on an 87 GTA, i want to use a set of lunati solid rollers, i have the oem rollers now, i am wondering does anybody know if a pushrod length is required, i am guessing i will need a longer rod. i was hoping someone out there has done this.

T.I.A.


Scott

 

well my set needed a longer pushrod but that cuz i went to a .9" base circle cam for the stroker motor.

just use a pushrod length checkr. makes it easier.

 

Just use regular 7.800" pushrods, but you might need +-.100", but i doubt it.

 

87,

In changing the hydraulic roller to solids, you ARE planning to change the camshaft too, right? After all, we know that you understand that a hydraulic cam lobe, whether flat or roller, had a fast preload ramp to hydraulically "lock" the lifter at a fixed height, while a solid lifter cam lobe, whether flat or roller, has a very gradual pre-lash ramp. Installing the solids over a hydraulic cam will make the valve actuation very harsh and noisy, and may make lash adjustment very difficult.

Of course, you already knew that.

 

Vader, yes i know that. the whole set up will be. 58mm lingenfelter, on a fully ported plennum,slp reworked siamese runners, tpis ported intake, l98 cast iron heads ported, with a bowl job, currently 1.95,1.5 valves, 1.6 rollers on the intake and 1.5 on the exhaust. havent decided on the headers or the cat back yet. cam will run .272/.242@50, at.572 lift on .112 centers.

thinking about 2.02,1.6 valves. any ideas on headers and exaust??? or whatever. all input is appreciated


Scott

 

Whenever you build a non-stock valve train, the optimum push rod length for your specific combination cannot be predicted accurately beforehand. You should buy a push rod checking tool to find the correct length for your engine.

Don't bother worrying about whether your existing ones will work, they probably won't be the right length. Although they might be. But don't count on it. Build the motor first, then measure, then buy push rods to fit.

 

That's a lot of duration and valve action. It should have a very eventful idle, at least. You'll probably be idling in the 900 RPM range just to keep the mounts from being beaten up.

As long as you are going through all that head work, and have a lot of lift, you might consider changing the valves to 2.02/1.60 and using Race-Flo or something else lighter than the stock pieces. Since your lifts are approaching 0.600", you're going to have to machine the other side for good springs anyway, so you might as well have the machinist flip the heads and bowl port/machine for larger valves. The seats in your iron heads should be hardened at least deep enough to support that, or can be flame- or induction-hardened after machining and before the final grind and lap.

You can either buy a push rod checker or make one easily with a 10-32 stud and tap and an old push rod.

 

im curious, how to use a pushrod length checker... heh..

i have 2 (Crane PR checkers) and im assuming you just adjust them till the rocker tip sits near the front-middle of the valve.

then you measure and order.

right?

 

from what i understand, you would set the cam at the base circle,( opposite of the lift side) take up the slack on the adjustment rod, and rotate the cam, keeping an eye on the roller tip, where it meets the valve stem. in the perfect world the roller tip would stay in the center of the valve through 360 degrees of rotation, however i understand an .050 deviation is acceptable. pull ot the rod measure and thats the length.

hopefully someone who has done this, will jump on and correct me if i am wrong

afast87

 

,

yea i know, its a ton of lift, i worry about vaccum. i figured on having the spring seats machined, i may just change the cam specs, i still want it to be streetable, and under 13.00

 

so it doesnt matter where the roller tip starts or stops, just as long as it doesnt move left or right?

 

damn that cam is huge... i hope you have solid motor mounts

 

i am not sure i understand the question, or i did not explain it properly. if you are working from the side of the engine,the roller should be set in the center of the valve stem. the pushrod length will change where the contact point is. the roller it self is wider than the valve stem, so any left or right can be absorbed. we may be saying the same thing, just not sure what your frame of reference for left/right is. in any case, from what i have read only .050 inches of movement from center in either direction is acceptable.


scott

 

okay i guess what im saying is....

The roller tip sits on the valve. when the pushrod is the correct length, the roller tip will sit in the MIDDLE (DEAD MIDDLE!) of the valve right?

Then as the valve opens, the roller will do WHAT:

A: stay in the DEAD middle of the valve
B: move towards the lifter valley(right) (to the middle of the engine) but stay centered on the valve (not move left or right, not move to the front of the car or to the rear)
C: move AWAY from the lifter valley (left) but stay centered otherwise.
D: Not move at all... (same as A
E: None of the above.

 

Optimum pushrod geometry is where the tip of the rocker moves across the valve tip the shortest distance during a cycle. This results in the least amount of side loading on the valve guides. Depending on the design of the motor, the rocker may or may not be centered on the valve stem, may go across the stem and part way back, etc. etc.

I use gear marking compound, or white lithium if I don't have any, and a checking spring, and look for the narrowest pattern.

http://www.competitioncams.com/catalog/278.html
http://www.competitioncams.com/catalog/279.html