Can 50 PMO itbs work on a 3.2 SS?

[Axel84]

I have a 3.2 SS on DC60R cams, twin plug big port heads 39 mm - full rarly longtube headers exhaust. I have The chance to aquire a set of PMO itb 50 mm from a 3.2 race engine , 43 port size for a good price. Can this work on my engine or just too big? I can take my port size up if needed Thanks

[Classic 911]

Interesting question

[prschmn]

You can make it work but I'd suggest not uping the port size, you need velocity there
to keep it driveable.

[zztot]

Several years ago a shop installed new carbs on my somewhat modified 3 liter. It would scream at full throttle but feathering was impossible. We talked with Richard at PMO and he said nothing wrong with carbs just too large. I recall him saying 3.6 was smallest suitable for 50s, but your 3.2 may be strong enough to handle. Went back to 46s and it was fine. My comment is not based on anything but that experience, but there are a several on here with the knowledge to weigh in ……like Henry.

[prschmn]

You should look to see what size chokes in in the 50s.
You may be able to get smaller ones.

[r lane]

They will definitely work on a 3 liter race car. Even if you have 12-1 compression, probably not the set up for the street. On the street you are operating between 2 and 6000 rpm. At the track between 5 and 7500 rpm. Big difference. Bob

[Axel84]

yeah wont have 12 compression, probably 10:1

[targa72e]

Many of the comments are assuming these are carburetors. Going with too large of a carb can make the signal to the carbs very weak making street driving hard.
It sounds like these are ITB's for electronic fuel injection. Larger size might hurt low end torque but is less of an issue than too big a carb.

john

[Axel84]

ITB EFI`s , not Carbs!

[zztot]

For those old enough to remember…..In the words of Emily Latello one of my favorite Saturday Night Live characters………….Nevermind!
Need to pay closer attention to what I am reading……Sorry for diverting your question.

[r lane]

Yep, saw PMO and quit reading and assumed carbs, so don't know but would still think a bit spongy down low. Bob

[prschmn]

Duh-guilty here too!

[Evan Fullerton]

If we look at the motorcycle world.

1000cc V-twin Super-bikes from the early 2000s all used over 50mm throttle bodies……. That would be a 3.0L 6 cylinder……. But they also rev’d them over 10,000 RPM.

On a 8,000+ RPM SS 3.2L race motor, 50mm should work, you might just loose some part throttle resolution vs. 46mm ITB.

The 914 I Autocross we are building a new 2270cc T4 for that we will spin over 8000 RPM. That’s getting 48mm Carbs as the 44s are already a restriction on the 2056cc motor that’s in there. 2270cc T4 equates to a 3.4L -6.

[winders]

Too big....

[stownsen914]

Agreed with other comments that they'd be a bit large. Notably if they are 43 mm at the base and your heads are 39 mm, that's a significant size mismatch.

[winders]

Originally Posted by stownsen914

Notably if they are 43 mm at the base and your heads are 39 mm, that's a significant size mismatch.

That is going to ruin airflow speed and makes things much worse. Increasing the intake port size to 43mm is a bad idea too. They are just too big for the engine....

[winders]

If you want a great performing ITB setup, get AT Power 42mm or 45mm ITBs matched to your 39mm ports. That will blow away any PMO setup....

https://www.atpower.com/products/porsche-911-throttle-installation-efi-kit-with-ecu-engine-harnesses-and-base-map-package-model-years-1978-1989

[Axel84]

Carrera heads Are 42.5 are they not? Port size. So why wouldnt opening them up to that size work

[Classic 911]

[Axel84]

Thanks 40/38 got it