Finally drove MFI

[jac1976]

I think most people here in the forum appreciate Porsche as much for the community the hobby fosters as for the cars themselves. This esprit de corps is reflected in the friendly banter and prodding here on the forums and during weekend get-togethers, drives and rallies. The folks I drive with run the gamut with respect to backgrounds, careers, etc. A handful are fiercely competitive with backgrounds in all matters of bikes and cycling where they have achieved national, if not, worldwide recognition. This competitive nature often translates to “spirited” drives in the hills and occasional track days and a desire to know their cars inside and out. They are simply competitive. And good. Like others on this forum with experience and earned respect, they don’t feel they have to prove themselves to everyone at every opportunity. Saying little can say a lot. Perhaps you should try meeting up with people in a more social setting. Nevertheless, I appreciate that you likely thrive alone in a car with a single seat in an environment in which you are inaudible.

[Tremelune]

[Jeff Higgins]

Originally Posted by winders

Oh, you mean the part where someone has an opinion that is contrary to another person’s opinion? Oh, you want a forum where no opinions or statements are challenged. Boring….and not at all educational.

I love the exchange of opinions on this forum. I love the "bench racing". The sheer depth and breadth of knowledge on this forum is amazing.

It is beyond apparent, however, that some opinions are based upon first hand technical knowledge and experience, and others are based upon... well, something else.

I find it interesting that the one guy with the least experience (apparently no experience) with the original topic, MFI, nor with this last diversion (Electromotive), has had the most to say about both. And nothing remotely "educational", really, just baseless, inexperienced nay-saying.

I do find it sad that the "signal to noise" ratio on this forum has gotten so diminished over the years. There have been a few guys in this thread, conversant in MFI, who have provided "signal" - Mark, Jonny, Jeff (just the ones I remember without going back, sorry if I missed a few). One guy has provided a disproportionate amount of "noise" - and a guy with absolutely no interest in, with absolutely nothing vested in, the (actually either) system. That would be you. Why? (That is a purely rhetorical question - I believe we all know the answer.)

[QueWhy]

Originally Posted by Tremelune

No kidding. Seems like threads go off the rails when Winders is involved. He’s derailed more than a couple worthwhile discussions in the engine rebuilding forum too.

[winders]

Jeff,

My mistake is I stepped into a religious pontification and had the gall to not bow down and worship the words of the Prophet Higgins!

I think MFI is great on cars that it is correct for or for people that want to use it on cars they building. My only gripe regarding MFI was with your definitive statement saying that MFI has better throttle response than EFI with ITBs. I have driven a nice 2.4L S with a nicely tuned MFI setup. It was a great to drive and I enjoyed driving it immensely. But, the throttle response was not better than what I get on my race car with EFI and ITBs. The MFI is fantastic. But so is modern EFI with ITBs.

I have not used Electromotive because I kept getting steered away from it by smart people that just plain don't like it. I have seen issues at the track that lend credence to the direction I have been given.

The idea that you have to have owned a car with MFI or owned a car with Electromotive to have a valid opinion on them is ludicrous. I used to race motorcycles but never owned a Ducati. But, I have ridden them, raced against them, and worked on them. I could give you very valid opinions on those Ducati bikes.

[winders]

Originally Posted by QueWhy

He’s derailed more than a couple worthwhile discussions in the engine rebuilding forum too.

You mean the one thread where Schmidt said that no Porsche Dilivar heads studs were any good yet the evidence is that the 993 Twin Turbo heads work extremely well?

Or the thread where Schmidt promoted using a single MSD 6AL ignition unit in a twin plug setup when MSD even says you should use two? No one else on the planet recommends using a single MSD unit but that's okay....

I am sorry that I bring up inconvenient facts there.....

[Quickstep192]

I hope this isn't too tangential, but..l

If you were converting an MFI car to EFI, would you put the injectors in the old MFI ports in the heads, or would you use injectors in the throttle bodies? (Or both?)

[tobluforu]

Wait, why is it that I no longer post on this board unless its absolutely necessary? Oh yeah, it's threads like this where the almighty get involved. I'll take my "noise" elsewhere. Go take your silver cables and shove them up your arses.

[winders]

I prefer Duelund DCA copper wire wrapped in an oiled cotton sheath. Silver wire tends to be too bright for my ears…

[RDM]

Originally Posted by jac1976

The behavior continues and yet still no answer to my question.

It's who he is. It's what he does.

Does that answer your question?

[Superman]

It looks like I started a fight, which would surprise no one on PARF.

Well actually, I didn't start it. I have found though, in my unscientific 64-year study, that argumentativeness is inversely proportional to experience and knowledge.

My home stereo and professional musical gear is all-tube. I do not listen with my eyes and I have never heard a data sheet. My 911 spark plugs are copper core. I have never driven a data sheet. In theory EFI could have throttle response just as quick s MFI. But if you even glance at the physics, you will see it is impossible for EFI to be quicker and possible for it to be less quick. And then you would argue the difference is not discernible.

In related news, I think that if Scott were to drive Dr. Higgins' 911 with an open mind, he'd turn to Jeff and say "Whoa! I see what you mean!"

[winders]

Originally Posted by Superman

In related news, I think that if Scott were to drive Dr. Higgins' 911 with an open mind, he'd turn to Jeff and say "Whoa! I see what you mean!"

I've driven well setup MFI cars....

If Jeff Higgins drove my car he would say "Holy $hit!!" if he didn't kill himself....

[Superman]

That's funny. I'm sure your car is very fast.

Fun facts: Jeff is an engineer and I don't know how many Ducatis he has owned but at least one was built to at least the performance extreme of his 11:1 3.0 MFI car. His driving and riding styles are befitting the machines he builds.

I'd guess he is not likely to visit this thread again. Perhaps no one will but Scott.

[winders]

Fun facts: I used to race motorcyles and once, 20+ years ago, raced a 200+ HP superbike that destroyed the most advanced Ducatis (available to the general public) of the day. That bike tried to buck me multiple times as it was a beast and rear traction was severely tested....

More fun facts: Regardless of how the fuel gets into the combustion chamber, MFI and EFI with ITBs both have air getting into the engine via butterflies. That is the gating factor and ITBs and MFI are the same there. The idea that EFI is somehow slower reacting than MFI is ludicrous. Both have to fire the spark plugs based on the location of the crank and the ignition timing. Just because EFI is "smarter" does not mean it has to be slower.

In fact, you could argue that an EFI/ITB system with 996.2 GT3 intakes would have better throttle response than MFI as the GT3 intake takes advantage of pressure waves to force the air into the ITBs which would improve throttle response.

[RSTarga]

Comparing apples to oranges, no point discussion.

[David 23]

I was initially very interested in the topic of this thread, and looking forward to hearing an intelligent and thoughtful discussion about the differences between EFI and MFI. I have a hot rod 3.2 SS with EFI, and have been seriously considering MFI in another car. This could have been informative and interesting to me personally. As it turned out, I've wasted a bunch of time reading posts from some individuals that have not been constructive nor on point, consequently stirring up petty arguments and "positioning" rather than thoughtful insight. Disappointing in the least.

[winders]

The thread has already covered how EFI with ITBs is far better overall than MFI. EFI is easier to tune, offers better fuel economy, is more flexible, and does not rely of hard to find parts to keep it running for years and years.

But, MFI is wonderful on the cars that came with it and is certainly worthwhile to keep around. If you want to have MFI on a car from the period that either did not come with MFI or had the MFI system replaced, it is great if you want to go (back) to MFI.

As I said previously, if I had a pre-1974 911, I would certainly strongly entertain MFI if the car did not already have it and would certainly have it on a car that came with it. MFI is certainly the best of the induction systems available in the long hood era.

[Jeff Higgins]

Originally Posted by David 23

I was initially very interested in the topic of this thread, and looking forward to hearing an intelligent and thoughtful discussion about the differences between EFI and MFI. I have a hot rod 3.2 SS with EFI, and have been seriously considering MFI in another car. This could have been informative and interesting to me personally. As it turned out, I've wasted a bunch of time reading posts from some individuals that have not been constructive nor on point, consequently stirring up petty arguments and "positioning" rather than thoughtful insight. Disappointing in the least.

If you stop reading at about the end of the first page you will find some useful comparisons.

Both MFI and EFI/ITB systems control intake air flow via individual throttle plates that are placed very low over the tops of the intake ports, pretty much like carburetors. Later Porsche induction systems utilize a single large throttle plate much further away from the intake ports, with a large plenum, of manifold, through which the air must travel before reaching the intake ports. This in itself is responsible for some of the throttle "lag" felt in these later systems.

The basic difference between MFI and EFI/ITB systems is in the fuel delivery. Both inject fuel in a timed pulse that coincides with the opening of the intake valve, so they are similar in that respect. But that is where the similarities end.

EFI injectors are typically located in the throttle bodies, either immediately above or below the throttle plates themselves. MFI injectors are installed in the cylinder head, right into the intake port itself. They are positioned in such a way as to actually spray the fuel directly into the cylinder, past the open intake valve. The functional difference is that with the higher position of the injectors found in EFI systems, they are reliant upon the incoming air flow to kind of "carry" the fuel into the cylinder, where with MFI that fuel is being sprayed directly into the cylinder, with no need for the incoming air to drag it along with it.

Injector opening pressure is a good deal higher with MFI as well. Most EFI systems only run at 30-40 PSI, where MFI runs at about 230 PSI. This substantially higher pressure results in far greater atomization of the incoming fuel charge, exposing a good deal more of its surface area (via the larger number of smaller droplets). It's a much finer "mist", in other words, thereby promoting more efficient burning. We can actually take advantage of this and get away with slightly richer A/F ratios with MFI than we can with other systems, while still seeing complete combustion. More fuel, more power...

Changes in fuel delivery requirements (with increasing or decreasing throttle plate openings) are handled differently as well. EFI measures input parameters such as throttle opening, RPM, etc. and its programming then determines how much more (or less) fuel is required. It does this very, very quickly, receiving thousands of inputs per second, and as a result responds very quickly. MFI increases (or decreases) fuel delivery through a simple mechanical connection, that is moving along with the throttle plates, at precisely the same time.

In summary, EFI introduces fuel much higher up in the air flow, at much lower pressure, and depends upon that air flow to get that fuel into the cylinders, but only after reading a variety of electronic input parameters to determine how much. It relies upon that turbulent intake "rush" of air to help atomize this low pressure fuel delivery during its journey into the cylinders. MFI introduces fuel directly past the intake valve and into the cylinder, thoroughly atomizing it through its 230 PSI operating pressure, and it has no parameters to read prior to determining how much.

In the end, however, MFI is very "rude and crude" compared to EFI. Because it lacks any sort of sensory loop, it has nowhere near the "fidelity" of EFI. In other words, A/F ratios vary a good deal more with MFI than with EFI. As a result, it will get notably less gas mileage, and it will always smell "rich". MFI will, however, provide more power through its inherently superior atomization. It will also provide better throttle response both by introducing the fuel directly into the cylinders rather than relying upon intake air to bring it along, and by virtue of the immediate, direct mechanical control over delivery quantity.

[Superman]

Originally Posted by winders

...EFI is easier to tune....

EFI is great for the laptop crowd. Enjoy your EFI. As Jeff has said repeatedly, EFI is superior on many levels. Certainly not throttle response however. As Jeff explains, repeatedly, MFI beats EFI for throttle response in two ways. First, for those who have experienced it, it just feels different. We have all driven tons of DFI cars. Meh. I started this thread because MFI just feels WAY different.

And also, EFI uses processes which take time, even if just milliseconds which MFI does not. Further, with MFI, better-atomized fuel is injected directly onto the back of the open intake valve. EFI lacks this too.

Look it up. On your laptop.

[RDM]

Originally Posted by Jeff Higgins

Both MFI and EFI/ITB systems...

I, for one, can't wait to read why you are wrong!

Thank you for this very clear summary. I enjoyed reading it.

Whoever mentioned Last Word-ism on Pelican was dead on. Here it comes.