924Board.org

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

I'm trying to get an idea of what I'll need to cobble together an EFI for the 931 (although the injector size and tuning is the only difference between EFI for a 931 vs. 924na). This is the list I've come up with-

-fuel rail
-injector inserts
-injectors (~35 lbs/hr for ~200hp ?)
-throttle position switch
-engine coolant temp sensor
-intake air temp sensor
-Megasquirt computer (has built in MAP)

Anything else? The fuel rail and injector inserts are going to be the trickiest parts of course. I was thinking about just using some aluminum stock with the proper tap & die to cut the injector inserts out. Seems simple enough. The easiest route to go may be to use a 951 fuel rail and injectors. The fuel rail could be shortened/lengthened and rewelded to get the size right. And it looks like there may be enough meat on the injector bodies to cut threads into them and just screw them directly into the head (or screw them into injector inserts).

here's what the 951 injector bodies look like-

and here's a 944 fuel rail-

Any thoughts?

-nick

81turbo · Joined: 03 Nov 2002 Posts: 1065 Location: Oakland, CA

The biggest problem with using a 951 fuel rail would be injector spacing. It may take three cuts and re-welds to get it right. At that point it seems much easier to fabricate a new fuel rail. I know that endwrench has already fabricated a fuel rail. Maybe we could get him to do a few more for those of us that are interested when it gets cold there in Montana.

Hugo · Posted: Wed Oct 13, 2004 7:29 am Post subject:

Hey,
I'm working on this right now, and you can't threat the injectors in. you can't turn the injectors around because the connector for the wiring gets in the way. I'm having a friend of mine make inserts for them, to screw into the head. also if you want to place them into the intake, it will be very diffecult. you have to place them at an angle of 45 degrees because otherwise you will spray it directly onto the bottom of the intake. and it will run like c**p. When placing them in an angle you won't be able to place the fuel rail on top because the throttlebody gets in the way. so as i see it you only have the choice to make inserts so they will fit into the head. If anyone has an other solution i would like to hear it.

sandgroper · Joined: 07 Dec 2002 Posts: 108 Location: in limbo

Nick,i reckon go down the junkyard and check out 87-89 pontiac sunbird turbo,its got it all as well as free software available on the net and lots of wisdom avaible from guys using it,i have got 3 of the ecu's and paid 25 each.
When i get all the other crap i have to do done,this is the way i am going,the hp rating of both cars are similar so i reckon plug and play to start with,peak and hold injectors,knock senser,boost control etc,etc its as good as the best aftermarket apart from no anti lag or traction control.

simsport · Joined: 06 Nov 2002 Posts: 573 Location: UK Warrington

The Webber Alpha kits come with separate mounts for each injector. This makes it easy to fit the injectors to any car. I use them for my bosch injectors with no problems. They cost very little and with a few feet of hose and a few clips, bingo!
Simon
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Blown is always best!

wdb · Joined: 02 Nov 2002 Posts: 2024

924 turbo · Posted: Wed Oct 13, 2004 12:02 pm Post subject:

Let me take a picture of the fuel rail I picked up at a junkyard for you. I believe it was from a '90s Neon, but I'm not sure if it was a SOHC or a DOHC, or if that even matters. It's only off a few millimeters over the spacing of all four injectors, so I'm confident that it will fit.

My digital camera battery is charging as we speak. I'll try to get a picture later tonight.

I'm also planning on using the Megasquirt system, so maybe we can work together, Nick.
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Jon Furst

Lizard · Posted: Wed Oct 13, 2004 12:17 pm Post subject:

why not go mega ultra squirt and have sequential EFI and have it control timing with a knock sensor.
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3 928s,

924 turbo · Posted: Wed Oct 13, 2004 1:22 pm Post subject:

As promised, some pictures. I don't have any EFI injectors yet, so I can't do a test fit. These are shots with the stock injectors screwed in a bit. They're not perfectly centered, but I figured that I could just cut the holes in the bosses slightly offset to compensate.

http://members.rennlist.com/jonf/rail1.jpg

http://members.rennlist.com/jonf/rail2.jpg
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Jon Furst

924 turbo · Posted: Wed Oct 13, 2004 1:31 pm Post subject:

As far as ultramegasquirt goes, it's certainly a possibility. I'm not convinced that an add-on knock sensor would be very effective since there are serious placement and tuning issues involved. Without the opportunity to bench test the sensor in conditions where detonation can be controlled and studied, chances are that it will either pull way too much timing out or not be effective in detecting knock versus the normal clacking of the engine. The 924 is a pretty buzzy engine anyway, which would really only serve to make the knock sensor even less effective.
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Jon Furst

Lizard · Posted: Wed Oct 13, 2004 1:34 pm Post subject:

in regards to the knock sensor as long as it was placed properly it should pick up only the correct noises needed
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3 928s,

Min · Posted: Wed Oct 13, 2004 2:15 pm Post subject:

apparently megasquirtn'spark (which is also megasquirtn'edis if you use that configuration) has knock sensing

http://www.jsm-net.demon.co.uk/msns-extra/index.html

you will have to splice in extra inputs for things such as water injection control and knock sensing, and may need to build extra circuity for that, but its the sort of thing you can add after you've completed the base system and have it running.

Min · Posted: Wed Oct 13, 2004 2:23 pm Post subject:

this topic has some pictures of endwrench's megasquirt system.

http://www.924board.org/viewtopic.php?t=12020&postdays=0&postorder=asc&start=0

kidporsche · Posted: Wed Oct 13, 2004 10:01 pm Post subject:

I wouldn't waste my time with a knock sensor, they add too many hassels. Just take the time to properly tune your system on the dyno in the first place.
You can get away without a TPS and intake temp sensor if you are using a MAP sensor, but it depends on what you want to do. A MAP sensor should be sufficient for accel enrichment, but I guess if you're in Mass temp compensation might be useful. I've never been bothered with it myself, but my experience is with bike engines in open wheel cars.
Have you considered a wide-band lambda sensor(s) and/or exhaust temp sensor(s)? One for each cylinder is very useful for troubleshooting (although it gets more expensive and complicated).
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Chris
1981 924 - RoW (Australian) spec

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Yeah, I've kind of given up on the knock sensor idea. They have to be matched to the engine being used and still they can be tricked into thinking usual engine rattles are detonation without much work, or they just don't pick up on detonation that is really happening. I found an article on how to build a stethoscope to place in the engine bay and listen from the passenger seat for detonation. This method picked up clear detonation that an expensive knock sensor didn't. Case closed in my opinion.

I' m still figuring out how all this EFI stuff works together. Wide-band o2 has crossed my mind a few times now. I'll put it on the list of things to look into.

Sequential injector timing doesn't do much outside of low rpm emissions.

924 turbo- I'm excited about this fuel rail you found! Did you determine where it came from? Does it look like there will be any intake manifold interference issues?

-nick