4" downpipe split to what size duals?

[Black R]

Hi guys,

I'd like to go from my current 3" downpipe to a 4", but my engine swap has this exiting on the passenger side (usdm).

There isn't much ground clearance right now as the exhaust has to cross under the frame rail to exit in the stock location.

Now in the future I'll be lowering the car another 1" and also going with the bigger downpipe.

My idea is to go with a 4" y into smaller duals (2.5"?)
I want to make sure that the sizing of the duals flows at least as much, if not more than the single 4" pipe.

I've scoured burns site, as well as google, just looking for the proper volume of duals compared to a 4". I could get anywhere from 2" to 2.5".

Thoughts?

[Chaluska]

I know on a few camaros ive seen the exhaust pipe crushed into an oval, so the internal volume is still 4" but it will be like 2" x 5.5"

not sure how the layout is of your exhaust, but that could be an option?

also your going to go FROM a 4" to a larger downpipe? wtf engine swap did you do, a diesel?

http://pdidiesel.com/website%20photos/product%20photos/Detroit%20Engine.gif
if you intentionally are wanting to go from 4" to dual pipes....

A (area) = π(pie)r(radius)2(squared)

A = 12.566370614359 in2 (at 4")
A = 7.068583470577 in2 (at 3")
A = 4.9087385212341 in2 (at 2.5")
A = 3.1415926535898 in2 (at 2")

so to go from a 4" and have equal volume, you would need 2-3" pipes, 3-2.5" pipes, or 4-2" pipes.

[Fred Allen Burge]

Well I believe you just use Pi to calculate it. Using Pi I get two 2.75" diameter pipes being closest without going way over. If you step up to 3" pipes you get quite a bit more volume than you need. Stepping down to 2.5" duals you end up loosing an awful lot. It looks like two 2.8" pipes would be about perfect but good luck finding that size!

I could be off on my thinking since I'm figuring area here not volume but I think it applies, and I'm no math guy to say the least.

[Black R]

Chaluska, I'm going from 3" dp to 4" dp.

Burns does have an oval conversion though, which is 2.5" tall...

[andrew600]

Why can't you exit passenger side? And there aren't any swaps youre needing 4" dp. That's talking 6bt size. And you don't have a 6bt in your 240

[R33E8]

lol is it that hard to figure out that he probably has a 2jz swap??? Some people actually like to make real hp and not some weak gt28 sr20... I would assume he is running like a 67mm turbo or larger..

[idahotuner]

i think a 4 inch straight pipe would sound awesome on my sr haha, just not worth the work

[Black R]

Why can't you exit passenger side? And there aren't any swaps youre needing 4" dp. That's talking 6bt size. And you don't have a 6bt in your 240


This is an interesting read:

3" vs 3.5" Exhaust. Interesting Read. (http://www.supraforums.com/forum/showthread.php?628143-3-quot-vs-3.5-quot-Exhaust.-Interesting-Read)

It's definitely worth it to me if I can get 50+ hp at the same boost level...

[andrew600]

cool read. what are the specs on your car??

[EsChassisLove]

lol is it that hard to figure out that he probably has a 2jz swap??? Some people actually like to make real hp and not some weak gt28 sr20... I would assume he is running like a 67mm turbo or larger..

still gonna be a 12 second car.

lawl