What to do, keep Cis or go with Pmo’s
 

My car is an 82 911 SC. I’m rebuilding the engine with euro pistons and I have SSI’s and I’ll buy an exhaust at some point appropriate for the build currently with SC cams. If I decide to go with PMO carbs what cam is recommended. What are the pro’s and con’s.
Part of me wants to keep CIS although would my new euro spec pistons/cylinders benefit more from PMO’s and with a slightly higher than stock compression.
Thanks in advance

70 914
67 912
76 911 S
82 SC
2014 C7
2001 C5

I'll just talk about the cons I've discovered firsthand, since the pros are easy to find elsewhere on the board.

1. Warming up your car - If you don't have the handbrake with the throttle knob on it, you're gonna have a bad time. It takes me between 5 and 20 minutes to warm up my car enough to drive it without it sputtering and trying to die whenever I accelerate. Imagine that. You get out of work, and go and sit in your freezing car for 15 minutes, THEN you get to brave the rush hour traffic. Wanna take a quick trip down to McDonalds? Take a different car. (Admittedly, there's no issue in the summer months.) The lack of a choke on the PMOs hurts. (CORRECTION - My tune was way off. Richened it up, now it's just a few minutes, not ~15m.)
2. Fuel economy - It's bad. 12-14MPG around town, vs (I think) 18MPG with CIS.
3. Power - It's okay, but you can get more with EFI for approximately the same cost, with none of the downsides. Expect a TON of tinkering to get to the same point you'd be at with a standalone on day 1.
4. Gas - If you don't drive your car daily, you're gonna want ethanol-free gas, which isn't available everywhere.

Carbs are okay for a weekend car. They make the right noises, smell happy, and have good looks. But man, they are not good for a daily driver. If I could do it over again, would I choose carbs? I don't know. I DO love being able to tinker with it on the side of the road. I just don't like NEEDING to tinker with it. I literally keep a piece of garbage (cut zip tie) on my passenger seat to stick in the idle screw slot just to keep it running for the first five minutes after a cold start. That's not cool.

My 1982 Euro with SSI's has the usual CIS and I like it.

But... If you really want to make some some changes you could look at a modern electronic fuel injection system.

Regarding what TJ said ,

Warm up, @ 20 degrees 2-3min max and then u can drive .
SSI heat ex will be making lots O heat. Keep the revs up , but below 4,000 up to 100* oil temp , then creep up, but hold of on a redline run until 180*

Fuel MPG, Town driving 18mpg with romping, and 22mpg highway @80mph. All based on proper jetting .

Power? , The build is the limit.

TJ, I think your carb set up could bennifit from a pro jetting job, Someone that makes their living doing the PMO or Weber.

I love the hand throttle !!!!!

M1 cam makes lots of power , comp ratio will wake it up!! 9.5-1, CIS is great too.

Ian

If you use SC cams, or even 964 cams, keep the CIS, for now and prepare for future upgrades by porting the heads out to early SC or 3.2 intake size

If your pistons allow for a more radical cams, and you chose to use more radical cams then you might want an intake with Individual throttle bodies - AKA, Carbs or an EFI with ITB.
Drivability can be tough when cold using carbs but it’s something you can probably live with.
And every time you stop the engine you’ll smell gas as they are venting, etc.

Regarding the “for now”.
You’ll really want to upgrade the intake on the 82 and port the heads even if you go with a mild cam.

I have a 3.2 intake on a stock 79 engine (big port) with a standalone programable EFI. It makes about 20 HP more than with stock big port CIS setup.


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EFI is pretty amazing in that there are so many controls that instantly become available to you. This is also a high hurdle to get over; you have to actually learn how to use the ECU- it’s not plug and play.

That said, with reading, watching videos and the investment of time, most of us can figure it out.

I will say that EFI with a hand throttle is downright awesome. No waiting, just start, set the hand throttle and go. 5 mins later the car is warm, WUE is gone and the hand throttle isn’t necessary.

I still need to do a few full tank tribes to get an MPG baseline; problem is that I like to drive fast and with a WOT… [emoji2369]

If your Euro pistons are CIS design it’s really not the ideal piston for carbs. You can certainly run them with carbs if you desire but if your in the rebuild now some aftermarket JEs or comparable is what you want.
The warm up period is not bad at all on the carbs. I just drove mine today when the engine was below freezing. Definitely does not take 15 minutes for it to be driveable if your engine is running right.
Fuel economy sucks for carbs

Carbs allow for good camshafts which makes the car a lot more fun than any NA cis engine
I use the gt2 102 camshafts from DRC

First I want to state my CIS was dependable. However, The air metering plate is sensitive to pulses traveling backwards thru the intake. Pushing the plate in the wrong direction and "lying" to the fuel distributor. Therefore, all CIS cams have to allow for this weakness and ensure valves don't allow residual exhaust to escape via the intake. The other intakes carburetors, older MFI or EFI don't put this restriction on your choice of cams.

That alone would push me to choose PMOs over CIS. Then the look of six carbs just sets off the engine compartment compared against the Rube Goldberg look of CIS.

Finally, the sound of 6 carbs at WOT is something special.

All that said, you've never mentioned what your goals are?

Michael J.
'78 SC w/EFI

Yes, what are your objectives? If you want to keep it as a regularly-driven street car, either stay with CIS, or go with digital fuel injection. If you just want to build a bad-ass engine compartment, go with carbs.

??????? Carbs are reliable and cheaper than EFI.

You can build an EFI system for about $4k maybe less if you’re super thrifty or find deals.

Of course you can also build a $20k EFI system if you like.

Not sure you can find a ready to use set of webers or PMOs for that price.

Carbs fun factor…looks cool…sounds cool… start up is little more temperamental(not a huge deal)… if you are a car guy / mechanically inclined you’ll be right at home with carbs on start up. If your wife wants to jump in the car and take off it might be a little bit of a challenge on start up. $5500 add.

CIS works great, start up is the same as your car is now. Performance wise almost identically and if you notice a difference it is minute. Won’t look as cool or sound as cool…but be honest how often is your deck lid open?

With this being said on my 3.2SS (222hp@crank)I dumped my CIS and went carbs. Would I do it again. Maybe.

On my 3.4L (297hp@crank)using the stock Motronics ( better than CIS) didn’t want to spend the extra $5500 plus it will start like a champ every time and gets great gas mileage. Now the “look” of Motronics vs CIS is very different to the eye. CIS has the big plastic air box but Motronics IMO can look pretty cool if it’s done right. CIS you can’t really trick up so it’s looks is it’s looks.

Kinda of wordy sorry. If you want to be practical and keep $$$$ in your pocket stay with CIS and the performance will be great! If you want to open the deck lid and enjoy the more mechanically look of carbs then do carbs. Both are excellent choices but different experiences.

That's interesting - thanks.

I’m thinking you’re saying ‘That’s interesting’ as in I’m not sure I believe that statement.

I don’t have personal experience but I also find it interesting that a CIS setup would have similar performance to carburetors even when the cams are mild.


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CIS will support up to 250 crank HP stock sc version , doing all the little tricks 280-290 HP

Finding a carb tuner or ITB tuner for that matter is not an easy task.

Most carbs that I have run across are short on the HP by 15-20%, that of a proper tune.
Not to mention fuel economy .

Ask Paul Abbott about this , oops sorry he has retired .

Ian

I’ve had 911’s with carbs (2.8 and 3.0), MFI (2.2s), CIS (2.7), Motronic (3.2 and 993) and aftermarket efi with individual throttle bodies (2.8, 3.6, and 3.8). They all have their pluses and minuses.

If you want a dependable daily driver with no foibles, it is hard to beat the factory injection setups. They already spent all the time and money sorting all the hot/cold/altitude/idle/cruse/fuel economy/tip-in/full throttle issues.

If you want to start pushing the performance envelope, itb’s can offer more tuning options (more aggressive cams) than are available with the common plenum of cis and Motronic.

For me though, the character of the motor and how it is to interact with is the key criteria. To me that means individual throttle bodies (itb’s). It’s not even that you can get more power running itb (which you can), but rather it is all about the induction noise, immediate throttle response, and responsive nature of a 911 motor with itb’s. Add a light flywheel and/or pressure plate and it makes the 911 motor feel like a light and lively dance partner with a great voice. This character is present at all rpm’s and not just when giving it the beans. I find it is hugely enjoyable just puttering around town. Blipping the throttle for a quick double clutch down shift just brings a smile yo my face every time.

Itb’s can be mfi (awesome stuff, best throttle response, tricky to tune, EXPENSIVE), carbs (simple, can be tuned to drive really well, but tricky to tune for all conditions and always have gas smell and usually poor(ish) fuel economy), or efi (well done systems can be as refined as factory, but to get there requires lots or time and/or money).

For me the answer is efi itb. I want the itb character, but want the better refinement, drivability and tuneability efi affords. I like to always be tinkering and learning, so I’m willing to tackle the complexity. It can be frustrating at times though. Your results may vary.

About the need for mods

"Twoblu"
"Regarding the “for now”.
You’ll really want to upgrade the intake on the 82 and port the heads even if you go with a mild cam"

It is amazing how much works well on the stock 3.0 engine parts, that were not made for emission reasons .

My small port SC 3.0 all stock internals except for M1 cams , Makes 230 hp @ crank
Ian

Ian your video is impressive showing the aggressive pull right to redline. You would dance at 7000 rpm, does one need to prepare an engine for high rpm reliability? Or is the stock SC capable of this?

I'm new to this and have reservations about revving daily over 6000 rpm, if the power is max up there I'd want to use it without worry.

Phil

Where you going to buy PMOs?

Empi bought PMO last summer and I received an email (Aug 22) from them stating the carbs and throttle bodies won't be available for some time.

I'll be happy to hear if they are available.

Bingo. This hits the nail on the head!