Will adding 1.6 rockers to an otherwise stock engine change the geometry causing me to install different pushrods? If so, could someone explain why to me?

 

I have been told that you would not have to change the pushrods but...... a buddy of mine put 1.8 RR on his normally 1.7 RR LS1 and it would not crank because there was no compression. It sounded like a DC motor running when he tried to crank it. He had everything setup right per the instructions but they still didn't work. So the moral of this story is I don't know but it is a good question that I would also like to hear the answer to.

 

I went through a simmilar situation. I used 1.6 to 1 aluminum roller rockers, and a racer friend of mine (dirt track) said that I needed to use +.100 pushrods. He said that the pushrod is tilted more toward the stud and requires more length to acheive the proper rocker geometry. In his situation, I later found out that this is bunk. He doesn't build his motor and has no clue why the longer pushrods are in there. I think the added length of the pushrod is because he is using a "small base circle" cam to achieve .750 lift, but I could be wrong.

I have other friends that have used a 1.6 with stock length pushrods on an un-rebuilt motor, with no problems yet.

I had to use custom length pushrods (7.650 inches, -.150 shorter), because I didn't know what I was doing when I had the heads off my 350 re-done. I ordered dual valve springs (1.46 dia.) that had an installed height of 1.8 inches, the factory springs install at 1.7. So to reduce (in my un-educated theory) the amount of machining into the heads for the springs, I ordered a set of valves that were +.100 longer than stock. When I got the heads back the springs all had shims under them that are around .100 thick!

I didn't take into consideration the amount of metal being removed to widen the pockets!

To make a long story short, I looked up the info on the CompCams website to get the scoop, and bought an adjustable pushrod to determine the proper pushrod that I needed. Every application is differen't because there are so many differen't variables to take into consideration, so I think the 12 or 13 bucks was worth the expence to know it was right.

<http://www.compcams.com/Technical/Products/Pushrods/>

EDIT: I forgot to state that if you buy the checking tool from ComCams and get it set in the motor where you want it, send it back to them and they will messure it and sell you a set of pushrods identical in length, and send it back to you with the new pushrods.

 

going to 1.6 rockers with a stock engine should not require a change in push rod length, however the only way to know for sure is to dummy up a pair of valves and check the geometry.

 

You shouldn't have a problem with stock parts. But when you deck the block, add aftermarket heads with thicker decks, stick in an aftermarket cam it gets worse.

Car Craft just did a good writeup on this. Link: http://www.carcraft.com/techarticles/116_0401_push/

 

I haven't had to get different length pushrods, but depending on the heads you use i have had to slot the pushrod hole a little bit. The length has more to do with the rest of your engine assembly, especially if you get a small base circle cam.