SC to Webers

[mcinturff]

Will webers/zeniths off of the early cars work on an otherwise stock 3.0 SC? Thinking about carbs and ssi's, carbs mostly because I'll be moving to an area with no Porsche mechanics/gurus, not to mention the irritation of CIS, fuel mileage of no concern. Also pics of all components required to convert would be nice, from fuel line to linkage.

[Flat6pac]

Zeniths wont work, there is no parts for anything but 2.2
40 Webers would work but you have to enlarge everything to adapt for 3.0 volume
POM might have the stuff to set up for 3.0
You need thin flange SSI for 78/79 and thick flange 80/83, nothing extra if youre running carbs. If you keep the injection on 80 to 83 you need an oxygen sensor tap in the SSI
Lastly on the SSI you will need the 77 oil return scavange line running under the bell housing and then the line to the external thermostat. 2 separate lines
Suggest you keep the injection
Bruce

[longhornchris04]

Also, according to the Porsche Performance Handbook (and some other threads here), Carbs won't net you much actual power increase because the rather tame camshafts used in CIS.

You will get better throttle response though. And if you ever rebuild you will have options for your cam choice (after all, if you already have the engine apart )

I belive PMO makes a set of carbs for the 3.0SC. Our host has a sub-section in the fuel section.

[MBruns]

If you have plans to develope the engine later on its a good first step, although CIS is tough to beat when its working, if you don't have plans to mod the engine later ie.. pistons,cams etc... I would leave the CIS on it. That said if you do decide to go with carbs spend the money and buy NEW PMO carbs and be done with it, Fooling around with tired old webers will wear you out and in the long run wont save any money.

Mike Bruns JBRacing.com

[mcinturff]

Thanks Mike, I think PMOs might be the way to go. This engine is already rebuilt (stock), but will be again in about 4-5 years to replace re-ringed KS pistons & cylinders. I'll be looking for a fun weekend car sporting about 250hp and won't care about mileage. Was thinking about the bitz racing kit, but I like old school much better (I collect and restore old 60s and 70s Hondas).

[MBruns]

I would go with a 46mm kit for where you are now and if you change or upgrade in a few years you will not be restricted by a set of 40's, I started working on Honda's in 1973 as my first job, I worked to race and started something I have yet to get over
Mike Bruns

[Rich76_911s]

One other thing that I don't believe has been mentioned is that with an 1983 you will have to have some work done to your distributor. I think it is "recurving" which I am sure Henery Schmidt or Steve Weneir can do for you.

Also you need a fuel pressure regulator. The fuel pressure the CIS pump puts out is way too high for Carbs.

I had a carbed 3.0L with 40 IDA-3C webers. It was really a nice motor. Throttle response and sound was awesome.

[eapcpa]

Just read the local Porsche club Pub "tobacco Roads" about converting CIS to electronic fuel injection. I am on vacation so I do not have access to it but it was an interesting option to CIS. It uses the CIS runners and some other parts but it will be Monday before I could get you the authors name. Someone here probably has it.

[chris_seven]

Zeniths running on a 204BHP, 3.0 SC

We made chokes and main jets, modified air correctors and emulsion tubes.

It also has headers and 2 in 2 out - giving about 220 BHP and runs well no flat spots revs to 7200.

Dizzy needs modifying and we fitted a damper on the vac advance as it is only connected to one cylinder.

We will probably remove the vac advance and re-curve in the next couple of weeks.

[Lapkritis]

Disable speakers/sound...

Here's a quick video I made more for reference as I'm in the process of pulling my engine and carbs for a refresh... it's a 2.7 RS spec but much will be the same. I made this so when the time comes to reassemble I will know what goes where in the case that I don't capture something in pictures. I have the original instructions/setup information as well. The resources I've read suggest 40mm for the 3.0L as well as the 46mm will not have smooth transition.

Porsche mail order 40mm PMO 911 Webers - YouTube