I just put my heads on and my cam in and i need to figure out what i need for pushrods! My Heads have been milled .010 and theres a new cam in the motor. Im getting new pushrod either way, dont want to run the stockers. Do i need shorter pushrods or will stock lenght suffice? I have an adjustable pushrod that i used, i assembled the valve train and put it in there.. with the valve all the way closed it seems like i ned a .050 shorter push rod. thats the measurement me and my dad both got. My dads friend who owns a shop measured and said he thinks the stock size is right.. anyone have any input on the matter? thanks!

 

Generally, if you're within .050 on a street motor it's plenty close. I set my motors up based on rocker arm geometry from valve-closed to max lift while watching the rocker arm tip travel across the valve tip. I could go into how I do this if you like, but there are many on here who could also describe the basic procedure.

You milled the heads .010 but did you use thicker head gaskets than stock? Remember than these 2 factors can, and often do, offset eachother to some extent. If you decked the block that's another thing to consider. This is not a substitute for measuring, but something just to keep in mind as a "quick sanity test" to compare to your actual measurements.

Here's the information you're really after once you're past all that other stuff: If you have a new cam with more lift than stock but it uses the same base-circle diameter then you may well find that pushrods slightly shorter than stock are what you need to keep dead-nut-correct rocker geometry. That's not at all unusual.

What IS unusual is being able to use shorter pushrods and not have the rocker arm start rubbing against the rocker stud's bottom radius, touching the valve retainer at valve-closed position or something else. This is usually true if you're using big fat aluminum roller rockers that are so popular these days even in street motors. Just keep this in mind and measure and check carefully. You do NOT want to fire up the motor and find out the rockers just "self-clearanced" themselves.

That's the long way around the barn to say that stock length pushrods will probably work just peachy. Double and triple check before you decide, however.

 

i used GM head gaskets (F-body ones) so they should be same thickness, and the block wasnt decked, motor stayed in car. Honestly im not sure if the base circle is the same, id assume so but not 100% sure

 

when measuring i put a mark in the middle of the valve long ways and i set it to where the rocker was just about to touch the mark, a little befor it. I dont know if that makes a difference at all?!?

 

On production heads the absolute location of the valve tip does not always put the rocker tip (or roller contact point) dead-center on the valve tip, even if rocker geometry is correct. Ask me how I know. Also, ask the guys who really know about that and they'll probably confirm it with their experience as well. Just putting machinist's dye on the valve tip and shooting for a contact patch in the middle of the valve tip can lead you down the wrong path on a stock head many times.

I set it up so the tip of the rocker (the contact point) starts on the valve tip towards the intake side of the head. Through the first 2/3 of the rocker's travel (up to 2/3 of max lift) the rocker tip contact point should move towards the point where it's as far toward the exhaust side of the valve tip as it's going to go. I call this the "inflection point" but that's MY personal term for it, not the CORRECT term for it, I'm sure. The last 1/3 of the rocker's travel (as it approaches max lift) the rocker tip should be working slowly back towards towards the intake side of the valve tip, but not get back to it's original starting point.

I used to shoot for an "inflection point" at 1/2 max lift, but I have since been schooled by others who know more than me that that's too early. The basic rationale is that you want the rocker tip to do most of it's "moving around" in the lower lift range, where valve spring pressure is lowest. When you're near max lift spring pressure is highest and you want less rocker tip movement. Hence, the rationale for shooting for it at a slightly higher 2/3 of max lift.

The absolute location of the contact points may not be centered perfectly on the valve tip. It's the sweep and motion of the rocker tip across the valve tip that is important. Production head tolerances are not tight enough that you can just screw in some rocker studs, slap on some off-the-shelf rockers, get some custom length pushrods and nail it dead-bang on the center of the valve tip most times. Believe me, I've tried. Rarely does it happen. Watch rocker tip motion- that will tell you the truth.

BTW- you'll be buggy as an anthill after watching it go through it's travel several hundred times with different length pushrods, trying to make sure your brain isn't seeing things that aren't there. But after a while you get an "eye" for it and you'll get close to sanity much more quickly. Alway start with stock length pushrods if you can- they'll often be pretty close to correct unless you cam has an altered base circle or really radical lift vs. stock.

 

awesome. thank you for that! ill try it tomarrow after work and post what i come up with.. basically its either gunna be 7.20 or 7.15 pushrods