My L98 short block is out getting rebuilt this week. I'm planning on porting the 083 heads myself.
I'm looking for a way to ensure that the full 9.3:1 compression is delivered even if a few cc's are added to the chambers during unshrouding and polishing. I'd rather not mill the heads, the decks are thin enough already.
Options:
1) Deck the block. Now's the time, it's in the shop.
2) Pistons with smaller dishes. Do they exist?
3) Thinner head gaskets. How much of a difference will this make?

What do the members recommend?

Here's the rest of the combo if it helps...
Ported stock plenum (sp?)
Aftermarket base & runners (not picked out yet)
ZZ4 cam
6-speed & 3.73:1 gears

Not a world-beater, but should be lively. And a big upgrade from the 180 hp/ 225 tq I started with.

 

i just put the fel pro 1094 head gaskets on mine. they are .015" thick. the stock gaskets are .041" thick. so it brings the compression up about .7 ratio. you will need to use copper spray a gasket to aid in sealing. and i cut the heads .010" that's not much more than normal resurfacing. i an also using the zz4 cam. i just put the edelbrock base and slp runners. so the dyno numbers are before the cam and intake stuff.

 

That's a pretty good sized adjustment in CR with just head gaskets. I'll talk to the engine builder about it this week.
Any other thoughts??
mmr23, how do you like the ZZ4 cam?

 

I'm not big on thinner head gaskets.......unless they are of the copper "shim" variety, that's just me.

It's been a few since the last L98 I screwed together, but I'm almost positive that one of the bigger name piston companies makes a forged piston that is right a 10:1 with 64cc chamber heads, why not use it? The guy who drove that motor had no detonation problems with the iron heads and pump gas, as he had the cylinder heads ported by a local shop. If I remember correctly, they were right at 67cc when we measured 'em after the porting and valve job.

Everything else being the same, a 1cc INCREASE in head chamber size drops the advertised compression ratio .1 , so with the stock GM head gasket he was right at 9.7:1


Actually probably a bit more, as when I build an engine, I normally always have the deck of the block swiped as well as the heads, it's minimal for clean up only, but it helps too...

The main thing I care about on a street engine is the quench area, I try to shoot for .040, but again that's just me.......


HTH

 

Hey Mrr23, how do you like that zz4? I just put my motor in and it's got the zz4 in it. Aluminum heads that were milled which brings the chamber CC to 54.8, stock style hypereutectic pistons and the compression comes out to about 10.3-10.5 or somewhere around there. Outta run OK......with 93 octane ($$$)