Thoughts on possible mods - 90 l98 automatic
Thread Starter
Instructor
Joined: Jul 2007
Posts: 236
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From: Mobile Alabama
Thoughts on possible mods - 90 l98 automatic
Here's my plan for mild mods which should improve hp and fun around town. On intake side open air box & 1.6 RR - on exhaust a true dual running off the stock ss manifolds, ditch the cats, air pump delete kit, and 3.73 gears for rearend. I know this is pretty steep for auto but I drive mostly around town. Some on interstate but not that much - I currently have 2.73's. What are your thoughts on this setup? Anything I should also do - I'm wanting to keep driveability good but improve hp and quickness. How do higher stall torque converters help in street quickness - do they act normally if you are just driving around town? The car has 90000 miles currently and seems to run good. Would I need to have a tuned chip?
Team Owner
Joined: Nov 2001
Posts: 34,124
Likes: 105
From: Pensacola FL
On my 1990 'vert, I did air-box and 1.6 RRs first. Unfortunately, my L98 puked shortly thereafter. Soooo, I had a budget 383 short-block built, cleaned up the 113 heads and added Hooker headers to 3-inch exhaust. Stock convertor, factory TPI intake and stock rear. It wasn't the fastest Corvette, but was a giggle-inducing, tire-melting, sideways-steering carnival-ride...
Pro
Joined: Jun 2007
Posts: 626
Likes: 2
From: Coquitlam British Columbia
I have a 1990 Vert that had the 2.73 gearing. Just went over to 3.54's but with the 2 series carrier still and went the thicker ring gear route. I find the 3.54's just right....pulls sideways and instint power. Watch your rpm's with the 3.73 route...Im running a good 400 rpm more now in the 50-75 mph range with the 3.54's.
Team Owner
Joined: Dec 2000
Posts: 21,094
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From: Phila., PA burbs
If you're gonna be using it mostly around town you'll be fine with 3.73s, but if you see any drag strip time I wouldn't go steeper than 3.07s with a stockish L98. 3.07s and a slightly looser converter (2500 stall or so) will be fine on the street. If you're doing the exhaust, you might as well put headers on it. None of the mods you mention will require a custom tune. 
Advanced
Joined: Oct 2003
Posts: 94
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From: Chattanooga TN
I agree
I agree that 3.07s would be the best for an automatic L98 with the TPI still on it. 3.73s, I believe will cost you acceleration and gas, b/c the motor will want to be revving past the peak torque/Hp band of the motor. Now, I do have 3.73s in my 1985, but I also have a Holley stealth ram intake, completely modified motor that produces peak HP at 6300 rpms. I had 3.08s in it before with an automatic 700R4, and it really liked the 4000-5000 rpm range, which is where I believe you will want your motor to hang out mostly. I also had a 2800 stall converter. Mind you, with all the power I was making, the auto didn't last long. But, if you're only doing the mods you're talking about, the auto the way it is, should be great. Anyway, my two cents. I really think you should be able to make a mean 1/8th mile car with that TPI, and 3.07s. I had a friend with that exact setup and he was running 8.5s in the 1/8th mile, totally owning some of the Z06s. Of course, the 1/4 mile is a different story.
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Le Mans Master
Joined: Jul 2007
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From: Tampa Florida
If you're gonna be using it mostly around town you'll be fine with 3.73s, but if you see any drag strip time I wouldn't go steeper than 3.07s with a stockish L98. 3.07s and a slightly looser converter (2500 stall or so) will be fine on the street. If you're doing the exhaust, you might as well put headers on it. None of the mods you mention will require a custom tune.
The mods you talk about doing in post #1 are pretty close to what I'm currently running except I have a 3K stall converter (maybe just a bit too much), a ZZ4 cam, port work and some other bolt on goodies. I'm very happy with my combo since it is fairly quick off the line. Getting 17.3 city ~ 22 Highway
