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88 L98 700R4 needs more power.

 
Old 07-06-2019, 06:39 AM
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JP90
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Default 88 L98 700R4 needs more power.

Since alot of the information seems to be gone (pages, links) and most parts referenced in such threads are no longer produced..
What are people who want more power doing besides nitrous?
Here is where I am, currently have a 88 corvette with 118k miles on it (purchased 1 year ago with 107k on it) I have gone through and tuned it up, fluids, filters, ignition and cleaned out debris from radiator. Previous owner somwhere down the line installed a shift kit, cut air filter lid, 160 thermostat and air foil. I have removed the pre cats, ran 3 runs down the 1/4 all 3 times I put down a 13.8 with 1.9 60ft. Car still has stock exhaust manifolds, stock intake, runners, heads and 2.59 gears.

Now, what I WANT the car to do, I want it to keep pulling when it hits 3rd gear instead of running out of steam, if I could get this thing to pull in 3rd gear as well as it does in 1st and 2nd I would be pretty happy. If it could run 12.9s on street tires with around a 1.9 60ft I would be thrilled.
Out of the currently produced parts, what are my options for waking this beast up? I realize intake, heads, cam and longtubes are where I need to go with it, but which intake set up should I be after? It looks like the Mini ram and First are the only 2 that will work while retaining fuel injection (also a must) unless there is something I am missing?
I am also looking into Promaxx heads, as I am not sure I am wanting to spend AFR money on this particular build. I know speed costs money, but I also know there are many wrong ways to spend that money, which is what I want to try and avoid lol. Also considering TPIS for headers and Y pipe.
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Old 07-06-2019, 09:07 AM
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Originally Posted by JP90 View Post
Since alot of the information seems to be gone (pages, links) and most parts referenced in such threads are no longer produced..
What are people who want more power doing besides nitrous?
Here is where I am, currently have a 88 corvette with 118k miles on it (purchased 1 year ago with 107k on it) I have gone through and tuned it up, fluids, filters, ignition and cleaned out debris from radiator. Previous owner somwhere down the line installed a shift kit, cut air filter lid, 160 thermostat and air foil. I have removed the pre cats, ran 3 runs down the 1/4 all 3 times I put down a 13.8 with 1.9 60ft. Car still has stock exhaust manifolds, stock intake, runners, heads and 2.59 gears.

Now, what I WANT the car to do, I want it to keep pulling when it hits 3rd gear instead of running out of steam, if I could get this thing to pull in 3rd gear as well as it does in 1st and 2nd I would be pretty happy. If it could run 12.9s on street tires with around a 1.9 60ft I would be thrilled.
Out of the currently produced parts, what are my options for waking this beast up? I realize intake, heads, cam and longtubes are where I need to go with it, but which intake set up should I be after? It looks like the Mini ram and First are the only 2 that will work while retaining fuel injection (also a must) unless there is something I am missing?
I am also looking into Promaxx heads, as I am not sure I am wanting to spend AFR money on this particular build. I know speed costs money, but I also know there are many wrong ways to spend that money, which is what I want to try and avoid lol. Also considering TPIS for headers and Y pipe.
A junkyard 5.3/6.0 will probably get you more power for less money.
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Old 07-06-2019, 09:41 AM
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Originally Posted by PacerX View Post
A junkyard 5.3/6.0 will probably get you more power for less money.
As much fun as an LS swap would be, I am not looking to do that on this car. I don't have enough power in my garage to run a welder or air tools, nor do I have the skills to fabricate something should I need to.
I will buy a 2nd C4 at some point and LS swap that, as the next car will be a manual which would give me more enjoyment from an LS turbo than this automatic will.
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Old 07-06-2019, 10:10 AM
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ctmccloskey
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Unfortunately JP90 The C4 was designed with a very unique attempt to make a car with a power band down low where it would be used more of the time. The runners are very long and that makes the engine produce it's torque again at the mid range. Most L98's have a problem where by the time you hit 5000 rpm you are done making power. It is more like 4600-4700 rpm on mine where the power just goes away.

Compounding the problems is the fact that this intake system was designed originally for a 305 cubic inch V8 and not the 350 that most of us have.

There are ways to pick up a few ponies here and there but without major changes the L98 & 700 R4 combination is very limiting. I have a 1988 C4 Coupe and my car has the 3.07 rear end. If you want to go faster changing out the rear end is a good place. Just be aware that most of the components in the drive line were designed for what you have in there. If you add 50% more power you will be breaking parts left and right. Now there are lots of guys who race the C4's and they have different Rear ends to handle the extra power. Those guys might be able to show you how to get a bit more power and make the car last while doing it. When I had my 700 R4 rebuilt I had them install a few upgrades to handle the extra power in case I went that direction and even then the mechanic was telling me not to push over 450 HP into that 700 R4 that I was using I was offered a LS3 engine complete for free and I seriously thought about putting it in the C4. Then I looked at how much it would cost me to do the swap and I dropped the idea.

Your 1988 Corvette is a great car to start with, you have the updated parking brake that I love compared to the rear drum in the rear rotors. Your 1988 L98 has a roller cam and aluminum heads that make up a great engine. With my C4 I have been able to get 30 mpg on the interstates going 60 with the cruise control on. At 100,000 miles my compression numbers were all very close together and quite healthy indicating a well designed engine that has been taken care of.

If the C4 was my only Corvette I might swap the intake system with better flowing short runner system in search of the missing horsepower. I even thought about swapping in a new intake like an Edlebrock intake manifold with injectors and throttle body which would certainly make more power but the question is will it fit under the hood?

There would be a lot of guys happy if a L98 could pull 12.9 second quarter mile times. Somebody with experience with the aftermarket parts will chime in and help with those specific answers as I have kept my C4 fairly stock.

I replaced the exhaust system with a Cat back Chambered Exhaust system and new high flowing catalytic converter. The exhaust sounds like a Corvette should sound, but with the exhaust and the catalytic converter the car gained close to 14 hp. Add Headers and you might get another 10-20 hp. Remove the air pump, negligible difference if any. Nitrous might wake this motor up but the the longevity is compromised.

There are ways to make power that would satisfy your need for speed. A lot of them will require a tuning by somebody who knows how to flash the eprom that came with your car. That can get expensive but there are guys here who can do that or point you in the right direction.

I hope that you find the tricks needed to make the C4 as fast as you want it without breaking the bank doing so. I love cruising in the C4 with the AC and the Stereo playing, it is a well designed car and a blast to drive on windy mountain roads. I get miles of smiles driving mine!

Good Luck and I hope to have helped a little bit!

Chris
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Old 07-06-2019, 10:35 AM
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There are many ways, its still just a SBC. Anything from a Gen 1 will fit it and those will be made many more years because of racing.

The first choice is the budget and then your goals. You can do a 1.9 60' right now, it just takes the right tire. I did it on my 86 back when it was bone stock with a new set of Kumhos at the time.

Getting to about 12.9 equates to adding roughly 100-150 hp, for about 350-360hp at the crank. You don't need new heads to get there, but you do need to have the '113 heads worked over with a full port job and redone valvetrain parts. They can support about 350 in unported form and ported would get them to flow over that.

You will need exhaust to get the air out, such as TPiS or Hooker 2149 headers. The stock manifolds choke you down a great deal. Keep a good cat if you want (Carsound, RandomTech), and then pick a catback exhaust based on sound preference since they all flow about the same. Otherwise go straight pipes at 2.5" from the headers back.

The real choice next is what intake to go with. Miniram will make the car behave like the LT1 engine from later years, and the mods thereafter should go with that. Superram can still be found on ebay for about $1K, or maybe in the sale sections here, this requires a different set of follow on changes. So few have posted FIRST results that I rarely recommend it, but its somewhere between TPI and SR, like the Holley Stealthram (which must be modded to fit under your hood).

If it were MR, I'd probably pick something like LT4 hotcam, TPIS ZZ9, or in that range. About 215-220 @050" on either side of intake/exh. Then 1.6 RR. Then you must have the chip retuned. You do not have to go into the bottom end at all for this level of power. Then a new stall TC because what comes in 88 is too low, 1500 stock and it should be 2200-2400rpm. Then you may want to change the rear gear ratio to 3.54/3.73.

Superram will only require a slightly less aggressive cam on the intake side, same 1.6RR, similar TC (2000-2200), but no rear gear change is necessary. Chip retune is still necessary for the cam change.

So what intake choice you make is up to you and that dictates where the rest of the package should go.
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Old 07-06-2019, 10:50 AM
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Originally Posted by ctmccloskey View Post
Unfortunately JP90 The C4 was designed with a very unique attempt to make a car with a power band down low where it would be used more of the time. The runners are very long and that makes the engine produce it's torque again at the mid range. Most L98's have a problem where by the time you hit 5000 rpm you are done making power. It is more like 4600-4700 rpm on mine where the power just goes away.

Compounding the problems is the fact that this intake system was designed originally for a 305 cubic inch V8 and not the 350 that most of us have.

There are ways to pick up a few ponies here and there but without major changes the L98 & 700 R4 combination is very limiting. I have a 1988 C4 Coupe and my car has the 3.07 rear end. If you want to go faster changing out the rear end is a good place. Just be aware that most of the components in the drive line were designed for what you have in there. If you add 50% more power you will be breaking parts left and right. Now there are lots of guys who race the C4's and they have different Rear ends to handle the extra power. Those guys might be able to show you how to get a bit more power and make the car last while doing it. When I had my 700 R4 rebuilt I had them install a few upgrades to handle the extra power in case I went that direction and even then the mechanic was telling me not to push over 450 HP into that 700 R4 that I was using I was offered a LS3 engine complete for free and I seriously thought about putting it in the C4. Then I looked at how much it would cost me to do the swap and I dropped the idea.

Your 1988 Corvette is a great car to start with, you have the updated parking brake that I love compared to the rear drum in the rear rotors. Your 1988 L98 has a roller cam and aluminum heads that make up a great engine. With my C4 I have been able to get 30 mpg on the interstates going 60 with the cruise control on. At 100,000 miles my compression numbers were all very close together and quite healthy indicating a well designed engine that has been taken care of.

If the C4 was my only Corvette I might swap the intake system with better flowing short runner system in search of the missing horsepower. I even thought about swapping in a new intake like an Edlebrock intake manifold with injectors and throttle body which would certainly make more power but the question is will it fit under the hood?

There would be a lot of guys happy if a L98 could pull 12.9 second quarter mile times. Somebody with experience with the aftermarket parts will chime in and help with those specific answers as I have kept my C4 fairly stock.

I replaced the exhaust system with a Cat back Chambered Exhaust system and new high flowing catalytic converter. The exhaust sounds like a Corvette should sound, but with the exhaust and the catalytic converter the car gained close to 14 hp. Add Headers and you might get another 10-20 hp. Remove the air pump, negligible difference if any. Nitrous might wake this motor up but the the longevity is compromised.

There are ways to make power that would satisfy your need for speed. A lot of them will require a tuning by somebody who knows how to flash the eprom that came with your car. That can get expensive but there are guys here who can do that or point you in the right direction.

I hope that you find the tricks needed to make the C4 as fast as you want it without breaking the bank doing so. I love cruising in the C4 with the AC and the Stereo playing, it is a well designed car and a blast to drive on windy mountain roads. I get miles of smiles driving mine!

Good Luck and I hope to have helped a little bit!


Chris
I agree this is a great cruising car. And I have thought about switching to the 3.07 gears but most of my driving with this car is highway, its great for road trips and I don't want to mess any of that up. I am not looking to rev to the moon, but if I could get it to make power up to 5200-5500rpm that would make me pretty happy. Smog pump took a dump on me so its gone, and the frisbee is as well (forgot to mention those in my first post). After getting the car caught up on maintenance I went through the stereo system with the goal of "top off, windows down I want to hear it at 100mph"..so its good to go too. Love this car, 11k miles in 1 year and that was with it parked for winter November-March. Did a trip to bowling green and tail of the dragon in May, ended up covering a total of 1851 miles in 3 days, and I absolutely loved every last minute of it!!

Originally Posted by vader86 View Post
There are many ways, its still just a SBC. Anything from a Gen 1 will fit it and those will be made many more years because of racing.

The first choice is the budget and then your goals. You can do a 1.9 60' right now, it just takes the right tire. I did it on my 86 back when it was bone stock with a new set of Kumhos at the time.

Getting to about 12.9 equates to adding roughly 100-150 hp, for about 350-360hp at the crank. You don't need new heads to get there, but you do need to have the '113 heads worked over with a full port job and redone valvetrain parts. They can support about 350 in unported form and ported would get them to flow over that.

You will need exhaust to get the air out, such as TPiS or Hooker 2149 headers. The stock manifolds choke you down a great deal. Keep a good cat if you want (Carsound, RandomTech), and then pick a catback exhaust based on sound preference since they all flow about the same. Otherwise go straight pipes at 2.5" from the headers back.

The real choice next is what intake to go with. Miniram will make the car behave like the LT1 engine from later years, and the mods thereafter should go with that. Superram can still be found on ebay for about $1K, or maybe in the sale sections here, this requires a different set of follow on changes. So few have posted FIRST results that I rarely recommend it, but its somewhere between TPI and SR, like the Holley Stealthram (which must be modded to fit under your hood).

If it were MR, I'd probably pick something like LT4 hotcam, TPIS ZZ9, or in that range. About 215-220 @050" on either side of intake/exh. Then 1.6 RR. Then you must have the chip retuned. You do not have to go into the bottom end at all for this level of power. Then a new stall TC because what comes in 88 is too low, 1500 stock and it should be 2200-2400rpm. Then you may want to change the rear gear ratio to 3.54/3.73.

Superram will only require a slightly less aggressive cam on the intake side, same 1.6RR, similar TC (2000-2200), but no rear gear change is necessary. Chip retune is still necessary for the cam change.

So what intake choice you make is up to you and that dictates where the rest of the package should go.
I am pulling 1.9s consistantly now, I just put that in there with my 12.9 goal so people understand I am looking for more usable street power not throw some slicks on and hope the D36 doesn't blow up kind of thing.
So based upon what you are saying, a superram is going to be the route I want to go for intake as I really do not want to change gears (if I do 3.07s are the max I want to do) as this car spends 95% of its miles on the interstate.
As far as budget, I don't realistically know what to expect to spend. I would like to be no more than $3k for a modest power bump that might reach my 12.9 if possible. I am also not dead set on running 12.9s, I just wanted to use that as an example of the kind of power bump I would like to see.

Last edited by JP90; 07-06-2019 at 10:51 AM.
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Old 07-07-2019, 04:24 PM
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I don't think you can do this for 3K.

Used SR will run about $1000-1500, you need the plenum, runners, and base manifold. Headers will run about $500 even used, custom exhaust work another couple hundred. Cam and RR together, $500-600. Head porting can be anywhere from $500-1000. You'll need all new valvetrain parts (springs, locks, retainers) for an engine this old and the new cam. Chip tune about $500 with a WB O2 sensor on a dyno. THe new TC can be anywhere from $400-800 depending on brand.

This assumes you're doing all the work yourself and not farming any out except the welding work on the exhaust and the chip tune.

Last edited by vader86; 07-07-2019 at 04:26 PM.
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Old 07-08-2019, 12:01 AM
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Buy a used Mini Ram, used headers, take off LT1 exhaust, and a cam. That'll get you there. And for less than $3k.
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Old 07-09-2019, 11:16 AM
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Originally Posted by vader86 View Post
I don't think you can do this for 3K.

Used SR will run about $1000-1500, you need the plenum, runners, and base manifold. Headers will run about $500 even used, custom exhaust work another couple hundred. Cam and RR together, $500-600. Head porting can be anywhere from $500-1000. You'll need all new valvetrain parts (springs, locks, retainers) for an engine this old and the new cam. Chip tune about $500 with a WB O2 sensor on a dyno. THe new TC can be anywhere from $400-800 depending on brand.

This assumes you're doing all the work yourself and not farming any out except the welding work on the exhaust and the chip tune.

Spending the last few days searching around now that I kind of have an idea of parts I want, I think you are correct.
I may just throw a set of headers on it, 3.07 gears and enjoy it for what it is, a fun to cruise in car that makes V8 sounds.
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Old 07-09-2019, 12:27 PM
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I'd recommend doing the TC first, the car should've come with it, then headers. All of which you can still keep for a later buildup. Don't do the gears first. At some point you can upgrade to a D44 with 3.07s, but for now you do not need it unless youre doing DRs or slicks at the track.
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Old 07-10-2019, 02:10 AM
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To run high 12s you will need to pull low 1.8s-high 1.7s. Also a 2-step launch will be needed with ~30lbs in rear tires.

While my prior '88 was building ~300chp with a very good DA once I was able to pull a 13.01sec @105mph run but could not beat that damn 12sec barrier. Typical passes were in the low 13s.

What is the typical DA at your track?
Do you know your launch weight? From that and trap speed you can calculate chp.

In addition to the mods you have made, I siamesed the intake runners, installed 1.6:1 RRs (Comp Cams Pro Magnums), used a HEI ign and had the shift points set to 5,800rpm. With the higher output ign I was able to cut back the spark plug ground electrode and open up the gap for better charge burn.
I also tossed the spare & jack and arrived at the track with ~1/3 tank of fuel. Remember dropping 100lb weight is like adding 10chp.

Have fun racing/moding your Vette and good luck at the track.
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Old 07-10-2019, 07:07 AM
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It's a slippery slope your headed down.....Ask me how I know........

D44 w/4:10 gears,
6 speed conversion
421 engine

15 grand later......

Do what Tom400 said, then leave it alone! (probably not possible).....lol...
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Old 07-10-2019, 07:37 AM
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Originally Posted by cadmaniac View Post
It's a slippery slope your headed down.....Ask me how I know........

D44 w/4:10 gears,
6 speed conversion
421 engine

15 grand later......

Do what Tom400 said, then leave it alone! (probably not possible).....lol...
Went down this road 6+ years ago. Ended up finding and buying a 1990 Corvette already done (done well). Builder invested around $50K for the car and then the build (I have receipts), and I bought it for $20K. Great car, but expensive and not currently worth anywhere near what I have in it, let alone what has actually gone into it. Investment value aside, My C4 has a 496 stroker dynoed at 530HP, 480 FT. Lbs, with suspension upgrades and is a blast to drive.
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