L98 upgrade?
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6th Gear
Joined: Mar 2020
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L98 upgrade?
I recently purchased a 1985 2D coupe with the l98 motor. I was curious on what upgrades, mods or even new engine I should consider. I have heard that the TPI is an awful thing on these engine and my car does need new injectors. It runs fine started on fluid. I was wondering should I consider a swap from TPI I have about 3000$ to spend.
Team Owner
Joined: Aug 2004
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From: Park City Utah
3 Grand? Are you doing the wrenching yourself? If YES, then I'd find a used TPIS Mini Ram, some good headers and dual exhaust and install those. Maybe add a cam if there were money left over.
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6th Gear
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Race Director
Joined: Mar 2018
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From: Golden Colorado
L98 get a lot of bad rap. Depending on emission laws where you live there is a lot that can be done to help them out. Maybe never be the greatest race car but can be made very good for street. If it only starts on fluid but runs fine check for a bad cold start injector.
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6th Gear
Joined: Mar 2020
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L98 get a lot of bad rap. Depending on emission laws where you live there is a lot that can be done to help them out. Maybe never be the greatest race car but can be made very good for street. If it only starts on fluid but runs fine check for a bad cold start injector.
Team Owner
Joined: Sep 2001
Posts: 62,178
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Depends on the goal you have for the car and how much you are doing yourself. If it needs new injectors, then I would spend the money on that item first. It should never need fluid to start, so figure out whats up with the fuel system.
85 is really restricted by the '624 Iron heads, but those can wait if necessary. The intake system at a minimum needs porting out, and the exhaust should be opened with 1 3/4" headers. Going to a Miniram would be fine but it would not run perfectly with those heads and the 85's factory tuning, you'd have dead spots and probably lack fuel on the upper RPM band.
Not as much choice is available for upgrading the Plenum/Runners/Base as there was a decade ago, but if you wanted to keep it looking like a TPI-intake, you can find some of them on ebay. Port the plenum, get bigger Runners, and a bigger base, and you'll help it a lot but stay under your budget.
85 is really restricted by the '624 Iron heads, but those can wait if necessary. The intake system at a minimum needs porting out, and the exhaust should be opened with 1 3/4" headers. Going to a Miniram would be fine but it would not run perfectly with those heads and the 85's factory tuning, you'd have dead spots and probably lack fuel on the upper RPM band.
Not as much choice is available for upgrading the Plenum/Runners/Base as there was a decade ago, but if you wanted to keep it looking like a TPI-intake, you can find some of them on ebay. Port the plenum, get bigger Runners, and a bigger base, and you'll help it a lot but stay under your budget.
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6th Gear
Joined: Mar 2020
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Depends on the goal you have for the car and how much you are doing yourself. If it needs new injectors, then I would spend the money on that item first. It should never need fluid to start, so figure out whats up with the fuel system.
85 is really restricted by the '624 Iron heads, but those can wait if necessary. The intake system at a minimum needs porting out, and the exhaust should be opened with 1 3/4" headers. Going to a Miniram would be fine but it would not run perfectly with those heads and the 85's factory tuning, you'd have dead spots and probably lack fuel on the upper RPM band.
Not as much choice is available for upgrading the Plenum/Runners/Base as there was a decade ago, but if you wanted to keep it looking like a TPI-intake, you can find some of them on ebay. Port the plenum, get bigger Runners, and a bigger base, and you'll help it a lot but stay under your budget.
85 is really restricted by the '624 Iron heads, but those can wait if necessary. The intake system at a minimum needs porting out, and the exhaust should be opened with 1 3/4" headers. Going to a Miniram would be fine but it would not run perfectly with those heads and the 85's factory tuning, you'd have dead spots and probably lack fuel on the upper RPM band.
Not as much choice is available for upgrading the Plenum/Runners/Base as there was a decade ago, but if you wanted to keep it looking like a TPI-intake, you can find some of them on ebay. Port the plenum, get bigger Runners, and a bigger base, and you'll help it a lot but stay under your budget.
Pro
Joined: Jun 2008
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From: Louisville Kentucky
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I think the L98 TPI is no slouch stop light to stop light, anything above 3500 RPM though is a different story!
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Team Owner
Joined: Sep 2001
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From: Athens AL
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I had assumed it was injectors because it had ran on starter fluid. Another user suggested cold start injector could be the issue. But thank you for the great suggestions! I was looking into porting but I figured I would most likely want to go to for bigger heads. Any suggestions on that?
Keep in mind that you have 76cc chambers now, so most heads will have 64cc or smaller, pushing you up from 87 octane to Premium gas because of the big jump in Compression ratio, unless you try to do something else to tweak it back down. 85 has TRW forged pistons, I would want to keep those.
Thread Starter
6th Gear
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Thread Starter
6th Gear
Joined: Mar 2020
Posts: 6
Likes: 0
Difficult to give a pinpoint rec on heads until you tell us more goals. If I were staying as a 350 for the long term, I'd look at 180-190cc AFR heads, but you can go with other brands like Dart Pro, or even find a head off an 88-91 engine, the '113 head is a good head up to about 350bhp.
Keep in mind that you have 76cc chambers now, so most heads will have 64cc or smaller, pushing you up from 87 octane to Premium gas because of the big jump in Compression ratio, unless you try to do something else to tweak it back down. 85 has TRW forged pistons, I would want to keep those.
Keep in mind that you have 76cc chambers now, so most heads will have 64cc or smaller, pushing you up from 87 octane to Premium gas because of the big jump in Compression ratio, unless you try to do something else to tweak it back down. 85 has TRW forged pistons, I would want to keep those.
