Well... Yes and no. The DFI system that I originally referred to from the 1952 Mercedes 300SL is essentially the same as the 911's MFI system -- the major difference is where the injectors are located and the arrangement of the pistons in the pump. The Mercedes pump is all in a row like the racing MFI systems from Porsche/Bosch, while the 911 pumps have 2 rows of 3 pistons -- I suspect for easier packaging.

https://cdn-5cc09704f911c81690a153f8...1-1024x913.jpg

I was referring to modern DI systems that aren't bulit using World War II aircraft engine technology.

MFI is by no means as "direct" as modern direct injection, which places the injector right into the combustion chamber. MFI is, however, far more direct than modern EFI/ITB systems that house the injectors up in the throttle bodies. The MFI injector is indeed screwed into the intake port, but it is low enough and positioned in such a way as to at least partly spray right past the open intake valve and directly into the combustion chamber. Granted, the intake valve cannot be made to get completely out of the way, so some of the fuel will be hitting the back of it - but the back of that open valve is already down in the combustion chamber. So, really, technically all of the fuel spray from the MFI injector is introduced at 230+ PSI directly into the combustion chamber. No modern EFI/ITB system, short of direct injection, can match that. Nor the resultant throttle response and power.

Note the location and angle of the injector - "5 Injection valve (nozzle)":

http://forums.pelicanparts.com/uploa...1631137318.jpg

I think he meant that di uses the cam to drive a pump just like the mfi.
I have an mfi that i wanted to learn about and they are works of art, never to be duplicated. The mfi pumps are analog computers with the throttle plates, stylus, the 3d space cam, flywheel, rack and screw plungers, injectors and rpm transducer working in concert like an induction symphony conducted by some invisible smiling maestro, but they are not better than efi

The injectors of my "direct to head" AT Power ITBs inject right into back the intake valve too so they technically spray all of the fuel into the combustion chamber just like MFI. My system is only running at 45 psi with much more modern Injector Dynamics ID1050x injectors.

Because of the 964/993 head design, the location of the MFI injectors is not all that much different than the injector location on the AT Power ITBs. See here:

http://forums.pelicanparts.com/uploa...1631142019.JPG

In fact, companies make MFI injector adaptors for 3.2/3.6 heads that put the MFI injectors in just about the same place and angle as the AT Power ITBs put their injectors.

The injector is quite close to the head and aims at the valve stem as it meets the valve head. It sprays into the head at the same perspective/angle of the lens. The injector is a lot closer to the head though.

The only thing MFI has going for it, besides nostalgia and period correctness, is the in the injector pressure. I could actually run about 100 psi with my injectors...but it just doesn't make enough of a difference to do it.

http://forums.pelicanparts.com/uploa...1631145231.png

It's a great system, I'm sure. Still, the injectors are at least twice as far away from the intake valve (possibly three times), and operate at less than 20% of the pressure of MFI. I guess those compromises are "good enough" for those willing to settle for less. :D

Mfi Myth
 

Well,I love the hype about the butt dyno torque.In reality it is a DIRTY inefficente system.In the North East town of Far Hills NJ.A number of people who bought their cars at Gardner Porsche-Audi Had serious problems.There were no less than 15 new 911 cars driven to the train station for there commute to NYC.The issue was the majority drove only 3-10 miles to get there.They only ran rich and every part suffered wear.Timing chains stretched at 30k.P&C by same mileage.They never burnt oil beacause the crankcase was refilled by gasoline from running in the rich circuit.Great system in CALI.But when it is 10 degrees in NJ.the poor car just runs rich and washes everything in raw fuel. A little education from The Fartherland would have helped.I have 2006 v10 Touareg tdi.It takes about 8-12 miles to get the 14.5 qts. of oil to 200 degrees.They recommend not to boost it before then.I love MFI cars.In the mid 70,s I bought Hi Butterfly RSR stacks for 2.8 cars for about $600 for a pair from Vasek Polak.A new 2.8 or 3.0 RSR pump was about $850.This was not a negative thread but just a reality reference.Just go with EFI.If you want a system that crosses the T,s and dots the I,s just by a MOtec System.Pay to have it set up and most likely never touch it again.The other ones are made for people who are masochistic by nature.Which means they will suffer a great amount to save a few dollars.Usually about 2-4k money.Thanks for reading.Ciao Fred

Seriously? The injector is 16.6mm from the mounting surface on the head. From the top of the head to the valve stem where it meets the valve head is another 66.6mm. So the inject or is 83.2mm from the valve stem where it meets the valve head.

The 3.2 and 3.6 heads have a lot less material on the intake mounting boss. Most of the material where the MFI injectors screwed in is not there.

You think the MFI injector is 27.7mm to 41.6mm from where the valve stem meets the valve head? I suggest you measure that.....

As far as compromises go, the MFI system is a cornucopia of compromises compared to a modern EFI/ITB setup. Again, the ONLY technical advantage the MFI system has is the injector pressure and we don't even know how much of an advantage that is because it is based on 60 + years old technology.

The sprint version of the 3.0L RSR, in its most radical form, engine made 345HP. That's 115 hp per liter. If MFI is so great at making power, how come it does not beat EFI/ITBs in power output?

Nah. I was just trying to get people worked up. Not that they need any help of course, but it seemed to have worked. SmileWavy

I'm probably just giddy from the fumes. Spent all day farting around with the MFI pump and grinding my space cam. Good times.

Never.

50 year old technology that only falls four horsepower per liter short of your modern day best efforts. Factor in camshaft profiles, port shapes, exhaust extraction, reductions in reciprocating mass, materials technologies, and a myriad of other improvements that Porsche engineers made over the course of that 50 years, and it would appear you have nothing to brag about. Much to be ashamed about, actually, now that I think about it. Only four horsepower per liter gained over 50 years. It appears you cannot write checks fast enough to pull ahead by any meaningful margin.

Too funny. You do realize that the bigger you go in displacement the harder it is to keep that high HP per liter number.

The Bosch MFI system is probably really 70 year old technology.....

Lighter weight materials helps with longevity, not peak power. Better materials help with longevity but not power. The RSR revved to 8000 RPM....my engine revs to 8000 RPM but makes peak power at 7300 RPM.

My 3.6L has a much flatter torque curve than the 3.0L RSR. With the same power curve as the RSR, I could probably get another 30 HP. But, I worry more about getting around the race track faster than I do peak power. My engine makes 94.8 ft-lbs of torque per liter. The RSR only makes 78 ft-lbs per liter...

Finally, 5 HP per liter more is no small amount when you get to 115 HP per liter......

Yet another thread going down the porcelain fixture....

Carry on

If the distance between the injector tip and the intake valve was worth that much, the CIS cars must be real rocket ships with instant throttle response!

That's a good observation, really. It serves to point to the differences between MFI and its successor, CIS. CIS is, in its essence, still a "mechanical" injection system. Its injectors are indeed very well located, pretty similarly to MFI.

Where CIS falls short, however, is in how it feeds fuel through those injectors. The fuel is not timed to the intake valve opening - it sprays all the time, on all cylinders. It actually puddles on the back of that closed intake valve. The only thing that gets it into the cylinder is that rush of air, that "pop" as the intake valve opens. And it is anything but atomized by then.

If you look at the top of a CIS piston, it has a very unusual shape. It does not match the shape of the combustion chamber. That shape is meant to induce a "swirl" affect, to cause turbulence upon commencement of the compression stroke. All in an effort to "stir things up" and atomize that puddled fuel.

How and where CIS introduces air is markedly different as well. It was the first of the single throttle plate, common plenum designs that Porsche introduced. That throttle plate is a loooong ways away from the intake ports, and a rather large volume of air needs to get moving before the intake valve "sees" it.

So, really, it's more than just one thing. While CIS had pretty ideal injector placement, there are simply too many compromises elsewhere. MFI does not have those compromises, with each component being much better optimized. Viewed individually, each one may not account for any great gains, but when combined as a whole, we see that old adage wherein "the whole is greater than the sum of the parts". It's not any one thing that provides MFI's superior throttle response and power - it's many little things working together.

I have serious doubts that injector tip distance to the intake valve is worth that much.

Regarding fast throttle response, engine torque is not going to be produced until the combustion stroke so the only thing you need for fast engine response is to make sure that the cylinder gulps all necessary fuel during the intake stroke.

Is the fuel mixture better in MFI? I guess specific torque figures would tell us that but I don't think it has anything to do with good throttle response.

The video below shows the injectors of a 300 hp/liter normally aspirated F1 engine. Injectors are far from the heads. Do you reckon that's due to regulations or is it a technical choice?
https://www.youtube.com/watch?v=9kX8asluuNg

Excluding GDI, mounting the injector as high as physically possible produces the most horsepower. Without exception. Some of us have actually tried these things on the dyno. Mind you, I'm not talking about driveability, fuel economy, emissions, or any number of other conditions, but raw horsepower and torque.

With respect to GDI, I can chat with some of my oem combustion engineers about it and find out more, but it's not really high on my priority list, and certainly not germane to this discussion.

Yes, those injectors are quite far from the heads. However, most (all?) of those glorious V-10's ran two sets of injectors for each cylinder. The second one was down in the intake port. Same with the 2.4 liter V-8's that replaced them. And, actually, many engines prior to the V-10 era ran multiple injectors as well. Again, as stated earlier, there are many reasons for having injectors that high up, with intake charge cooling being one of the very important ones.

At the dawn of the current turbo hybrid era, the FIA began to specify only one injector per cylinder, that being a direct injection type. Intercoolers now cool that intake charge.

High Injectors
 

My 88 Imsa GTU 911 ran a set of Slide Valve stacks that were 45mm and the injectors were in the top of the stack spraying in at at a 45 degree angle.I carried 2 fire bottles.It was 66 stroke with 100mm bore.I was always afraid of the backfire.It was the ex Dennis Aase car that won the GTU Championship in 1987.The car had been acid dipped twice.Now owned by Scott Townsend from this forum.Scotts Mom BOUGHT THIS car from me for her husbands birthday way back.Cool car with upside down 915 box.The fire bottle was empty and the needle stuck on full.I think the Cali boys came to race.I always liked the Aase boys.Dennis was a great driver.I bought a NOS set of Factory RSR heads from Dennis in the mid 90,s for $2500.I bought an NOS unstamped case for $2500 at the same time.Thanks for reading.Ciao

When you watch videos like this, I see why!!!

https://youtu.be/u_E14RKskbM

With the risk of throttle slides sticking and the fire breathing backfires, it must have been quite an experience driving that car!