00Wildcat

'04 5.3 iron block engine all stock top to bottom except '02-'04 Z06 cam. checked lifter preload w/dial indicator on rocker tip at pushrod cup. From top of plunger travel stock pushrods .075", Texas Speed 7.400 =.080, unknown moly 7.450=.138 preload compressed from top. I'm not using stock pushrods, so do I use the 7.400 TS or 7.375 for .055 preload? I really want to put the engine in the car tomorrow but can wait a couple more days if .055 is really a much better choice. Oh it has new yellow GM springs and will probably get some form of turbo charging in the near future and is a Daily driver.

00Wildcat

If anyone is interested I already had the 7.400 TS pushrods from my '04 6.0L with LS9 head gaskets, LS9 heads, ARP studs and COMP 3720r/3712R (which I know is very mild and *** backwards for rectangle ports) w/7.400 preload is .109". Glad I checked looks like I need 7.350 pushrods for it.

Just had a thought, less than 1/2 mile up the road is "Pushrod Factory" who makes custom pushrods they will be pressed ends though. any thoughts on multi-piece vs. one piece rods?

TrickyTransAm

I would double check it with a pushrod length checker.
I tried the method you did, and it left a larger margin for error.

I would go with the shorter first. See if it's noisy.
They aren't that hard to swap out in the vehicle with most of it being modular anyway.
Everybody I have talked to recommends .050-.060" preload.
0.080" if the shorter is noisy.

If you go too long, you could have noise too from the lifters not being able to pump up, and backfiring. (with lower manifold pressure and compression)

I might be interested in the 7.4's. Doing a trial and error on mine.

00Wildcat

anyone else?

Rat Chevelle

Hi, I am jumping in with a few questions of my own.
The lobe tips do not extend beyond the cam journals (of course or they would never go in) and because of that the only way to add more lift is by reducing the base circle.
Therefore it would make sense to think that you should add half the difference in lift to the new pushrods when changing a cam.
The reason being is that I am changing a cam on a 6.0. This engine had a .550" lift cam (Z06) and when the owner changed it (from the original .500") he had to increase the pushrod length by .025. That is because the Z06 cam had a base circle which was .050 smaller in diameter, therefore to keep the same preload and all it requires half the change in lift (on one side only from the centerline up).
Now with that info, it stands to reason that now that I am changing to a .620" lift the pushrod should be .035" longer (and a full .060" longer than the original one) based on half the reduction in base circle diameter.
None of this should affect the geometry since the fulcrum position will remain unchanged in relation to the valve tip.
What do you think? does it make mathematical sense? of course I will check the pushrod length tomorrow and see if there is any sense to this madness.
Your comments are appreciated.
Rat Chevelle

00Wildcat

you must measure, don't assume that x cam will require y pushrods without measuring what your engine needs.