Air horn length for ITBs?
 

I'm planning to install ITBs on my street-ported S5 13B this spring and am wondering what air horn lengths I should be looking for.

I know this is typically a loaded question since intake tract length is not one-size-fits-all answer and depends on the type of powerband the user is after. That being said, I will primarily be using the car for lapping days and do not daily drive it, so I would be after a mid to high range powerband. I will be addressing any low-end power losses through the installation of a 4.77:1 ring and pinion set. And if it matters, I will be running the auxilliary ports using electric solenoids for tunable actuation (and because I believe leaving the aux ports open is giving me an unstable idle). Engine RPM limit is set to 7000.

I'm planning on running a Jenvey DCOE fitment throttle body (118mm long) with a Racing Beat DCOE side-draft manifold and the OEM S5 lower manifold.

I suppose anyone running DCOE carbs or similar ITBs could chime in.

Looking forward to hearing your input!

you should try a few and see what you/the engine like.

just for reference, the GSL-SE and S4 intakes are 500mm long, they measure from the trochoid surface to the throttle plate, so the actual intake is ~2" shorter.

the S5 i think is 600mm/400mm, but you should double check that, there is a graph floating around, and an SAE paper too.

they have lengths for the race engines too, but i'm not sure they apply. the engines up to 1990, were 400mm long, and the 1991+ engines were 370mm. the R26B is unknown, but best guess is 370mm whatever the intake trumpet stroke is, its listed in the SAE paper

Thanks for the reply. I will have access to a 3D printer soon so experimenting with different lengths won't be too expensive.

I'm guessing Google is the best place to look for the SAE paper? Any tops on what I should search for?

shoot me a pm