intake match question for carb fit

[70SWT]

Will carb manifolds from a mid-year 2.7 fit a 72 911E 2.4? i.e., are the two engines dimensionally the same with respect to the intake ports where the carb manifolds mount - Thanks

[356RS]

Yes they should fit fine except for the port size as you noted.

[304065]

And that is the problem.

A 2,4 E has 32mm ports. All 2,7 engines, with the exception of 1974, have 35mm ports. On the intake side, a correctly sized manifold has the same bottom diameter as the port in the head, e.g. 40mm at the top and 32mm at the bottom for the most common Weber or PMO manifold. A manifold for a 2,7 would be 40 at the top and 35 at the bottom. The trouble is that if you go from 35 to 32mm where the manifold meets the head, this stops airflow into the engine and will contain reversion pulses so they bounce off the restriction, not off the intake valve, leading to reduced performance.

[70SWT]

Sounds like the answer is no - the mid year carbs will not be suitable for my 72 E, which happens to have been upped to 2.7L in displacement. No work has been done to the intake ports AFAIK.

Thanks

[304065]

You can't make the MFI work? Carbs are a retrograde step from MFI and will cost you at least 10 HP, perhaps more on a 2,7.

[70SWT]

Originally Posted by john_cramer

You can't make the MFI work? Carbs are a retrograde step from MFI and will cost you at least 10 HP, perhaps more on a 2,7.

I would actually love to go back to MFI. But it would require finding ALL of the MFI system components. A PO converted the car to Webers and sold it all.

I pulled the engine and sold the Webers, thinking I was going to go to a 3.6, but the deal fell through.

Now I am looking at the options for the 2.7E engine, which was also upgraded to Euro P&Cs, aggressive cams by the PO...they seem to include going to EFI, back to MFI, PMOs...not sure which way to go.

[jpnovak]

Al, Why not port the manifolds to match your heads? This is simple to do with a rotary file in a drill or similar tool.

[304065]

I see the quandary. If you go PMO, a couple grand. If you go MFI, $1500 or so for a complete system and if the pump and stacks need rebuilding, you can add on another $1200 each. Once in that territory. . . EFI doesn't seem so bad- although complete ITB EFI systems will set you back $5750 (PMO ITB and electromotive)

[sww914]

I have a set of early carb manifolds that are 32mm at the heads. I need to port them to 35mm or trade for a set that are 35mm like my 2.7 heads. Would you like to trade?
Thanks, Steve