1977 Porsche 924 EFI conversion

[Crazy Striker]

Hi folks,

Just remembered I forgot to make a forum thread for the build, so here it is.

Last December I bought a 1977 Porsche 924 from my grandma's brother. The body is in pretty good shape for a 924, with a rust free battery compartment and only a hole on the floor on passenger foot well.


Engine was turning by hand after putting a bit of diesel in it so no big deal on this side. Fuel pump was dead (gasoline sitting in it), fuel tank was really rusty, and CIS was stuck. After changing fuel pump and dismantling CIS distributor it was working but was leaking so I gave up on CIS System and decided to go EFI ASAP.

I started by removing all the CIS shit to save space and weight.


I cleaned up fuel tank by removing fuel (40L of 10yo stinky fuel) and loose rust. Then filled with 3L of hydrochloric acid to remove heavy rust. Then cleaned and passed phosphoric acid inside and out, and finally painted the outside out. I replaced all fuel tank rubber parts (filler neck, breather and overpressure).

I then redrilled injector holes to 16mm to fit MX5/RX8 denso injectors.

I made custom fuel rail using cheap 330mm extrusion from AliExpress. First iteration was shit, second was better but leaking and the third one did the trick. I used 1/2" NPTF taps on both side for feed and bleed, 11mm holes for injectors, and an extra 1/8 npt for a fuel pressure sensor. Bleed is a Schrader valve.

For fuel lines I replaced steel hard Lines with a single nylon line from fuel pump, using a filter/regulator module from VW, and placing a GM flex fuel sensor inline with the fuel rail. The system is now returnless 4 bars unreferenced.

For wiring the whole EFI harness is custom made from 0.5/1.0/2.5/4mm² wire, AMPSEAL 16 connectors and lots of textile tape. Fuel pump wiring is now taken directly to battery through a relay and 4mm² wire.

Ignition is handled by 4 LS truck coils from Maxpeeding (good Chinese stuff). Injectors are yellow RX8 (420cc@3 bars) for now.
Crank sensor is cherry GS hall sensor on custom bracket, aired at a custom laser cut trigger wheel which bolts behind damper.
Soon I'll install a cam sensor using the same kind of setup.

Map/IAT sensor is 3 bar Tmap, bolted into OEM manifold. CLT is GM closed element.

Throttle body is a VDO unit from BMW E46, and pedal sensor is from a Citroen Xantia, currently not working.

ECU is a v0.3 #rusEFI Proteus, without enclosure for now waiting for 3d printed one.

For now this post is a bit a mess, trying to capitalize and keep photos from disappearing from my phone. I'll try to sort it up and place pictures at the right place.

Cheers,

Gwendal

[Crazy Striker]

Here are more pics

[klthr84]

Hi Crazy Striker,

Nice job! I'm also looking for fixing my 924 (ignition and fuel distribution issues) by replacing the K-jetronic (beautiful but obsolete). Your project is a welcome example for mine. Did you already start the engine? I have plenty of questions to ask to you!

- <<I then redrilled injector holes to 16mm to fit MX5/RX8 denso injectors>> Did you drill the culasse in order to dispose your new injectors? x_x
- Are the injector not oversized? I thougt 205 to 240cc/min would be more adapted than 420.
- what is the diameter of your nylon line?
- I planned to use a microRusEFI. Did you pointed out an advantage in the Proteus?

Good luck
PS: I'm french too