RME1993

Hello Everyone,

I have a 1985 Corvette and in the past year and a half I rebuilt the engine with performance parts. I have a new timing chain, new harmonic balancer, new Trickflow mild camshaft, new high performance aluminum Trickflow heads, smog delete and bigger injectors with a few other upgrades.

I'm contemplating adding a mild supercharger or a turbo to the L98. However, the bottom end of the engine is still stock.

And any idea how much HP the transmission can support before I have to start thinking of replacing it?

Has anyone here ever added a small turbo to a L98 engine with a stock bottom end?


I'm seriously considering going that route but don't want to bend a piston or blow a ring.

vader86

Did you pick the heads with the idea that you would put forced induction on this? What is the new compression ratio with the new heads.

85 has forged TRW pistons so you're fine there. You just have to worry about age. It may last a long time, it may not.

The transmission does not break from HP, Torque breaks things in the 700r4, and the resulting heat stress. 375-400 is going to be about the limit for reliability long term. I ran 500 lbft through stock 700r4 for a few years, so long as you don't gun it every chance you get and arent racing, it can handle the power, but that varies for different people. Finally my 1-2 shift went bad and I replaced with a built one. If for whatever reason you cannot do the tranny anytime soon, add an additional cooler.

RME1993

Hi Vader,

I think we spoke a few months back when i was adjusting valve lash on the heads. Truthfully, I'm not sure what my compression is yet on the heads. I'm about to have a compression test done with a dyno test as well.

I'm actually having a rough 1-2 shift right now which is why i brought up the transmission in the first place. I believe the acculumator spring/housing is going bad so I'm dropping it off at a transmission shop next week.

I do remember hearing that the crank/pistons are forged and are actually very strong.

When you had a rough 1-2 shift you had to replace the transmission altogether?

RME1993

Iv'e read that the acculumator spring is actually very common to replace on the 700r4 transmission due to rough 1-2 shifting.

vader86

I knew a the transmission would eventually go out, so I had been saving for a new on already when I felt the 1-2 was so bad that it was time to put in a beefed up unit. So yes, I replaced altogether before it actually failed.

Did you find the specs on the heads, to get the CC on the chambers? That will be the main thing. 85 had 76cc originally.

aklim

IDK what the specs were for torque when I put an LPE short block with TFS heads. With his massaged heads, the 383 was rated at 430 CHP. I suspect mine was 400 tops since I had the crappy TFS heads and neither that nor the intakes were ported. Even then, Lingenfelter asked if the trans was stock and I told him it was a fresh GM rebuild under warranty a short while ago. He told me it would die soon. He gave me a year and it died in 9 months and I wasn't stomping on it.

RME1993

Here's the paperwork for the Heads

vader86

Looks like 62 cc? From 76 cc and with no other changes, your current CR is likely too high for a turbo addition. What thickness of head gasket did you use

RME1993

Unfortunately I don't have the info for the head gasket on hand. I Installed the head/gaskets over a year ago. They are Felpro gaskets tho. I'll double check my paper work when I get home.

RME1993

Intake runner volume: 195cc
Combustion chamber volume 62cc
Exhaust runner volume 75cc

RME1993

So in other words my compression should spike with these heads.