Billiumss

iTrader: (11)

Ok, you have a stock engine, it comes with 7.400 pushrods, correct length for best performance and reliability, according to GM design.

You add a aftermarket cam to the engine with the same base circle as stock along with using the stock heads, GM head stock gasket (heads never pulled) , & stock 1.7 rockers, you use aftermarket hardened 7.400 pushrods. 95-99% of the time, this is the most accepted practice and usually no one ever has any problems.

When you install some aftermarket heads that are out of the box and were never milled, technically you should still be able to use a 7.400 pushrod since the aftermarket head is suppose to model the GM design as far as rocker height mounting in the head when compared to a stock head.

Stay with me, I'm going somewhere with this...

When you mill the heads (aftermarket or stock) by like say .025" and use the same type/kind of head gasket (thinkness) wouldn't you use a 7.375 pushrod to compensate for the milled heads?

My thinking it that this should work fine for most people. Most people don't have either the time, knowledge, experience or tools to properly check pushrod length with hydraulic roller lifters, myself included.

So basically what I am asking is, is it safe to say: mill your heads by x amount and reduce your pushrod length by the same x amount if all other things are equal/same?

racer7088

Yes in general you are right.

Billiumss

iTrader: (11)

I asked a similar question 4 years ago:

https://ls1tech.com/forums/generation-iii-internal-engine/68763-should-i-have-my-heads-milled-010-a.html

Ferocity02

iTrader: (60)

As Erik said, you are right to a certain degree. If you mill the heads .024", you would technically want 7.376" long pushrods. However, you will never find any off the shelf pushrods of that length so you would go to the next closest length. Now, how much difference in length you can get away with is a whole different story. Getting a longer pushrod than what you want will increase your preload, which isn't a bad thing, as long as you aren't opening a valve. This is real general though. I can't give you exact numbers.

racer7088

I am keeping the different .025 increments in stock myself as this happens a lot but your right that they are not normally available easily at least.

BriancWS6

iTrader: (18)

The stock 7.400s actually measure out to ~7.385, so you would increase preload a little if everything was the same. But another thing to consider is that most aftermarket camshafts will have a smaller baselcircle, somewhere around .050.

Here is an example of my setup that is on the way, and how I determined "on paper" what the proper length PR should be for my application....

Heads milled .024, .040 gasket which is ~.016-.018 thinner than stock, ~.050 smaller basecircle camshaft. So the .050 smaller basecircle would reduce pre-load by that much, then you would get some of it back with the mill and thinner gaskets and are within ~.008-.010 shy. Now with the closer to "actual length" 7.40 aftermarket PRs over the stock reading 7.385s, you gain some pre-load and are left with ~.005 more preload than stock. Here's the math: 7.385(stock length PR)-.050(smaller basecircle)=7.335+.040(mill and thinner gasket)=7.375+.015(longer aftermarket PR)=7.390=~.005 more than stock

black_knight

iTrader: (1)

Your concern is valid. Engine builders who know their stuff will measure pushrod length and put in a custom-length pushrod. It says in big letters on my cam card: "MEASURE AND VERIFY PUSHROD LENGTH!"

MIGHTYMOUSE

iTrader: (59)

i have dealt with a lot of pushrods lately and i say if you are within .050 of perfect then you won't notice any difference.