You will be able to tell from the questions that we are new to the "world of Corvettes", so kindly be patient.

A couple of our customers are continuing to ask us to explore the possibilities of preparing C4 vintage cars for racing. Having already done most of the basic (easy-to-find-answers) homework, we now need some specialized advice:

1. How difficult is it to disable or eliminate the ABS, including the Lateral Acceleration Switch?

2. How difficult is it to disable or eliminate the ASR (Acceleration Slip Regulator)?

3. How difficult will it be to replace the leaf springs with coils? (Difficulty? Time?? Mechanical implications???)

4. What difficulties (particularly electronic) are we apt to encounter when we replace the gas tank with a fuel cell?

5. What are typical costs involved in replacing the fuel injection system with carbs?

We will appreciate factual, experienced answers, as well as educated guesses.

Thanks in advance,
Ed LoPresti
607-535-4237

 

Well these will be educated guesses, but here you go.

I BELIVE there is a fuse that will disable the ABS. This should effectively eliminate the ASR as well. The fuel cell shouldn't really be an issue, there isn't anything special about the fuel pump and sending unit that I am aware of.

The biggest problem with swapping to a carb on a C4 is hood clearance, that will likely be your biggest cost.

There are a few coil over suspension kits that will eliminate the leaf springs. Doug Rippie sells some kits, you should be able to get some idea of cost from them.

 

my car has both a coilovers and a carb on it. my car picked up almost 1/2 sec going to a carb from EFI. i have an after market hood on the car . Mike1985 also runs a carb and he cut the stock hood and had a body shop put a cowel on it, it looked great .

if you looking for the best 60ft and ET keep the leaf spring. going to a coil over your moving them in front of the axles/ halfshafts so the car dont transfer as good . my car lost 60ft goint to a coil over

the cost of going to a carb is about the same if you go with a good carb. i paid over 1200$ for mine , 300$ fuel pump, 200$ sump the tank, i also run a crank trigger you dont have to but you cant go wrong using them . lot more things that you have to change if your trying to build a race car . street car is alot less money alot less than an EFI setup.

 

Assuming you want to do more than merely disable the ABS ...that you want to remove all the weight possible....just start removing the sensors. They just plug in to the wiring harness.
Once you go with carbs, you'll lose the Traction Control (its part of the FI throttle system). By the way, it sounds like you are referring to DRAG racing in this post. If so, consider a Ford 9" in place of the nice IRS in the C4.

Coilovers are a popular mod on this forum...check over at the Forums/General Corvette/Autocrossing and Roadracing for more information.

Larry
code5coupe

 

It's kinda hard to say if drag racing was intended or not.

Agree from the weight removal standpoint, but not so much on the suspension work? What type of racing are you looking at?

 

I agree with Nathan, just remove the fuses. That will disable both items. Removal? The ASR has a throttle interface on the inner fender, but if you remove that, you will have to get a different one piece throttle cable. I would think one from a 1991 Vette would work fine.

The ABS computer is in the rear, but it's interconnected with the brake system, so I am not sure how that would effect things. It could be a good place to install a brake bias controller.

See #1

Coils are rather easy. Doug Rippie, Exotic Muscle and QA1 have kits in varing degrees of completeness.

I agree with Nathan again, I don't see a problem.

If this is for drag racing, carbs are better, but for road racing, I would tune up the injection system. However, the cost are just that, intake, carb and things of that nature. The rest is labour. Don't forget, you will need a lower pressure electric fuel pump.

hope this helps!

What vintage vettes are you dealing with? I didn't know that 1992 qualified!!

 

Gentlemen,

Thanks for the well-thought-out and knowlegable replys. Sorry - I should have specified ROAD racing. And the "vintage" reference I used generically - "the C4 vintage Corvettes" - meaning 1984 thru 1996 - NOT vintage racing.

The consensus of opinion has raised another question:
Why is a carburated setup not preferable to FI for road courses as well as drags?

My primary reason for asking all these questions comes from our experience preparing road-going Porsches for road racing. We have found that the electronics (designed for the street) actually get in the way of a good driver going quickly on the track. Thus my supposition that we shall need to work around things like ABS, FX-3, etc.

Now, did I open a bag of worms?
Ed

 

I can't speak for the Porsche variation on the Bosch FI theme, but later LT1 and LT4 Corvettes have a good injection system that would benefit from a simple tune (which is very easy to have done if you find the right shop) and bigger injectors to better match the engine size and performance options.

I understand that programming Porsche's ECM can be tricky, if not impossible... that is not the case for the C4 ECMs. The upside to Porshces is that you can install a nice pair of Weber 3bbls and be done with it. I am just not a fan of 4bbl carbs on a central intake... it just isn't as nice a method of fuel delivery. If I had the perfect carb setup, I would want 4 Weber 2bbls on an appropriate intake! That would be trick - think Ferrari 308 or Cobra 427.

Carbs are better for drags, but that's due to their efficient WOT performance properties; at least a single 4bbl...

There are also several aftermarket injection systems available, too. DFI from Accel and Holley, FAST and a couple of other hightech systems whos names escape me.

The other thing: 1994+ are programmable via a hand held programmer; they don't require special hardware to update.

There are many folks here who can help with tuning, too. Nathan is very well versed with this process on 1992 and 1993 Vettes, for example.

Working around ABS and ASR isn't needed... just unplug the fuses, and leave the mechanics.

FX-3? Just remove the actuators from the shocks and tie them up.

the best thing you could do is the fuel cell. The factory tank is prone to starvation problems during high load cornering if holding less then 1/3 of a tank.

It's not a can of worms... just a need for info!

 

And FI systems deliver better full RPM range A/F ratios.I wonder what is done with the O2 data in a carb there is no adjustability so there will not be an efficient A/F ratio.That is why I would think FI is the way to go for anything other than WOT applications.

 

One thing about the ABS system....I don't know if you'd really be better off disabling it. If the mechanical bits and wiring are going to remain, you can benefit from leaving it enabled. The driver shouldn't be depending on the ABS in every braking situation, but there are times when ABS will save a tire from being flat spotted. Especially with certain tires, like Hoosiers.

 

ASR can simply be turned off by pressing the button.

 

Thanks again, Gentlemen, for all the great information. This Forum, and the individuals on it are a GOLD MINE of information!

Nathan - if you would email or PM to me with a telephone #, I would like to discuss a couple general questions about the motors.

Also, does anyone have a telephone number for Doug Rippie? I wish to speak with him about his coilover options.

I have still not heard a convincing reason to prefer street-style EFI to carbs for road courses. We are not concerned so much with traditional "effeciency" as we are with THE MOST air-fuel mixture per throttle, delivered instantly and with great velocity, and equally, shut-off instantly. From SCCA events, it seems those Corvettes which use fuel injection are required to by their class regs. For those classes where the descision is "open", carbs seem to be the overwhelming preference. Perhaps Nathan can help me with that one too?

Once again, thanks to all for your valuable input.
Ed LoPresti
607-535-4237
RaceProEngineering@ATT.net
Watkins Glen, NY

 

Doug Rippie Motorsports


1117 Highway 25 North
Suite 2
Buffalo, MN. 55313

Sales Dept Phone: 763-477-9272
Sales Dept E-mail: drm@tcinternet.net

Fax: 763-477-9277

 

Slalom - thanks much,
Ed

 

You have several good responses, I can make a few more comments as I have done all of the things you mention to my 1993 C4 (except the carb)

As stated above, it's easy to disable. It's also easy to remove. You will need a new throttle cable but I'm guessing if you're building race cars you have the competance to do that. Just pull out the ASR hardware in the engine compartment. You can also remove the electronic module (EBTCM) behind the driver's seat (on 92-96 cars, anyway). There is a lot of wiring you can eliminate as well. However, I'd leave the valving for the ABS intact, it's not that heavy and redoing all the brake lines isn't something I would mess with. There's also an accellerometer in the IP you can eliminate. Easy if you're removing the interior, pointless if you're not.

See above

Easy. Coil over kits for the C4 bolt into stock mounting locations and are adjustable. Bilstein will custom valve shocks to match up with your spring rates for a marginal cost. It's easy to remove the leaf springs, just be careful to take as much load off as possible so they don't kill you. The main negative is that you're putting all loads (shock and transient) through mounting locations on aluminum knuckles that were designed to only hold the dampener load. When I used to drive my car on the street I once hit a pothole and shattered the rear knuckle (broke it at the hole for the dampener bolt). Something to consider if any of your customers that also drive on the street.

There are a few drop in fuel cells out there for the C4. I haven't done one, but check with R/D racing. Their C4 project car has one. They're all over the forum.

Probably not much different than getting a stand alone FI or a good tune. I'm considering this but have not done it yet.

Keep in mind that a few of your questions (specifically carbs and coil overs) will have a huge impact as to which class your cars will be placed. You're fast turning this C4 into an "unlimited" class car competing with C5's, C6's, and Vipers.

 

Here's a question - due to the fact that LT1 timing is not adjustable (except via ECM) and runs directly off of the cam, how would one optimize the timing on a carb'd conversion?

 

If I were to start offering racing preparations to C4s, I'd offer packages. For instance: One package would stiffen the frame, ie, cross-bar, camber brace, and X-frame. Another package might increase the horse power with a top end job, ie, cam, heads, exhaust and tuning. I'd also separate the type of racing the customer would rather do, Drag, auto-cross, road course. Have packages for each. One thing I haven't seen covered here is supercharging. The LT1/4 do very well on blowers without modifing the hood. What about roll bars? Are you just interested in all out track cars? There seems to be a market for installing aftermarket race items on all Vettes, especially here in Charlotte.

 

Some good points Strick no one has mentioned the Flex in the frame problem.RD Racing has the solution of course.On a road course upgrading the suspension will not work as well unless the flexing issues are solved.

As far as EFI vs. Carb I think you are not getting it RacePro.Sure a carb can dump lots of fuel into the engine but that does not in itself make it faster especially if the throttle is changing. Try looking for some dyno numbers on each set up but my thoughts are with EFI the tuning options are numerous you can richen the mixture easily if that is what you want.A Carb will not work faster than an injector.It will create a much more difficult situation to tune on the fly.If all your looking at is dumping fuel in you can increase the injector size and duty cycle easily via computer on the fly. You may be more familiar with carbed engines but EFI is not that daunting to learn and it is much more flexable.As was said before if your drag racing mabey it is a better soulution but I don't think road racing requires it to be the best solution.

Mabey Alvin or one of our other tuners can step in here and confirm or dispute this.Mabey what you are thinking will aply to L98 engines with a conventional distributor and their woefull TPI but the LTx engines are a different thing.

 

If you are building serious hp, stay away from EFI! To most people on this forum their 450 hp EFI engine is adequate. In our open class car we kick out over 800. Carbs are king on race engines due to their ability to deal with large cams. You will not get the EFI to run with the huge solid roller that you will want if you have the bottom end to spin it. We shift our car at 8200 RPM's all day long when we race. If these are the things that you are looking for either run a large single four, or fab a intake for dual 4's if you want to go that route. If you are looking at moderate performance and have a LT1 equipped car you can stay with it, but it will need to be built for a certain class with rules followed closely to be competitive. If you want to avoid that and go open, you will need lots of power and a carb will be the way to go. Just my 2 cents, but racing a C4 is what we do.

 

Deakins are you drag racing or road racing?Sounds impressive none the less.How much do you have tied up in the engine if I may ask?