4 cyl paired-runner exhaust manifold runner length
08-20-2007, 10:13 PM
#1
0.0 BAR
Thread Starter
Join Date: Aug 2007
Posts: 1
4 cyl paired-runner exhaust manifold runner length
Couple books say that your swanky turbo exhaust manifold should have equal length runners. But I saw a Saab Viggen mani the other day (divided outlet, with paired 1-4 and 2-3 runners) that had 1 & 4 @ equal-length, but 2 and 3 @ unequal length compared to each other, and both shorter than 1 or 4. This car runs 20 psi stock, so what's the deal here -- Saab's been in the turbo game since the '70s. Is there some equation to determine some percentage length the shorter runners should be vs the longer? It appears from looking at this manifold that the whole equal length deal just doesn't matter.
Thoughts, experience, and some tech is appreciated.
Thoughts, experience, and some tech is appreciated.
08-21-2007, 09:23 AM
#6
1.5 BAR
Join Date: Oct 2004
Posts: 877
Re: 4 cyl paired-runner exhaust manifold runner length
THey certainly don't have to!
I had the chance to test quite a few manifold designs. Free flowing merges and wastegate placement are far more important.
here's an example: very unequal, yet surprizingly good working manifold!
I had the chance to test quite a few manifold designs. Free flowing merges and wastegate placement are far more important.
here's an example: very unequal, yet surprizingly good working manifold!
08-22-2007, 12:49 PM
#7
1.0 BAR
Join Date: Dec 2002
Posts: 604
Re: 4 cyl paired-runner exhaust manifold runner length
a good OEM puts its focus on reliable, then cost effective, then its appeal to the masses, then finally performance.
a bad OEM goes cost effective, appeal to masses, reliable, performance.
a bad OEM goes cost effective, appeal to masses, reliable, performance.
08-22-2007, 05:32 PM
#9
0.0 BAR
Join Date: Feb 2003
Posts: 0
Re: 4 cyl paired-runner exhaust manifold runner length
Originally Posted by crxvtec91
equal length runners= no proven improvement, just a lot of internet noise based on "it's obvious" with nothing to back it up after 40+ years of claims
08-23-2007, 01:12 AM
#10
1.0 BAR
Join Date: Jun 2005
Posts: 213
Re: 4 cyl paired-runner exhaust manifold runner length
It seems like it wouldn't matter at all. How fast is all that exhaust gas coming out of there anyways? It seems to me like it's being expelled so quickly that it doesn't make any kind of difference unless the lengths were waaaaaay off.
