What flows better?

[Jamo]

Which flows better for a downpipe? A tight 3.5 inch 90 degree bend or a 3 inch 45 degree bend into a 3.5 inch reducer?

[K7ERG]

What power?

[Jamo]

Say 650 bhp

[willg54]

3.5" 90 deg will flow more than the 3" 45 deg bend before you even count the 3 - 3.5 reducer

[Henkjan]

nice, a process engineering question

just the bends: a 90° will give approx double the pressure loss than a 45° (duh), if the 90° bend is tighter than the 45° this will be higher. the smaller diameter will result in a ~35% higher velocity, so ~85% higher pressure loss. so the smaller diameter with 45° bend will have a slightly lower pressure loss, expanding to 3½" from 3" should not give any pressure loss, maybe even a small a gain. this is only an approximation of course....

[Jamo]

That apply to A tight 90 degree not a mandrel bent one?
Reading on airflow not so sure

[Henkjan]

maybe the reduction to the 3" after the turbo has a greater effect...

[Jamo]

Should have added this is straight from the turbo vband

[EspenW]

Oooh, good stuff, I haven't calculated pipe flow and friction factors since the mid 90's. Gotta dust of me olde Fluid Dynamics books.

[Jamo]

This is the tight 3.5 90 degree in question

[JP]

Air doesn't like going round corners so to go a mild 45 3" and then expand into a 3.5" will be the optimum as the 3" section will offer improved low midrange response and the pressure drop from 3 to 3.5" will help scavenge in the upper midrange onwards. No scientific calculations I just know it works that way. I got this weird habit looking at pipes/ports and being able to visualise motion in 3d through it. Seems to have served me well in the last 15yrs

[Jamo]

Cheers guys, I will go 3 to 3.5 on the 45 degree rather than the tight 90 degree

[Rusty]

Can you get 80mm or 3.25" pipe and gain a couple of mm while keeping the 45 deg bend?

[Jamo]

I've just checked urs4guy thread and he runs 3 to 3.5 from turbo output
If he can do 750 at the wheels me thinks I should be ok

[urs4guy]

Hey Jamoman

Here's what I'm running.



The outlet from the CT43-6768 BR Comp Turbo is 3" so we ran the 3" initially with a gentle 45 degree turn. Then the expander to 3.5". There was a lot of forehead pounding as we deliberated this ad nauseam. The obvious friction from head loss and bends must be balanced with the turbulence factor. What is the loss, if any, from dumping a 3" outlet into a 3.5" pipe? Another item of note is the waste gate return to the down pipe happens well downstream to again, not provide interfering turbulence to the flow. I like what we came up with and the results bear out our theories, I think???

Hap, wit dakine head thoughts not from Evahboost, Maguire