S-trim Fox - Which exhaust to buy?

FastSVO · Dec 2, 2010

Hey Guys,

I am debating whether to go with a 2.5" or 3" cat back exhaust for this car.

Motor is stock minus the GT-40 intake, 70mm TB, JBA headers, BBK catted 2.5" h-pipe, and 3:73 gears.

This car is driven on the street and I need to find a setup that will flow great and be drone free.

Any ideas?

Thanks!

t76stang1Day · Dec 2, 2010

If a panhard bar is in your future parts list, then get a 2.5" cat back exhaust that will work nicely with a panhard bar setup to avoid clearance issues

2000xp8 · Dec 2, 2010

There is no reason to use 3 inch on pretty much any stock block mustang.
As far as panhard bar, that really doesn't matter since there is only 2 maybe three catbacks that exist that will work with one anyway, regardless of pipe size.

NIKwoaC · Dec 2, 2010

I wouldn't hesitate to run 3" exhaust on that car. Maybe it will help, maybe it won't, but it will definitely allow room for growth in the future. Plus, 3" tails look bad ass.

On a side note, I'm not sure you can run a 3" cat-back with a 2.5" mid-pipe. Maybe someone here can verify that one way or another...?

2000xp8 · Dec 2, 2010

NikwoaC said:
I wouldn't hesitate to run 3" exhaust on that car. Maybe it will help, maybe it won't, but it will definitely allow room for growth in the future. Plus, 3" tails look bad ass.

On a side note, I'm not sure you can run a 3" cat-back with a 2.5" mid-pipe. Maybe someone here can verify that one way or another...?

Grow into what? You can run 700rwhp through a 2.5.
Many kit's have 3 tailpipes anyway.

No need for clearance issues, 3 inch will be hitting the frame rails, upper control arms and the gas tank.

FastSVO · Dec 2, 2010

I thought the 3" tailpipes out there are designed not to interfere with these items?

NIKwoaC · Dec 2, 2010

2000xp8 said:
Grow into what? You can run 700rwhp through a 2.5.
Many kit's have 3 tailpipes anyway.

No need for clearance issues, 3 inch will be hitting the frame rails, upper control arms and the gas tank.

You could also make 700rwhp through the Cobra intake if you were willing to feed it enough boost. The point I'm trying to make is that there is no harm in going with the bigger exhaust, especially if more power is planned down the road.

My 2.5" exhaust rubs in spots. I think it has more to do with what suspension parts are used and how well the exhaust is put together than diameter. A 3" pipe is really only 1/4 inch bigger in any direction.

Rick 91GT · Dec 2, 2010

In no way would I put 3" on that car, 2.5" is plenty fine now and in the future... not an opinion but fact from lots of dyno testing, be surprised what stepping down from a 3.5" exh to a 3" on a 800hp car does, made more power and tq. Most guys dont need the 2.5" but that is what most aftermarket cat backs are.
Drone free well, that will be the hardest thing, do you care how quiet it is? The Borla Pro XS is a good choice, doesnt rob a ton of power either.

FastSVO · Dec 2, 2010

Yeah, I would like to keep it quite(r)...the only comparison I have are my current 2 chamber flowmaster with the stock tailpipes.

The blower itself is pretty loud.

Kdubslugga · Dec 3, 2010

2000xp8 said:
There is no reason to use 3 inch on pretty much any stock block mustang.
As far as panhard bar, that really doesn't matter since there is only 2 maybe three catbacks that exist that will work with one anyway, regardless of pipe size.

Well said

FastSVO · Dec 3, 2010

2000xp8 said:
There is no reason to use 3 inch on pretty much any stock block mustang.
As far as panhard bar, that really doesn't matter since there is only 2 maybe three catbacks that exist that will work with one anyway, regardless of pipe size.

Which ones are those?

SVT32VDOHC · Dec 3, 2010

I would stay with 2.5" just because you will have clearance around your UCA's and other areas. Sometimes 2.5" stuff gets tight depending on how well it fits, what UCA's you are running and how your brake lines run. I know on my mod fox's the way I ran a couple brake lines 3" exhaust would have been tough.

2000xp8 · Dec 3, 2010

FastSVO said:
Which ones are those?

One of the Flowmaster kits (don't know which one), and the dynomax ultraflow.
I do not know either to be fact (yet), but it's what i've come up with during research.
Pipes have to be factory routed to work with a PHB.

We'll see, i'm going to the ultra flow soon so i can put the PHB i have on my car.

Boostedpimp · Dec 3, 2010

2000xp8 said:
Grow into what? You can run 700rwhp through a 2.5.
Many kit's have 3 tailpipes anyway.

No need for clearance issues, 3 inch will be hitting the frame rails, upper control arms and the gas tank.

I agree totally

90lxcoupe · Dec 3, 2010

2000xp8 said:
No need for clearance issues, 3 inch will be hitting the frame rails, upper control arms and the gas tank.

My 3" tails tuck right next to the gas tank and dont hit the frame or UCA's

2.5 is plenty for that combo tho, also, you will have to spin the blower faster to compensate for the bigger exhaust. On my stock block/novi2000 motor i went from shorties to bassani LT's to a 3" xpipe and spintech 2.5 inch mufflers, before the 3" it made 10psi, after i only saw 8psi on the gauge, and the car actually lost some power. If i had it retuned it may have picked some power up, but i would have also had to put a smaller pulley on the blower to see if there were any real gains

FastSVO · Dec 3, 2010

2000xp8 said:
One of the Flowmaster kits (don't know which one), and the dynomax ultraflow.
I do not know either to be fact (yet), but it's what i've come up with during research.
Pipes have to be factory routed to work with a PHB.

We'll see, i'm going to the ultra flow soon so i can put the PHB i have on my car.

How are the Ultra Flow's on these cars? I believe I read somewhere that they are prone to droning and there is a report out there showing the flow rates of many mufflers and I was surprised not to find the Ultra Flows on top of the list.

NIKwoaC · Dec 3, 2010

90lxcoupe said:
My 3" tails tuck right next to the gas tank and dont hit the frame or UCA's

2.5 is plenty for that combo tho, also, you will have to spin the blower faster to compensate for the bigger exhaust. On my stock block/novi2000 motor i went from shorties to bassani LT's to a 3" xpipe and spintech 2.5 inch mufflers, before the 3" it made 10psi, after i only saw 8psi on the gauge, and the car actually lost some power. If i had it retuned it may have picked some power up, but i would have also had to put a smaller pulley on the blower to see if there were any real gains

I thought you had 3", couldn't remember for sure though.

Did you actually see a power loss on the dyno? Was the car slower at the track?

A reduction in gauge pressure isn't always a bad thing, in that case it was the result of the engine's VE increasing...

In my experience/from what I've learned, when a car loses power after moving to a "bigger" exhaust system, it usually has to do with tune and/or exhaust valve events. Like anything, it's all about the combo, and if the cam can't take advantage of the free flowing exhaust, no gains will be realized.

If it's true that free-flowing exhaust is counterproductive to performance, then why do drag cars use open headers or cutouts? Why are these high-dollar builds using large cross section oval tubing? Hell, why are 3" systems becoming so popular for the 4.6L cars (never mind the Coyote)?

Not trying to stir the pot, gentlemen. Just wanted to bring a few points to light.

2000xp8 · Dec 3, 2010

FastSVO said:
How are the Ultra Flow's on these cars? I believe I read somewhere that they are prone to droning and there is a report out there showing the flow rates of many mufflers and I was surprised not to find the Ultra Flows on top of the list.

I think all catbacks drone somewhat.
I've had borla, Flowmaster, magnaflow and mac mufflers all at some point on a 5.0 vehicle, they all droned.
Some worse than others, but the difference isn't enough to try and purchase based on drone level.

clement · Dec 3, 2010

yes you can make 700hp through a 2.5, and....but if you ever back to back track test a car running the restricted exhaust vs. uncorked; the difference is what some refer to as accelleration. does a bigger exhaust pick up huge numbers on a dyno, usually no. but around here we dont race dynos and at the track where it counts, it makes a difference. it also doesnt eat up exhaust valves and seats as fast when you have a correctly sized exhaust on a combination.

2000xp8 · Dec 4, 2010

I think some of you guys need to take into consideration the setup and use of the vehicle in question when giving advice.
The OP is obviously building a mild street car setup. As so, your advice should be tailored to such.
Look at his combo, if he is going to turn it into an all out race car, he has alot more to worry about than buying a 3 inch exhaust.
A 3 inch catback is going to waste extra money for absolutely no reason. He's about 12 grand from needing a 3 inch exhaust.
Size parts for use now, not in the future.

S-trim Fox - Which exhaust to buy?

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