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Old 02-21-2001, 08:53 AM   #1
gtguy
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Post Muffler pipe question: does 2.5" give a top end advantage that 2.25 doesn't?

Hey, how's that for a precise topic heading? Wouldn't mind seeing more of those...

As long as Stromung has my muffler and they're tweaking on it, I'm wondering about the 2.5" tubing difference vs. 2.25". It now has 2.5", and I thought it was fantastic past 4K rpms. I especially notice the absence of this extra pull with the stock muffler being back on the car.

So I was wondering if there is a difference between 2.5 and 2.25 in terms of torque and hp. Does 2.25 give better low-end while 2.5 is superior higher in the rev band?

Also, is 2.25 the standard N/A midpipe diameter of choice, or are people going smaller, like 2"?

Thanks,
Kevin
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Old 02-21-2001, 11:30 AM   #2
Aspen
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It's always a give and take issue.

You pretty much hit it on the spot. 2.25" is good for broadband power while the 2.5" will give you a little more on the top end. The 2.5" can also give you broadband power if you are running more extensive mods than just an intake.

FYI, Mike Shields has actually dynoed the 2.25" and 2.5" piping and had verified that the 2.5" did lose a little in the low end. Although, I'm not sure what setup he had.
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Old 02-21-2001, 04:53 PM   #3
P.K. Motorsports
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I snickered when I read your topic, because the RS doesn't really have a "top end". You hit power peak only 700 RPM shy of a relatively low redline. 2.5 might make a difference at 8500 RPM, but keep in mind that by any "piping size calculator" you are already bigger than what's typically recommended for a 2.5 liter motor which makes power peak at 5600. Mustangs have dual 2.25" on a 5 liter and are considered to be overpiped from the factory by a lot of knowledgeable people, including a local welder I know who owns an NA Mustang good for middle 11s. Recently HotRod had an article on a Camaro (5.7 liters, single 2.5" exhaust) which had been tuned to the point of running 11.6 with nothing else but a set of slicks. 2.5 is BIG, over double the diameter of your stock exhaust, and you can't generate the exhaust volume necessary to justify it without a turbo.

In addition, if all you're doing is messing around after the stock 1.75" cats then I really doubt it will make much difference, with the possible exception that you will AEBE lose more gas velocity with the 2.5". Headers and a high-flow cat pipe would push more through a 2" exhaust than you'll ever get through just a catback, no matter how free-flowing.

2.5" is probably good for more low-end loss, but I really doubt there's any gain over 2.25" on an otherwise-stock RS.
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Old 02-21-2001, 06:23 PM   #4
gtguy
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Sorry P.K., but I just don't buy that argument. With the stock muffler, the car pulls well until about 5K, then begins to poop out. With the Stromung, it didn't have that flat spot. The car sounds better, and feels better.

My only question was an issue of what effect a different diameter might have on the performance, and that was answered. Beyond that, I'm happy that I was able to provide you with a bit of humor.

Kevin
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Old 02-22-2001, 12:44 AM   #5
Diz
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If you are going to stay NA, I would go with the 2.25. I had a 2.5 on my car before the turbo and I wasn't too crazy about it. I did notice a minor loss of low end power.

-Paul
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