ITB Sizing
 

Is the rule of thumb for ITB sizing the same as for carbs? The 40 MM carbs have a venturi which provides some restriction. I am trying to determine what size ITB I should use on a stock 3.0 euro motor. Thanks for your help.

Tom

40 will be good. I have a 3.2SS and I use 40s. I was told by several pros that they are good and that I'm not leaving anything on the table. In fact most told me that 46 will be too big.

Use the intake port diameter.

I think the intake port size on the "big" port SC heads is 39MM. If that is the case, then the 40MM ITB would be about the correct size. Thanks,

Tom

Tom,
Here's some reference info.

Tuning ITBs - 77e21.info

regards,
Al

I just went through this and decided on 42mm Suzuki GSX-R750 throttle bodies for fabrication on my 3.2 engine. 40mm intake port. Close enough and leaving a bit of (small) room for expansion!

http://forums.pelicanparts.com/porsche-911-technical-forum/741911-d-zug-tours-rsr-dyno.html#post7547875

Here's a link to the Dzug RSR project. Justin and the crew have just installed my Speed Triple EFI/ITB kit and if you scroll down the thread a bit you will see the drive by.

This RSR has a 3.2SS, formerly using CIS...now with the ITB's installed. They are 42mm. The sound that the RSR makes as it goes by is.........excellent. They are headed to the dyno shortly.

regards,
Al