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Any experts on air horn and airbox design for ITBs?


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I've been running MegaSquirt on my car for the last couple of years using the fairly standard 318 intake manifold. However, my longterm goal has always been to move to individual throttle bodies, and just recently I picked up a set of TWM ITB's. I need to pick up some of the linkage pieces, but the key parts (from a performance standpoint) that I still need to source are the air horns and air box. From what little I know, I understand that the design and length of the airhorns is really quite important, but I'm hoping some of the experts on this board might be able to point me in the right direction for sizing, and/or an education.

My car has a stroker motor with a ported E12 head, a 2.3L S14 bottom end including the crank, 9.5:1CR, etc... The TWM ITBs are 45mm.

Thanks in advance.

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errr... no. I keep bumping into the inner fender-

as in, it's too close to the carbs to really get both nice

trumpets and an air box in there gracefully.

Everything I've bought or made is a big performance increase- when I take it off!

Now, this is with DCOE's so you might fare better with injection-

you don't need as much room as the carbs do for emulsion-

but 2 diameters clearance around any horn is really hard to get.

Especially with a brake booster.

frikkin' science...


Wish he had some dyno info from after the plenum- I found one like that

cost me the 15 he got for the longer runners...


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Thanks guys. Yes, I've seen the E21 and the work he did it pretty impressive. I know it is completely vain of me to say this, but part of the reason I've wanted to go to ITB's is that I just love the look of dual side drafts, but want the tunability of EFI. As such, I'm hoping to find a solution a little more elegant than the path he took. I've attached a couple of photos of the parts I'm starting with; the guy I bought them from had pieces made for a couple of spare airboxes so I've got some decent starter blanks if I need to make modifications to them to accept the airhorns; he was running this set-up with forced induction.

As for the use of my car, it is primarily a street car, I try to do maybe two track days a year in it. However, if I have to sacrifice torque vs. HP, I'd probably be inclined to sacrifice a little top end HP prior to giving up torque.



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Hey Grover,

No expert here, but i've been running the 45mm twm itb's on my car with a large oval itg airfilter. The itb's rock! The biggest problem youll have trying to run an airbox, as Toby mentioned, is clearing the booster. I've heard that none of them fit. Not dbilas, twm, or pipercross. Throttle body extensions are usually necessary to get the filter backplate (or airbox) to clear the fuel rail, which pushes everything too far out. You'll either have to delete tHe booster, or get a manifold that is quite short and not angled, so the throttle bodies actually follow the line of the intake ports, slight angled upwards, to help with booster clearance. I have a setup, not installed at this point, fabricated/modified by Lee Vuong, which does just that. I does not accomodate airhorns, so not sure of any flow penalty there, but I'd be happy to show it to you one of these days. if you're interested, hit me up.

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