PMO's or CIS?

[p.smitty]

I have a 73.5 coupe that has approx. 200K mi. on the original 2.4 and PMO 40's on it. It runs O.K.(and I mean just O.K.) I want to take out the original engine and store/pickle it. I would like to replace it with a 3.0 that a good shop will build (top end) for me. I want to use my PMO's and a new cam grind but some say I should use the 3.0 CSI for reliability. I know it will be harder to start the carbed engine, it will get worse mileage, and it won't run as well at altitude, but, I want fun more than practicallity. I also don't want to be stupid about it. Any thoughts or advice?

[James Brown]

Stick with the carbs, once properly set up for a 3.0, it is a thing of beuty and acceleraition! Way mor responcive than CIS. You already mentioned all the down sides of having carbs but CIS has some downsides like slow throttle responce, balkey if not set properly, hard to set properly!, expensive parts, butt ugly looks, weak sounding.

Contact Richard at PMO and tell him what the engine size and what mods you did (cam, exhaust, P&C, ignition, ect.) and he can set up your's to get in the ballpark, good luck sounds like a fun project. SEND PICTURES

[rfuerst911sc]

I have a 83SC with 46mm PMO carbs and love it. First off in my opinion it makes the engine bay look like what a Porsche engine bay should look like ! On the highway I average around 17 - 17.5 mpg if I keep my foot out of them. Sound is great along with throttle response. I've had mine for 2 years now and once they are set I haven't had to touch them. Richard Parr knows what he's doing with these carbs. If you are having a top end rebuild done and changing the cams I assume you are also changing the pistons ? If you're digging into the engine you really should change the pistons to optimize performance. You should be able to easily get 240-250 hp and still be a very driveable street car. I'm still running the CIS internals and she still runs good. When my engine needs a rebuild I'll change the internals. One other thing to consider has your distributor been setup/modified to run carbs ? This helps with performance also. And some say that multi-spark ignition boxes like MSD,MALLORY or CRANE will also help with cleaner burn and a little better performance. I say stick with the carbs .

[moneymanager]

Use the PMO's, scrap the CIS. A better solution in every way. I really question the idea that CIS is more reliable; when I had it I spent an enormous amount of time chasing little tiny leaks etc. The PMO's, once set, rarely need attention.

[jpnovak]

Since you already have carbs, its a no-brainer decision. Install them on the new engine. Just make sure to properly jet them for the increased capacity.

You can install a 964 or 20/21 grind cam with stock CIS pistons for a nice improvement over the SC cams. Using carbs I would also suggest discussing a custom cam grind with John Dougherty (DR Camshafts). He can make a custom grind to maximize the exhaust lift and duration with the CIS dome while optimizing intake lift and lobe center to get maximum performance out of the carbs. Call. You will be glad you did.

[ckissick]

I have a 3.0 with Webers and 20/21 cams. It starts fine on cold mornings, but around here, cold means 40's. I'd imagine the newer PMOs would work even better.

[911st]

PMO's.

Get a 81-83 3.0 with higher compression if you can. Carbs, headers, and dyno tuning will make for a very nice responsive and flexable motor. Chasing that next 20hp w cams and compression is expensive and if you go to far starts needing closer ratio gears to work its best.

[Formerly Steve Wilkinson]

PMOs.

As knowledgeable previous posters have said, once set up they stay that way. Best way to do that is jet and adjust them on a dyno, with somebody who knows what they're doing.

Yeah, they're a little hard to start when it's cold--no choke--but it's not a deal-breaker by any means. In normal NY temps, I can often catch it on the first try, if I prime just enough with the accelerator pump. Cold temps it usually takes three tries and a lot of priming.

One thing about PMOs, you need scrupulously clean fuel or you'll be blowing out an idle-jet circuit once a week. The engine will suddenly run on five cylinders at anything but hard throttle, then you have to identify which idle circuit is clogged, then blow it out. A pain. I have a big Racor diesel filter plus the usual useless $10 in-line filters--they won't trap the stuff that's small enough to affect PMOs--and I also replaced my stock fuel tank with a fuel cell when I began to suspect that it was making rust. Yeah, it would have been cheaper to remove, clean and seal the stock tank, but it's not the gold-plated Porsche for nothin'...

[rfuerst911sc]

When I had the PMO's installed I put in a new OEM CIS fuel filter. I plumbed from that to the pressure regulator and it seems to work fine. Anyone know if the CIS fuel filer is " good enough " in regards to filtering efficiency ? It's been good for 2 years which reminds me I should probably replace it.

[911 tweaks]

good advice here... your call as to what you want to do... if cis is working fine, just remove it (carefully) and store it and try the carbs...when & if you get tired of the carbs, put back on the cis and sell the carbs...either way it all works out in the end...
Best of luck here & enjoy!!
Bob

[SCOTITUDE]

I just put carbs on this past summer. Stock sc motor. HUGE difference. mostly in low and midrange throttle response. She squirts out of turns now. And she has a bit more grunt. very happy.

[911s55]

Put the PMO's on the 3.0 liter and find the correct intake for the 2.4, both will be worth it.

David

[James Brown]

so that's 11 carbs 0 CIS. a no brainier!! Don't forget the pics!!!

[p.smitty]

O.K...O.K....O.K... SOLD! You ALL told me what I wanted to hear. PMO's it is. Thank You. This was my first thread and I appreciate your input. You have made it an easy choise.

[Porsche-O-Phile]

Carbs are great and seeing as you already have them, there's no reason not to stick with them. If you were considering changing from CIS to PMOs I might have different advice (I think anyone who spends the money to buy PMOs off the shelf is insane at the prices they're charging) but if you've already got them, just get them tuned up and live happily ever after!

[p.smitty]

Sorry, I didn't spell "choice" correctly and I don't know how to edit. I guess that I owe you all a beer, or a 73 RS, or something.

[Carrerax]

Originally Posted by Porsche-O-Phile

I think anyone who spends the money to buy PMOs off the shelf is insane at the prices they're charging!

Dammit, I must be insane because I just ordered a new set of PMO's from Steve at Rennsport and couldn't be happier. The peace of mind having an expert set up the best available carbs will make my life much easier in the long run. Now if I was an expert with carbs, I may have just worked with an older set of Zenith/Webers. Knowing my lack of love (and intelligence) for working on carbs this was my best bet. They arent cheap but honestly, by the time you get a good set of webers rebuilt and all the inherent issues with 40 year old carbs addressed I dont think it cost that much more for what you will end up with. Just my .02 cent. Happy New Year to all!!!

[James Brown]

Smitty: if you look at the right corner of your post you will see an edit button, click to edit...Also, if you "go advanced" with a reply, you can spell check.
Irish whiskey will be fine by me!!

[911st]

We all love carbs. Especially in a long hood.

However, there is nothing wrong with a well tuned CIS. Better MPG, emissions, do not starve in a high G corner and it dose not cost over $3k.

[Formerly Steve Wilkinson]

You're certainly right about better mpg and cleaner emissions, but I have _never_ had my PMOs "starve in a high-G corner" at either Lime Rock or Watkins Glen. Maybe I'm just not fast enough on the track, but it's certainly not a factor on the street.