I need to find the correct pushrod length for my build. I have the comp high tech pushrod length checker that measures from 6.8-7.8 inches.
The more i read the more confusing it gets.

My parts- new comp 850 lifters installed, custom cam, pac 1218 springs installed, and gm 1.6 roller rockers with poly locks.
Any good advice how to go about getting the correct rod length would be appreciated. I understand how to use the exhaust open, intake closed cam base circle method and how to find 0 lash. This is where my knowledge ends unfortunately

 

http://www.hotrod.com/articles/how-t...ngth-pushrods/

Or get one of these and do

 

So you spin the motor at 0 lash, you dont add any lifter preload by tightning the rocker nut?

 

I don't think you'll be far off the stock length of 7.2". If you have an original PR, check the sweep and see if it's necessary to adjust the length.

http://www.hotrod.com/articles/ctrp-...rain-geometry/

 

7.05 sweep, unmarked pic is 7.1 inches. Seems to get the same sweep with 0 preload or one full turn of preload.

 

You want the sweep to be off center more on the exhaust side.

 

So are you saying the 7.1 is better than the 7.05?

 

Pic of 7.05 with 0 preload. Pic of 7.05 with 1 turn of preload on 850 lifters.
Pic of 7.1 with 0 preload. And pic of 7.1 with 1 turn of preload.
Which gives the best pattern?
This is with the comp high tech pushrod measuring tool.

 

I'd do a 7.2 just for ***** and giggles to see what's up. Yes, the 7.1 has a good, narrow sweep on the exhaust side so that would be the one I'd use if the 7.2 is no good.

 

Alright thanks for the info. I will post up pics of the 7.2 in awhile for the hell of it. I remember the 7.2 being to long though.

 

7.0 through 7.15. Looks like 7.05 is money with the most centered patten.

 

I'd do 7.1. Sweep is narrower and is not as centered.

 

I did notice the 7.1 is narrower. But is it good that it extends more towards the exhaust side than the 7.05? Im thinking you are prob correct in that the 7.1 might be the ticket. I didn't use a solid lifter for this but rather the actual comp 850 lifter set at one full turn preload with my pac 1218 spring already on the heads. Ohh well it seems close!

 

The way I understand it is you want to use the narrowest sweep possible. This means the rocker is opening/closing the valve in the most efficient manner. And if that sweep is not exactly on center then you want it to favor the exhaust side.

 

^^^^this

 

Okay that makes sense thanks. Def the 7.1 then! Pushrods are my last piece of the puzzle then i can get this thing on the road for a few weeks before winter hits.

 

SSRRR is correct, you want the sweep as narrow as possible while not on the edge of the valve stem. That gives the least friction and theoretically the most power and lowest wear. Ideally it would be a narrow line off center to the exh side.

Your 7.1 looks on the money .

 

Cool thanks. I need to use a old stock lifter and make it solid also. I will still prob get 7.1.

 

If you used the Proform tool shown in video, you don't need to make a solid lifter.

7.100 is a very common PR size for people with rebuilt motors where the block & heads have been decked. Obviously you still need to measure PR length but from the pics the 7.100" size is the winner