Weber VS CIS

[d S coupe]

Hi!
I have a 1977 911S with CIS, and I would like to know if it's a good idea to change to carburators. Thanks in advance.

[Joe Bob]

LOTS of threads on the subject....check the archives....

The short story is, carbs look nice, sound cool but gain little or no performance unless cams are changed....gas mileage goes into the crapper in MOST cases....

[Superman]

I like CIS, and my comments should be taken in that light. Nevertheless, Bruce Anderson says that among upgrades for 3-liter engines, Webers 'feel' like an additional 50 hp. I think this may assume that the 3.2 liter P&Cs are installed, etc. But performance engine folks will all tell you that throttle response is greatly improved with carburetors, causing this '50-hp illusion. In actual fact, carburetors do not increase hp, in fact they probably do not meter or atomize the fuel as well as injector systems do.

I'd agree whole heartedly that carburetors look and sound much better. All in all, I'd probably put Webers on my car if I had a pair. But there are other upgrades I will spend money on first.

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'83 SC

[RarlyL8]

It all depends on your driving style and habbits.
If the CIS works well and your car is a frequent driver I would leave it be.
If you are a hotrodder looking for some extra oomph and a cleaner engine, go for the carbs.
Having done this conversion I can tell you the the additional throttle responce of carbs does feel like 50hp. I can also tell you drivability, reliability, and fuel mileage are all reduced.

[Formerly Steve Wilkinson]

I replaced my '83 SC's CIS with PMO carburetors, but only as part of a program that involved S-grind cams, 3.3+-liter pistons/cylinders, twin plugs, headers and several other things. To simply replace CIS with carbs would be akin to mounting a turbocharger with the wastegate wired full open.

stephan

[d S coupe]

Thanks! I will fallow your advices.
Daniel

[hilandscott]

Advice I received recently concerning carbs for my '78 SC 3.0 Euro:

Get a new set-- don't try to save money with someone else's trash, apparently a new set of PMOs is in the area of $1800

change the cams to increase airflow by going to 964 grind

backdate the exhaust to pre-75

get the distributor re-curved to work with the carbs, not CIS (services offered in back of Excellence)

tune them -- as they are tuneable, fun and driveable and easy to maintain compared to a forced induction (turbo) modification. 25mpg highway is possible.

Perhaps 250HP is possible as well, but that is best left to the dyno...

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'78 911 SC 3.0

[campbellcj]

Originally posted by hilandscott:
Get a new set-- don't try to save money with someone else's trash, apparently a new set of PMOs is in the area of $1800

Well, only if $2600-3000 is "in the area"



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Chris C.
73 914 2.0
70 911E Targa
campbell.chris@gte.net