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Discussion Starter #1
I have a 2000 bone stock gt mustang. I'm wanting to get 2.5 inch tubing MAC catback exhaust. What are the real performance gains? I have heard anywhere from none-15 horsepower. The stock size of exhaust is 2.25 inches and it'd be going to 2.5.

The exhaust link is: MAC Catback Mustang Exhaust (96-04 GT, Mach 1) TK9635 - Free Shipping!

Anyway what would the real horsepower gains be if any?
 

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From catback probably no too much meaning 1 or 2, if you want a few more you need to go with an O/R (off road) mid pipe without the cats then you might be in the ball park of 6 or 8 most will tell you. Either way it wont be much of a difference as far as feel goes but it will sound better.
 

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Discussion Starter #3
Really? I've always thought it would be somewhat significant because of the reduction of restriction of flow.
 

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Someone correct me if Im wrong, but unless your using power adders or running some serious HP, 10 is about what you can expect (being optimistic) with no other upgrades. Do it for the sound if nothing else. Get some underdrive pulleys, intake etc to help your HP
 

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Just save ur money by not buying all the little things that don't really make power and save and buy a used supercharger system. And buy some mufflers and weld them in for the sound you want.
 

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The stock exhaust tubing already has a pretty decent flow from factory. It's the catalytic converters and your mufflers that mostly restricts it. I believe an O/R X-pipe is what gives you the best flow, in combination with long tube headers and some straight through mufflers (Not the chambered box types). The size of the tubing doesn't matter too much as long as you stay N/A, a quarter inch larger tubing won't be noticeable. Go for the sound, not the performance of the exhaust. :bigthumbsup Look at the few HP as a added bonus to your meaner sounding Mustang!
 

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Discussion Starter #7
Has anybody done dynos to have any backed up numbers?
 

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Like doing dyno runs after simply adding a cat back? Only if you don't like money...

I have an idea! You do it, and let us know how much hp you gained. Sounds dumb now, huh?

Don't go off manufacturer claims, because they're BS for the most part.

As stated, your power is gonna come from an o/r midpipe when it comes to exhaust. A cat-back isn't gonna net you much, if anything.
 

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I used to get to do all that testing back in the day for free. I lived down the road from one of the contributing editors for one of the major Mustang magazines, so I got pulled in to do a bunch of tests with my '99.

We couldn't get any catback to give any real gain outside of dyno variance. As has been said before, the 4 cat setup is the largest restriction in the factory setup.

The offroad X Pipe gave a pretty good gain, it averaged out to about 8rwhp peak to peak. One of the best gains you're going to find for under $200.

Quality longtube headers on a naturally aspirated, bolt-on car were only worth 4 additional (average) over the offroad midpipe on a bolt-on car. They averaged about 12rwhp gain over the stock manifold/cat setup.
 

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On a N/A car, won't you in fact lose some low end torque by adding LT's and an O/R midpipe? From my understanding, the back pressure created by the stock exhaust actually boosts your low end torque some, even though it's restrictive and doesn't yield as many HP's. Some gears would easily fix this problem though :shigrin
 

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The term back pressure is very misleading. It's the velocity of the exhaust inside the pipe and the effect it has on scavenging the cylinders that is important. There is a given velocity that works best, and the diameter of the pipe affects what rpm that velocity is achieved. The lower the rpm, the smaller the pipe.
 

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The term back pressure is very misleading. It's the velocity of the exhaust inside the pipe and the effect it has on scavenging the cylinders that is important. There is a given velocity that works best, and the diameter of the pipe affects what rpm that velocity is achieved. The lower the rpm, the smaller the pipe.
D'uh, I knew that... Just tried to explain it for the kids :smartass:
 

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So your saying l/t's over the stock manifolds are really only good for around 5-6 rwhp? I would have figured just by looking at the better design of l/t's and the larger diameter that they would be at least net you 8-10 rwhp.. At least! Right..?
 

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So your saying l/t's over the stock manifolds are really only good for around 5-6 rwhp? I would have figured just by looking at the better design of l/t's and the larger diameter that they would be at least net you 8-10 rwhp.. At least! Right..?
Not on these motors, unless you have forced induction.
 

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2v's don't breathe worst a shite 4v's get a much better gain from LT's
 

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2v's don't breathe worst a shite 4v's get a much better gain from LT's
N/A 4V's are the same way.

It's not that they don't flow, it's that the exhaust side of the heads and the manifolds flow amazingly well for bolt-on cars and don't need much upgrading. Even when you get the 2V heads ported, the exhaust side doesn't need much actual port work.
 

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N/A 4V's are the same way.

It's not that they don't flow, it's that the exhaust side of the heads and the manifolds flow amazingly well for bolt-on cars and don't need much upgrading. Even when you get the 2V heads ported, the exhaust side doesn't need much actual port work.
Bullsh!t, everybody knows $1000.00 KooK headers give at least 30+ hp! Because they come with these new microscopic nano robot mechanics that are fused into the platinum pipes... They come out when the headers heat up enough to release them. then they run up into you heads and do some port work here and there...then they re-size your valves.
 
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