and EGR valves – Needs Fewer Detergents


Additive clash occurs when two different additive chemistries interact antagonistically resulting in dips in protection. The high levels of detergent in API oils can contribute to Additive Clash.

Typical Break-In Procedure:

Three different lubricant chemistries working against each other.

Joe Gibbs Driven System Approach:

Matched lubricant chemistries working together to provide sustained protection.

Establishing an effective anti-wear / EP film in an engine is not unlike painting your car. Think of this system ofassembly grease followed by break-in oil and then synthetic oil like the primer, sealer and base color of automotive paint. It makes a difference when you apply the right products for the job in the correct order!


Viscosity is a measure of flow. Oil viscosity is generally thought of in terms of SAE grades, like 15W-50.

  • An oil’s flow rate increases as temperature increases.
  • SAE grades are ranges, not an exact measurement of an oil’s flow rate.
  • The number before the W is measured at -22F. The Number after the W is measured at 212F.
  • Kinematic Viscosity measures the exact flow rate of an oil at both 100F and 212F degrees.

SAE grades are only measured at 212F. The number before the “W” in a 15W-50 or 0W-30 is a cold cranking index that is measured at -22F.


Wider Bearing Clearances Require Higher Viscosity Oil To Maintain Hydrodynamic Oil Wedge


The “Operating” viscosity is the Centistoke flow rate of an oil at the operating oil temperature of an engine. Some engines run low oil temperatures, and other engines run extremely high temperatures. Low viscosity oils work well in low temp applications, and high viscosity oils work well in high temp applications. The SAE Grade viscosity of these oils are very different, but the operating flow rates are very similar.


– Polymer based oil additive – makes multi-grade oils possible
– “Shrink” under shear forces
– Shear forces in race engines are greater than in production engines
– Prone to permanent shear loss under extreme pressures
– Adds friction modifying and dispersant functions

Choosing the proper type of oil

Let’s face it, the days of just choosing your favorite brand 20W-50 and putting it in your muscle car, race car and lawn tractor are over. While each engine is a 4 stroke, the engines themselves and the motor oils are more specialized.

That means you have to decide which oil is right for your muscle car, which oil you will use in your race car, and what oil you will use in your lawn tractor.

So when should you use choose a racing oil over a high performance street oil?

How the engine runs determines what type of oil to use:

The key to selecting the right oil for any application is matching up how the engine is used with oil chemistry for that type of use.

Back to your lawn tractor. If you are just cutting grass, the factory recommended oil is just fine, but if you are drag racing the lawn mower, please remove the blade! And while you are at it, drain the oil and put in some racing oil.

A car that makes a short drive to work 5 days a week needs more TBN than a race car that runs 50 laps each weekend.

What is TBN you ask? TBN stands for Total Base Number, and it measures how much acid neutralizing power is in the oil.

You may not realize it, but corrosive wear is one of the major forms of wear in your engine. In fact, one of the main reasons for increased engine life today has been the reduction in corrosive wear.

That’s right, many older engines did not wear out − they corroded.

Short trip driving is the worst for producing engine killing acids. Water is a by-product of combustion, so some water vapor always makes its way into the crankcase of your engine.

If the engine does not run long enough to get warm enough to evaporate the water vapor out of the engine, the water vapor builds up. When the engine cools down, the water vapor creates condensation, and now you have water in your engine. The water mixes with the sulfur in the oil and the partially burnt fuel to create a very corrosive chemical cocktail.

To fight this, oil engineers have developed detergent and dispersant additives to fight corrosion. The power of the additives relates to the TBN value of the oil.

A very strong detergent and dispersant package will have a high TBN value, and that signifies oil that is good for frequent short trip driving.

Ok, so why not use a high TBN oil in my race car?

Simply put, the harder the engine runs, the less TBN your engine needs. That may seem counter-intuitive, but it actually makes sense when you know that detergents and dispersants compete against the Zinc anti-wear additives and EP (extreme pressure) additives your race engine needs.

Nobody building a race engine lowers compression ratio, installs lighter springs and a smaller cam to turn a production engine into a race motor. You do the exact opposite, and when you do, you increase all the contact pressures in the engine. The increased pressures and loads in the engine need extra anti-wear protection, so the oil engineers add more anti-wear additives like Zinc (ZDDP, ZDP or ZDTP) and EP extreme pressure additives like Molybdenum and Sulfur.

These anti-wear and EP additives form sacrificial films that protect your race engine from adhesive wear due to the higher loads in a race engine. Anti-wear and EP additives like ZDP and Molybdenum Disulfide act like armor to shield your engine parts from adhesive wear.

The detergents and dispersants that fight corrosive wear are trying to strip that armor off your engine parts. All of these additives are needed to protect your engine. The key is selecting the right balance for your engine.

While race oils provide more anti-wear and EP additives to fight adhesive wear, the lower level of detergents and dispersants requires more frequent oil changes to control corrosive wear.

Since a daily driver is more prone to corrosive wear, the right oil for your daily driver needs a higher level of detergents and dispersants, and the engine in your daily driver is built with a smaller camshaft and lighter valve springs that safely run on lower levels of anti-wear additives.

When you have an older muscle car that does short trip driving and sees extended periods of sitting in a garage, you need a higher TBN oil to protect against corrosive damage. However, many older muscle cars also have “old school” pushrod valve trains and good sounding camshafts.

Now what do you do? Don’t worry, oil engineers have found the right balance of increased anti-wear additives and TBN for your hot rod − enough ZDP for your camshaft and enough TBN to protect your engine during winter storage.

So what about that drag racing lawn tractor? Use a racing oil, and keep a good eye on it.

Drag racing is a combination of the worst of both daily driving and racing − short trips, low temperature and really high loads. The best recipe for low adhesive wear and low corrosive wear in a drag racing engine is to use a high quality racing oil and change it often. Again, keep a close eye on the oil.

As long as the oil looks good and smells normal, it’s good. If the oil turns dark, begins to smell like fuel or turns milky, change it. These are all signs of fuel dilution ands chemical attack on the oil, so the best defense for your engine is to send in fresh troops with the correct weapons designed to protect it for the way you use it.

This process takes a little more thought and work since engines, especially race engines, cost a lot of money. But spending a little extra time and money on your oil program will more than pay off in extended engine life.

Keith Black Engine Calculators

Click on the link below and To help you figure out exactly what parts you need to build that perfect machine.

High Performance Piston Rings

Click Here to View Some helpful information on Total Seal Rings and FAQ

Frequently Asked Questions

Do I need a crank hub or balancer? For most applications a balancer will work better than a crank hub for eliminating harmonics in the motor. We recommend the use of a quality aftermarket balancer since stock balancers do not hold up well on blown motors. Crank hubs are recommended for high boost race applications.

What makes the blower Surge? This is caused by a rich/lean cycle at idle. As the motor leans out the RPM’s increase and richen up the motor, when the motor richens the RPM’s decrease and the motor leans out again. This continual cycle is known as “blower surge”. With proper tuning, some of this surging should be able to be eliminated.

How tight should I run my blower belt? The blower belt adjustment should be done with the motor cold, and have 3/4″ deflection in or out on the long side of the belt. This should give you 1 1/2″ total deflection. Once the motor is warm this will decrease to roughly 1/4″ deflection in or out, or a total deflection of 1/2″. Over tightening the belt can cause severe damage to the blower and/or crankshaft.

Will my stock fuel pump work on my supercharged motor? No. Your supercharged engine will require at least 120 GPH (gallons per hour). It can be either a mechanical or electric pump.

Do I need blower carburetors? You can modify your naturally aspirated carburetors to work on a supercharged engine. This will require extensive carburetor knowledge and a complete understanding of the fuel demands of a supercharged engine. We do however recommend the use of a Blower Calibrated Carburetor.

How many ft/lbs should I torque my supercharger too? You should torque the supercharger to 10-12 ft/lbs. for most applications. Some Intercoolers that use long steel studs may require more torque for a proper seal, normally 25 ft/lbs.

What Type of Oil should I run in my supercharger? You should run a High Quality 80w/90 gear oil with a GL-5 rating with Zinc. Synthetic oil or Synthetic blends are OK to use.

Mickey Thompson Frequently Asked Questions

Click Here to View Some helpful information on Mickey Thompson Wheels and FAQ

Technical Information

Carb Class: Baseline settings for your new carburetor
A question frequently asked here at Quick Fuel Technology is how to properly install and setup a new carburetor. Our focus is more on the setup than installation in this commentary. Some racers are very thorough with a new carburetor and others will just “bolt it on and go”. It is essential to go through the basic steps for a pain-free set-up that will save you headaches down the road.

Installing a carburetor is one of the more basic race car procedures so we won’t go into detail on it. However, there are a few crucial items needing special attention. A carburetor is designed to precisely meter fuel and air; if the sealing surface is damaged or obstructed the carburetor will essentially have an uncontrolled source of air – the dreaded vacuum leak! A common mistake that can also lead to trouble is over tightening. Moving in a crisscross pattern will evenly distribute the torque of your wrench and ensure that the mounting flange of the carburetor is not damaged. Once the carburetor is properly mounted, take a few moments to move the throttle linkage. For your own safety it is imperative that the throttle returns to the closed position on its own and moves freely.

After the carburetor is mounted on the engine and everything else works properly the initial tune- up can be dialed in. Float level is very important to the overall performance and consistency of your race car; there are ill-side affects if you deviate from this a crucial step. Once you have filled the fuel bowls and primed the engine, start it up. Set the float levels while the engine is running at idle. Normally, a Quick Fuel Technology carburetor will have the fuel level half-way up the sight window with 6.5-7 PSI of fuel pressure. Other brands and some older carburetors will require a sight plug removed to check this. Take precaution make sure that you keep fuel away from any ignition source. The next step will be to set the idle mixture. Most carburetors have an adjustable idle feature whether it is 2 screws or 4. Four barrel race carburetors typically have 4 screws, one for each barrel. The ideal method for setting idle mixture is with a manifold vacuum gauge. Setting the screws to attain the highest reading of vacuum is the standard method but not every engine and combination will follow that setting. Some modern race engines require more fuel at idle. Too lean of a mixture could cause the engine to die once you click it into gear. Idle mixture is a part of the process you will simply have to play with to determine what you prefer, take it slow and go a half turn at a time. Always remember that not all 4 screws need to be turned the same amount out or in.

Once you have set the float level and idle mixture; the last step is adjusting your idle speed. Many carburetors have a transfer slot that aids the carburetor in its transition to wide open. If the throttle plate position is too far up (and into the transition slot) your idle quality will be low and the car might stumble at the starting line. The plate position can be corrected by adjusting your mixture screws (again something you will have to experiment with). The goal of a proper idle speed and mixture is to have the engine have a suitable idle while in neutral or in gear. The main idea is to have an idle that makes the car smooth and predictable.

A properly set-up carburetor will give a solid baseline for fine tuning to achieve maximum performance. If the carburetor is not dialed in correctly when first installed it has the potential to compound other problems and potentially cost more money (and time) to fix.

Carb Class: Air Bleed Basics

You’ve heard of them, but what do they do? Air bleeds, sometimes referred to as “air jets” or “air bleeders” play a vital role in the operation of your carburetor. Air bleeds are responsible for determining the amount of air that will mix with each circuit in the metering block. Virtually every carburetor you come across will have these which make this a universal discussion. The amount of air bleeds a carburetor will have is dependent on the number of throttle bores and circuits the carburetor has. In the context of racing carburetors, it helps to think of them as (4) one barrels. Most racing carburetors will have either 8 or 12 air bleeds depending on whether they are 2 or 3 circuit. Each barrel will have one bleed per circuit.

Idle Air Bleed: The idle air bleed could be the hardest working one of them all. Air to be mixed with idle fuel is provided by the idle air bleed. The idle mixture screws rely on air provided by this bleed. Often racers have complained of poor idle quality and no response to adjustment of their mixture screws, this is due an incorrect idle bleed. Many idle issues can be addressed by simply adding or taking away air.

Intermediate Bleed: The intermediate bleed is found on 3 circuit carburetors ONLY. The intermediate bleed provides air for the 3rd circuit. The intermediate circuit is only adjustable externally by the air bleed and to tune it otherwise would require you to take the fuel bowl and metering block off of the carburetor. On most large flange carburetors this would be the bleed found in the middle.

High Speed Bleed: The high speed air bleed or also referred to as the “main bleed” correlates to the main system. The high speed air bleed controls how much air is fed to the emulsion channels of the metering block. To explain further, the emulsion channels distribute that air further to different parts of the main well where it mixes with fuel and ultimately goes to the booster. The high speed air bleed is generally located closest to the squirter when looking at most race carburetors.

Now that we know what each air bleed does, how do we tune them? Tuning with air bleeds is often easier than anything else on a carburetor. Most modern race-style carburetors have screw-in air bleeds that can be exchanged externally with a simple hand tool. Gone are the days of pin drills and dial calipers. Air bleeds often resemble a main jet only slightly smaller. Tuning is simple in that you just need to remember the size of the hole determines how much air is coming into the carburetor. If you want to richen up the idle simply replace your idle air bleed with a smaller one (less air in the system = more fuel = richer idle), this will help you get your mixtures screws within the 1-2 turn range. What if you want to lean out the intermediate so you can get your car to come off of the transbrake a little cleaner? Increasing the size of the intermediate bleed will lean out that circuit. Just remember that too much of a good thing can get you into trouble – before fine tuning a carburetor you should take note of the stock specs so you can always come back to where you started.

Carb Class: Fuel Bowl Basics

In past issues we have discussed that horsepower can be found in the individual components of carburetors – one often neglected component that is integral to the performance of your race car is the fuel bowl. While no one component is more important than another, the fuel bowl is integral to the performance of your engine and the way your race car goes down the track. All carburetors (no matter the size or brand) will have some type of system that controls fuel delivery to the carburetor. For the purposes of this article we will assume that most people use the same style of carburetor and have a removable “modular” style fuel bowl. Fuel bowls, for those that might not know, are the pieces of the carburetor that you would have to drain and remove to change the jets of your carburetor. If a fuel bowl is incorrect for the application or built with improper components the performance of your race car will ultimately suffer.

Fuel bowls come in different shapes, sizes, materials, and even colors. The choices a racer has when it comes to a carburetor can be overwhelming but with a little research and some good communication racers can ensure they will be satisfied with the combination and hopefully go some rounds. The first question you should consider when discussing fuel bowls is what type of fuel does your car use? E85, E98, race gas, and methanol all have a different BTU output and require varied amounts of flow to make best horsepower – ultimately you must determine if the fuel bowls can support the flow your engine requires. Another issue to be aware of is that certain fuels are corrosive, with that said, fuel bowls should be outfitted with components to resist any damage; if there is corrosion then one can assume there will be some particulate matter getting into the fuel system which will cause issues elsewhere in the carburetor. One of the last things we usually consider when outfitting a carburetor is the footprint of the carburetor (is there enough space between other components or another carburetor that you need to account for when choosing the size or type of fuel bowl?). With this information laid out one can now see that there is some considerable importance in the selection of a proper fuel bowl.

Modern race carburetor fuel bowls come in two basic configurations each with their own type of float. The first we will go over is the side hung bowl – named due to the nature of the way the float is situated inside the bowl itself. This type of fuel bowl is generally used in situations where a 2×4 set of carburetors must be mounted inline or on certain class carburetors where the rules require its use due to it being factory equipped. The side-hung bowl is compact, and because of that characteristic, has some limitations. One major drawback of side-hung bowls is that they do not offer much float drop – this compromises fuel flow by not allowing the needle to fully open. Another drawback to the use of the side-hung bowl is the float design itself. The float design of a side-hung float does not produce a high amount of leverage and therefore it cannot withstand much fuel pressure (the float has difficulty overcoming the fuel flow and shutting the needle). The other main configuration of fuel bowl is the center-hung style. Center-hung bowls are generally dual inlet (or dual feed) and unlike their side-hung brethren, you can opt to plumb them from either side. Named for the way the float is mounted within the bowl, a center-hung float offers more drop, flow, and leverage. A center-hung bowl is physically larger than a side-hung bowl and will have more capacity (something required on methanol and E85/98 race cars) which decreases the chance of running out of fuel and going lean down the track. Widely adapted and seen on the majority of carbureted race cars in the pits, the center-hung fuel bowl was the one of these two mentioned fuel bowls that was designed with performance in mind.

The last thing to consider when reviewing your fuel bowl setup are the specific components inside the fuel bowl. There are several brands and types out there for each little component so finding a quality piece is never an issue. Diaphragms, floats, and needle valves come in all shapes and sizes in a wide variety of materials to suit your application and should be selected with the help of a specialist. The right combination of components are what add up to a winning race car and your carburetor components play an integral part.