Thanks in advance. I have a very nice, low mile 1989 with the L98. It has a very slight rough start issue but smooths out immediately. The car injectors replaced at some point in the past. Rather than purchase a chip with unknown coding on it, I'd like to hear from other C4 owners who may have successfully tuned their cars and gained HP? I am planning on changing plugs and wires for a start.

 

If you arent making modifications to increase the air into or out of the engine, you will not get gains from a chip retune. Tell us what youre doing there, otherwise youre wasting time & money.

The aftermarket chips claim gains but don't tell you those gains are under specific conditions, like bumping the timing curves way up which requires you to keep the engine running cooler than it would without other significant mods to the cooling system. When they get hot they will knock because of that timing curve change.

If you want to smooth out the initial idle then that issue should be looked at as a separate one, like checking out the injectors and the TPS setting and IAC counts.

 

When I inspected my recently purchased '89 I found it already had a 160deg T-stat and K&N air filter.
All I needed to do was cut open the air filter lid, clean/oil the K&N and toss that damn "frisbee" from front of the WP pulley.

If you do some exhaust mods to also increase air flow, install an AFPR so you can bump fuel pressure to match air flow increase at WOT. Remember that max fuel flow goes at the sqrt of pressure increase.

 

I had my e-prom re-flashed and some parameters such as cooling fan on and off temps changed in my 85 but nothing for performance. I do highly recommend having the fan set points revised.

 

Hello there Highlander1732,

Like the above posters were telling you there is very little power gain if any at all from the aftermarket chips with a stock C4 Corvette. The best thing for a new Corvette is to take a few months and "Get to Know" the Corvette before you start modifying it.

You have an awesome shop not far from you, Tony's Corvettes at the Gaithersburg Air Park is a short ride away. IF you decide to modify this car he can burn you a custom Eprom that addresses issues from your personal Corvette. Tony has a one stop shop for any year Corvette and you will not find a more honest individual in Tony. He restores cars from start to finish and they do absolutely great work and they REALLY "know" their Corvettes.

Your L89 you say has low miles and that may seem like a good thing initially but the lack of use does affect some of the components. How Mechanical are you? Have you ever worked on a car like the C4 before? I am sorry to ask but it is important. By the way there is a Corvette club at Crisswell Chevrolet that Tony and several of his staff were affiliated with.

I have a 1988 C4 Coupe with the L-89 and I like the car just the way it was built. They did some neat engineering on this model and I will keep one around as they are fun to drive and look great. The engine is pretty well laid out and easy to service most components with the Clam-shell hood that we have. I have broken 30 mpg on I-95 going back and forth to Baltimore from Fairfax, VA. The car is comfortable once you get in, and is a blast to drive fast on windy little roads.

If you ARE new to Corvettes take your car over to Tony's and have them check it out to be sure that you don't need any repairs. I do 99% of all the maintenance here in the driveway but it requires some specialized tools to get the job done.

Here are a few things you will need to work on your Corvette:
Factory Service Manual for your particular year, use the factory manual only and you will save yourself some headaches
Fuel Pressure Gauge
Volt Ohm meter
Time

Good Luck with your project!

 

Thank you for the info. What temperatures do you recommend having the fan reset to? Mine kicks on at 228 degrees now...

 

Thanks for your input. I may not have done a good job with my initial post as I DO NOT want to use a chip because you never know what you're getting. I am now looking into having the Eprom changed as almost all others have said (including you, thanks). The car is still original down to its exhaust believe it or not, so I'm hoping to keep the performance mods limited to things that won't necessarily change the car in a way that may compromise that aspect. I agree with the other posters regarding the air in/out via updated intake, exhaust changes, but that strays a little too far from my "tune" objective". I'm comfortable under the hood, so that shouldn't be too much of an issue. I agree with your thoughts on Tony's as he has done a bit of heavy lifting on my C3 in the past for things I was hesitant to do. I appreciate the Eprom information as I didn't know it could be modified. Do you have a list of things that could be modified that may increase performance while limited to the existing heads and exhaust? Thanks again!

 

Hello again Highlander1732!

I have been cheating, I use the A/C switch to control the fans and the engine's temperature when I am worried about the heat building up. These cars are supposed to operate around 200* (F) but with fans coming in at 228* then your engine is already hot. My C4 has the booster fan in front of the radiator and the fan on the backside of the radiator so when the fans are on the engine stays nice and cool. I want my fans to start working at about 200* on my C4 and 150* on my C3. Fortunately my C3 has a PWM (Pulse Width Modulation) controller that starts the fans at 50% power at 150* and will ramp up automatically as the heat builds up. It makes the interior of the car so much quieter without two 11" SPAL fans running at 100% all the time. One thing that I also do to help my C4 stay cool is to run only 30% antifreeze in the coolant, I live in Fairfax, VA and we don't get that cold here so I have still have plenty of freeze protection. If you live higher up that might not be a good idea. A/F is not as good as water is at transferring the heat so the more water the better as long as you have enough freeze protection.

Sounds like you have a nice car there! What options did your C4 come with? Mine is very close to a base Corvette but it has the 17" rims and the smaller 12" brakes. I love driving these cars when the roads are tight with lots of curves. It is SO much more refined than my 1968 C3 with it's 427. I use the C3 for scaring myself with HP and the C4 is my Sunday go-to-meeting Corvette. Did you ever notice that the number "4" key is also the "$" key? I guess because it cost $ to have and drive a C4.... Not really, they are easy to work on and are great track cars if you choose to go there. I hope you enjoy it as much as possible!

I changed the catalytic converter to a higher flowing unit from Summit Racing and installed a chambered exhaust system. This change over made close to 14 hp gain according to my GTECH Pro! I also installed a aftermarket DUI coil and cap and replaced the little controller inside the distributor. I have been using MSD wires on it since I bought the C4.

My biggest problems were electrical because I put the car under a cover in a car port for a couple years and my fuel line rusted shut (Thanks to ETHANOL) and I ended up replacing the fuel line. It was a challenge as the fuel was flowing but not at a high enough rate to allow the engine to run. One good thing to check is the post on the frame rail behind and slightly under the battery. You can follow a large RED wire going to supply the power at the post. This post has 7 Fusible links on it and affect virtually the whole car. Check this post for corrosion, if there is any be sure to remove the ring terminals and clean each one and re-assemble, I put three wires under the battery supply wire and then the remaining four on top of the battery lead. I also greased these terminals after cleaning them hoping to keep corrosion at bay. If there is any corrosion on the post you should wire brush it and grease it as well. I slipped a vacuum cap over the left-over threads. This is the supply line for the (12 Vdc) power to be distributed throughout the car.

Being in Ijamsville, MD Maryland I suspected you might know Tony and his staff. He has worked on both of my Corvettes at one time or another. He is the only mechanic that can say that, nobody else touches my toys.

The problem with the L98 engine is that is was designed with those long runners which limit the power-band considerably. Long tube headers are supposed to help as well as re-mounting the Intake Air Temperature sensor from the aluminum intake housing on top of the engine and mount it where it will see the real air temperature. I also have a K&N Air filter which is supposed to help a little bit... Cold air intake makes a couple HP.

The best person to talk about this with would be Tony, he would know the tricks that most of us are not aware of and he knows how to do them right.

Good Luck with your New to You Corvette!
Best Regards,
Chris a.k.a. ctmccloskey

 

My fan settings are 215 on 195 off, with a 195 factory t-stat. 180 stat would be fine too for summer. But I also have a DeWitt radiator to keep it right in that range so it doesn't run all the time. I also have the hypertech aux fan switch that goes into the drivers side head that activates the pusher fan in front earlier. You could also just use the AC for force them.

As for relatively simple mods that dont require a chip re-burn, look to bolt-ons. Aftermarket runners & base manifold, or at least heavily ported, ported plenum. 1.6 RR and valvetrain parts replacement from the age, and then exhaust. At that point youre about at the limit of the factory tune. You can play with FP somewhat, and advance base timing from 6 to 8*. However a cam change will require a chip tune to optimize.

 

Wow! I really appreciate the detail and tips. I will have to inspect the terminal post near the battery. My car is a base model convertible with the only real options being the Bose system which only works half way now (soon to be changed) nothing else really to speak of. White over red with a white top and automatic. I originally bought it for my wife but she never really got into it while I slowly fell in love with it. Handles like no other car I've ever driven and while not as much fun to drive as my '75 4 speed, it more than makes up for it on the highway and cruising - much like you said - Sunday go to meeting Corvette...30,000 miles with it's original exhaust in tact and A/C blows nice and cold. A real time capsule actually so I'm going to keep this one for a while.

 

Thank you for the reply. I like the idea of the 215 on/195 off. It just sounds like it would keep the car happier for sure. I may end up breaking into the motor and swapping the cam and porting the heads, but that inevitably leads to a new exhaust too! It's too bad there is such a divide in the sophistication between the L98 and LT motors. Maybe an LT swap is in order?