Okay, I just talked to a buddy yesterday who knows a fair amount of information about vehicles and performance and he said something about even having cooler exhaust helps. And it really made me wonder because I've seen if racing magazines some special wraps for the headers and stuff. Does keeping the exhuast cooler really make a difference? Thanks for any information.

James

 

The wrap used on headers is to keep the temp. under the hood down. I've seen a few of the header manufacturers will void any kind of warranty they have on their headers if you use wrap on them.

 

There's actually supposed to be a bit of science behind it. Think of it this way - the hotter the exhaust gases are, the more they expand. (Basic principle of warm air expanding). In an exhaust system, where the gases are confined, the more they expand, the greater the movement will be to an open area (ultimately, the tailpipe, where they can equalize in pressure with the outside air). I've seen it recommended that larger diameter pipe be used closer to the engine with smaller diameter pipe used behind the muffler, at the tailpipes. The theory holds that, as gases leave the heads and travel down the headers, they will be at their hottest (header wrap, while also keeping underhood temperatures down, also serves to keep the exhaust gases hot, which will help flow as they rush toward cooler air). As the gases get closer to the tailpipes, they begin to cool. As they cool, they contract. If they are still contained in a large diameter pipe, pressure drops, and exhaust flow slows. By reducing to smaller diameter pipe towards the rear of the exhaust system, pressure is kept constant as the gases cool and contract, and exhaust flow doesn't suffer.

I can't tell you that I've ever put an engine on the dyno and tested this theory, but I've seen it explained in my readings. And, I guess I do tend to understand why manufacturers will sell a muffler with a 2 1/2" inlet and a 2 1/4" outlet. The basic idea is to keep the exhaust gases hot as they leave the engine (I've even seen "H"-pipes, as well as headers, wrapped.). The hotter they can stay, (and thus the greater the difference between their temperature and that of the atmosphere), the better the flow characteristics of the given exhaust system.

 

Hmm...that actually does make a lot of sense. And it actually helps explain why they say you should never have more than 0.5" difference between your pipe going into your muffler and your exit pipe.

So if I go from my headers, to a performance cat, then pipe (3" or should I go smaller) to a performance muffler, and then the exit pipping being about a 1/4" smaller. That would pretty much be exactly what you're saying if I'm right. And sounds like it should work too. I would ask you how to get the two different pipe sizes to fit on the muffler but that part will be taken care of by the muffler shop. The guys here know how to do things better than I've seen elsewhere and a lot cheaper and longer lasting, just that I like to know how things work before its done.

Thanks again for the information.

James

 

Sounds good. Do bear this in mind (just when you know what you want!), the scenario I mentioned was in theory, in a perfect world. I really don't know if we're talking a significant difference (1 hp? 10 hp? more?) by keeping pipe diameter consistent with supposed temperature drops, or not. In practice, it's easier for most to run constant-sized pipe all the way back. This summer, I guess I'll be testing the theory (though I really won't be able to measure any gains or losses) by running a 2 1/2" dual H-pipe into two 2 1/2" inlet / 2 1/4" outlet mufflers and out the back through 2 1/4" tailpipes (I'm doing this more for convenience...... clearing bigger tailpipes past the fuel tank on my Mustang won't be easy!) The easiest way to step the size down is through the muffler..... using a larger inlet than outlet. I doubt if you'll see many systems stepped down like this in actual practice. Just consider fake duals...... single inlet / dual outlet muffler with dual tailpipes. This is exactly the opposite of what I've described, but it sells, as people want the sound and the system IS less restrictive than a stock-sized single in / single out system. But does it flow well? Or, does flow slow down as you get closer to the end of the pipes? Do people really care as long as it's less restrictive (and louder) than stock? For your purposes, if you're going with a single 3" high-flow cat, you may consider going into a single 3" inlet / single 2 1/2" outlet muffler and 2 1/2" tailpipe. Or, if you want the sound, go with a single 3" inlet / dual 2 1/2" outlet muffler with dual tailpipes. The latter choice ignores the science, but if you're running a y-pipe up front and necking the system down into a single exhaust (which is understandable in the interest of keeping it legal), you've already given up the benefits you'd realize from true duals with a crossover pipe. I don't want to overly confuse the issue, as I probably already have. Suffice it to say that, if you raced the truck and wanted to tweak the true-dual exhaust to perfection, you would want to consider everything from pipe bend radius to pipe size to end up with the perfectly tuned exhaust. For a street truck (with street-legal single exhaust), you should probably just worry about lowering restrictions in the system you have, which would involve high-flow cats and mufflers. Stressing too much over diameter and stepping sizes down with length may be a waste, given the application (the effort may not be worth any appreciable gains). Your call. Hope this novel has offered some sort of insight. Good luck!

 

Well I actually think you're on the right track with this all. Cause just like a garden hose, if you open the valve to say 30PSI and use a 1" hose and use a 3/4" hose, the 3/4" will be better. I don't remember exactly how to word or prove it but I know it works. And I too will probably find out this summer if its going to work or not.

So here's what I'm thinking I'm going to do and I hope that it works either just as it normally would or better, not worse. Figure start with a decent set of headers, depending on the warranty on them, may just wrap them from the start. Pretty hard to find emmission certified headers for the 2.3L though. Then go with a Catco Cat (only peformance cat that I know about). 2 3/4" or something like that to feed to the muffler. Then some kind of performance muffler (Flowmaster has one that is supposed to increase 15-30HP and have a cool sound but doubt it fits my truck). Muffler is a muffler though, aint it? And then 1/4" smaller pipe out behind the tire as it is now but put a tip on it too.

I think that after making all these changes I should be able to gain at least 10HP over my stock exhaust. I would love to try true dual pipes but I think with just a 2.3L under the hood it would end up doing less than this will.

I guess we'll pretty much both be trying out just a theory this summer and hopefully for both of us it'll work better than stock. But I guess really...as long as it doesn't perform less than stock then its better than nothing.

I too don't have anything like a dyno or anything to test to see how much of an improvement but I guess as long as I don't see a huge drop in gasmileage then should be okay. Thanks for the help and good luck.

James

 

And likewise to you! While we don't own dynos, it may be interesting to take a vacuum @ idle reading, as well as a vacuum @ say, 2000 rpm reading before the exhaust mods, and then after. You may see some measurable change in the numbers. (I would think that, if the exhaust mods improved flow, engine vacuum would measure higher @ idle as well as at throttle). Wrenching on these things is, if nothing else, a continual learning process. It's so easy to fall into the trap of buying and bolting on those nice, shiny go-fast parts that come with a pretty decal you can slap in the rear window without really thinking about the science or physics of what you're actually doing. Sometimes testing a theory can give you some pretty surprising results. Good luck!