Mike_ONeill

I have a 1983 911sc with CIS. The car is primarily a DE track car. I am considering removing the CIS system and installing either a kit with a set of rebuilt Weber's or new PMO carbs.

The PMO kit is about twice the cost of the Webers (4k vs 2k) and I am sure they are the better solution. However, the PMO's cost more than I want to invest in at this point. Any opinions on whether the Weber kit would be a reasonable solution for a DE type car?

Thanks for any help.

earlyapex

I bought a set of PMO's from Steve Weiner at Rennsport Systems. My mechanic installed them so I cannot comment on how difficult it was. He's tuned them a couple of times. They otherwise have had only one problem. They have gotten fouled from debris from my gas tank. The car still has the original gas tank so there is debris on the bottom that did not bother the CIS, but is an issue with PMO's. The short term solution was to put in marine fuel filter which have a much smaller pore size than automotive fuel filters and still flow well. I will put in a fuel cell soon.

Yes, PMO's are better than Webers. You do not want to spend money twice so save your money for the best carb's on the market. You are after all using the car for DE's. I guarantee that your engine is not what is keeping you from getting faster.

dbanazek

The main thing you get with PMOs is they are new. Many of the Weber's are pretty worn out by now. I have used both and would have to agree, you are better off spending the money for some nice new carbs. The do have some differences that seem to make them work a little better too. That being said I would not put webers on a fuel injected car unless I was looking to do other performance modifications like using a big camshaft. You won't make more power, you will loose fuel economy and easy cold starts. But if you are going to use ****** camshafts, you need the carbs.

racer

x2 for wahat dbanazek said.. Unless you change your cams, you will not notice a performance gain running the carbs over the CIS. You might be better off having your CIS checked over for any deficiencies. CIS is much more tractable than Carbs too. Plus, if you wanted to ever Club Race the car, Carbs would hurt your classing.

Steve Weiner-Rennsport Systems

Not to be a contrarion, but I'd offer a different perspective on CIS vs carbs.

First, the advice about PMO's over Webers is sound; the PMO design is FAR superior to the Weber and now those old carbs all need a lot of work due to neglect over the years.

Second, Bosch & Porsche no longer support CIS so there are no new parts and the effects of ethanol-blended fuels is taking their toll. Its now a totally dead-end street and when these FI systems develop trouble, its very tough to make effective repairs when all one can get are "rebuilt" parts (except for injectors).

Third, while the other kind folks offered sound opinions about diminished fuel economy, installing carbs on a CIS engine yields FAR superior throttle response and a very nice bump in power, especially with a good exhaust setup. Installing more camshaft is certainly nice, but not necessary and a piston change is required for any significant upgrades, anyway.

Lastly, one can set up and maintain carburetors without special tools and if correctly configured, installed and adjusted, they are easy to start with some pointers from a knowledgeable individual. Whoever might provide a PMO kit should be able to do that for you.

Greg Phillips

You might check out the current Excellence for another option to upgrade to a newer EFI system using the Megasquirt controller.
Kit from Bright Racing (?)to convert CIS cars, more programmable and probably more HP than webers or PMO, certainly better mileage and drivability. Very programmable via laptop.

Greg Phillips

stv951

i ve read the excellence article too, and was impressed. any more experiences on these EFIs ?
Steve whats your idea ?

Steve Weiner-Rennsport Systems

The only CIS conversions we've done are with carburetors (PMO or Weber) or with race-type EFI systems using ITB intakes such as our own manifold package.

Its all about one's budget, skills, resources, and objectives.