PMO Throttle Body Size Recommendation

[OSC911]

I am about to convert my ‘76 to EFI with a PMO/EFI kit. I have a 3.0 litre small port that has the intake port openings enlarged to 39mm and the intake runners have been opened up to 37mm. I guess you could call it a mid port now. I am running a Euro big port CIS system, SSI exchangers and a Monty 2 in 1 out muffler. I plan on upgrading to JE/CP non CIS pistons and cams once I get the EFI up and running.

I am hoping someone on here can assist with first hand experience with sizing. I’m led to believe that with carbs it is way more critical to get the sizing right and not so much with throttle bodies. My concern is the with 40mm might be ok now but too small when I complete my mods in the future and 46mm too big now. Any assistance would be appreciated.

[Classic 911]

I have run 46mm PMO ITB’s on both:

3.0 original P/C with 964 cams, SSI’s + 39mm in and 35mm out. Made 250PS and 295Nm

and

3.2 SS Mahle Motorsport P/C with RSR cams, Eisenmann 39mm primaries + 39mm in and 35mm out. Made 290+PS and 345Nm.

Both engine worked great.


Sent from my iPhone using Tapatalk

[winders]

I would talks to the guys at Reno Rennsport about the AT Power ITBs. Those ITBs easily out perform the PMOs......

[al lkosmal]

It is smart to research your options. I would also recommend that you visit the ITB manufacturers websites. Often they will have a useful guide regarding ITB sizing.

Here is a good example, provided by RHD Engineering...




Many people still are using carburetor experience and standards for sizing their EFI Throttle bodies. This is not typically correct.
A 46mm carb, for example, may have a main venturi that will reduce the diameter to 38mm diameter or so, while a 40mm EFI/ITB is actually 40mm as there is no main venturi used.......


regards,
al

[OSC911]

Would the 40mm be too small and the &6mm too big? I feel that I am somewhere in the middle. I had a look at the AT power units. They are very nice. Might be an option.