Serious ITB discussion

[ericjon262]

so, I'm thinking about designing, and building a custom ITB setup, but I haven't been able to find anywhere to start. anyone have any good reading on ITB design? things like appropriate runner lengths and butterfly sizes? I did a couple of searches on the google machine, but must be using all the wrong words...

[Shaun41178(2)]

general question so I will give a general answer.

runner length and butterfly size will depend on your displacement, what you are going to rev it to, where you want the tq peak to be, and how much power you are looking to make.

my itb is around 49-50mm. I haven't sat down and done the math but I think that size is good for about 325-350 crank hp.

I would research NSX itb setups and Porsche itb setups since the displacement is similar, and I am guessing you would be wanting to make more top end power. Casting is going to take a ton of time. I would look at finding one, and maybe machining or casting an adapter plate.

[The Dark Side of Will]

What engine?
With the appropriate taper in your runners, you can put the throttle at any point and have multiple potential throttle sizes.
It's the cross section of the runner that matters and the throttle just had to not impede that.
The runner length and area and plenum volume calculations are the same no matter where the throttles are in the system

[ericjon262]

I'm wanting to do this for project Full Retard, so, about 5.8 litres, up to 10,000 RPM, and 800+ HP. no one makes ITB's for an R07, and there's only 2 single plane intakes out there for them, both of which are too tall for the prospective applications. I'm thinking somewhere between 60 and 70 MM for the throttles, I don't intend on this being an easy project, or a quick throw together either.

[The Dark Side of Will]

Ahh... a "no holds barred" build.

As I mentioned, the rules for sizing intake primaries and plena are the same no matter where in the system the throttles are.
So... design a good intake for it, then put the throttles where it's convenient to put the throttles. Size them so they cover the area of the intake runner

[ericjon262]

Ahh... a "no holds barred" build.

As I mentioned, the rules for sizing intake primaries and plena are the same no matter where in the system the throttles are.
So... design a good intake for it, then put the throttles where it's convenient to put the throttles. Size them so they cover the area of the intake runner

definitely a "no holds barred" build. as much as I'm spending on this engine, might as well truly go full retard with it. I even plan on going as far as cutting my own butterflies, similar to how it was done here:

http://www.jalopyjournal.com/forum/thre ... ly.225266/

[The Dark Side of Will]

Cutting your own butterflies is straightforward with a mill... you just have to make on fairly simple fixture. It's just a PITA to make without a dividing head or indexing head.

Kinda like the guy in your link did it... except I'd probably do circular interpolation on a CNC mill, vice his interrupted cut on the lathe... could most likely end up with a superior surface finish where the edges of the butterfly seal.

Case study: Ferrari
The 355 has throttle per cylinder, while the 360 has evacuated plena. The 360 has a dual path intake tract that added a bunch of weight to the car, but was useless at part throttle if they kept the throttle per cylinder... so they went to single throttle per bank. I haven't have the pleasure of sampling each car's throttle response.