L98 turbo
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Joined: Apr 2018
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L98 turbo
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.
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.
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
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.
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.
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Joined: Apr 2018
Posts: 61
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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.
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.
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?
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Joined: Apr 2018
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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?
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?
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
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.
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.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
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.
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
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
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Joined: Apr 2018
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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.