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How to gain performance 1998 automatic ?

red and black

Active member
Joined
Dec 17, 2012
Messages
34
Location
new jersey
Corvette
1998 red vert
Hello and I sure hope someone can start me down the right path. I was fortunate enough to obtain a low mile 1998 convertible with an automatic trans. The car is virtually new with only 6,500 original miles. It has the stock 345 horse engine and I'm not looking for massive gains just modest improvement in perhaps the 30 to 50 horsepower range. With my last 2002 car with a 6 speed they said it was an easy gain to simply swap out the plenum for that of a Z06 and add the cold air kit but however now with the automatic (gear ratio), the gains would be negligible.

Are there any computer mods available for these early cars? With my 2008 Saab, I did have the ECU tuned for a (nominal) gain from 280 to 320 horsepower and with the (heavy), weight of the all wheel drive, though you can't (as some claim), light the tires up, I,m quite happy with the results.

Thanks and any advice is appreciated.
 
A 50 horsepower increase is nothing to sneeze at with add-ons rather than getting inside the engine. The old standbys: a good tune, wires, plugs, intake and exhaust, typically will get to 40 horsepower. After that you have to get serious. You will see ridiculous increases thrown out on forums. Believe the numbers at your risk.

There was an optional rear end for the C5 automatic that really wakes up acceleration, and it is making its way into salvage yards now. I think it makes a big difference.
 
... There was an optional rear end for the C5 automatic that really wakes up acceleration, and it is making its way into salvage yards now. I think it makes a big difference.

That would be the Performance Axle with the 3.15 ratio, RPO G92. The standard axle ratio was 2.73, RPO GU2. Check your vehicle's RPO decal to see what you've already got installed. For '98 model-year vehicles, it's located underneath the driver's side cargo bin cover in the trunk area; at least that's where it is on my '98 coupe. If it's not there, check the other usual location (glove box).
 
Thanks! Yes, there is a marked difference between this car and my 2002 with the manual trans so it must be the 2.73.

I guess with the later cars and those with turbos, from what I can see, the horsepower was there and GM/Saab just made it available with the amount of turbo boost available. They used the same engine in a number of platforms and the same tune would take you from 255 horses to 320 that when done on my car it went from 280 to 320. In my case I had them use HP Tuners through Vtuner (of Vermont), and was very pleased with the results. I know that it's nominal and not "at the wheels" power but the power came in smoother and had an added gain of 3 miles per gallon over the past year. It's no secret that the trick with the Saabs is just allowing the computer to free up more boost and you can see that on the gauge that now goes freely into the red zone.

So am I stuck with the gearing and perhaps the cold air mods only? Supercharging seems a bit out of my needs and financial reach.
 
... Yes, there is a marked difference between this car and my 2002 with the manual trans so it must be the 2.73...

Probably. But I'd still check your RPO decal just to verify it. It could influence what you do next to improve the vehicle's response. Especially since the manuals have yet another axle ratio (3.42) and about 25 lb-ft more torque, so direct comparisons are a bit difficult (comparing apples to oranges to tangerines, as it were)...

... So am I stuck with the gearing and perhaps the cold air mods only? Supercharging seems a bit out of my needs and financial reach.

Those would certainly be the quickest, easiest, and least-expensive things to do. If it's not enough, you can always do more. But the 3.15 axle ratio on the automatic is pretty peppy; that's what I've got in my '98 coupe. It's still not as quick as my '04 with a 6-speed, but it does all right -- for something with a 'slush-box' tranny...
 

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