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.

 

Might want to post this in the tech section.

 

I have seen this and L98 turbo is a great combo.. not sure about stock bottom tho

 

You can run about 6-8 lbs of boost with a good tune.
how long the tranny lasts is largly based on its condition and how you treat it.

Hard "launches" will kill it pretty quick

 

Hi,
do you have the 4+3 DNE or the TH 700R4?
I have the 85 stock L98 for 5 years on the drag strip with a 150 hp shot of nitrous.
She is doing fine and sees street usage even on german Autobahn´s .
Remember : 85 with 4+3 DNE means you have forged pistons,
with the TH 700R4 you only have cast pistons.

Hard launches are not a problem on my stockish engine and transmission.
Both were never refreshed all the way down. For me it works that way.......running a 12.666 on a 150 hp shot
on Hoosiers QTP`s.

 

Depends who you ask. The guys on YouTube and sloppy mechanics would say it will be reliable with 800hp.if you pulled it out of a junkyard.

 

All 85 to 86 e have forged pistons with both trannys.

 

Sure? Where is the proof?

 

The 1982 and 1984 Cross-Fire Corvettes also have the same TRW 464664 forged pistons as the 1985.

The same pistons were also used in the some high hp stingrays.
Same as I read in all forums
I have never read otherwise.
Leftovers from 80s

 

Engine-.350-400 TOPS IMO unless forged, then the block becomes the weak link.
400r trans- = 400hp for a little while in stock form.
Rear end- if auto it will not like it, but if babied some made them last, if a D44 they will take a bunch of power.
DougNash- some people put some good power through them. They are a super T 10 with OD unit on the back.

Many have made 450 supercharged power on stock stuff if tuned right and babied.
Don't forget cooling etc... when you start building you start buying. A LOT!

Your car is old now, that in itself makes for risk.

I have a c4 that was built around power... it is a slippery slope and they were never intended for it.

If your suspension sucks and you don't have c beam plates IMO after 450hp you feel it, the car does not love it, at least mine did not.

 

84 and 85, not 86. 86 has cast.

 

And here's the proof. 86 MVMA specs, Page 26

https://www.gmheritagecenter.com/doc...t-Corvette.pdf

 

And specs for 85 which the OP has, definitely forged.

Page 62

https://www.gmheritagecenter.com/doc...t-Corvette.pdf

 

My 85 with auto trans original engine had TRW forged pistons, you need forged pistons on a blown engine.

 

 

A few years ago I bought a 1991 with 80000 miles and a Procharger on it. I was informed by the previous owner, who had the Procharger added, that the rest of the engine internals were stock. On the dyno when it was being tuned the car made 320 HP at the rear wheels and 390 ft. lbs. of torque. Before buying I consulted Tom Wong, who is the Corvette guru in the area and he said that would be fine with a stock bottom end. So far, I have not had any problems with it, but I do not drive it hard very often. But when I do step on the gas it does go. Below 4500 RPM it made more power and torque than my somewhat modified 2002 Z06.

 

This is a fairly decent guide BUT most engine failures come with rpms not with outright power. Plenty of LT1 guys out there have made 500-600 hp with a turbo on the stock bottom end. (LT1 bottom end is basically the same as a gen 1 sbc) Keep the revs down around 6k and the stock bottom end will probably live for a long time.

One thing I'm not sure I agree with is your claim that the block becomes the weak link after 400 hp... A SBC doesn't crack in 2 like the Ford V8's... Lots of 700+ hp sbc's out there using the stock blocks... Maybe I misread what you meant to say?

 

What I am saying is if you go forged, those parts will then take more than the block, and then the block is the limiter. This game gets expensive.

Yes you can go higher power through a stock block. smart would be 500-600 max! anything else is foolish unless a good builder and lots of time and money for rebuilds. HP is hard on everything.

People make 434 out of gm 400 blocks, but it is not wise and almost always will fail.

You want to make power usually there are no shortcuts. For what he wants he will be fine.

Mustang guys slap top end kits on stock junk and claim 700hp for years and YT is full of vids showing what happens on the road.

My motor is 700n/a and can take a 500 shot.too. It's not stock, even 700 is crazy claims on sbc unless LS and even then to make real 700hp it has to take boost. Unless LS I question all SBC guys with those claims unless they are big cubes, or pumped up LS stuff. If it was that easy myself and others would all have it.

Unless you are talking about just building a rad motor and knowing it will fail when you hammer it after a while. To me that is like throwing a 300 shot on a stock car and saying you have hp and you do a few times, but eventually BOOM.