Since the post was revived…
My V6 was rear ended, so I kicked in an extra few dollars for the GT bumper cover.
My intention was to add an inoperative exhaust tip to the left side but the independent muffler shop was able to do a cat back dual with x-pipe and GT stainless tips for about two thirds of the price of a kit.
Only negative I chose the wrong mufflers, Flow Master 40.
Great sound outside but resonates inside. Should have gone with 50 or 60 series.
This was done purely for looks, not HP gain, though may have gained a few at higher RPM.
When a car had a spec of 200 and it goes up with new exhaust to 205 or higher what does that mean?.I’m just tired o reading when I research. people say that alot. Go to a drag strip any extra is gain .lol js
Technically if the HP goes up just because of an exhaust it means the engine was already capable of the the HP, but the exhaust was limiting it. So the engine didn’t gain hp it is just able to use what it already had. So it really is just freeing up hp available. 
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It’s actually hard to notice the difference between 200 and 205 horsepower. The outdoor temperatures and relative humidity changes can make that much difference, or using someone else’s dyno to measure the horsepower.
There’s an old hot rodder’s adage, “don’t mistake noise for horsepower”.
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A lot depends on the rest of the intake and exhaust system. The muffler might not be the main restriction in the system. It could be intake manifold, cam, heads, exhaust manifold, cat, etc. Reducing the muffler restriction may have almost no effect, or a significant effect, but that’s less likely these days. And it only matters at wide open throttle.
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Make that wide open throttle and at the upper rpm limits.
When you look at stock verses aftermarket exhaust system dyno results, almost invariably, the power and torque curves at the lower rpms are nearly identical, even at wide open throttle. It’s only at the very upper limit of the rpm range where the modified system shows measurable gains.
And, measurable is not necessarily feelable, except to those who mistake noise for horsepower.
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It’s pretty much impossible these days. Before an engine is built they know exactly what exhaust to use for optimum results. The gain with a glass-pack will be insignificant.
Unlikely? Yes. Impossible? No. For example, here’s the Ford factory add-on (air filter, computer reflash, and mufflers) that adds both hp and torque to the 2011-2014 Mustang GT:
I’m sure it’s quite a bit louder than stock.
But all the ‘louder’ cat back systems in the Ford web site don’t list any power gains. Like you and I said before, it’s a system, and just adding a louder muffler is unlikely to make much/any difference.
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I have seen restricters in Thrush glass packs and they are likely in other brands and the length and diameter of a glass pack relative to the bore and stroke and camshaft grind must be considered. Long stroke high torque engines sound best with long small diameter tubes while short stroke high rpm engines sound better with short fat tubes. It seems that the resonance of the engine and muffler must match somehow.
I can not remember the details, but back when Nissans were Datsuns there was a racing category that included Datsun 510s. The competition complained the exhaust system was shorter than the rules allowed. Datsun complied, lengthening the pipes. The result? Five more HP.
My experience with modifying motorcycle exhausts is that it adds more noise than power. Then I started just leaving my bike’s exhausts alone and something remarkable happened. It seems like you can nearly get away with murder on a quiet motorcycle. I have come to call it “quiet privilege”. I have left my bikes quiet ever since.
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I remember an article where a magazine dyno tested a number of aftermarket bike exhausts. Many did no good, or even hurt power.
I honestly believe that the overwhelming majority of those who put aftermarket mufflers on their cars do so to get attention by making the vehicle noisier rather than to gain horsepower. I doubt if more than a small percentage actually think they’ll add horsepower. And I believe that covers cars, trucks and motorcycles (bikes). On bikes, we used to cut or remove the baffles, but I don’t know if that’s still done. Loud bikes are illegal in many municipalities, and in my area the restriction is enforced, albeit not 100%.
My neighbor has a Taurus with a loud aftermarket muffler. I think it’s a V6, and it sounds like a junker. When I first heard it I thought he just needed a new muffler, but then I noticed the coffee-can tailpipe and realized he’d done it on purpose.
Open exhaust ports eliminate all back pressure but likely rob more horsepower than a luxury car’s multi stage mufflers.
That Taurus’ aftermarket exhaust: AKA “fart can”…
could you elaborate on this? thanks.
After owning a few raucous motorcycles and routinely getting pulled over by the police, mostly checking my license and lecturing me to “slow down”, I finally bought a 1974 Honda CB550 four. At 55 mph, all you heard was the wind noise, it was so quiet. With that bike, the cops pretty much ignored me. I didn’t drive any slower, I just didn’t make a big spectacle of it.
Little old ladies didn’t call the cops complaining about “somebody racing through the neighborhood on a motorcycle” when I used that bike.
I remember one time when I was hanging out at Luchenbach, yes that place that Waylon Jennings sang about, I lived only about nine miles away from there. Some elderly lady walked up to me and asked me what I did to make my motorcycle so quiet. I replied, “nothing, I just left it alone”.
The police just seem to have a completely different attitude towards riders of quiet motorcycles. Today, I call it “quiet motorcycle privilege” or just “quiet privilege”
When other motorcyclists wonder why I don’t put a loud pipe on my bike, my answer is “I want my neighbors to use all five fingers when they wave at me”, and no matter where you ride, you are in SOMEBODY’S neighborhood and I want to be welcome there.
It looked a lot like this one.
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Great!! wish all the other bikers had the same attitude. I sometimes dread spring because of all the motorcycle noise that brings.
Here’s another bike I owned that got a lot of positive reaction from non-motorcyclists, particularly farmers and ranchers. There’s something about a well muffled blue and white off road bike that says “I’m not an outlaw motorcycle gang member”.
94 Suzuki DR650 in its element. It was actually a little heavy for a true off road bike but it was a great dirt road bike, and Llano County, TX is cris-crossed with county maintained unpaved public roads.
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