PMO Webers?

Has anyone had experience with PMO Webers and emissions? I have a 79 ROW SC. I have to pass three more years of sniff tests before it is considered a "classic." The previous owner said that she had to have the CIS adjusted before getting the test and have it returned to the original setting afterwards or it had no power. I am looking for more power and would like to scrap the CIS. Can Webers be adjusted to pass a sniff test? Would increasing the compression help lower the emissions?

Thanks

I do not believe Webers will increase power or performance. I believe that ROW SCs had different fuel distributors than my car. This would have been so that fuel volume would be tuned to an engine with a more free flowing exhaust system.

I believe that Webers become necessary when you change the air flow characteristics, such as when you change cams, pistons and cylinders, or perhaps exhaust. But I feel convinced that, without other modifications, you will decrease the engine's power and smoothness if you remove the CIS system. It is already "jetted" perfectly for the motor it was developed for.

This has been my expereience with CIS systems, but I admit Porsches are a new game for me.

Webers look tougher though. More manly, if you'll excuse the expression.

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'83 SC

My intent is to backdate the exhaust, enlarge the displacement to 3.2 liters and increase the compression, and use a mild cam. In terms of performance and cash flow, I assume it is best to first improve the exhaust. Everything else would have to come at once since the CIS would not work with the cams and the Webers would have to be dialed into the final package. Anderson talks as if this package could produce 280hp.

Cool. You get to use the Webers. Perhaps the exhaust and Webers can go in as step one. Then use different jets when the engine is rebuilt.

I wish I could answer your question about Webers and emissions. It's tough to get carburetors to run lean enough for emissions but perhaps someone has done it.

Good luck.

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'83 SC

This might be a little 'expensive' and extreme to pass emissions, but (and wouldn't you have a big grin for the SMOG POLICE) how about keeping the 'stock' SC engine around in your garage under a tarp just for emissions tests, complete with stock exhaust?

And for fun, the rest of the year, build up the 'hot' 3.2 with Solex or 'E' or 'S' cams, SSI's, and Webers ... you could probably sell off the Motronic system from a 3.2 you bought, for perhaps the cost of SSI's and part of the cams' cost ...

You could probably get so used to pulling the engine, and making the swap ... you might be able to get it down to three hours or so!!!

Good luck!

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Warren Hall
1973 911S Targa

Interesting thought. I wondered about going one less step; just switching out the induction system. I have not worked on it so I'm not sure how hard it would be. The best bet may be to wait until 2004, pass one final emissions test, and never have to worry about it again. But, if I were a patient man I would be content driving my wife's Honda to work.

RK - It is true that you won't see a noticable power increase on a stock CIS engine by changing to webers, however you will see a big change in throttle response. The power increase comes with cams and P/Cs. I can't say anything about passing smog. It would be my guess that you could not. Webers tend to run rich to run well. I don't mean gas puking rich but too rich for the smog police.

It depends on the smog regs of your State. I would check with the agency that administers your smog testing....

In California to pass smog, you have to have the original fuel delivery system, to pass the visual test...switching form CIS to carbs, flunks you immediately...UNLESS the local smog cops certified an alternative fuel system.

Respectfully, I'd like to hear more bout this throttle response thing. I've heard from other folks that going to carbs instead of CIS improves "throttle response." I find this curious for at least two reasons. First, when I put pressure on the gas pedal on my CIS cars, the engine produces more power. No delay. It happens NOW. Perhaps the "throttle response" thing has to do with the accelerator pump on carbs to give more kick when the throttle MOVES.

And if fuel injection systems have throttle delay problems, then someone should tell the NHRA folks. ALL dragsters are fuel injected and they don't seem to have a throttle response issue. To say the least. Someone help me understand this.

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'83 SC

Big S - the throttle response issue is specific to CIS. This system was created for emmision control alone, not performance. Think about how it works - you push the throttle, this opens the throttle body, the vacuum created pulls down (or up) the metering plate, the plate pushes (pulls) the fuel plunger and gas is sprayed. Custom built for lag. Carbs are instant.

Thanx. I really wasn't just trying to be cute. And this explanation makes sense. The big rubber thing can flex (implode a little) under negative pressure, and air itself is elastic. Thanks again. Perhaps there's more 'lag' than I think...

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'83 SC

I've heard Webers are a bear to tune. Does this apply to the metering as well? I live down the street from the local testing station and it would be easy to reduce it to a lean mixture just for the test (assuming it is easy to adjust the carbs). My car has an exemption from the visual test so all I have to do is pass the sniff test.

RK - webers are very simple in design, performance only. No choke, no vacuum operations. The idle circuit spans from 0 to around 3000RPM. This could be temporarily leaned with a jet change. The car would be a little harder to start and would spit back at the transition RPM. If they check your pipe at idle when the car is warm you may get away with it. There are a few good books out there on the subject if you become more serious obout doing this.