Power 202, Exhaust
By: Ron Lee
I hope that you at least glanced over the first two power articles before jumping here. This article will cover exhaust modifications. Remember to make power, you have to get air into the engine and then get that same air out of the engine. Having a huge aftermarket intake system and a stock exhaust system will limit what all those fancy intake pieces can do, and vice versa. Balance is important. Again, doing all of the modifications will result in a lot of power being gained, more than you think, while doing just some of them will result in less power than you think. In general, intake system changes (heads #1) will result in more horsepower gains than exhaust system changes, at least initially. The two best exhaust system changes are an X pipe and long tube headers (long tube headers are not for everybody) with a 2.5 inch cat back system deserving honorable mention.
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Okay, I am going to hit the cat-back system, which includes flow tubes, mufflers, and the tailpipes, first because most of us want that mean sounding car. If you have single exhaust (factory for 79-85), you should convert it to dual exhaust first. Converting it to dual exhaust will require adding the double hump crossmember available for about $65. A lot of people simply remove the mufflers to get that mean sound that we all know and love. Assuming you leave the cats in place, and run the exhaust out the back, the noise level will probably be quiet enough to keep you out of trouble with the police (if you're not getting on it). Flowmaster and Dynomax are probably the two most popular cat back exhaust systems. Dynomax is a little quieter than 2 chamber Flowmasters, and a little louder than 3 chamber Flowmasters. You should run a 2.5 inch exhaust and I advise you to tie down your fuel lines (with a nylon strap) above the rear axle assembly where they are very close to the 2.5 inch tailpipe. Most of the aftermarket cat back exhaust systems will generate a resonant noise inside your car from about 1600 to 2000 rpm which can be annoying. Some of the newer, expensive ($100 each) mufflers are said to eliminate this resonant sound. Most of us just live with it. I did for years. I recently added long tube headers and an X-pipe to my car and that did eliminate the resonant sound (the car is also too quiet now for my taste). Typical prices for a cat back system is $250 for the parts and they are a relatively simple bolt on affair. The only real problem (assuming you don't have a lift) is getting the back of the car high enough in the air to get the tailpipe to clear the rear axle assembly, but you can do it with common jacks and jack stands. Always support a car on jack stands, not a jack. You can expect to add about 5 horsepower with a stock engine, more with a modified engine. Gas mileage should not change.
Next are the headers, and you do have some choices here. Basically the choices are shorty (unequal length), equal length shorty, and full length. You also get to choose between 1.5 inch and 1.625 inch tubes (1.75 and 2 inch available for race engines). If your engine is fairly stock, and you plan to leave it that way, the 1.5 inch tubes are the best choice. Going to the larger tubes will hurt your bottom end performance (torque) and with a fairly stock motor, there is no reason to give that up. Most other people should get the 1.625 inch tubes which are intended for modified engines, but not race engines. As to the length of tubes, they are listed in order of the additional power they will make, from least to most. Full length headers will impress you with the additional torque they will add to your engine. One problem with full length headers is that the factory catalytic converters will not bolt up to them. Equal length shorty headers are definitely more hassle to install, and you will have to carefully route spark plug wires and the nearby pollution hoses, but they do make more power than the regular shorty headers. Most headers are available with a ceramic coating ($90 adder for shorties, $150 adder for long tube) which helps retain heat in the exhaust system which does increase power output (a little). The best reason for a ceramic coating is if you are running long tube headers and oxygen sensors, the oxygen sensors will work better at the higher temperature. Technically, the full length headers are not smog legal, but they are available now with oxygen sensors which means they may pass the sniffer tests. The factory wiring harness will reach to the oxygen sensors on the long tube headers if you reroute them a little bit. I did mine. If you are going to change out the cats at the same time, I highly recommend the long tube headers, the bottom end torque improvement is impressive (but keep in mind if they are sticklers where you live on smog legality, you could be in trouble with them). I would not do the shorty headers unless you have already modified your engine in several ways. Shorty headers start at $175 and long tube headers start at $230. Shorty headers are relatively easy to put on while long tube headers are more involved. If you have aluminum heads, remember to use anti-seize compound on the header bolts.
Next are the catalytic converters. First comment, if your car has less than 50,000 miles you cannot legally change the catalytic converters. If you have over 50,000 miles, you can get 2.5 inch H pipes with high flow catalytic converters from several companies which are a vast improvement over the factory 2.25 inch cats. All the ones I've seen are also smog legal. You will notice after installation that your car will be louder. Catalytic converters, especially high flow types, take virtually no power out of the engine. If your location has smog laws, keep catalytic converters on your car. The new style X pipe is much better than a H pipe because it will add a few horsepower to your engine output. The X pipe is available from several companies, with or without catalytic converters, and it will make your car quieter (which will allow you to run louder, more free flowing mufflers). The X pipe is about the same price as the H pipe, so the choice is easy, get an X pipe instead. New high flow converters with an X pipe will run you about $400. This is a relatively easy bolt on for most of the available versions. I've heard that the Dr Gas brand is a kit that requires welding, so ask questions if it matters to you (it would to me).
©Copyright 1998 Ron Lee