Max flow for MFI injectors?

[Flieger]

If only BP had consulted Bosch

[stownsen914]

Originally Posted by jcge

Injector maximum flow...

The MFI injector will deliver whatever the MFI pump FORCES through it. Do not confuse its operation with an EFI injector where pulse width determines fuel delivery. Metering is acomplished by the MFI pump plunger assy. The injector is just an atomising assembly.

Assuming you could "overload" the injector....it would still deliver what was being forced through it, just the pintle no longer chatters on its seat and remains constantly open, and atomisation suffers. Your next point of concern would be pintle "choking" resulting in enormous line pressures and the resulting mechanical failure (rupture) of a line, fitting, pump barell, pump cam etc.


The difference between the Mercedes Benz/ Aston Martin and Porsche injectors....

Early Mercedes (and Aston Martin DBS V8) injectors (DC 8 C 45 R1) used a 1.8mm pintle - these were superceded by DC 8 C 45 R2 which used a 1.2mm pintle (the same pintle as the Porsche EP/DCC 45 R3 ) The body lengths of the MB/AM injectors are shorter than the Porsche injector, and they also use a M14x1.5 mounting thread instead of the M12x1.5 of the Porsche injectors.

The AM DBS V8 is 5.34 liters......667cc per cylinder....equate that to 6 cylinders and you get 4.0 liters.....so you can see that your MFI injectors have ample headroom for your MFI engines (they even have sufficient capacity for your turbo MFI engines ala 935) By headroom, I mean the pintle's capacity to effectively atomise at the requisite rate of fuel delivery.

Thank you for this information. Do the standard Porsche MFI injectors really have capacity to feed a MFI 935 motor? I don't need that much capacity, but am considering converting a ex-GTU 911 race car from carbs to MFI. To leave a little buffer, I'd like to have injectors capable of feeding 400 hp. Will stock injectors safely allow for that?

Scott

[BigD9146gt]

Originally Posted by stownsen914

... I'd like to have injectors capable of feeding 400 hp. Will stock injectors safely allow for that?

Scott

After talking to a handful or so of the most respected engine builders on the west coast, the answer is yes. They have been proven to support motors making upward 500-600hp without there being any issue.

[kenikh]

I offer this information regarding turbo MFI applications:

Smaller stem valves for 46/40 heads?

Read the posts by aws on his past MFI turbo project.

[Flieger]

Porsche 934.5 Racecar - a set on Flickr




Make sure you get a turbo boost pressure compensator.

[jcge]

Originally Posted by stownsen914

Thank you for this information. Do the standard Porsche MFI injectors really have capacity to feed a MFI 935 motor? I don't need that much capacity, but am considering converting a ex-GTU 911 race car from carbs to MFI. To leave a little buffer, I'd like to have injectors capable of feeding 400 hp. Will stock injectors safely allow for that?

Scott

You have a lot of work ahead of you if you want to go from carbs to 400hp MFI...I think fuel metering will be your primary concern, and injector capacity way way down the list.

Steve Weiner reports a 3.0RSR "24 hour motor" delivering over 400hp - you might want to give him a call.

[kenikh]

Before considering an MFI turbo, consider the following nuggets of experience which dissuaded me:

Originally Posted by aws

The diaphragm I used to run the mixture rich on the MFI had too much travel to adjust the mixture correctly. The Buick set up (programmable sequential EFI) is when it came alive, which made me realize that with true programmable fuel injection I was going to be able make serious horsepower. After the frustration of the MFI system I would never use anything but the modern programmable fuel injection.

aws

[stownsen914]

Don't worry guys - I'm not doing an MFI turbo! I don't need that frustration!

I was just wondering if stock MFI injectors would handle 400 hp so I can safely use them on a 350+hp race engine, with a bit of buffer to be safe. Sounds like that's a go ...

Scott