JJ

On stock L98 cast heads, with proper springs, how much lift is safe with press the stock press in rocker arm studs ?? I would like to get .525" - thanks

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87 IROC, 350/5 speed. gmpp 350, vortec heads w/some work, XE268, 1.5rr's, 650dp, rpm intake, MSD ing., ect.
89 formula, L98.

RB83L69

It's not a question of there being a limit to the lift as such; it's more determined by the max open pressure. Interestingly enough, most higher-performance valve springs have lower pressure at any given lift, but more seat pressure; so by upgrading your valve springs, beyond the minimum recommendation for the cam even, you in effect take load off the studs.

Call Comp and see what they have to say. I think that using that much cam with stock studs is a bad idea. It's a matter of risk: even though it will probably work OK at least for a while with the right springs, it's a bunch of trouble if it screws up which it eventually might, and I hate to do things twice. Personally, I will not put together a motor with over .500" of valve lift without doing the machine work for screw-in studs and 1.45" springs, for that reason; but then I'm a wimp, I like to do it once and forget it, and never have to come back and touch it again or worry that something is going to come through the valve cover at 6500 RPM.

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"So many Mustangs, so little time..."

Vader

JJ,

Two words - Screw it! (or more correctly, THEM.)

You can install a set of screwed rocker studs for less than $20.00 if you have even basic machining skills, a couple of wrenches, and a 7/16-14 tap. The stud kits are about $15.00 from GM (P/N 12371058).

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Later,
Vader
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"I cannot take this any more... Saying everything I've said before..."
Adobe Acrobat Reader 4.0

[This message has been edited by Vader (edited January 09, 2001).]

JakeJr

Well, I've got sad story to tell about L98 cast iron heads and 1.6 RRs.

Interference will often occur at the point the pushrod enters the head at the slot.

I had this happen to my iron L98s and I ended up bending a lot of pushrods. This was after I'd pulled the heads and had the studs pinned to prevent them from pulling.

So the studs weren't the problem.

Anyway, I had to pull the heads again, have the slots elongated for clearance and this time I had the stud bosses milled down and screw-in studs and Moroso guide plates installed.

New .080 Trick Flow hardened pushrods and problem solved.

BTW, I was running a ZZ9 hydraulic roller at the time with .515 on the intake (using 1.6s) and .520 on the exhaust (using 1.5s)

So not only is stud pulling a concern, but pushrod clearance has to be checked too. TPIS warns of this in their 'Insider' booklet. Too bad I didn't learn of it 'til after the fact.

Hope this helps.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

JJ

thanks guys - points I will certainly follow.