I have a stock 1990 C4 and I'm looking to repalce my current exhaust for some additional horsepower.

I will be changing my pumpkin from stock to a Dana 36 307 gear in the very near future.

Was wondering if anyone has any suggestions or recommendations for the best bang for my buck and something that will compliment the car as well.

Thanks In Advance.

You don't indicate what state you live in. That helps dictate some of my recommendations.

If it was my car and had the freedom to go nuts, this is what I would do:

The L98 is strangled by its intake and exhaust.

With that said, a good exhaust is a great step forward in gaining power. This is NOT just a cat back, but a full on exhaust solution.

1. Headers, I would suggest long tubes that has the EGR port. I like EGR, it helps stop detonation and NOx emissions.

2a. I highly recommend the Corsa system, but for this application, you would want the LT1 setup. It is expensive, but you will never get tagged for being to loud!

This option will require LT1 hangers. They are cheap enough on the used market, www.vette2vette.com is a good source.

2b. Piece together an exhaust. Use an x-pipe with some good aftermarket mufflers. Magnaflow or Borla. The only concern here is resonance. The C4 cabin is a resonance chamber as it is, add performance exhaust, and it can be nearly deafening. Please note that the Corsa system solves said resonance.

If you do just the exhaust, I expect a 25hp pick up. Do the intake, another 30hp.

I agree with prettymuch all of what Andy said. I can add:

Dual outlet tips cause alot of resonance. When I did my system I started at the engine and worked my way back. Resonance never went away till I got rid of the stock mufflers and tips.

Go with the Corsa's if it fits the budget. If on a tight budget, buy a used LT1 stock catback. I did that, cut the cat off and used it from just in front of the differential, so I have true dual exhaust. The stock LT1 catback pipes are stainless, plenty large, mandrel bent, and have nice mufflers. If not going Corsa I wouldn't foot the money for anything else. I bought mine for $50 used.

I have custom midpipes going from the headers back to the differential. If I had to do it again (and I probably will do this part again someday) I'd have put in a pair of small aftermarket performance cats and an H or X pipe. Car smells now at idle no matter how rich or lean it is. I think performance cats would clean it up some and not hurt performance much at all.

For headers, go with long tubes. If you want underhood looks, durability and lower underhood temps go with ceramic coated headers. If you are going on a budget go with non coated as there is no performance difference with the ceramic coated's. I went with Hooker Super Comp's and I like them. They fit up nice and spark plug changes are easy.

If I were you I'd save up till you can do it all at once. The L98 exhaust manifolds and exhaust system flat out suck and I don't think you will see major gains by replacing just one piece, it needs done as a complete system.

Oh, I forgot one thing... if you still have to pass a sniffer, use a couple of high flow bullet cats.

I recommend them anyway, really. They are not expensive, are so efficeint that they don't cost performance and do help a lot in keeping the air we breathe a little nicer.

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lung cancer, bronchitis, emphysema, leukemia, heart disease, is no fun, neither is smelling your car letting that stuff in the air is either

Do you have emissions, ie California, etc? Do you have to pass a visual?

I currently have stock manifolds, precats eliminated, stock converter, and magnaflow 2.5 SS catback. It's pretty loud, a little louder than I'd like now. Minor resonance 1200-1400 rpms. When I get my headers on and my high flow cat I'm interested to see the sound difference. If I did it all over I'd buy a used LT1 dual exhaust and save some coin and have a quiet and decent looking exhaust at the same time.

Matthew

I just want to really thank all of you for all of your informitive advise.

By the way sorry I forgot to mention that I'm located in West Palm Beach Florida and fortunate enough to have a convertible and I'm really not that concerened with cabin acoustics.

Thanks to you guys,..It seems that I now have a whole lot of thinking to do and a great bunch of information to consider.

Thanks again all,...I will fill you all in and let you know how it all works out when I make my changes.

Jeffrey

The cabin accoustics are still a consideration for a vert. My brother had an 89 with Flowmaster exhausts. I found the accoustics and resonance irritating. I have a 91 with a Magnaflow system. Much nicer at the lower speeds but a slight drone at highway speeds that could get bothersome after a couple of hours unless you crank up your music to cover it. Finding the right setup is well worth the time and money invested. Happy hunting.

My '89 is a convertible also. The resonance was horrible with headers, custom midpipes and stock catback. It was the stock mufflers and dual outlet tips that caused it. I blocked off 1 of the 2 outlets on each muffler and the resonance wasn't near as bad. That's how I knew for sure not to go with dual outlet mufflers when I replaced the stock system.

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Will the entire LTx exhaust system mate up with the L98 exhaust manifolds?

yes. It should. but you would have to use the LT1 cats.

With all this great info that I've been taking in,...I guess my next question is , does anybody of a handle on where I can get a used LT1 set up, E-bay only has one and the guy wants more to ship it then the entire exhaust costs.

Also,...I'm a bit fuzzy on if I should go with the exhaust manifolds as well or just from the cats back.




Thanks again guys!!!

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Yes, I meant everything behind the exhaust manifolds. What about plugging in the O2 sensers? IIRC, the 96 has four and the the 92-95 has one or two less. No idea what the L98 has.Also, any updated tune necessary if the exhaust is freer flowing?

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Can't use LT1 cats on earlier cars. Frame is a little different in the front. Been there, done that. I had to cut the cats up and reweld them more narrow to clear the frame on the earlier car.


Oddly enough, long tube headers, into a stock LT1 catback (resonator, two mufflers) with no cats was more quiet than the h-pipe, dual cat, small tube combo I had before and it pulled harder too.

-- Joe

Best bang for your buck? Run dual 2.5" with an X-pipe straight back. Find a shop with a mandrel bender, or else purchase 2 wide radius mandrel U-bends from Summit. These can be sectioned and welded in place by the shop if they don't have a mandrel bender. This can be done for under $200 parts+labor, then add mufflers and whichever tips you wish.

It will be cheaper than any "bolt on" exhaust system out there, and fit better.

If you want a cat, put a single 3" carsound ($50) in place of the x-pipe and buy two 2.5"x3" wyes from summit to weld on both ends of it.

I have no idea if the LT1 system will fit an L98 car from the differential forward. I just have headers, 2 straight pipes coming from the headers to just in front of the differential, then a stock LT1 exhaust from there on back. I used hanger pieces from the LT1 and L98 system combined and they worked, didn't need to buy anything for hangers in the rear. I do have a custom hanger in front of the differential coming off the top of the C-beam.

System as I described above is about as cheap as you can go as far as cost, and it sounds good with no resonance, and all the bends are mandrel and the system is stainless. Doesn't get much better than that if you are on a budget.

I picked up mine from corvetteforum. Put in a wanted ad. If someone has the complete system and you don't want it, tell them to cut it off behind the cat. You will then have 2 separate pipes and mufflers that can be stacked together and heat shrinked or whatever for shipping. If you get it with the cat then the system will be together and will take a huge box for shipping.

Yeah, most LT1 systems seem to go for almost free, you just have to pick them up locally because people don't want to hassle with shipping them.

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This is true.

When I put my Corsa on (the first time) I gave the stock LT1 cat back away - to a guy from Raleigh NC with an L98 car. He drove down picked it up at the shop and got to spend the weekend with his GF at Atlantic Beach. Shipping was just too much hassel and $$$ for an otherwise free stock exhaust system.

Shipping just the mufflers and under axel pipes is much easier. When I bent my first Corsa up (loading the car on fricken trailer), I sold the bent up stuff to a guy in GA on CF. Shipping cost was fairly reasonable since it was a box and not a 10ft long 40 lbs section of welded together pipes and mufflers.
Will