Dump Pipe Question

[Jman]

Hi guys.

I'm getting my first lot of mods done in the next month or so.

I'm planning on doing the front half of the exhaust dump/cat (using the stock exhaust minus middle muffler)... then doing a catback custom job on the 2nd round of mods.

For the first round I'm trying to push over 330rwkw's.

I've been looking around specifically for a 4inch dump pipe. Most of the brands that I've seen the 4" dump pipe starts as a 4inch pipe then tapers down to a 3.5 exit for the cat. Is this the case with all 4" dumps?

Then with the 3.5's that I've seen... they taper down to a 3inch.

I'm trying to find a 4" dump pipe which stays that thickness right through.

Any advice please... I'm all ears.

Cheers,

Jarrod

Edited 11/11/08 04:51 PM by Jman

[typhoon_freak]

yeh, the most iv seen start as a 4in and taper to 3.5.. I think this is cause u have the air comming from the turbo as well to be joined into the exhuast? depends if u want a joined dump and split dump.. I got a split dump with 4inch that runs thru a twin 2.5in.. I dont think having a 4in all the way thru would matter, as the dumps can support a far amount of airflow as it is.

[Guest]

SMB are 4' all the way through

[Jman]

What are the advantages of having a single vs split system?

[Guest]

The smaller the dump, the quicker the car spools up. The larger it is the more power it can make.

In a nutshell, I don't see a difference in having a split 3"/1" dump compared to a straight 4". there's still 4" of space to fill

Could be completely wrong though?

[senna_T]

The main arguement for the split pipe is that it keeps the flow from the wastegate separate from the main exhaust flow. This is supposed to reduce back pressure and increase response.

[straughsberry]

Turbulence.

I've spoken to a tuner or two who likes the split dumps for the sub 400 region. I spoke to a bloke from QLD who said he went from a 4inch to split and ended up making more power. My friend at pro flow also prefers split dump pipes. Everyone has an opinion...

*actual results may vary

[bigmat]

The smaller the dump, the quicker the car spools up. The larger it is the more power it can make.

In a nutshell, I don't see a difference in having a split 3"/1" dump compared to a straight 4". there's still 4" of space to fill

Could be completely wrong though?

Hmmm lets see I don't think it is quite that straight forward....

Area of a circle = pi * radius2 (dump pipe) in this case

3" and a 1' equal (in metric to stop confusion about multiplying halves etc ) 38mm = 1.5' = radius of main pipe and 12.5 = 0.5 radius of wastegate pipe.

so

3.1428 x 38 x38 = 4536 cm squared

+

3.1428 x 12.5 x 12.5 = 491 cm squared

Totals = 5027 cm squared

BUT

1 x 4" pipe = 3.1428 x 50.8 x 50.8 = 8106 cm squared so by rights the 4" should flow about 60% better....

Then I could be wrong too.....apart from a bit of rounding, I think I was once or twice in the past.

[XRSCAR]

To much maths for a Saturday night bigmat! hahahahah

[bigmat]

To much maths for a Saturday night bigmat! hahahahah

yeah possibly it was just about sunday morning here too....

but I think one 4 inch pipe would flow better than a 3 and a 1

but then you take into account scavenging effect and back pressure, separation and all those other things like thermal dynamics bla bla (I almost sound like I know what I,m talking about... wrong....) and the 3 and 1 may work better then the 4.... in all but the biggest horsepower applications...