How do I gain horsepower?

[87vettevert]

I recently bought a 1987 corvette convertible automatic with 105000 miles on it stock motor. im very pleased with the way it looks and runs. I was wondering how to gain more horsepower without tearing down the motor.

 

[ZumZum]

The L98 has on of the most restrictive exhaust systems. A good place to find some horseys is to install a cat back exhaust system or better yet install true dual exhaust and maybe a set of long tube headers.

The intake side is pretty restrictive too. Without tearing apart or replacing components, the best you can do is expand the air filter lid opening (or buy a pre-cut lid from Mid-America or others) also putting in a K&N air filter will let it breathe better.

 

[87vettevert]

Thank you zum zum for being helpful but it does seem like it will be a ten knuckle bloodfest changing these headers. What about excell ignition packs do they work with vettes.... I had them put on my old 72 chevy nova and it made quite a gain in power.

 

[RAYinCA.]

Thank you zum zum for being helpful but it does seem like it will be a ten knuckle bloodfest changing these headers. What about excell ignition packs do they work with vettes.... I had them put on my old 72 chevy nova and it made quite a gain in power.

No need...... Go with Zum Zum. Cat Back and filter lid, K&N.

 

[87vettevert]

what are type of equipment do you recommend for the cat back.....Borla?

 

[Hib Halverson]

It won't increase power output of the engine, but you'll get an increase in seat-of-the-pants acceleration feel if you change to the 3.07 axle ratio.

As for bolt ons that work on a stock L98, the exhaust mod is one but in New York, you have emissions testing so "true duals" are out. You'll gain 5-7hp by going to a low restriction "catback" exhaust and a better cat converter.

Adding headers might gain another 7-10 hp.

Lastly, keep in mind that any bolt-on mods might be somewhat dulled in their effect by the engine's 105,000 miles. For example...my guess is the valve springs are probably pretty tired by this point. Mods typically work better at high rpm, but if the valve springs are tired, the engine won't rpm even to the stock rev limiter.

 

[87vettevert]

Thank you Hib for the information it sounds very logical. I just dont want to tear the motor apart yet cause she's still purrrin like a kitten.... Maybe next year when I dig up the coinage and know I can afford the best.

 

[ZumZum]

Not knowing anything about the previous owner(s), don't overlook the obvious for recouping power that you may be missing. New plugs, dist. cap, rotor, plug wires. Check the timing, etc.

 

[TedC]

I agree with zumzum. Start with the basics. Also, check your exhaust tips, are your getting exhaust flow out of all 4 tips. If not, replace the mufflers with ones that have all open tips. It is my understanding that L98s with a 2.59 rear end only had one working tip per side. With the optional 3.07 rear end HP increased by 5, and all 4 tips were open. In NY they just do a visual inspection that the converter is in place on my 1989. I'll agree with Hib regading the axle difference. I've had both axle ratios, and with a 3.07 axle, not one single car has every walked me in an 1/8 mile run. That includes newer C4s and C5s. The L98 is a low end torque monster that runs out of steam around the 1/4 mile mark, and this is where the newer C4s and C5s have the advantage.

 

[rmagee7]

remember it aint a race if it's not over in 4.50 seconds,John force June 2000 never did like the idea of driving in a traffic jam at 200 mph Tony Schumacher May 2002

 

[87vettevert]

I don't know much about axle ratios but I'm going to have to look into it. I did notice that there is a bit of a clunk when I'm on and off the pedal driving...I'm thinking stressed out u-joint is ready for replacement. Is it an very expensive mod to change the ratio from 2.59 to 3.07? Where do I purchase