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3inch Or 4inch

rbgtst33

By rbgtst33,
in Engines & Forced Induction

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R33GOD Grand Master

R33GOD

Posted
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hey ive got a 4inch stainless steel catback exhaust sitting in my garage jus waiting to get fitted, but ive been told that a 4" is too big and wont b as effective as a 3" exhaust. Whats the deal here, should i sell the 4" and look for a 3" or just chuck the 4" on.

opinions anyone?

depends on what u want. a 4 inch will give u good top end and average low to midrange and a 3 inch will give u good down low/ mid range power

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rbgtst33 Rookie

rbgtst33

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stock turbo basically car is all stock except for a shitty pod which has to be changed and a dump pipe. Originally when i bought the car it had a turbo back exhaust fitted, 3inch from the turbo through to a 4inch from the cat, which is currently sittin in my garage because it had to be taken off for the roadworthy.

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nisskid Grand Master

nisskid

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I thought when it came to turbo cars Biggger is Better. No exceptions.

It's only NA's that require back pressure etc...

But if its a road car then you have to wrry about police/EPA noise.

i beleive if ur exhaust is too large on an exhaust u will lose alot of bottom end due to no backpressure etc, but for high revs, yes better flow will mean better performance.

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R33GOD Grand Master

R33GOD

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ohk that helps, but is it worth goin to the effort to gettn rid of the 4" n finding a 3.5 or a 3" or would you guys just chuck on the 4" since its jus sittn in the garage.

just run the best of both worlds. run a 3inch front/ dump and 4 from the cat back if its already sittin there :D

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GeeTR Grand Master

GeeTR

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just run the best of both worlds. run a 3inch front/ dump and 4 from the cat back if its already sittin there :)

Go biggest you can. Considering your current mild setup, keep the 4" cat back, grab a 3.5" Turbo > Cat section.

If your planning big numbers later on, then a diff m.fold / turbo will require new front section anyway.

- M

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SLIPPERY Experienced

SLIPPERY

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yeah a lot of funny information floating around with people saying youll lose performance with decreased back pressure lol . Yes, thats the theory with naturally aspirated motors

any exhaust you have is gonna have more than enough back pressure since the gases have to pass through our little friend, the turbine wheel.

as said by GeeTR, go the biggest you can

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BHDave Grand Master

BHDave

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Even back pressure in NA cars is a myth. It has been proven that the gains in NA exhausts are made in the headers. Biggest pipe possible after that with the compromise being the noise.

In this case. Chuck the 4 inch on, nothing to lose. If you don't like the noise then swap for a 3 inch. You may end up smack in the middle of the rich and retard mapping as a result with either a 4 inch or 3 inch though

In bigcarls example I think you'll find there are gains to be had by going bigger, though it's not necessary by any stretch.

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