02_ramair_ta

iTrader: (35)

I am putting my 91.5 turbo into my 72 Nova, running the truck manifolds, and building the whole setup little by little, myself..


My question is, If I take the 5" down pipe, run it out about 6 inches and then split it into 3" duals, how much if any effect would of could that have? I understand that you want as little backpressure coming back against the turbo, so would I run into any issues.. or would it maybe help, like a venturi effect, if done right?


Thanks for the help!

Fireball

iTrader: (21)

dual 3s is smaller than a single 5. need to be 3.5-4"

2001WS6Vert

I did the exhaust on Mark Koehler's car which is 5" split into dual 3 1/2 right out of the turbo. Fireball is right, you need to be at least 3 1/2 to equal the flow of a single 5". Some people questioned the way that the exhaust is done on Mark's car but it seems to not hurt it too much, it has run 7.50 and this year should knock that number down some considering the changes being done.

02_ramair_ta

iTrader: (35)

Awesome, thanks for the info, I'll do dual 3.5s. Glad someone with real world experience could step in on the this! I knew someone had to do it. You don't by chance have any pics of that car with the downpipe setup? That would help give me an idea of what works! Thanks again!

Phil99vette

iTrader: (11)

I purchased a 5" 90 degree elbow and some cones from Woolf Aircraft, I cut the 90 degree elbow into a pair of 45s and welded the 5" to 4" reducer cones on from woolf.

PRAY HRD

iTrader: (119)

Great question! So with a t4 turbo with a 4" outlet, i'm guessing the dual 3" would actually do pretty well?

02_ramair_ta

iTrader: (35)

Phil, that's about what I was thinking, I was worried that putting the split close to the turbo would cause back pressure, I like the reducer cone idea, that would squeeze the airflow, just enough to work kinda making a Venturi effect, now if I could use the Bernoulli principle, then taking it back to a larger section further down would increase the speed, creating a vacuum, and helping pull the exhaust out the pipes???

I know I am WAY over thinking this, and it's just splitting the exhaust, but I'd like to try and help the system with any tricks I could, the more efficient it is, the more power it makes!!!

koolrayz

iTrader: (26)

The quick and easy way to calculate how two different size pipes will flow in relationship to each other is to square the line size.
Example as an answer to the about question about dual three's from a 4"
3X3=9 times the two lines = 18
4X4 = 16
So the dual 3" has more flow cabacity.
This does not tak into account line lengths or other restrictions like 90's and a like but is perfect for line size comparisons

dual 3.5 or single 5"
3.5X3.5 = 12.25 X2 = 24.5
5 X 5 =25
very close to being equal.

PRAY HRD

iTrader: (119)

That's great info Koolrayz! Thanks!

lifeisgood

iTrader: (4)

nice explanation, i even understood that. haha

Fireball

iTrader: (21)

I merged two 4" bends into a 5" transition.

Fireball

iTrader: (21)

close approximation, but its really pi*d^2/4. so you multiply the diameter by itself and multply by .79

koolrayz

iTrader: (26)

It is what I call street math. I can do it in my head anywhere in a matter of seconds. Given the other variables in fabricating automotive piping systems it works fine. I would not use it when I am designing a system at work, but for a guy that has to ask on the Internet it will work better than a lot of the answers they would otherwise get. Not to infer there was bad information in this thread but, I know we have all seen plenty on the interwebz.