What is CFM of a CIS

[bossladys 911]

Does anyone know the CFM flow of the 77 2.7 CIS system. What are some possible carb setups for replacing the CIS ?

I was interested in there is a max flow CFM rating for the CIS system in the same way a carb is rated. Like 400, 600, 800 etc

[Porsche_monkey]

Shouldn't that be calculated from the bore, stroke and RPM?

[Walter_Middie]

Here's a carb sizing calculator:

http://www.4secondsflat.com/Carb_CFM_Calculator.html

[bossladys 911]

Rex, thanks for the link.

[jluetjen]

Originally posted by bossladys 911
What are some possible carb setups for replacing the CIS ?

In order of increasing costs...
- Zenith 40's
- Weber 40's
- PMO 40's
- Weber 46's - Pretty much for race motors only
- PMO 46's - " "

Sure you can put a Holly 4-bbl on a 911, and it will run, but it will never run as well as the other options because of...

- A common plenum will introduce distribution issues which will result in unequal mixture to each cylinder. In this regards a 4-bbl will be worse off then CIS.
- The large plenum and long runners downstream of the single throttle means that the throttle response will be no better then with a CIS system. (Individual runner carbs and MFI have significantly better throttle response then CIS).

[bossladys 911]

Know of any rebuildable sets with manifolds hats etc ?

[jluetjen]

Have you checked Pelican's classifieds or Ebay for things like "Porsche 911 Zeniths"?

BTW - Welcome to Pelican's Porsche Forum!