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Pushrod TechHigh Energy™MagnumHi-Tech™Semi-FinishedCheckingTools
Pushrod Tech
COMP Cams® Pushrods

Pushrod Tech

Prior to extensive research at COMP Cams®, it was thought that the pushrod only had to be strong enough not to fail, bend or burn up at the ends. But engineers have learned that the frequency of the pushrod must match that of all the rest of the parts in the valve train, as well as the rpm at which the engine will be run.

As cam profiles get more aggressive and valve spring pressures increase, the importance of selecting the right pushrods has never been more critical. COMP Cams® carries a wide selection of precision pushrods to handle any application from stock replacement to hardcore race.
Pushrod Length & Rocker Arm GeometryMeasurement Techniques
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 fi ts 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.
Invest in a checking pushrod. They are on page 295 of this master catalog. 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, plastic pieces 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.

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 on the following page.

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.

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