MFI vs CIS

[javadog]

Originally Posted by Flieger

In seriousness, though, you should check out how MFI works.

What makes you think I've never owned or driven MFI cars? Or own one now? Or that I don't have pretty much all the documentation Porsche wrote about it?

Originally Posted by Flieger

Actually, some EFI systems and ignition systems do not differentiate between cylinders like MFI does.

Okay. Tell me how MFI fuels one cylinder more than another. Be detailed...

Originally Posted by Flieger

My thoughts on the MFI to CIS transition was cost and ease of setup.

Cost, and the need to meet tightening emissions standards. Read what Porsche wrote about it, back in the day.

Originally Posted by Flieger

I see no reason why properly tuned MFI needs to waste more fuel than CIS.

Ask Grady Clay, or Ed Mayo, or others.

Cheers,
JR

[onlycafe]

Originally Posted by Flieger

Define "environmentally friendly". Someone.

when i said "environmentally friendly", i meant in terms of passing through the emissions hoop of the early seventies.
i did not mean in a fuzzy green way.

[Flieger]

Originally Posted by javadog

Okay. Tell me how MFI fuels one cylinder more than another. Be detailed...

Cheers,
JR

Originally Posted by Flieger

However, MFI injects fuel only into the cylinder that needs it. Have you ever studied the inner workings of an MFI pump? They have a cam like the cam actuating the intake and exhaust valves. These push plungers in the right sequence and at the right time to increase the pressure in the fuel lines to overcome the MFI injector's spring loaded valve and spray fuel just in front of the intake port.
Then there is the 3D space cam that works with the flyweights and throttle position and barometric compensator and the thermostat to change the fuel delivery based on load, engine speed, air pressure, etc.

By that I mean the fuel is only injected into the cylinder when it is drawing air in. The injectors turn on and off rather than just adjusting flow rate like the Continuous Injection System.

[Flieger]

[javadog]

Originally Posted by Flieger

By that I mean the fuel is only injected into the cylinder when it is drawing air in. The injectors turn on and off rather than just adjusting flow rate like the Continuous Injection System.

And that's not at all what you said before, which made no sense.

So now, elaborate on why that matters. Or, why it doesn't. Either viewpoint is fine with me.

JR

[Flieger]

"MFI injects fuel into only the cylinders that want it" meaning, the cylinders on the intake stroke. Meaning pulsed injection, not continuous.

If the earlier statements were unclear then sorry but I was trying to explain the same thing each time.

CIS is a mechanical carburetor- injection far upstream. There is opportunity for the fuel to condense on the intake runner sides and to pool behind the closed intake valve, hampering efficiency. Thus the need for the swirl inducing pistons. MFI injects at fuel pressures higher than anything but a diesel or a direct injection system, and injects it right upstream of the open valve. Therefore, more precise fuel control and better mixing (finer atomization, which improves combustion efficiency).

Not to mention the restriction of the CIS barn door.

[slodave]

Max, it's Friday evening. Tear yourself from the computer and go find a party. There will be plenty tonight in SLO town.

[pwd72s]

Originally Posted by svandamme

Oh, and MFI sounds better then anything else.

That I agree with...I miss the moan of S velocity stacks at 7,000 plus.

On the other hand, noticed this morning that my Ford was due for it's 7,500 mile service. Called the dealership at 11:00 A.M. Got a 2:00 appointment, back home before 4...and the engine noise isn't bad in my Ford.

[Flieger]

I'm too serious about learning mechanical engineering to fit in with anyone at a party. I see no fun in what would be colloquially termed a party, just as I see no fun in video games.

I need to meet someone like Angela or tweezers74 that is into cars or other engineering. There are a few girls in engineering but the place to meet them is probably not at a typical party.

It is interesting how most people here are just in a class to get a grade and a diploma. These higher level courses are so interesting and useful in my opinion.

[Flieger]

Plus there is baseball on. I want the Tigers to go all the way since they are in the White Sox' division. I want Milwaukee and the Cardinals in the NLCS.

[slodave]

Then go to a sports bar DT!!!

You're young. Get out and have fun while you can! There's plenty of time for full time seriousness later in life, if you so choose. Join the waterski club at Cal. Those guys are a hoot! And you'll be surprised at the broad range of people you will meet.

Enjoy your studies, but enjoy the young life!

P.s. I'm still waiting for you to bring me a Tia's burrito.

[azasadny]

The best thing I ever did to my '74 911 when I had it was to replace my CIS with Webers. My CIS was completely goobered up and the fuel distributor was shot, so the Webers made a lot of sense to me and they performed well and were reliable. Sounded great, too!

[svandamme]

Originally Posted by gtc

CIS was good enough that Porsche used it for the 930s entire run and into the '90s, well after everything else in their lineup was using motronic.
That seems like a pretty good endorsement to me.

Actually, Porsche endorsed MFI well into the eighties for racing.. CIS simply didn't cut it for racing, only when EFI came along was Porsche able to retire the MFI technology.

For production cars they simply compromised performance for fuel economics and production cost. Fact.
The 930, well, it simply took em longer to get a reliable EFI for turbo'ing.. Different parameters and all that.. So it took em a bit longer to get the turbo EFI into the production line.

I really fail to see where the CIS endorsement is..
No Factory Racing Porsche has ever used CIS. They used MFI for that.

Every seen an 911 RSR turbo with CIS?
or a 917? a 935 perhaps? Or what about the 936? how about the 956/962?
Please tell me which racing legend from Porsche, owned the race tracks with CIS injection...
Not even the 924 Carrera GTR and 924D variants used CIS, no. When Porsche really needed power , they used a Kugelfischer Mechanical injection and individual throttle bodies on the 924.

If you want to play find the CIS gear, try looking for a triangular Kugelfischer logo.


There' s your endorsement for CIS. They never used it when they needed reliable high end power. Not even for a 924 or 944.
Bringing CIS to a 70'ies and early 80'ies race , would have been like bringing a knife to a gunfight so they simply skipped from MFI to EFI.

[javadog]

Originally Posted by svandamme

I really fail to see where the CIS endorsement is..

I'm not actually trying to endorse it, just to correct some of the errors of fact in this thread. Like this, for example:

Originally Posted by svandamme

No Factory Racing Porsche has ever used CIS. They used MFI for that.

So, you forget about the 934 race cars. Hard to forget those... And the various 930 variants Porsche built for Group B racing at Le Mans in the '80's, before they got the 959 program done. And the C2 930 cars they raced in the Supercar championships here in the USA (they won in 1991, if my memory is good...) and, there were serveral hot-rodded versions of the 924 that were raced in various national championships...

Porsche used CIS where a set of rules required them to use the same type of induction system as the street car model they homologated a race car on. Some of them made a fair bit of power, like the 934 at just under 500hp.

Carry on,
JR

[svandamme]

Originally Posted by javadog

Porsche used CIS where a set of rules required them to use the same type of induction system as the street car model they homologated a race car on. Some of them made a fair bit of power, like the 934 at just under 500hp.

Carry on,
JR

That's like saying Carbs were the better option over EFI , because after all, NASCAR used nothing but carbs untill well into the 21'st century..

Riiiiiiiiiiiiiiiiiiiiiiiiight.

allow me to correct your statement

Originally Posted by javadog

Porsche only used CIS where a set of rules handicapped them to use the same type of induction system as the street car model they homologated a race car on. Some of them made a fair bit of power, but still suffered from lower power and throttle response compared to the same car with MFI.But because all other competitors has similar handicaps, it still worked out in the end.

Carry on,
JR

[javadog]

Ha ha...

I never endorsed CIS as "better" for power than MFI. And, I never even mentioned carbs. Quit putting words in my mouth.

I just think that you and Flieger ought to do a little fact checking before you write stuff. You can have any opinion you want, just stick to the facts.

JR

PS: The funny thing about the 934 (remember those?) is that the Group 4 rules also limited the amount of tire that Porsche could stuff under the rear fenders. The tires were too small for the amount of power the 934 made and the cars were a handful to drive. Imagine the irony... a race car using CIS that made too much power to suit the drivers...

[svandamme]

Just acknowledge that MFI is better then CIS for everything except smog and cost of production..

When all else is the same, MFI will make more power, have better throttle response and even look and sound better then CIS...
CIS is a compromise technology in order to produce cheaper cars that have better fuel economy, those 2 things are the only things CIS is better for then MFI.

That's the facts right there. Learn to love em cause they aren't going to change anymore.

[Rick V]

Who ever said CIS was better economy needs to feed my car. My truck cost me less to run. 18 mpg average

[svandamme]

I was able to empty my 83 liter tank in less then 200 km with my 2.4S.
And that was on a good day, after a pump rebuild and lot's of time spent to get it better.

[Flieger]

Originally Posted by javadog

I'm not actually trying to endorse it, just to correct some of the errors of fact in this thread. Like this, for example:



So, you forget about the 934 race cars. Hard to forget those... And the various 930 variants Porsche built for Group B racing at Le Mans in the '80's, before they got the 959 program done. And the C2 930 cars they raced in the Supercar championships here in the USA (they won in 1991, if my memory is good...) and, there were serveral hot-rodded versions of the 924 that were raced in various national championships...

Porsche used CIS where a set of rules required them to use the same type of induction system as the street car model they homologated a race car on. Some of them made a fair bit of power, like the 934 at just under 500hp.

Carry on,
JR

Notice he said factory race cars. The factory never raced 934s. Those were all privateer cars. The factory raced 935s and 936s which used MFI.