Middle Year and CIS Flogging
 

Maybe I'm ignorant but I fail to understand an oft repeated phrase in these threads about how heinous a CIS engine is. I'm used to the 2.7 jabs (which also have always surprised me) but fail to understand what is wrong with a properly set up CIS. Mine has had no mechanical intervention in 3 years and seems to run, start, rev and go like a scalded dog. I even blew by a new Turbo and a GT2 last sunday...ok they were pulled over by a trooper but, can someone explain what I'm missing?

I think most people just don't like them for their lack of High Performance capability. The CIS system doesn't allow to many engine modifications for more power like carbs or Computer controlled FI.

Dude, don't take it to heart what some bozo's say about CIS..
It's one of the most stable fuel delivery systems ever designed.
With little to no electronics other than for starting of the engine.
These motors are rock solid. when they act up if ever are easily diagnosed.
Now they will say that you lose HP having CIS because of Cams and Pistons. Just keep in mind that some P-car owners don't race and could really care less for additional HP. JMO

Jorge (Targa Dude)

Targa Dude hit the nail on the head. We have a 79 with CIS and it has NEVER failed us. I can't say that about all our other cars. The CIS cars still make decent power and you can still change pistons and cams (964 or 20/21) to get a little more hp if that is what an owner is looking for. SmileWavy

I kinda like having one car that's 100% mechanical (and keepin it that way). And one that's got all the new technology goodies and I can just hook up the laptop!

2000 GLX 1.8T 225HP New Beetle
K04.001 Turbo, GIAC 1.0 Bar Chip, 4-Bar Fuel PReg, N-75H BoostControl, Techtonics Stainless Cat Back and Down Pipe, Bailey DV, Neuspeed Intercooler Tube and Turbo Inlet Pipe, Eurosport Cool Flo, Z-Engineering MK4 Rear Engine Pendulum Mount, Eurosport Upper Stress Bar, H&K Sport Springs, Bilstein Sport Shocks, VAG-COM Software.


Hey at least it's still German!

I've never driven any other Porsche except my 74 so I don't really know what I might be missing. And I think I understand the limitations on HP improvement which appear to be minimal at best and probably not even worth the time and money. I agree its nice and stable, trustworthy. I suppose it needs some kind of occasional maintenance from the shop but I'm not sure what.

I really need a good lesson in 2.7CIS. Mine is just plain dead slow. Really. The engine has less than 50K ORIGINAL miles on it, but it just won't move! I'm glad to hear some of you guys say yours is fast, but I need to know where to start working on mine before I get impatient and buy a bigger engine.

Can you refer me to a good 2.7 CIS guide that will help me go through mine step-by-step to see why it's so darn ssslllloooooowwww?

Count me in with you guys. I quit *****ing back at all the 'mid-year bashing' on this board over a year ago. This car clearly doesn't appeal to the masses on this board, but they obviously do to us. My '74 likewise is clean, pristine, stock and has proven totally reliable for years. What many trade for performance with carbs they lose in reliability. Ok, we all make our choices, right? Factor in my enjoyment/$ spent and you'll be hard pressed to beat me. This is the only car I've ever owned in over twenty years as a driver that I relish driving every day without the feeling abating. I think we have the best kept secret in Porschedom. The 'early' guys hate the bumpers...at least we don't get that from sc owners!;) Anyway, leave them to their opinions and enjoy your cars. No matter what anyone wants to say they still are and always will be Porsche 911's like everyone else's. Do I speak for anyone else? Muuahmuhahh!:D
Ryan

Ray,
I have heard mentioned here that the reference book of choice is a Bosch fuel injection manual. I don't know much more than that. I should probably pick it up to see what sort of maintenance it needs. Wayne's book may also cover it a bit.
When I said mine goes fast I only have one data point and that is my car. Although last sunday I was at 5000 RPM in 5th gear and I felt like I ws going REALLY fast (that equates to 115 mph by my owners manual).

CIS isn't that bad. It's just not sexy, thats all. The best Porsche managed from CIS was just over 65hp/litre (NA, not turbo). The early S cars have 80hp/litre. The tradeoff is driveability.

At least the cars are light - it makes the hp go a long way. My '75S is pretty quick.

Basics for the CIS, not in any particular order,

Fuel Highest octane you can afford.
Clean fuel injectors are very important
CO mix set at Idle to 2%
Remove or plug Vacuume at Dizzy
Set timing to 5 deg @ 900-1000
or 35 deg @ 6000
Remove or disable Smog Crap.
Change exhaust to 2in 2 out
upgrade exhaust system ei. SSI's No thermal reactors
Make sure your Throtle linkage is optimized
Remove Belt to your AC
add efficient Oil cooler
Make sure you have good Spark plugs.

Jorge (Targa Dude)

If I new more of how CIS works I could comment more. All I know is mine works. You can always spend money and make it faster, but it works.

2.7 with CIS
 

I have owned this car for 20+ years and enjoy the reliability.
It is light, tight and runs like it is supposed to. As a former
race driver I can assure you, it is quick enough for Interstate
or Autobahn driving.

Ray, I have all the books you'll need to familiarize yourself with CIS. After the first 3 or so books, they all start to sound the same. As for tuning your CIS, bring it over and we'll go over all the subsystems. Once your have struggled with it, it is not so complicated. I don't claim to be a CIS guru, but I won't get stranded on the side of the road somewhere because of a poorly tuned CIS. After struggling with my CIS 3.0 motor for months, I feel I have to share or all that work will be loss in my head somewhere.

I have a mid-yr 911. I went to a 3.0, but I am having a hard time parting with my 2.7. So it sits in the garage until I get the time to build it right.

Jim Williams has a nice CIS webpage. I can't remember the url now, but if you run a search you'll find it, it has been posted before.

CIS is great -- if you want an obsolete economy car FI system. It would be great on a 70's Subaru for instance. It's just not a sports car type system and does not give sports car type performance. Drive a '74 or '75 and then drive a '72 (which has a smaller engine). You'll be amazed. I have a CIS car and a carb'd car w=from which the CIS was removed -- it's like night and day.

I don't know - CIS supported turbos up to 1987, I think.

Randy,
I don't doubt that many technologies from 1974 are obsolete. But what made the Porsche engineers go from MFI to CIS? It can't just be for fuel economy! And I think dd is right, CIS was used in Turbos for a long time.

Smog laws forced the change from MFI to CIS for the most part...but the posters above are right, it's a reliable injection system. Pop-off valves to prevent the blowing of the air box have been around for a long time now, so I'm guessing all you guys have one?

Jorge,

You say:

Basics for the CIS, not in any particular order,

Fuel Highest octane you can afford.
Clean fuel injectors are very important
CO mix set at Idle to 2%
Remove or plug Vacuume at Dizzy
Set timing to 5 deg @ 900-1000
or 35 deg @ 6000
Remove or disable Smog Crap.
Change exhaust to 2in 2 out
upgrade exhaust system ei. SSI's No thermal reactors
Make sure your Throtle linkage is optimized
Remove Belt to your AC
add efficient Oil cooler
Make sure you have good Spark plugs.

I get all of the recommendations except one. I don't understand the octane reference. Given my compression ratio and the specs in my manual, I use 87 for all but the most demanding applications (a drive across the desert, track days, etc...)

Do you recommend high octane for the health of the CIS system?!? Help me understand.

Well.. I ment High octane in a relative way.. I don't mean racing gas..
what ever is the highest at the corner pump. and stick with leading brands such as Chevron, Union 76

Your tuned CIS will respond better with proper timing and CO mix set correctly with higher octane

Jorge (Targa Dude)