• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

4" DP on a 16v?

Tfrasca

Active member
Joined
Apr 20, 2015
Location
Ben Lomond, CA
I am building a 16v B230 with a BW s252 (I have a 1.00 twinscroll housing, but may want to use a .85 instead). My thought is that I want it to flow enough to make decent power at around 8k rpm. Not super concerned with peak power, but I'm assuming the 350 whp range.

I realize that a 3" down pipe would be fine for this, but I'm wondering if I stand to gain anything by using a 4" one. Better spool characteristics, and more flow at high rpm? I will be dumping the two 38mm waste gates back into the down pipe.

It would obviously be a tighter fit with the 4" tube, but I already have a 4" v-band for the housing, which is what started me down this road.

Thoughts?
 
how much power are you looking to make?

3" isnt really a restriction until you get up over 500-ish hp.
 
if you can fit a 4" downpipe easily then sure, why not. Granted a 140 series engine bay is a little harder to work with I would imagine fitting a 4" downpipe would be a pain in the ass.
 
Hi Tfrasca.

If we do a quick comparison of those numbers:
Capture.png


I would expect that the hp gained per inch^2 of surface area would decrease with increasing diameters.
In other words, the relative gains from increasing DP surface area becomes smaller with increasing DP size. Do you people agree?

However, if we compare those numbers we see an opposite trend is the case, which leads me to believe they are not telling the whole story.
 
Hi Tfrasca.

If we do a quick comparison of those numbers:
Capture.png


I would expect that the hp gained per inch^2 of surface area would decrease with increasing diameters.
In other words, the relative gains from increasing DP surface area becomes smaller with increasing DP size. Do you people agree?

However, if we compare those numbers we see an opposite trend is the case, which leads me to believe they are not telling the whole story.

Why do you expect that? Over a certain size, absolutely. But if we believe these numbers, it just means that they didn't hit the size at which gains per inch^2 level out, then decrease. Or am I misreading your comment?
 
Also, i missed the design of those pipes. Twin turbo which merges into one pipe with short harsh bends, which are way less pronounced on the 6.5 inch version. This could be a bigger improvement than the dp size itself.
 
No reason to use over 3" with that build. 3.5" exhaust was enough for 800hp with "B6284T" and E85. No screamer.
 
Also, i missed the design of those pipes. Twin turbo which merges into one pipe with short harsh bends, which are way less pronounced on the 6.5 inch version. This could be a bigger improvement than the dp size itself.

Yeah, I wish they had done this test on a single turbo car. That twin setup looks horrible. But I still don't know if the results can be completely disregarded.
 
No reason to use over 3" with that build. 3.5" exhaust was enough for 800hp with "B6284T" and E85. No screamer.

I don't doubt that at all, and I'm not under the impression that a relatively mild 16v redblock needs bigger than 3". I'm mainly thinking out loud about quicker spool with the 4" DP. 3.5" was enough for 800hp with your build. But you don't think 4" could have been better?
 
I did swap to a 4" dp later on because goal was to reach higher numbers. Didn't go that route, but with 700-750hp the results have had the same relation to boost as with 3.5". No difference whatsoever. Biggest change after 700hp was changing the rest of the exhaust from 3" to 3.5". The first version had 523hp @ 1.5bar on regular gas, 3.5" dp, 3" front muffler and over the axle, 2.5" rear muffler and end pipe.

Many have had pretty decent numbers with 3" dp. It does not choke a ~400hp redblock. Power and boost go hand in hand if the engine is otherwise working.

Friend dynoed 575hp(not whp) from a 2.3l 16V with a 3" exhaust. Turbo was a Borg Warner, couldn't find the model. That result was with 2bar boost, he did drive it with 2.3bar too.
 
Last edited:
ran a 3 inch into 2.5 inch system with a 650bhp 1jz. next owner took it to 900hp same exhaust. no need for 4 inch unless its a mack truck.
 
ran a 3 inch into 2.5 inch system with a 650bhp 1jz. next owner took it to 900hp same exhaust. no need for 4 inch unless its a mack truck.
If you have a screamer then the situation is a bit different because there is less gas going through.
Changing my exhaust size to 3.5" upped the power level from 727 to 789hp and torque from 870 to 935Nm(690lb-ft). 2 degree less timing on max torque and around 0.1bar less boost. No other changes.
 
Well I ignored all your advice. It wasn?t that hard to fit, so I figured why not?
 

Attachments

  • 9919ADB3-F9C6-4231-8646-3BF25666C338.jpeg
    9919ADB3-F9C6-4231-8646-3BF25666C338.jpeg
    170.7 KB · Views: 109
Back
Top