MFI vs CIS

[javadog]

Originally Posted by Flieger

I disagree that CIS is more environmentally friendly. CIS injects fuel into all cylinders all the time no matter what. It just varies the amounts. MFI injects fuel into only the cylinders that want it, and only when the driver is on the throttle. There is a microswitch to shut off fuel when off throttle and above 1500 rpm. It is a high pressure injection, too, so the power you get out of the fuel I would say could be double the CIS.

The difference is that CIS cars are slow and slow cars are not going to need as much energy to go slow. MFI cars are fast so they need more energy. If you made a CIS car as fast as an MFI car the MFI car would get better mileage.

It is also the tuning. You can make either one rich or lean.

MFI was actually adopted for the 911T in 1969 because it was the only way to meet the emissions regulations.

Originally Posted by Flieger

I think that is more than balanced out by CIS dumping fuel into all cylinders like a garden hose.

I've highlighted everything that just isn't true. Your homework assignment is to go back and correct these things.

Have fun,
JR

[boba]

Originally Posted by javadog

... in the US. Euro models kept the carbs.

JR

I will extend my remarks.

[RWebb]

CIS is more environmentally friendly than MFI and meets later, more stringent emissions stds. EFI is much better than either in that regard.

CIS is also gives much better fuel economy.

CIS was a significant advance when first introduced by Bosch for the technology extant at the time in terms of fuel mileage.

If (for some reason) you have an old Volvo and want to keep it stock (period correct) then CIS is the way to go.

CIS is not a good choice for a sports car* and I'm told it is more susceptible to EtOH fuel problems than MFI, EFI or carbs.

MFI is a period-correct, concoursmobile correct performance injection system.

Direct injection is top dawg right now, but for the best performance on our old air colled motors, just take a wad of $10,000 bills to Motec and PMO.


* yes, MFI is derived from a diesel tractor system, and yet somehow...

[svandamme]

Nobody mentions one of the biggest feats of MFI:

MFI has the best throttle response money can buy in terms of classic 911 engines.

"money can buy" is pun intended, because it's more expensive to get a non or poor running mfi injection to work, if the pump is out of wack, it's probably going to get costly.. whereas CIS will probably work out cheaper...afterall, CIS was the mass production thing, it was not about performance, at all.

[red-beard]

Why is this in OT?

It should be in PARF! The MFI people are religious fanatics!

reporting to the mods

[svandamme]

Oh, and MFI sounds better then anything else.

[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.

[Flieger]

Originally Posted by javadog

I've highlighted everything that just isn't true. Your homework assignment is to go back and correct these things.

Have fun,
JR

OK, 1972 was the year that the 911T got MFI in the US. So there. The rest is correct.

[Flieger]

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.

That logic is flawed. Porsche went through some tough financial times and the 911 was wanting to be phased out. Nothing new was going the 911s way until they realized that the market wanted 911s and not 911 replacements, so they brought in Motronic from the 956 and then finally upgraded to the 964.

[Flieger]

Originally Posted by RWebb

CIS is more environmentally friendly than MFI and meets later, more stringent emissions stds. EFI is much better than either in that regard.

CIS is also gives much better fuel economy.

CIS was a significant advance when first introduced by Bosch for the technology extant at the time in terms of fuel mileage.

If (for some reason) you have an old Volvo and want to keep it stock (period correct) then CIS is the way to go.

CIS is not a good choice for a sports car* and I'm told it is more susceptible to EtOH fuel problems than MFI, EFI or carbs.

MFI is a period-correct, concoursmobile correct performance injection system.

Direct injection is top dawg right now, but for the best performance on our old air colled motors, just take a wad of $10,000 bills to Motec and PMO.


* yes, MFI is derived from a diesel tractor system, and yet somehow...

Define "environmentally friendly". Someone.

I agree electronic, direct fuel injection is best.

[RWebb]

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.

or does it just mean they did not have the development dollars to put an improved system on a turbo (not that easy either AFAIK)

we know they were way short on $$ during that time period

[Flieger]

Originally Posted by javadog

I've highlighted everything that just isn't true. Your homework assignment is to go back and correct these things.

Have fun,
JR

Most of my statements were opinions, which are not provable or dis-provable therefore.

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.

[RWebb]

= meets later, more stringent emissions stds, Flieger

improved fuel economy also translates directly into lower CO@ emissions, tho that danger was not well appreciated at the time

I thought you were an engineering student - has this not been covered in the curriculum anywhere?

[Flieger]

My BMW is pretty dirty. It just squeaks by 1983 emissions but I am not allowed to improve the fuel injection by California law. I wouldn't say CIS is doing it any favors.

That is why I was talking about the speed of the cars. If you drive a car hard you will use more energy and so more fuel. CIS cars are tuned pretty anemic, so they can't go so fast (accelerate as hard). I venture that since MFI has much more precise fuel control as far as pulsed injection that MFI has lower brake specific fuel consumption.

I think the oil and stuff old cars burns is probably more polluting than the part of the exhaust that is actually combustion products.

[RWebb]

the oil and stuff old cars burn = gross polluters

[javadog]

Originally Posted by Flieger

Most of my statements were opinions, which are not provable or dis-provable therefore.

Ahh, not so fast, whippersnapper. Let's have a look...

Originally Posted by Flieger

I disagree that CIS is more environmentally friendly.

Well, Porsche went to CIS beacuse it enabled them to meet economy and emissions standards that they didn't feel they could meet with MFI, so I guess they would disagree with your statement, as do I.

Originally Posted by Flieger

MFI injects fuel into only the cylinders that want it.

Yeah, I've studied MFI but this statement really makes no sense.

Originally Posted by Flieger

It is a high pressure injection, too, so the power you get out of the fuel I would say could be double the CIS.

Double? Ahh, no. In fact, recall that the first CIS car, the 1973 T, made the same power with CIS as it did with MFI. The CISs car actually had a half a pound foot of torque more, or 3, depending on which numbers you believe, so...

Originally Posted by Flieger

The difference is that CIS cars are slow and slow cars are not going to need as much energy to go slow. MFI cars are fast so they need more energy. If you made a CIS car as fast as an MFI car the MFI car would get better mileage.

This also makes no sense, so I'll go on.

Originally Posted by Flieger

I venture that since MFI has much more precise fuel control as far as pulsed injection that MFI has lower brake specific fuel consumption.

No. ANybody that has spent much time with MFI realizes that those systems don't offer near as fine fuel metering control as CIS. They make great power and sound nice, but they aren't frugal with fuel. Not even close. The CIS cars were eventually developed to the point that they got fuel mileage an MFI car couldn't even dream about.

And, if you look at the BSFC curves, CIS cars yielded 20% better numbers, give or take.

Cheers,
JR

[Flieger]

Whatever. I can't convince you to mend your CIS ways so I will continue having fun in the MFI 911 which is so much more fun than the CIS BMW. Idles better, better throttle response, doesn't stink like fuel.

[Flieger]

In seriousness, though, you should check out how MFI works. It is basically EFI done mechanically. The space cam is the fuel map and there are various sensors that input into the MFI pump which can be seen as a sort of mechanical computer.

Actually, some EFI systems and ignition systems do not differentiate between cylinders like MFI does. Throttle body injection, wasted spark.

MFI is quite sophisticated.

My thoughts on the MFI to CIS transition was cost and ease of setup. I see no reason why properly tuned MFI needs to waste more fuel than CIS.

[Flieger]

Coolness >>>>

MFI Pump - Open Heart Surgery

MFI Open Heart Surgery III - Reworking the Space Cam

[Zeke]

Why is this in the OT forum? the subject has been discussed ad infinitum on the 911 BBS since 1999. David E. Clark even consolidated the thread into one massive thread.

Come on, let's discuss something interesting like hookers and blow, legs and butts.