kodiak

iTrader: (1)

What Hp numbers dictate the size of the pipe ?

Full-Force

iTrader: (11)

I would just go head and get the 3" unless you are lowered enough to where ground clearance will be an issue.

Longtube headers and 3" duals was one of the 1st mods I did to my car.

MM98

iTrader: (13)

I went with 2.5" because I'm lowered an 1" & clearance is important to me... I've actaully got better clearance now then when I had my 3" y-pipe... In addition to the duals, I can definately feel a difference almost everywhere in the rpm range.

Mike

SUX2BU

iTrader: (14)

Clearance isn't a problem if you have good duals.
BTW get 3".

FstBlkz28

iTrader: (13)

2.5" should suffice for well up to 500hp ... and would have more efficient scavenging at lower rpm's due to the higher exhaust velocity. That being said ... 3" duals sound mean as hell and have a real nice deep throaty growl to them. So if you didn't need the extra ground clearance I'd go with 3" for the sound alone.

SUX2BU

iTrader: (14)

Just cause something can support a certain amount of HP doesn't mean you won't gain anything by getting something better.
will an LS6 intake support 400 rwhp? Yes Would you gain hp by switching to a FAST? YES!

Full-Force

iTrader: (11)

I agree. Alot of people have not noticed but I have. If you notice, the exhaust for mustangs 5.0 and 4.6 engines most all of the time have dual 2.5 exhaust and also most all of the time have 1-5/8 headers. Now most all headers for the F bodies both LT1 and LS1 use 1-3/4 headers. The GM engines obviously make more power and benefit from 1-3/4 and even larger headers. It only seems logical that the exhaust system itself would be larger.

I think a dual 3" system is the only way to go on these cars with a minimum of 1-3/4 header.

magius231

iTrader: (8)

heh bigger is not always better guys a full 3" pipe will likely lose you a lot of low end torque on a car that doesn't really need it.

Here's a real good diagram to check what you need (wish the numbers went higher though):

http://www.dynomax.com/techsupport.stm

according to this, a 427cid motor making 500hp only needs dual 3" pipes, I doubt most of our cars need anywhere near that big.

99Hawk262

iTrader: (19)

2.5" here. Went from 13.6 at 103 to 12.9 at 107. Actually ran a best speed of 108.5 on a 13.0 pass. Good enough for me!

00SLPSS

iTrader: (15)

i'm all about the american way. bigger, louder, and more impratical. if you are like me get the 3".

weestro

2.5" is more than sufficient plus the ground clearance will be better. Most header makers use 3" collectors tho and the front half of the X pipe needs to match.

98OCT/A

iTrader: (5)

i just ordered the x pipe from dr. gas that is 3" to 2.5", just cuz im lowered

GM Muscle

iTrader: (9)

How fast or what kind of power are you planning to run in the future? The fastest that I have ever run with my 2.5" duals is 10.40@130, car runs 10.1 with open headers. Back when I was running just bolt ons and a 150 shot, the fastest the car ever ran with them was 11.2, same set up ran 10.95 with open headers. I'd say if your looking to push 400rwhp or more in the future go with the 3". And these days, that number is easily acheavable with just a cam.

tylerdj

iTrader: (31)

In my opinion - 3"

_JB_

iTrader: (33)

It depends on what you plan on doing to the car. If you keep it stock, 2.5" will do fine. If you plan on some sort of forced induction, then go 3".