daveSS1987

Ok here is the question, I have a 1989 L98 from a GTA. I also picked up a set of heads from a 1989 Corvette (113 casting) and a ZZ4 roller cam. If I don't to do a complete rebuild (still have to pull heads & check bore) my question is are the Corvette pistons different from the GTA pistons in the L98? what compression ratio will changing from the 64cc L98 iron heads to the 58cc aluminum Vette heads do? I have an early style Edelbrock intake to fit the Vette heads, am going to run a Quadrajet, and replace the L98 cam with a ZZ4 cam. What kind of power will this make, and will the compression ratio be pump gas friendly? looking for some basic facts regarding piston size on the 2 diff. engines. Are the L98 pistons similar to the ZZ4 pistons or do the ZZ4 give more compression ratio? Also what is the compresion ratio using the iron L98 heads?
Thanks for the information...
Dave

sofakingdom

iTrader: (1)

That should give you a CR somewhere in the high 9s to low 10s. Perfect for that cam.

That's a known good combo, should be a good driver.

I'd leave the destination bottom end alone, if there's nothing obvious wrong with it.

Damon

Watch your valve lift with true production line Vette heads. While the later ZZ4 heads use the same casting they underwent many subtle upgrades since their use on production line engines from the 80s. Most notably they can handle a TON more lift than the original production line heads, mainly becuase ZZ4 heads have to deal with the .510" lift of the exhaust valves that the ZZ4 cam provides. I've actually worked on a couple sets of original L98 Vette heads and the retainers hit the guildes around .480" of lift, just like many other factory stock heads of that vintage.

I beleive Vettes listed a higher static compression than the same year F-body L98 motors. If true that's almost certainly the result of the smaller ~58cc chambers those heads have. I think it was 9.5:1 vs. 9.3:1 for the F-body motors until ~1990 when it was bumped again to 10:1 (same as the current ZZ4). I'll bet they were dished pistons in the early lower-compression L98s and flattops in the later ones with the higer compression.

daveSS1987

so ZZ4 springs & retainers are all that are needed to upgrade the Vette heads to ZZ4 specs? sounds good. I just want to be sure the cr is not too high switching from 64cc to 58cc heads with the stock pistons.

five7kid

iTrader: (14)

The CR won't be too high.

Springs and retainers might not be enough. You need to check the travel of each valve w/o spring, using the retainers you intend to run, to make sure they have at least .570" travel from seated to the retainer hitting the top of the guide/seal.

Kevin91Z

iTrader: (1)

The Manley 22410-16 and 23652-16 +.050" retainers will work with the Corvette heads up to .540" lift, as I had those springs and that lift safely with my previous combo.

daveSS1987

Will the LT4 valve springs work with these heads? These are the hot cam springs, do not want to machine them, just looking for some drop in springs that will be safe with the ZZ4 cam...
Thanks,
Dave

Kevin91Z

iTrader: (1)

The LT4 valve springs are supposedly the same ones the ZZ4 engine came with, so they'll be fine.