DanielRicany

Hi guys, I have a 1985 Corvette, I already have everything set up to utilize these heads but I just want to make sure on the specifications.

My stock heads have a 76 CC chamber I believe, and 9.0:1 Compression ratio. The newer L98s, such as a 1991 car has a little bit higher compression with 58 CC chambers. So, is there any difference between the piston design for compression ratio from 1985 - 1991? Because I would like to special order the 58 CC heads so that I can get the same compression ratio as a 1991. Or should I go with 65 CC?

Thanks a lot.

GREGGPENN

The pistons are different. Get the 65cc heads. Don't fool with angle-milling below 60cc. If you know enough about what you're doing (and compression) and want to flat-mill a bit, fine. Make sure you setup your head gasket in the .035-040" range.

DanielRicany

Okay. Thanks. This is the gasket that AFR offers, it is a #1003 Fel Pro. Summit racing has this listed with the specs here. I believe that the compressed gasket size is .041" for this gasket. Will this work? Thanks! http://www.summitracing.com/parts/fpp-1003

cumbercr

Stick with 65cc chambers. Any smaller and you will restrict what you can do down the road. With a stock bottom end you should get a nice boost in compression to about 9.75:1.

The question is how long you intend to stay with the stock bottom end. Today you likely say this is it. But a year or two from now the bug may get you to bore and stroke. Then you'll be glad you stayed with 65's.

Your stock heads have straight plugs. You probably want to go with angle plugs for better clearance with headers. 7/16 rocker studs might also be a good add. Have you selected rockers?

DanielRicany

I haven't chose any rocker arms yet. I was going to use the stock ones for now and maybe go to 1.6s in a few weeks.

cumbercr

You definitely want to go with roller rockers. You can pick up horsepower just from the reduced friction as well as the ratio. But be advised, you will need different valve covers. Roller rockers of any make will have clearance problems with stock covers. Stay with short valve covers or you'll have interference with the wiper controller on the drivers side. AFR makes some nice covers for a reasonable price and you can be sure they'll clear.

vader86

Yeah I'm using the AFR crinklecoat covers, they'll clear.

cumbercr

The 85 is a different animal. Trust us, they're 76cc.

Tom400CFI

You can run stock covers with roller rockers if you break or grind the oil dripper tabs off the inside and (maybe) do a very little grinding on the inside of the intake side of the cover. They'll fit. I've done it.

GREGGPENN

FWIW...there is a mindset of people who believe an increase in compression -- w/o redoing bottom-end -- will increase the odds of early blow-by. That COULD mean looking at a bottom-end sooner than you'd like. All the more reason to plan for the future.

A .041 gasket is a good choice. FWIW: Cometics are the Cadillac of head gaskets. There is a Victor NitroSeal that some use to bump compression (higher) without milling. It's a .028" gasket. As long as you have the piston/valve clearance, going smaller than .035" works. Larger than .040 is what tends to increase odds of detonation.

DanielRicany

So will my stock valve covers with the AFR 195s clear the windshield wiper motor?

vader86

Yes if you grind inside for clearance.

cumbercr

Yes. The potential interference is when you go to roller rockers. Rollers are a little taller and will interfere with the tabs on the top of the covers. Those tabs can be removed. They also will contact the inboard wall of the valve cover. One remedy is to grind out the inside of the valve cover wall to eliminate the interference. How much grinding is needed will depend on the roller rockers you select. I had one set where I had to grind off the corners of the rockers which is something I did not want to do. If you have some extra bucks, the easy answer is a new set of covers that are designed for roller rockers.

l98tpi

Nice choice with the heads. Are you installing a different cam at this time and I would suggest to go ahead and get your roller rockers since you have it apart.

powerpigz-51

So....just for discussion here.....saying your pistons are around 20 thousands in the hole (flat tops)....is it better to go with a thin gasket (smaller quench) and more compression? At 65cc with a thin gasket, the compression is getting up there. So what would be better for taming detonation....proper quench (in the 40 thousands range, high compression) or less compression, higher quench measurement? I understand zero deck would be optimal, but stock, those flat tops are gonna be down in the hole a ways. It seems to me that a larger chamber head set at proper quench would be optimal.

DanielRicany

Okay, also, what size push rods will I need for these heads? I need to get hardened pushrods and since there is a change in the chamber size, I assume there will be a change in pushrod length. Thanks!

cumbercr

With .020 deck and .041 gasket thickness he's looking at approx. 9.75:1 CR. I'd say compression won't cause detonation. I'm running 11.2:1 CR with my AFR 195's. But AFR heads are known to need less timing. The OP has the equipment to burn a new chip. So changing the timing table shouldn't be a problem.

A thinner gasket would improve quench.

cumbercr

Chamber size does not effect pushrod length. I found the stock length worked. The only way to know is to check with the heads on.

DanielRicany

So what is the stock pushrod length for the 85?

DanielRicany

Also the 870 computer does not record spark counts and timing tables and stuff, so can I just retard base timing to make up for it?