Advice on EFI injector to replace MFI

Fdalgas911T · 02-19-2006, 08:23 AM

I am rebuilding/upgrading my 72 2.4L 911T to a 2.7L 9.3:1 with Mahle 90mm Nikasil cylinders and pistons and modified S dc40 camshafts from camgrinder. I am also removing the MFI unit and replacing it with EFI using the same heads. The plan is to use a Motec to control EFI and ignition. I need to purchase EFI injectors and machine the threaded injector holes in the head to fit (see picture).

Which EFI injectors should I use for this? The mechanical injectors (also in picture) seem to be significantly longer than electronic injectors that I am familiar with. I have heard there are a couple of choices for the EFI injectors. One choice being Bosch and the other being some Ford Mustang injectors that are affordable and work well in this application.

I also expect (but don’t know for sure) that the fuel pump feeding the MFI pump is not appropriate for use with the EFI. As such, I also need some suggestions on a good fuel pump for use with the EFI. Do any of you fellow pelicans have any experience on EFI injector choices and fuel pump choice that may be helpful for me?

Lukesportsman · 02-19-2006, 08:30 AM

I don't think you'll want EFI injectors in the heads. Too HOT. I would look at something between the head and throttle body. Traditional EFI injectors are intended to be installed in the manifold and cooler the better.

Don't stop thinking, many have looked into this and some have accomplished it. Some have even installed them above the TB and in the air cleaner.

Lukesportsman · 02-19-2006, 08:32 AM

There are a ton of manufactors and Ford uses the Bosch style. You will need to decide between peak and hold (OEM Porsche low impedence) and the low impedence style like many domestic OEM (Ford) use.

Fdalgas911T · 02-19-2006, 08:50 AM

I am under the impression that there is an injector that has successfully performed in this application (connected to the head below the throttle body). I could be mistaken as I have not actually witnessed such. Is the heat concern you expressed a melting or malfaction of the injector or a vapor lock issue?

304065 · 02-19-2006, 09:21 AM

MFI fuel pressure is 1 bar, relief valve opens at 2 bar. Most EFI run three or four times that, you will need a new pump.

Fdalgas911T · 02-19-2006, 09:55 AM

Thanks John, that confirms it then, I need a new fuel pump. Got any suggestions?

Lukesportsman · 02-19-2006, 12:22 PM

Along with heat (no expert here, just have heard issues) there is an issue with spray in comparing high psi MFI and lower psi EFI. The droplet size and spray patterns are dissimilar. That is the idea behind Jerry Woods installing the injector up in the trumpet so that it would have better time for the fuel to mix. Obviously this is an art to some degree with trade offs. Direct injection seems to be the trend these days much like a diesel so trends are shifting.

I by no means am trying to state that it won't work. I guess I'm simply sharing my concerns as I've thought of this same conversion. Do some searches because his name excludes me right now, but someone on here has done a MFI to EFI conversion.

BoxsterGT · 02-19-2006, 02:12 PM

I am planning a similar conversion.

I will watch this thread with great interest & contribute if I can.

Keep smiling, you own a Porsche.

Len

Nitrometano · Nitrometano's Garage

You can buy a used set of CIS runners and throttle and make a custom intake manifold and fuel rails.

Lukesportsman · 02-20-2006, 03:50 PM

You can also add the CIS to EFI conversion blocks for 930's though the port size might be off outside of custom sizing.

Fdalgas911T · 04-29-2006, 05:28 AM

It has been a couple of months and the longblock is finally together for me (my first). Here is a picture of the challenge. Now which EFI injector will work in those heads? The injector sure needs a long snout and possibly a high tolerance for heat.

BoxsterGT · 04-29-2006, 09:08 AM

Still watching this thread & will contribute when I can.

I have some spacer blocks that were made up to accept Bosch EFI injectors with a fuel rail to hold them in place.

I will try to get some pics posted in a few days.

Cheers,

Len

Fdalgas911T · 04-29-2006, 09:22 AM

It would be great to see those pictures Len. I am starting to look for new throttle bodies but such an option is proving to be expensive! At this moment I am hoping to find a TMW 3003 Throttle body.

Fdalgas911T · 05-19-2006, 07:11 PM

OK, here are a couple of pictures of the progress so far.

SLO-BOB · 05-19-2006, 07:27 PM

subscribing

Shuie · 05-19-2006, 07:31 PM

subscribed also. This is good stuff...

rvanderpyl · rvanderpyl's Garage

Anything furtrher on this? What injectors did you end up using

Fdalgas911T · 07-01-2006, 10:54 AM

Don't have the numbers available on the injectors at the moment but these are the blue top injectors made for the Ford Mustang V8. From the research I have done these are used much in racing applications. All the internet sites list these as no longer available. The guy I bought the fuel rails from had a few new injectors on hand in the shop.

As far as other progress, the wiring harness is almost finished. this includes the sensors for throttle position indicator, barometric pressure sensor, air temperature, injector control and crank position. All this to connect to the Motec control unit.

Makin a little progress all the time.

Chuck Moreland · 07-01-2006, 11:01 AM

Who did you get the rails from? And how did you address the length issue?

Good stuff. Keep at it.

Mr Beau · 07-01-2006, 11:20 AM

What about the spray pattern of the injectors? I looked into a solution like this a while ago, and when I worked out how far back the injector nozzle would be it looked like the injector would spray a large amount onto the MFI-injector-hold-adapter-thingy. Perhaps not a huge deal but not ideal...