Damn, Preload makes a difference!

[Jon89LE]

Well i just took my car to the track and by going from the 1/4turn of preload to 3/4turn i went from a 17.1 to a 16.5 with a 60ft of 2.21. Anyone ever figure out how much each turn on the iron head studs equates to on preload?

[Wolf]

I think a motor gaining power with more preload means it would make more power with a bigger cam

[geoffinbc]

What is the thread pitch? I calculated it before and 1.5 turns (factory spec) was .060 I believe. Cant remember for sure

[Jon89LE]

Oh Damn. Yea, you calculated it before but never got back to me on it! lol. If thats right then i should still tighten mine a bit more.

[geoffinbc]

I will go and get on of my old studs an throw a thread guage on it one day. Dont rush me :P . I will do it some day.

[Jon89LE]

Haha, it cool dude. I never knew preload could make such a big difference like that. Once break starts i may go ahead and tighten them a bit more depending on your PENDING information . If i can get my 60fts to around 2.1x that will be good for a few tenths off my quarter.

[geoffinbc]

Ok got it. The thread pitch is 1 thread per MM
So 1 mm advancer per turn. Stock instructions say to advance it 1.5 turns. So that is 1.5MM of preload which is 0.0590551" close enough to .060" I think hey?

Now crane suggests to adjust between .020 and .060. So adjusting to stock is right at the high side. But acounting for wear over time it is probabally optimal.

[RacerX11]

You are forgetting to take into account the rocker ratio. By tightening the rocker adjusting nut 1.5 turns, you are moving the rocker pivot ball down by 1.5 mm. The valve end of the rocker stays put, so with a 1.5:1 rocker, the pushrod end of the rocker would move down by only 1mm (1.5mm / 1.5 rocker ratio), or 0.040", right in the middle of Crane's spec.

Marty

[geoffinbc]

Right. Forgot that part.

[Jon89LE]

With what you said about the rocker ratios, im not sure if i have it right so let me know. Say you have a 1.5 vs a 1.6 rocker, would a 1.5 turn on each result in more preload on the 1.5?