I'm looking to revamp my exhaust on my 1990 Vette. The old one is worn out with holes in the mufflers cat is toast ect. I do not need emissions on my car so I think I'm going to going to get rid of the cat completely. I was wanting to hear your guys opinions on a good set up for free flowing exhaust without too much excessive noise but want it to sound mean as help when on the gas! How much if any backpressure do I need to keep? Looking to do this on a tight budget as well. Thanks

 

"keeping backpressure"= myth.

Just dont size the system too big.

 

For the LT1, a Cat that creates back pressure is plugged. Testing the back pressure system on the A.I.R. pipes, should register Zero back pressure according to the FSM.

 

I see well I failed to mention this has the L98 motor but I'm guessing it is irrelevant. I was thinking about running straight pipes back to a pair of mufflers only. Will my car have the precats and will that require a new x pipe from the headers back? What would your recommend is a good performance muffler for the Vette while keeping the dual tips?

 

You can buy complete bolt in dual exhaust systems from the major venders, that's the easiest way to go. Add headers when you can afford it and you'll be all set.

 

As little as possible. None. You want NO back pressure.

As for recommending an exhaust on a budget; it depends. How "handy" are you? Can you weld? Do you need a direct "bolt in"? Tell us more about your resources.

 

Run pre-cats and a main cat with muffler eliminators. That kind of setup sounds good.

 

Not sure I buy the no back pressure answers. The L98 is a torque motor and backpressure shapes the torque curve. There are plenty of sets out there that he can put on, and if emissions aren't a concern it makes sense to go headers back if you can dig up the coin.

 

I'd like to think of myself as "handy" and I can weld. Maybe I should salvage what I can from my stock exhaust and piece in new pipe in place of the main cat and purchase new mufflers?

 

You better believe that Back pressure "shapes the tq curve"....it lowers it! And the higher hp you're attempting to make (and RPM) the more it "shapes" that torque for you -negatively.

Please do not confuse "back pressure" with "tuning" of the exhaust. They are totally different and provide different results. "Back pressure" -which is resistance to flow, will do nothing but lower tq and hp...period.

To the OP, if you can weld, and you're up to it, you can buy sections of bent and straight pipe from Summit etc and fab something very nice, and as good or better than most aftermarket systems, for less than $200. I did that very thing on a Camaro I had and the results were fantastic. Other wise, there are plenty of off-the-shelf options.

 

If you don't have to undergo emissions testing, then going with a set of true duals and performance mufflers will provide an HP gain. My 87 has true duals with an X-pipe located where the main cat sat and a pair of DynoMax UltraFlo Race mufflers. I did this in two stages, first the duals and mufflers which were pretty loud at WOT. After the X-pipe, the sound dropped but so did interior resonance. My car is mostly for autocross and track days so resonance was not a big deal.

One thing about removing the old stock system and going to true duals is being able to work with a muffler shop. It's a violation of federal law to remove cats and not replace them and could bring a 5-figure fine to the shop for doing so. So you need to find a shop with a tube bender that will do the work. What I did with my cars was to remove all of the old exhaust by myself, leaving the manifolds. I removed the plates and trailered the car to the shop and told them it was "for off-road use only".

This would also be a good time to consider headers. Look at the Hedman Elites either with or without AIR connections. With no emissions testing, you can remove the AIR pump.

A good muffler shop can bend the pipe to fit and install the mufflers and any tips you want. If you go with the stock manifolds, make sure the O2 sensor is installed in the same spot as the stock pipes.

DIY welding can work, but it's much easier to have a shop do all the work. They will get all the bends in the right place, use good (and brand new!) 2 1/4 or 2 1/2" pipe based on engine mods, and align everything so the pipes tuck up where needed and the clamps and hangars will be in the right spot. A good exhaust guy can install a complete custom dual system on a C4 in about an hour.

 

Back-pressure doesn't create the torque curve (or at least it doesnt create a good curve), its the exhaust design and exhaust flow that is important...

The key to a good exhaust is for it to flow well... By well, I mean it should have a scavenging design and the diameter pipe shouldn't be too large or too small based on your engine.

I think the basic design of the LT1 exhaust is really good! Add some stepped headers, get some high flow cats and an X-pipe with no mufflers (or relatively free flowing mufflers) and you will have one of the best flowing exhausts. The 2.75in pipe diameter and dual exhaust is perfect for a stock or medium (400hp) modified engine!

 

If you are handy you might want to try LT1 exhaust. Its dual 2 3/4 all the way back.
Im putting some on my L98 vette.

http://forums.corvetteforum.com/c4-t...ome-input.html