Exhaust Manifold Technicallities

[WidebodyWoody]

Hey guys

I am putting it out there, has there been proof as to which is better? Tuned length runners or not? I am talking about all 4 runners being perfectly the same length vs the other extreme where the runners run directly into the flange, so 2 are long and 2 are short.

I am interested in what has been proven or even some concepts about which is better. I have heard stories but I would like to hear from you guys.

Cheers

[TOMSUN]

Tuned length. It more work, but it's worth it.

[1320ft]

From my experience, longer runners, give you better low down in rev range.

[djalpha]

Thats true for inlet manifolds. Forced induction engines don't gain great benefits from tuned length exhaust manifolds. Most factory cast manifolds are good enough. An extravigant exhaust manifold is one of the last mods you do to a turbo car. More for look then anything. Have i just sparked a great debate?

[redzone]

no real scandal there aaron..

tuned length will make it spool slightly earlier, and gain a couple of hundred rpm of rev range up top.

usually a custom exhaust manifold is fitted when upgrading to a turbo that wont fit on the stock manifold, not really worth doing as a stand alone mod

[jk]

Proof? I think the fact that you see tuned length exh manifolds on early 80's F1 turbo's is proof enough that it's the ultimate for all out efforts.

But I would probably side with DJalpha in that for street duties the benefits would be very minor, manifold for manifold given an otherwise identical setup.

As for debate, I once heard long turbo manifolds actually hurt response due to the extra loss of exhaust gas heat ie. energy to spool the turbine. Once again this may only be a marginal difference.

[jk]

sorry to jump over you Dave, you wern't there a second ago

[redzone]

if that was true, those rear mounted turbo setups the yanks love wouldnt work would they :P

[jk]

if that was true, those rear mounted turbo setups the yanks love wouldnt work would they :P

yeah, good point :)

[redzone]

all good :)

[Alspos]

if that was true, those rear mounted turbo setups the yanks love wouldnt work would they :P

Maybe they'd work better if they were mounted under the bonnet? But it's a packaging compromise, it won't work if it won't fit.

[OLD FART]

I wouldn't be too worried about the length of the runners being too long.Just check out some drag Evos
My ex manifold is not equal length due to the more forward position of the turbo but no doubt equal lengths look great and they would be a fraction better/efficient if one was chasing the last bit of power possible.

[Mick]

dont stress mate if everything else is done properly you wont miss a few nM of torque.

[WidebodyWoody]

This is what I thought. The old theory I always heard I believe was only for NA cars. Cool thanks, these talks have helped me heaps. :beer

[docile]

The only reason you want long runners, is to reduce the manifold back-pressure (by verge of more volume), which improves the performance of Turbo cars with ridiculous overlap, ie 280+ deg camshafts. This is why you see long manifolds on drag Evo's and F1 Turbos. Not to mention the F1's used inconel manifolds which absorb even less heat than stainless steel.

Anything less than that, and you will find a shorter manifold will boost sooner and still hit the same peak HP.

Its all about how much energy is lost between the head and Turbine and obviously a longer manifold has a greater surface area and mass to absorb and rob that energy from the exhaust gases.

Also, because of this back-pressure effect on power, you ideally want equal length runners, so that you don't have to dial your tune to the worst performing cylinder, or go as crazy as tuning each cylinder.

It is not difficult to make short, equal length, manifolds and very much worth the effort.