73 MFI vs CIS

[johnbri]

Hi all,

Im new to Pelican but a long time Porsche owner & racer. I'm considering purchasing a 73.5 911 CIS. I don't know a whole lot about the pros and cons of the MFI vs CIS. All of my early Porsches with the execption of a real 73 RS have been weber cars.

My "sportscar market" price guide says the 73 CIS should be worth $2,000 more over the MFI version. But I've read where some people don't think the CIS is better.

Can anyone please take the time to explain the thinking on this?

Thanks,
John

[ossiblue]

I certainly don't qualify as an expert, but I happened to ask my mechanic--who is one--his opinion of both systems. He was trained in Germany to work on the MFI when it came out, and he much prefers the CIS. There are many more "wear" parts (ie. butterfly valves) on the MFI, and as the system wears, it becomes more and more difficult to run smoothly. He finds the CIS by comparison, more economical and easier to work with. He feels both systems are good if in running order, but he prefers the CIS. Again, I really don't know specifics, but this was one opinion from one who I respect, and will get this thread started.

[Gogar]

I also am no expert, but I know a few things:

In 1973, Only the 911T came w/ CIS. I think there was also a version of the T with MFI (up to 1973.5).

E's and S's in 1973 were MFI.

So, your value guide may only be considering T's, because E's and S's are obviously much more desirable.

That said, in a practical sense, it depends what you are going to do with the car. If you're going to drive it a lot, the CIS might be a better idea. If you're going to go to the track or something MFI might be loads of fun for you. CIS parts are cheaper and more available, too.

[garrege]

IMO, you'll find the market softer on 1973.5 CIS cars, they're not as prized as the MFI cars.

i think the comment about it being a driver versus a hotrod is fair; the CIS car is a simple driver.

[techweenie]

Originally Posted by ossiblue

I certainly don't qualify as an expert, but I happened to ask my mechanic--who is one--his opinion of both systems. He was trained in Germany to work on the MFI when it came out, and he much prefers the CIS. There are many more "wear" parts (ie. butterfly valves) on the MFI, and as the system wears, it becomes more and more difficult to run smoothly. He finds the CIS by comparison, more economical and easier to work with. He feels both systems are good if in running order, but he prefers the CIS. Again, I really don't know specifics, but this was one opinion from one who I respect, and will get this thread started.

14 points of adjustment vs. one. It all boils down to that. CIS is bone simple. Ideal for a car you're going to use. MFI will be best for owners who are able or willing to deal with tuning and adjusting. The point about wear is well taken. When MFI wears out, it will easily cost $2500-3000 to rebuild the throttle bodies and pump and re-set everything, assuming you can find a mechanic who is able or willing.

There are buyers who will only buy MFI and buyers who will only buy CIS, so value comparisons are similar to sunroof vs. non-sunroof. An overall market survey might show CIS cars bring more money, but that may be equally related to them being the 'last of the longhoods.'

Having owned several of each, I'd add that a CIS T is going to deliver approximately 60% better real-world gas mileage.

[blau911]

I have had them both and I must say that my 73.5T CIS ran great. I didn't think I would like it after hearing how other people disparaged it. But the CIS ran like a clock, never stuttered, popped or felt sluggish. It also got great gas mileage as Techweenie above already mentioned. Lastly, it pulled better than any 911T I have ever driven (I have driven maybe 12-15 911T's over the past 10 years). It had really nice smooth acceleration, with really nice power between 3000-5000 rpm's.
The other big advantage of having an 73.5 CIS car is that when the engine finally does die, it is REALLY easy to swap it out for a 3.0 SC motor (early 911S hp and lots of low end 91T torque) without any wiring issues.
Anyone who has owned and/or driven many early 911's, and has also owned a 73.5 CIS will tell you that the CIS is a superior fuel delivery system. It is also one of the nicest driving early 911 cars ever built.
Don't let others kid you about its shortcomings. There are none. If your car is rust free and in good shape, your 73.5CIS will command good money if you sell.

[Sunroof]

As an owner of a 1973.5T with the first CIS, at the beginning I had to replace several components only because of wear, but they were readily available even in aftermarket versions. The 73.5T/CIS is the only system that does not use the thermotime switch. Rather the cold-start hand throttle is used, which to me is remeniscent of the old choke pull switches on my earlier Triumphs. So when starting the 73.5T your pulling up on the hand throttle and find your running around for awhile with a fairly higher idle waiting for the warm-up regulator to do its thing. Its really a kick!!

Another unique feature about the 73.5T CIS is that the fuel injectors are set into the cylinder heads not the intake manifolds like later models. They are a bugger to get out!

The 1973.5T/CIS 2.4L is a great power source. They are not known for overheating, are excellent in day to day stop and go traffic and have impressive pulling power. For me the CIS has it all over the MFI, but then the 73.5T I believe did not come with MFI. The last of the longhoods in good condition are commanding good money.

Bob
73.5T Sepia of Course

[acegx]

The MFI cars go for more money and seem to be more highly favored by collectors any day of the week. I have only had MFIs and never had issues. If you live in a small metro area there are probably not a lot of mechanics still around that can work on the old cars. They either
retired or passed on. One of the leading authorities on this topic is Ed Mayo from Mayo Performance in Euless, Texas (Dallas), mayos@imagin.net . He handles all the Early 911 questions for PCA in the Pano magazine. Good luck.

[wgwollet]

I just bought a 1973 Porsche 911T with MFI.......they only build 871 units for US, then in Jan 1973 they used a CIS and were called the 1973.5 model and CIS was used up to 1983.....

The MFI is worth much more understand all long hoods had MFI except the 1360 built for the 1973.5 T only..........for a driver yes CIS but old school the MFI is the best........and desired the most because all long hoods are MFI (RS, T, E, S) but only Jan 1973 to Sept 1974 model had CIS in T only

[McLovin]

If you want an easy to tune car that gets great mileage and no hassles . . . get a Honda.

If you want an early 911 in its full glory . . . get MFI.

[blau911]

Originally Posted by McLovin

If you want an easy to tune car that gets great mileage and no hassles . . . get a Honda.

If you want an early 911 in its full glory . . . get MFI.

Spoken like a guy who has never had his MFI pump fail and had to fork out more than $1300 to get it rebuilt, or a guy who has never had a cold start mechanism malfunction and spent lots of time and money trying to fix it. Porsche went with the CIS over the MFI because it was a better fuel delivery system and Porsche used the CIS on all of its 911's and turbos until 1984 - long after the Bosch MFI proved inferior and inefficient.
I like the MFI for its throttle response at higher rpm's, but the CIS for drivability is better.
With CIS, you didn't need to buy a Honda to get a good sporty 911 that offered 911 performance, good mileage and was hassle free. The 2.4T with MFI had a hp rating of 140. The 2.4T CIS was 148. There was no performance sacrifice when Porsche moved to the CIS system. Quite the contrary. The problem with the CIS system was that Porsche couldn't figure out a way to use it with aggressive cams so the inevitable consequence was to increase the displacement and develop a motor with more performance from low end torque rather than higher compression and higher rev's.

[wayner]

I just found this old thread and have been wondering if CIS is so good, why the factory out MFI on their 1984 SCRS homologation special to get 280 hp?

I was always led to believe that CIS was a compromised system for emissions purposes??

I'm all ears so let's hear any ideas?

[Rawknees'Turbo]

^^^

Wayner, I can't answer your specific question, and I don't think of CIS as "good" (I think it is a royal pain in the arse to trouble shoot and customize, that utilizes way too many band-aide-style add ons to function well), but I do know that CIS can be set up to support serious power - many of the 934s ran highly modified CIS back in the day (big power, buttofcourse), and currently there are those that are going beyond 400hp with their CIS fueled Turbos (400+ requiring substantial modifications to the system, however).

I've also read the claim about "emissions" being a driving factor for CIS, but don't understand that at all considering how wasteful the system is - it keeps dumping fuel even at initial closed throttle, among other shortcomings!

[ficke]

Originally Posted by wayner

I just found this old thread and have been wondering if CIS is so good, why the factory out MFI on their 1984 SCRS homologation special to get 280 hp?

I was always led to believe that CIS was a compromised system for emissions purposes??

I'm all ears so let's hear any ideas?

CIS is "so good" on a car for drivability and gas mileage>911T what the original post was about and also are about "touring" what the T stands for in 911T.
911T's were never about power.
The S and RS with a lot of cam overlap could use MFI that did not have a mass air flow sensor and were not bothered with S and up cams.
Those people and Porsche opted for the MFI in that circumstance and it delivered in spades.
Do not confuse the T and the S and the L as the same car with the same engines and purpose.
The CIS is a better fuel deliver system for the T model 911 ( The 911T was discontinued after 1973) and commands a premium over the MFI in 1973 T 911.

[LakeCleElum]

Owned my 73.5 with CIS for over 26 years. Current engine is a high compression 3.2 with CIS.....I've never had a MFI, but love the CIS over the carbs on my '69 Coupe....Best ever for torque and reliability.....My only issue ever was a plugged injector I cleaned myself....

Resale value? Don't care as I won't sell till I'm too old to drive.

[wayner]

My 73T was delivered with MFI.

My other assumption other than emissions was that CISwas a cost saving measure over MFI??

This made sense to me when someone suggested it since after all, the T had steel cylinders/fins instead of the Aluminum barrels that the E and S had ( E and S shared the same cylinder part numbers, but not the T)

I find all of the different opinions interesting

I also find it interesting that CIS came in at a time when the US market was tanking due to the US economy compared to Germany and the unfavourable currency exchange
(In 74 they also downsized the CV joints and other cost saving measures)

[techweenie]

The declining number of specialists who can whip an MFI system into shape vs. the tens of thousands who can "tune" CIS is an argument in favor of the latter. MFI has 14 adjustment points, and once they are all set, you go back through all 14 again, and maybe again, still. CIS has one hex head mixture screw.

That being said, I doubt most of us are drawn to early 911s for the convenience or economy. Given the choice between two roughly comparable 73 Ts - one MIF and one CIS, I would choose on the basis of other merits than the injection system.

[wayner]

Originally Posted by techweenie

The declining number of specialists who can whip an MFI system into shape vs. the tens of thousands who can "tune" CIS is an argument in favor of the latter. MFI has 14 adjustment points, and once they are all set, you go back through all 14 again, and maybe again, still. CIS has one hex head mixture screw.

That being said, I doubt most of us are drawn to early 911s for the convenience or economy. Given the choice between two roughly comparable 73 Ts - one MIF and one CIS, I would choose on the basis of other merits than the injection system.

I think that this is the best post yet on the subject

[manbridge 74]

Originally Posted by wayner

My 73T was delivered with MFI.

My other assumption other than emissions was that CISwas a cost saving measure over MFI??

This made sense to me when someone suggested it since after all, the T had steel cylinders/fins instead of the Aluminum barrels that the E and S had ( E and S shared the same cylinder part numbers, but not the T)

I find all of the different opinions interesting

I also find it interesting that CIS came in at a time when the US market was tanking due to the US economy compared to Germany and the unfavourable currency exchange
(In 74 they also downsized the CV joints and other cost saving measures)

For 75 the axles were downsized. 74 retained bigger hardware of previous years.

[manbridge 74]

Maybe I'm one of the last Mohicans but I leave for a week long put on by Porsche MFI fuel class in March.