I have a Chevy with 454 large blocks and fitted a hydraulic roller cam, which also meant I had to use longer hydraulic roller lifters. Putting it all together, it’s pretty clear that older hydraulic lifters’ push rods are now very long. How can I choose the right length push bars? I have read a bit on the internet and looked through some camera catalogs but the push rod lengths for these cameras look different. What is the correct push rod length?
Because there are many different variables that can affect the push rod length, a “standard length” push rod for a high performance application may not be close at all to the “standard” length, especially with an upgraded hydraulic cylinder, and may not be optimized at all.
This is because of a ton of variables like the length of the lifter body and even small things like the reduced base circle diameter of the cam you are using. Cams with more lobe lift feature reduce the base circle diameter creating additional lift. This directly affects the push rod length.
Measuring Push Rod Length
The easiest way to do this will involve several adjustable push rods that you can use to measure the length of the push rod. Years ago, Steve Lambert, engine manufacturer Lingenfelter Performance Engineeringshowed me how to quickly determine the push rod length, and I’ll gladly pass this little tip here.
One pair to perform this length test Comp adjustable push rods Because big block Chevy uses different length push bars for intake and exhaust. I love using Comp’s adjustable push rod for this procedure because it makes finding the right push rod length really easy. Adjustable push rods use an internal gear design in which one turn on the two-piece push rod moves the length of the tool exactly 0.050 inches.
Comp offers these push rods in several separate lengths. Big block Chevy will need two different control push rods – the entry version accommodates lengths between 7.80 and 8.80 inches. Also, the adjustable push rod on the intake side may need to be slightly shorter than 7.80 inches, which means you may need a second push rod that ranges from 6.80 to 7.80 inches. The exhaust push rod tool can be longer than 8.80 inches, requiring a third adjustable push rod. (See the parts list at the bottom of this article for part numbers and links.)
How to Use Push Rod Length Control Tools
We will now learn how to use the tools correctly. We will check the push rod length of the Number One cylinder, the leading cylinder on the driver’s side. Remove the valve cover and eight spark plugs to make it easier to turn the engine by hand. The first thing we need to do is place an original push rod on both the intake and exhaust lifters. Now turn the engine over until the exhaust pushrod starts to rise. This tells us that the entrance lift is in the base circle of the entrance lobe.
The technique for determining the optimum push rod length is simple enough. Start by using a black Sharpie to color the valve stem end. Next, we’ll estimate the input push rod to be roughly 7.80 inches, so CCA-7703-1 Attach the push rod tool to the Number One intake lift then attach your rocker arm. We’ll also assume you’re using roller rocker arms. Place the rocker on the push rod and then move the rocker arm over the valve end to create a witness mark on the black mark on the valve end. Remove the rocker arm and find the witness mark on the valve end.
The push rod length plays a crucial role in ensuring proper rocker arm spool end movement along the top of the valve. If the push rod is too short, it places the rocker arm at the innermost end of the valve end. If the push rod is too long, it places the end of the rocker arm too far from the valve end. The ideal position for the rocker end is about a third of the inside. The photo below this article will make this clear. If the witness mark is too in, just extend the Comp adjustable push rod until the roller rocker is roughly one-third of the inner side.
The reason for this placement is that while the valve lift is produced by the cam, the rocker arm end begins to move outward along the face of the valve end that moves internally, crossing the centerline of the valve end. At maximum lift, the valve end will pass the half mark and then begin to return to its starting position when the valve closes. The ideal push rod length will minimize the distance the rocker end travels, but will approximately replicate the middle half of the valve end or the like. It will make up most of its travel in the middle of the valve end, starting at roughly one-third of the inlet.
Once the push rod is set to its ideal length, all you have to do is count the number of turns that come out of its original length with each turn of 0.050 inches. This means that if you turn the push rod three turns, this is equal to adding 0.150 inches to the initial length of the push rod. So if we add 0.150 inches to the adjustable push rod starting at 7,800, the desired push rod length would be 7,950 inches.
To apply the same technique to the exhaust pushrod, first rotate the engine until the intake pushrod is about halfway to the closing ramp of the lobe. This will place the exhaust lobe and lifter in the floor circle. Then follow the same process that determines the ideal push rod length.
Getting the Suitable Push Rods
When you have lengths for both intake and exhaust push rods, you can order the push rod from any of the pusher rod companies. Almost all cam companies like Comp offer push rods in 0.050 inch lengths. Then all you have to do is order eight intake and eight exhaust push rods and the task is complete.
As a warning, do not attempt to use these adjustable push rods against normal spring pressure to control movement along the valve end by opening and closing the valve with the rocker arm. These push rods are intended to be used against a control spring and will bend if used to open against normal spring pressure. If you want to measure the actual rocker action, install a light control spring instead of the regular valve spring.
This is a simple and effective way of determining the proper push rod length. There are other procedures that some people can comment on attempts to minimize rocker action or to place the rocker valve at a 90 degree angle in mid-lift. These operations usually require a different push rod length.
We will not go into this ongoing battle, except to say that these other procedures are aimed at racing engine applications for ultra-high rpm use. The process we just presented is easy, concise and will offer great durability in all street engines.
Parts List to Ask: Big Block Chevy 454 Push Rod Length
|CCA-7702-1||COMP Cams Hi-Tech Pushrod Length Check Tool,
6.80 “- 7.80” (Intro)
|CCA-7703-1||COMP Cams Hi-Tech Pushrod Length Check Tool,
7.80 “- 8.80” (Intro)
|CCA-7704-1||COMP Cams Hi-Tech Pushrod Length Check Tool,
8.80 “- 9.80” (Exhaust)
|CCA-7900||COMP Cams Magnum Control Push Rod Set *|
|* Master Kit: Five individually adjustable push bars from 6.125 “to 11.50”.|