PMO Carb Conversion

[Lawson]

I have a 78SC with CIS injection and am considering a conversion to PMO carbs. Anyone have any experience with these carbs and this type of conversion? What size carbs should I go with? My mechanic claims it should be good for 30 to 40 hp.

[RLJ]

IMHO the way to go is PMO, if you have the bucks, in fact I think if you are going to go with carbs, force the new carb thing. Buy Webers and you are getting used carbs and maybe someone elses problems along with the purches, then it isn't a deal anymore. The PMO's are a great carb, they seem easy to work on and Richard Par is a very helpful guy. I'm running 46's but you should probably run 40's on a 3.0 motor. A side note, I was suprised at how much attention they draw. New product and everyone needs to take a look.

Randy Jones
1971 911

BTW- Buy the tallest manifolds you can.

[Lawson]

Thanks for the information. What size motor do you run the 46's on?

[pbs911]

I would suggest changing the cams with the CIS to carb converstion. You'll definately get more bang for the buck. Bruce Anderson stated in him handbook that a carb conversion in itself provides a small increase in horsepower. The carbs only make the engine feel as if it has a 50hp increase. I would also avoid the used webers unless you go with rebuilts from a reputable source.
I can't recall the jets off hand, but check out Bruce Anderson's Handbook, he gives specific advice on the jetting carbs for the 3.0.


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Paul
78SC Targa

[john walker's workshop]

if you go with a cam change,you will need pistons that will clear the valves. CIS pistons won't clear with any kind of worthwhile grind. there are a couple of grinds that will go in with the stock pistons but they would only offer minimal improvement.

[RarlyL8]

In order to make the carb swap worth while you should go with new cams and pistons as well. Quite expensive. If you are looking for a cheap bang for the buck just get a set of $1000 - $1500 Webers. You can work on them yourself and will still get the throttle response you desire.

For the money ($2600 PMOs) I would ditch the CIS and go with an EFI system. Should easilly be more streetable than carbs.

[Lawson]

Some good thoughts. As usual, one modification brings up the need for several more!

[RLJ]

I'm running the 46's on a 3.2 motor that was born an 1983 SC 3.0, I changed the pistons to J-E 10.2:1 compression, added so called "Big Cams", added 1988 3.2 twin plug Carrera heads with high rev valve gear, bored and sleaved the cylinders to 98mm, SSI's into a S-Car-Go Racing dual in dual out stainless muffler. 281 HP,244 FT/Lbs. torque at 6500RPM

You can do the Motech thing, but you are talking $75-8000, plus you will need a laptop. You can add the carbs now and do other things later, its not like your splitting the case or anything.

Randy Jones
1971 911

[JmuRiz]

Where can I find more info on PMO carbs?
Thanks!

Nathan

[eddiek]

what kind of dependability could i expect from the carbs compared to the cis?would the power be worth it?sorry,of course it would be worth it if i could get 40 more hp,as long as it's dependable power.

[RarlyL8]

Unless you change pistons and cams you will only see maybe 10 extra HP. The big draw is the throttle response. Carbs feel a lot more powerful than CIS.

One issue not covered - fuel mileage. Yes, in theory it should not go down much. But it does. A lot. Another issue is temperament. Carbs don't like hot, humid air. They also don't like quick climatic changes (ask me how I know all this). I like carbs, they are cool - but only if your 911 is a hotrod or you like a raw feel and a simple clean look.

EFI is not that expensive. A Haltech or like system, injectors, pump, and intake should set you back less than a set of PMOs. You should see increased throttle response AND a significant increase in power using your stock long block.

[Formerly Steve Wilkinson]

I'm running 46mm PMOs on a 3.0 SC engine uprated to 3.3+ liters with 100mm p/cs, plus twin-plugging, S cams, headers, free-flow muffler and several other modifications. I don't have much experience with them yet, because I'm still in break-in mode, but they sure seem strong and responsive. Certainly you can't just slap PMOs on an otherwise unchanged engine and expect miracle horsepower. The basic thing is that you're exchanging the convoluted, power-robbing CIS intake system--in comes the good air, the good air goes round and round, the good air finally gets to the combustion chamber, then the bad air gets dumped into a restrictive exhaust system--for a system that dumps the combustion mixture straight--literally--down into the combustion chamber and cleans it out by expunging it into an unrestricted exhaust system via the work of camshafts profiled to do this efficiently rather than being profiled to cancel out the pulsations that upset CIS. Otherwise, you're not gaining much benefit from the carburetors.

As for the PMOs themselves, they seem to be of high quality, and the instructions that come with them, re. how to set them up, are comprehensive and literate.

Stephan

[rscupper]

I'm not sure but I think there are emissions issues to consider, also. I'm told NO carbureted P-motor can pass smog. Can anyone confirm?

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Brian
'73RS (soon)

[john walker's workshop]

as long as there is no visual inspection, cars up to about 1980, with stock or real mild cams, should be able to pass emissions. sometimes plugging one mainjet gets them thru. (one cylinder becomes an air pump). retarding timing helps with HC. of course the mixture screws all have to be leaned out just to the point where the HC doesn't start to go up.

[pwd72s]

Randy, my apologies...I sent an e mail saying I thought your engine was a twin plugged 3.4! It's a 3.2? Well, I was half right...

[MRM]

How would a PMO or Weber conversion work on a 3.2? I am considering something like this for my 84 Euro.