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Signifance of manifold length for ITBs or DCOEs


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I'm aware that airhorn lenght is quite significant to HP and torque numbers, but I'm curious to know if the depth of the manifold bolted to the head is similarly important. I've got two, one of which is about an inch deeper than the other but will take considerably more work for fit as it needs a couple of ports drilled into it, port matching to the head and ITB, etc... Given that modern cars now have direct injection I wonder if getting the injector closer to the intake valves could actually be a positive??

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the whole tract length and volume tunes the weight-thus inertia-

of the intake column.

its a smaller effect on an independent runner system, tho, as

you can't 'borrow' flow from one to help the others,

like in the exhaust. Or on a v8 with a holley 4 bbl.


"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Okay. So the TOTAL length of the runner from the face of the head to the tip of the airhorn is the key. Where the injector is located (as dictated by the depth of the manifold) is not crucial. And, any length lost by having a shorter manifold can theoretically be made up by having longer airhorns. Is that a correct interpetation of your feedback Toby? Thanks so much.

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Yo Grover,

Yeah, the longer length manifolds add to the total intake track length, coupling with the carb-width plus length of the horns. I believe my Warnifords have the longest tract length of any manufactured 02 DCOE manifolds - providing extra mid-range grunt for a big cam carbied set-up.

Not sure what's better for a fuely - might be same effect. Where the fuel is injected along the tract might have little effect (as long is it's far enough away from the chamber to atomize/mix properly). Shorter length tract moves powerband upward (cam a factor obviously too). Given you're likely going individual runner - not sure what Toby was referring to with the V8 with shared runner ref.

True that - you can make up shorter manifold length with horn length (but I don't think it's 1:1 since in-manifold flow is better than at the outer part).


Where we goin’? … I’ll drive…
There are some who call me... Tom too         v i s i o n a u t i k s.com   

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yeh, as Oldguy says, it's not going to be massive, and it'll actually be rpm dependent.

(the Holley thing is how plenum intakes work- they use pulses from some

cylinders to modify how others get fuel/air)

And, any length lost by having a shorter manifold can theoretically be made up by having longer airhorns.

Grover, where I start to get fuzzy is when you start to close the throttle.

That's going to affect the way the stack works, disconnecting the

horn from what's on the engine side of the throttle.

So yeah, with the throttles open, intake is intake, but when you start

to close them, that's going to start separating the 2 parts into separate

resonant chambers...

I think that's one reason BMW and others went to 'valvetronic' throttle

where the intake valve becomes the throttle.

The injector position DOES matter in terms of atomization- race cars

with long trumpets used to (60's- 70's era) inject in all sorts of ways

to get more even filling. Looking at what emission controlled cars do,

I bet hitting the base of the intake valve's considered state of the art these days.

If you can't squirt right into the cylinder, that is.

Me, I would use whatever packages well- and then spend the time I saved

dicking around with it to make the rest of the inlet passage work well

(DCOE's really HATE things in front of them, and that's hard to avoid)

But I'm only a genius in my own mind.


"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Tom -

Marc here from COS Taji, Iraq. I see you are thinking about changes to your present setup. I know you will only go with the optimal/best/most bitchin looking parts. :)

Anyway I hope you are doing well. I miss being home, being with the family getting my car running. Actually I was in the Bay in late June on R&R. I took the family on vacation to Monterey, Santa Cruz, SF and Marin. I wish I had time to play golf or go see 2002 folks - talk about cars.

I decided (recently) to get the 02 running again. I bought a bunch of pieces but never had a chance to work on the car. I did remodel the whole bathroom (did it myself - hard work). Most of my back home time has been with the family and working around the house. I will allocate $$ to get the car road ready by Christmas. The Kerman Stroker is still there with no miles. I pickled it with Marvel Mystery Oil, etc.

I'll try to follow along, been staying away so I don't get the fever, but it is time to start working and driving again. I'll have two months off work so that should be enough time to install the MS and other interior stuff.



The Road of Life Should Be Driven in a BMW2002!! Happy Trails!

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