Hello, I posted a few questions the other day on the General Discussions Forum with relation to an '89 coupe that I was looking at. Well anyway, I am seriously considering buying the '89 and was looking for a few suggestions on the first performance mods that I should think about doing. The engine has 71K and is bone stock. I already know that I should remove the Frisbee as it is still mounted. Any suggestions would be appreciated.

 

First mod, for me, would be a full exhaust. So long as you're not in CA, get a set of long-tube headers (as low as $450, as high as $1200), a pair of high-flow bullet cats ($75 to $150 I think), and a full dual exhaust ($500 - $1000). This'll get you some performance, especially with an L98 car, and the sound will be nice as well. Depending on your budget, you could do more or less.

Also, make sure your tires are good. Probably the best bang-for-the-buck mod is tires. Without them, nothing else really matters.

 

maintenance before mods

if you have any deffered maintenance i would get that done first, that would make your car perform at least to factory levels including safety.

 

Exhaust, intake, heads, and cam - in that order. You go as far as your money goes, but if you want to gain power after each mod then you must go in this order for mods to compliment eachother.

Get rid of the stock mufflers at any cost, as well as the stock main cat and pre-cats. You can either go LT headers and true duals, or keep the factory manifolds and go to a 2.25" front Y into a high-flow cat then an aftermarket cat-back or factory with perf. mufflers. Get that exhaust moving efficiently!

Next is intake: The TPI "Wall" of 4500 RPM is a bummer. You can get around this in numerous ways, consisting of aftermarket intakes, porting, and/or siameseing the intake/runners. Or if you like the low-end grunt, you can go for a torque monster with a big lift, low duration cam.

Heads.. well, you may NOT need new heads if you're looking for less than 400hp, but some port matching would be nice if you want to get over 300.

A camshaft should be chosen by the powerband it generates, not by the amount of lift it offers. The target powerband for TPI is 1500-5000. Anything higher is useless with the stock intake. A perfect cam for a stock L98 would be 208/212 duration, .450-.460 lift, and 112+ LSA.

Hope this helps you out.

 

I don't have any dyno #'s but, I'm pretty sure i got a slight performance gain from match porting the plenum with the runners and romoving the extra plenum material behind the throttle body.

I'm a "no" vote on removing the MAF screen, just because the sensor is so fragile.

with exhaust + a 6psi supercharger with some gaseous intercooling

 

Thanks to all. I will take all suggestions into consideration. The maintenance is pretty much done already by the documentation provided from the previous owner. I will keep you posted.

 

I agree with the order of importance show above -- though heads & intake could be reversed. Depends on goals. I've seen arguments both ways.

Absolutely with out a doubt, the exhaust system is the worst part of the L98. With stock manifolds, I'm using a 2.5" front "Y" with 2.5" pipe behind it. One main cat might be enough for sound control -- depending on how you like it. Add front cats in next -- if more sound-control is desired. I doubt you'll even need mufflers if you like a bit of growl. It's the name-brand cat-back systems that slam the pocketbook. Headers aren't cheap either -- unless you pick Hedman Elites. They're pretty darn reasonable.

Agree with the rest, expect maybe the cam lift. 208/212 with .450 lift is damn close to stock #s. Yeah, LSA is a little better.... Otherwise 1.6 rockers can get you close to the cam suggested.

A LT-4 hotcam is a low-cost alternative. It's compatible with L98 motors. 218/228 duration with .485 lift using 1.5 rockers. Extra split would help with factory manifolds and/or lowish factory cylinder head intake-to-exhaust port flow percentage. A Hotcam would work well with ported/aftermarket heads later too. 1.6 rockers get this cam to .520 lift. Good results with with long or short-runner intakes. A hotcam setup is about the most reasonably priced cam upgrade.

I agree with making sure factory-installed systems are working properly first. Make sure of you base-line satisfaction -- and what it is.



Edit: Oh yeah, don't forget about gears. Depending on gears in your rear end, this could move up to #2 on the list above -- especially for the price.

 

Years ago TPIS sponsered a buildup of a '90 L98; build and test data is on my site.

 

Good write-ups and reading on 65Z01's website! Click on his name and you'll see the link!

I've read it. Nicely done!

 

Don't start fuc-ing with it leave it stock and enjoy!

 

You haven't even bought it and you are already messing with it

 

if you want to mod it a good start is determine what your budget looks like and the your goals in power.

 

don't buy it buy save your money there will be a better one for a good price, then you wont have to ask about mods they will be done! there are many here for sale to choose from. good luck!

 

well to buy a somewhat stock one, allows you to do-it-up to your taste, maybe you may not like what the po has done and how they have done it,

but there is no arguing that modded cars will never allow the owner to recoup what they have spent, they'd be lucky to get 30 cents on the dollar for any mod.

so if you don't mind redoing the hardware, or just tinkering with it until you think you own that modification, go for it.

on the otherhand, most corvette owners who have maintained their cars have done some things to them....imho


and as far a labor forget about it, turns into a labor of love, all those hours, on your back in the cold or heat, busted knuckles, and trips to the hardwarestore, is all the pleasantries of motorsports...

whatever turns you on.

 

If it has stock fuel injectors, they're going to have to be changed as the ethanol in the gas eats them up.
Check with Jon at http://fuelinjectionconnection.com

 

From alot of what I have read this makes good sense. Not all but many of the people that have done heavy mods on there cars have trouble afterwards. It seems like when you change something theres something else that is a problem. I have had many street/track cars in the past that were heavily modified, but that was back in the carb days when cars were a lot simpler..I have just gotten back into cars recently and a lot has changed, I was going to build my vette up but have changed my mind because of the problems I have seen from others that have done heavy modifications on there cars. To each there own but I think I will just stay with the simple things like exhaust on mine..WW

 

There are many mods that help quite a bit and will not impact reliability. Exhaust like mentioned above is a good one as is a converter. 1.6 roller rockers, under drive pulleys, a tranny shift kit, are some other good ones. Lightening the car can help a lot and pay for other mods in salable parts.

An inexpensive TCI shift kit in mine has provided many smiles, it cost about $30 and took an afternoon to install. These cars are so very slow stock. Consider new heads, cam, and intake. I pulled a full second off mine with few mods and little cost. Keep the best tires on as traction is very important.

 

b and m short throw shifter hits the list of mine. I love that shifter.

 

CHICKEN!!! Haha, just kiddin' man. But yeah, to each his own. There's a lot to be said for just getting a car you like and enjoying driving it. Me, I enjoy working on it as much as I do driving it, and I love the satisfaction of doing it myself. Cool thing is, the Corvette is a great choice either way. So pick your poison, and enjoy!

 

Where can you get long tube headers for $450?