The good news of this weekend has me thinking I should "freshen" my motor. Right now it's leaking oil from several places and is burning about a quart per tank (optimistic estiamte). It has ~125 psi of compression across all 8 cylinders. The 78 Corvette has 1969 300hp 041 heads on it, and a 010 block. Both I am told are good places to start. I was planning on grabbing some Keith Black flat top cast pistons, hone the cylinders (bore only if necessary), replace all the gaskets and rod/main bearings. I have good oil pressure so I wasn't going to touch the cam bearings, although I might pull the cam out to see what it is. The idle is VERY lopey, but I still have minimal top-end. I plan to do a 3 anlge valve job to the heads. Opinions are welcomed and I have a couple of questions:

1. what compression would I see with 64cc heads and flat top pistons. 10:1? My goal is about 9.5:1

2. What is a good stall converter rpm? I was thinking about 2200-2400 rpm. I still have the original rear gears (3.08 I think).

Thanks,

Aaron

 

Compression will be about 10:1 depending on the head gasket you run. I am running a very thin steel shim head gasket with 64cc chambers and it comes out to around 10.3:1 C/R with the forged factory flat tops. Small chamber heads make more compression which will work fine as long as you get a cam to match. Go with a Comp 270H or the "962" factory 350/350 cam and you will be fine. I would seriously consider doing a pocket port job on the heads before you send them out for a valve job. That is worth 30 HP with no trade off at low RPM. Stock converter will work with either cam. I run a similar setup to this with the "962" cam and it works fine with the 3.08 rear end.

-Mark.

 

Hmm;

Sounds about right. I'm doing the same thing, but starting with a
separate block so that my vette still runs until I'm done with the motor.
041 heads, 80's 4bolt block, looking at flat top pistons.

Which pistons are you looking at? KB sells three sets,
KB120 the standard one 5/64 rings,
KB 3418 - a claimer piston
KB 231 a lightweight piston 5/64 rings.

I've been looking at the lightweight one - it weighs 93g less than the '120.
This becomes 744g less weight for the pistons and weight to be removed
from the crank.

Both these pistons produce 10.0+ : 1 for 0.030 pistons on a 64cc head.

 

I'd say you'd be about 10.1:1 for flat-tops even w/ a good modern composite (thick) headgasket presuming the heads have never been milled (do you know that for sure?)

I would recommend a thicker modern head gasket like say from Felpro - roughly .040 thickness compressed. It will seal well and accomodate any slight imperfections in your decks.

For pistons rather than flat tops I'd consider some valve reliefs - roughly -6ccs displacement would get you to 9.5:1 in combination w/ 64cc heads, and the gasket mentioned above. How about hypereutectics from Silvolite, TRW etc...?

I agree w/ your approach of keeping a bit south of 10:1 for a comfortable safety margin esp w/ iron heads.

If you cam is lopey - see what it is and if it turns out to be a more radical high RPM cam as I suspect - for a little extra change go ahead and spring for a new cam/lifters more appropriate to the RPM range the engine is built for and you operate under. My hunch is your engines top end and your cam's top end are NOT the same thing(?). Perhaps a modern cam that is no more radical than an L82/L46 cam or that ballpark would be a good fit. That's where I'd start at least. I know most folks are entralled w/ hi RPM cams but I'm one of those that believes there's something to be said for a cam that delivers good broad torque across the lower (operational) RPMs - say 1500-4800 rpms.

good luck and don't forget to dial in your ignition curve if needed.