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.

Re: 4 cyl paired-runner exhaust manifold runner length
 

they should be, but not always.

unless your running some serious HP, it doesnt matter.

Re: 4 cyl paired-runner exhaust manifold runner length
 

its more important that they flow well

Re: 4 cyl paired-runner exhaust manifold runner length
 

:y :y :y :y :y :y

Re: 4 cyl paired-runner exhaust manifold runner length
 

Log manifold

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!

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.

Re: 4 cyl paired-runner exhaust manifold runner length
 

equal length runners= over rated :P

Re: 4 cyl paired-runner exhaust manifold runner length
 

Fixed it for you.

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.