2.7 911S Heads
 

Can anyone tell me for certain if the '74 or '75 911S heads have larger valves than the standard heads. Anderson, in his book, states that all the 2.7 heads (911 104 342 2R) are the same with 46mm intake and 40mm exhaust and these were used on all engines from 1970 to 1977. I have seen some heads for sale on Fleabay and elsewhere advertised as 911 S heads and they claim to have larger valves. If they do will they fit my stock 2.7 with CIS and will they provide any better performance?

Ventana

This should help:

http://www.carquip.com/parts/911/engines/cyltbl/index.asp

cgarr;
Thanks for that very informative link. So, the valve diameters are the same but it is the port sizes that are larger. Do you know if the larger port diameters will make any appreciable difference in performance if used with the stock CIS? I am getting ready to have my 2.7 rebuilt and am looking for some improved performance.

Thanks;
ventana

IMO, They will certainly breathe better, but any performance gain with larger ports alone with stock CIS and no other modifications would be marginal. Still worth a little extra money just to have in case you want to do some additional performance upgrades down the road. Additionally a good option for added (low cost) performance would be to use SC cams.

wowzer911;
Thanks for the input. That was my plan. I can't afford a Bitz Racing EFI unit on top of the rebuild right now but I would like to make some modifications to my 2.7 while I have it apart that will compliment the conversion to EFI later on down the road. CIS here in the Midwest is not much good (it runs very poorly in the cold) and I just can't see the point in Webers. I will look into the SC cams. Do you know if using the the SC cams would require any other modifications? I had planned on bumping the compression to 9:1 which should still work with the CIS.

Thanks;
ventana

wowzer911;
Thanks for the input. That was my plan. I can't afford a Bitz Racing EFI unit on top of the rebuild right now but I would like to make some modifications to my 2.7 while I have it apart that will compliment the conversion to EFI later on down the road. CIS here in the Midwest is not much good (it runs very poorly in the cold) and I just can't see the point in Webers. I will look into the SC cams. Do you know if using the the SC cams would require any other modifications? I had planned on bumping the compression to 9:1 which should still work with the CIS.

Thanks;
ventana