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C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Need more power

Old 09-15-2018, 01:15 AM
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Cloud92
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Default Need more power

Ok I'm not super rich....so no forced induction or ls swaps lol.......but I'm looking for more power out of my 85 tpi 3+4 I have done a few mods and weight reduction striped the rear hatch spair tire compartment mods I can think of are....

​​​​​​3" exhaust after cats(muffler delete)
air box mod
Coolant/throttle delete
Frisbees off
Ac Delco plugs
10mm plug wires
Big new fuel pump....


That's all I can think of that I have done mod and preformance wise
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Old 09-15-2018, 11:19 AM
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project C4
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Full length headers with a true dual exhaust. 2.5" or 3 pipe depending on intended future goals for power, 2.5" is good for most anything
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Old 09-15-2018, 12:41 PM
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First of All: Welcome To the Corvette Forum!!

You need to understand that this whole L98 intake system was designed for a 305 cubic inch engine. The L98 is a poor flowing system on its own. You need more air in and more air out to improve the power. It is very hard to do with simple add-ons. Like project C4 suggested the exhaust is one of the easiest places to improve your performance. I still have the shells of the Pre-converters and then I installed a High Flow Catalytic Converter with a Chambered Dual exhaust system from Allen's Stainless Exhaust. Even that makes a difference on your performance, my GTECH showed almost 14 hp increase just opening up the entire exhaust system. I have a otherwise stock L98 and with the automatic I can break into the 30 mpg range while cruising on the highways.

Long tube headers will help your L98 make a bit more power but unless you address the intake and heads you won't go much further making horsepower. Even a complete re-tune of the computer will not make the power as it is limited by the cam and the l-o-n-g runners in the intake system. If I had to make power using what I have in my stock L98 I would pull the intake and the Tuned Port injection system, replace it with a older style intake manifold and use a throttle body if needed. The cam would have to go and that means the heads would have to opened up by somebody who is good at porting and knows our limitations regarding the L98. Any way you look at it it is going to be some "serious" money to make some "real" power.
Like the old saying: "If you want to play you are going to have to pay". The fastest way to make power on the L98 might be squirting some Nitrous into your engine and I am not talking about a 500 hp shot, maybe just a good 50 HP shot would be fun and let your engine live a while longer.

Take some time and read all these threads regarding "making power with the L98" on this forum, there are plenty of ideas and answers on this site. HP numbers are nice but remember, "Torque talks" and the C4 has plenty of torque even though it is down on the HP numbers.

Is this your First Corvette? Are you mechanically inclined? Do you have a place where you can work on your car? Do you have any prior experience with Corvettes?
If this is your first Corvette then you need to spend at least six months driving and "learning the car". Even with the L98 the 33 year old C4 is a car that can get you into trouble fast,be careful and take your time to learn the car. Once you have some experience the things that need attention will identify themselves. Corvettes like a lot more maintenance than other cars, they can also fall apart very quickly if neglected. I see that you have a list of things that you have done already, the muffler delete might be the one thing that actually might make a couple HP but it might tick off the neighbors and especially the Police if you leave it like that. The Chambered exhaust I have is great, it has no mufflers either, it simply replaces the exhaust system but is legal here in Virginia. If you removed the original catalytic Converters you might pick a couple HP, I ordered a large replacement High Flow catalytic Converter which flows much better than the stock ones do and it still makes my exhaust clean. The one thing I really like about the Chambered Exhaust system is that it sounds like a side pipe but the noise is out the back of the car and I don't burn my legs. I have two of these Chambered systems from Allen's Stainless, I have one on my C3 with it's 427 and the other is on the C4 I own. I have had the one on my C3 since the mid 1990's and it still looks great and works like a charm. Btw I did not buy either of my systems in Stainless.

Another important thing that you should check is your Fuel Injectors and the Fuel Pressure Regulator. The original injectors do not like Ethanol in the gasoline and should be replaced, check to see which injectors your car came with and post a picture on line. Somebody will be able to identify it for you. It is good you installed a new fuel pump as that is a common issue with older Corvettes. Check your fuel pressure while running at idle and while driving. Many people here tape the fuel pressure gauge on the windshield to do the driving part of the test. A good question to ask is how long did the pressure stay in the system after you shut the key off?

Do you have a set of the Factory Service Manuals for this particular year of Corvette? If not buy a set before you go any further. My 1988 came with two books, one is for the car and the other is the Electrical Supplement for the car, Both are critical if you want to work on your Corvette. Here is the link you will need for your car: http://www.helminc.com/helm/result.asp?Style=helm They FSM for your car is $82 and is in stock. Please don't try a Chiltons or a Clymers repair manual, they are useless when you compare them to a FSM.

I wish you the very best with your Corvette! I hope that you both survive happily.
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Old 09-15-2018, 01:28 PM
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Originally Posted by ctmccloskey View Post
First of All: Welcome To the Corvette Forum!!

Another important thing that you should check is your Fuel Injectors and the Fuel Pressure Regulator.
Yes Welcome aboard! on FPR ,,, this is what a bad one looks like and it will cause all kinds of bad things like oil in the gas and bad running:


Bad FPR diaphram

PS: I have muffler eliminators and they aren't very loud because I still have the original CATS.

Last edited by rharker; 09-15-2018 at 01:30 PM. Reason: added
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Old 09-15-2018, 01:50 PM
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If you are mechanically inclined you can go the route I am. Through good fortune and having a feel for good pricing I sourced an LT1 intake for $35 and heads for $100. While I am busy porting these heads I can keep the 113 heads on my 90 L98. After blocking a few cooling ports and creative plumbing for coolant this should be a fairly strait forward swap.

the LT1 intake alone is a good swap if you are willing to do the machine work for relocating intake bolts and adding coolant and a distributor port. These are the reasons I went with LT heads.

Good luck and take time to pick out your parts. You dont want to grab something that wont work with your setup, ie, a big cam on stock top end.
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Old 09-15-2018, 03:50 PM
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Since you're on a budget:
-160deg F. T-stat
-hi-flow cat (indeed 2 1/2" front Y & cat-back will work fine). Of course FL headers with true duals will bring the most exhaust mod gains (if affordable).

You might bump base timing to around 8deg BTDC and advance TPS to ~0.7Vdc for a little more "snap" from the throttle.
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Old 09-15-2018, 07:27 PM
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Originally Posted by Cloud92 View Post
Ok I'm not super rich....so no forced induction or ls swaps lol.......but I'm looking for more power out of my 85 tpi 3+4 I have done a few mods and weight reduction striped the rear hatch spair tire compartment mods I can think of are....

​​​​​​3" exhaust after cats(muffler delete)
air box mod
Coolant/throttle delete
Frisbees off
Ac Delco plugs
10mm plug wires
Big new fuel pump....


That's all I can think of that I have done mod and preformance wise
Going to burst your bubble here but nothing much says "performance". The frisbee might be worth a couple ponies but that is about it.

I think the most important thing that people leave out are

1. How much money do you have to spend? I'm not super rich doesn't say a number. No number, no way to tell. I'm not super rich either but probably thrown about 20K into the car over the years. First part says nothing, second part gives an objective number.

2. What are your goals? Do you want to have a 10 second car? How about 11? How about 12? Without knowing that "more power" is rather vague and useless.
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Old 09-15-2018, 07:32 PM
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Throttle body, big wires, fuel pumps, coils etc are a wallet drainers. A 2.5 or duals with headers works better. Not a ton but you should feel it.
Sometimes used ones come up for sale.

Member David Frederick sells converted LT1 intakes to fit the Gen 1 heads, affordable upgrade. A machine shop can do this upgrade, too.

Last edited by cuisinartvette; 09-15-2018 at 07:34 PM.
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Old 09-15-2018, 08:25 PM
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Originally Posted by rharker View Post
Yes Welcome aboard! on FPR ,,, this is what a bad one looks like and it will cause all kinds of bad things like oil in the gas and bad running:


Bad FPR diaphram

PS: I have muffler eliminators and they aren't very loud because I still have the original CATS.
I replaced my dyaphrdiam when I was first having fuel isuiss

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Old 09-15-2018, 08:50 PM
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The simple fact is money buys speed. Most performance mods will require tuning and tuning isn't cheap. Good Luck with your quest
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Old 09-15-2018, 09:23 PM
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Gears are about the easiest way to get more performance. The 4+3s came with 3.07s. They used 3.33s for 89 manuals and were up to 3.54s later in the 90s. You can probably sell your Dana 44 with 3.07s for about the same as you can find a later one. Maybe only be out 200.00.
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Old 09-15-2018, 10:19 PM
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Cloud92
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Originally Posted by Space387 View Post
If you are mechanically inclined you can go the route I am. Through good fortune and having a feel for good pricing I sourced an LT1 intake for $35 and heads for $100. While I am busy porting these heads I can keep the 113 heads on my 90 L98. After blocking a few cooling ports and creative plumbing for coolant this should be a fairly strait forward swap.

the LT1 intake alone is a good swap if you are willing to do the machine work for relocating intake bolts and adding coolant and a distributor port. These are the reasons I went with LT heads.

Good luck and take time to pick out your parts. You dont want to grab something that wont work with your setup, ie, a big cam on stock top end.
Thanks!! I'm definitely investing in an intake and heads!!
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Old 09-15-2018, 10:48 PM
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Originally Posted by Cloud92 View Post
Thanks!! I'm definitely investing in an intake and heads!!
Remember stock LT1 heads dont flow much better than the aluminum 113 heads you can get from a 90 or 91 vette. I am porting mine myself for some extra gains. This combo will also cry for a better cam. The one you have is not designed to flow well past 5k.
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Old 09-16-2018, 12:08 AM
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Originally Posted by aklim View Post
Going to burst your bubble here but nothing much says "performance". The frisbee might be worth a couple ponies but that is about it.

I think the most important thing that people leave out are

1. How much money do you have to spend? I'm not super rich doesn't say a number. No number, no way to tell. I'm not super rich either but probably thrown about 20K into the car over the years. First part says nothing, second part gives an objective number.

2. What are your goals? Do you want to have a 10 second car? How about 11? How about 12? Without knowing that "more power" is rather vague and useless.
My goal is to push over 300 hp.......I'm not rich meaning this car is my daily driver i am 25 and work 6 days a week I don't see me putting 20k into it....I'm sure of one thing tho.....my 5.0 mustang only had a bigger cam and exhaust....and was able to hit 160 at the top of 4th gear with 5 gear to go.....I feel like the c4 struggles after cracking 110
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Old 09-16-2018, 12:31 AM
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Originally Posted by Cloud92 View Post
My goal is to push over 300 hp.......I'm not rich meaning this car is my daily driver i am 25 and work 6 days a week I don't see me putting 20k into it....I'm sure of one thing tho.....my 5.0 mustang only had a bigger cam and exhaust....and was able to hit 160 at the top of 4th gear with 5 gear to go.....I feel like the c4 struggles after cracking 110
It would be easier if you had a number in mind as to your hard limit. The Mustang has a better intake that the L98 does not. Say you spend 3000 and it isn't enough to make the system more efficient and needs another 3000,you just wasted your money because you hamstrung yourself.

I bought a 383 from LPE to make 430HP. It wrecked the trans in 9 months and later on the rear end. Also the F-body needed bracing tuning and other misc stuff. This, that and the other adds up. 20k is to make a 383 doing 420 RWHP. If you dump a cam in this, it won't work to it's full potential so you are leaving something on the table and got less returns than you would if you made it a SYSTEM
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Old 09-16-2018, 12:53 AM
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From what your goals seem to be and constraints, I will recommend getting an LT1 intake and having someone machine it for you to use with stock heads. It's cheaper and requires less precision than my route of heads too. Add a mild cam and you will be close after a tune to your goal. 300 is attainable but at a cost. It's not just the gofast parts, you need to support it and I'm not sure your 4+3 will take much of a beating.
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Old 09-16-2018, 01:59 AM
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Originally Posted by Space387 View Post
From what your goals seem to be and constraints, I will recommend getting an LT1 intake and having someone machine it for you to use with stock heads. It's cheaper and requires less precision than my route of heads too. Add a mild cam and you will be close after a tune to your goal. 300 is attainable but at a cost. It's not just the gofast parts, you need to support it and I'm not sure your 4+3 will take much of a beating.
Assuming everything is goog, $5000 should be good. Not. Sure what intake will be used and how much it costs. Also there are incidental parts so. Should be a good 320 start If he can find a good tuner to build out this combo.
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Old 09-16-2018, 06:41 AM
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1985 l98

STOP THE INSANITY. Bolt-ons for a l98 is like putting **** on a bore.

Keep it. Cherish it for what it is.

Don't fall prey to these interweb gurus.

Save your money. Buy a C5 next year....when the mid engine comes out...prices will drop.
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Old 09-16-2018, 07:47 AM
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Originally Posted by Bigpoop View Post
1985 l98

STOP THE INSANITY. Bolt-ons for a l98 is like putting **** on a bore.

Keep it. Cherish it for what it is.

Don't fall prey to these interweb gurus.

Save your money. Buy a C5 next year....when the mid engine comes out...prices will drop.
I agree as far as that goes. C5 will have less tuning issues. He might also take notes so he can sell it to the next guy with a notebook full of ideas about what may be as far as potential
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Old 09-16-2018, 08:58 AM
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Originally Posted by Bigpoop View Post
1985 l98

STOP THE INSANITY. Bolt-ons for a l98 is like putting **** on a bore.

Keep it. Cherish it for what it is.

Don't fall prey to these interweb gurus.

Save your money. Buy a C5 next year....when the mid engine comes out...prices will drop.
Not entirely true.....besides the intake and exhaust, I deleted the air, put aluminum heads with roller rockers and a bigger throttle body....had to get it tuned but got a pretty fair boost out of it.....wasn't all that much.....not popping wheelies or anything but she does have a little more pick up.....

Last edited by playsdixie; 09-16-2018 at 08:59 AM. Reason: add
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