CIS or Carbs

[jcc911]

I have done the search and still can not decide....

I have decided to discontinue the turbo conversion and want to get my car running again, but the question still is. CIS or Carbs?

I have a 78SC, am not planning on any cams or hi-comp pistons at this time, so which route should I go.

I know carbs are a pain to tune, but should be easier to install. Carbs cost ALOT more. CIS can be problematic with cold/hot start problems. Carbs consume more fuel, but sound better.
CIS parts are hard to find and expensive.
HP out put about the same for both on a stock motor....

Any thoughts, I really am having a difficult time deciding.
Thanks!

[Zeke]

I don't think CIS would be my first choice especially if I didn't have one on a shelf. Getting each and every last component and installation would be difficult at best. Have you looked at aftermarket EFI? Other than that, I'd go carbs.

[poorsha]

Performance:
carbs and SSI or headers
Driveability:
CIS and SSI exhaust

I have had both setups over the years.
Carbs are (were) a major pain in my arse but what a ride (2.7 Euro p+c, headers, etc).
My SC has the CIS and it runs like a champ.
Nowhere as much fun as the RS clone but I hop in, turn the ley and she starts. Every time (still keeping my fingers crossed).
Plus you may want to consider the price of gas these days and it ain't getting any cheaper.
My RS clone was an absolute pig on gas (but I always had a smile on my face).
Something about the sound of a carburated 911 with headers

[Porsche-O-Phile]

As someone who has just rebuilt his CIS system, I can say first-hand that sourcing the individual parts (banjo bolts, fuel lines, copper washers, seals, etc.) is a HUMONGOUS b*tch. They're "NLA" from virtually everyone and I had to source many of the pieces by painstakingly measuring each individual component and then ordering them separately from different distributors (one for the fuel line, one for the banjo bolts, one for the fittings, one for the washers, etc.) It's a monumental pain, although I feel confident that my CIS is now "good to go" for the foreseeable future.

Carbs are more fun, look better, sound fantastic and enable you to run much more radical cam profiles, but there are a couple of drawbacks:

1. They are expensive. A good set of used Webers that doesn't require extensive rebuilding will probably run $1,000 or more. A "cheap" set can be had for around $500, but expect to put $500-$1,000 worth of rebuild parts into them. PMOs are nice, but outrageously expensive at well over $2,500.

2. Gas mileage. A consideration if your car sees anything other than "fun" duty where you don't care about economy. I think a 3.0 with PMOs sees something like 15-18 mpg, less if you keep your foot in it a lot.

3. Legality. They're illegal in many places, including CA. Technically even the pre-'74 cars (which are smog check exempt) cannot be modified in this manner. If you get caught, you could make life very unpleasant on yourself.

[Gunter]

Originally Posted by jcc911

I have done the search and still can not decide....

I have decided to discontinue the turbo conversion and want to get my car running again, but the question still is. CIS or Carbs?

I have a 78SC, am not planning on any cams or hi-comp pistons at this time, so which route should I go.

I know carbs are a pain to tune, but should be easier to install. Carbs cost ALOT more. CIS can be problematic with cold/hot start problems. Carbs consume more fuel, but sound better.
CIS parts are hard to find and expensive.
HP out put about the same for both on a stock motor....

Any thoughts, I really am having a difficult time deciding.
Thanks!

My choice would be to get a '78-'79 US CIS with the larger intake runners $3-400.-(No Lambda) and re-grind the cams to a 964 profile. (~$300.-)
Lots of fun for minimum $$, especially if you have stock Mahle P/C's.

[RWebb]

not clear where you are starting but what about EFI?

[LakeCleElum]

For torque and fuel mileage, it's hard to beat a CIS system that has been sorted out. You see complete CIS systems here on Pelican from time to time for $300 or so.....I spent a lot of time replacing parts on the 73.5 CIS about 5 yrs ago and couldn't be happier...

[ael911]

I love the PMOs. Tuning was not bad at all, but YMMV. If your car is smog exempt and you don't commute with it, I'd seriously consider carbs or if budget is not an issue, MFI. EFI would be my next choice and CIS last. I am averaging 12 to 15 miles to the gallon now but I have not checked the AFRs. With 135 mains, I am probably a bit rich, but the power is great and oil temps are about 10 degrees cooler than with my CIS. It's a trade off I am willing to make for great throttle response and better performance over fuel economy.

Carbs do have the downfall such as the lack of altitude compensation that does not apply to other fuel delivery systems.

By the way, I have a complete CIS unit with plastic lines minus two fittings if anyone is interested. The intake runners are also Extrude honed.

Andy

[Zeke]

As I understand it, if you order new PMO's and give them all the parameters of the motor, they will set them up for you, plug and play with minor adjustments.

[ael911]

Yup, I gave my parameters to Steve Weiner at Rennsport System and a large package arrived at my doorstep about a week later. Everything was in the kit and complete plug and play if you can get your fuel pressure to drop to the appropriate level, I couldn't. A little creative thinking solved that problem and I was on the road 20 minutes after the intitial start up and adjustment.

Steve said Richard will get the setting close, but they do recommend putting the car on a dyno and check the AFRs to be on the safe side.

[JP911]

CIS can be a great system, but when stuff goes wrong it can be both frustrating AND expensive. Even well-versed P-car mechanics can have a hard time identifying the source of nagging issues. While new PMOs are pricey, so are CIS replacement parts and labor for a good mechanic. If gas mileage is truly a consideration, skip both CIS and carbs and go for EFI.

[Dick Shift]

From your thread info. You should go with CIS. Drive ability, mileage, cost, all the above better with CIS.

[911st]

My $.02.

I do not know where you are starting from. If the CIS fuel head has been sitting around it can be a problem. There is a procedure for storing them but few follow it.

Trying to put together any induction system from scratch is a PITA and or expensive.

How about selling your box of motor parts or short block and just buy a turn key stock 3.2 EFI motor.

Mine with just a cat bypass & chip puts puts out 217rwhp (apx 250hp) and gets 20-28mpg.

Good luck.

[JohnJL]

If you decide that way I have a complete CIS system from my 83SC for sale. Everything is there, guaranteed to work. Cheap.

[ralphnct]

Go to EFI. It is outstanding!

[azasadny]

I love my Webers on my stock '74, it makes the entire driving experience much more pleasant. My CIS was possessed by Satan himself and I haven't had any trouble with the Webers after over 8,000 miles of driving.

[JohnJL]

Yeah, but Art didn't you have a devil of a time getting those carbs working?

[jcc911]

Thank you all for you input.
Right now I have a 78 engine that was torn apart because of a broken head stud. In the process I started converting to a turbo, and I would say that I am 95% there but have run out of steam and the wife is quite tired of having a vehicle that is not running. (Personally I don't blame her, it has been over 1.5 years and has been really patient up to this point.)

My goal is to simply get it running again. Budget is liited as I spent a ton on the turbo conversion and am hoping to get some of that back.

I have a 3.2 intake with MS2 on the car right now and I just do not have faith that it will run (Just seems too custom and am not sure if I set it up right.)

I would like carbs, but the thought of having to tune them continuoulsy does not appeal to me. At least that is the impression I received from Henry at Supertec.

So, I think I have found a "good" CIS set up for a reasonable price. My thought would be to go the CIS route for now and maybe when I have some ambition again, to go with Tbitz kit as it has already been sorted out.

Thoughts??

Thanks Again. J

[Porsche_monkey]

Why not look for someone to get the MS running for you? Or use the resources of this board? It looks complicated, but CIS isn't the simplest thing in the world either. Both sytems will take some time to troubleshoot and get into a drivable condition. Seems early to give up on MS.

If you really want to just get running reliably ASAP, just buy PMO's.

[jcc911]

That certainly is an option seeing as I already have the MS, but I am not sure if there are fuel tables for an NA 3.0 yet. I only have the tables for a Turbo'd engine.

It is worth a shot since I am so close, I just think there are less variables with putting the CIS back on.