924Board.org

[Cedric]

Ive driven a bunch of these in all sorts and shapes and injection/ignition systems (havent driven a carbed 924 yet though), and other similar cars. My conclusion is that if you have a perfectly working Kjet you wont notice any difference in driveability with EFI, at least in Euro spec, never driven any US spec stuff(might be more strangled in std form). Though its not always easy to get to that point with crusty old parts, and if you dont have the skillset or patience it can get quite costly, so going EFI makes a lot of sense when trying to get some old crappy car to work, or going to do serious mods (especially with boost), big tweaking of kjet is not for everyone for sure, but a lot of things are possible if you really want to open that door

My Kjet has served me well over two decades, and seems fine up to what should be approx 240ish hp. If i want more power in the future or everything craps out i will probably get Ciprians system in there The thing im most bothered with is not having control of the ignition system, the DITC does stuff by itself and its hard to observe.

I remember back in the youth days I daily drove a 924 all year around. The heater was really struggling at -20degC, took ages to clear it out. Though it was a hoot to slide in the snow on narrow winter tyres..
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1980 924 Turbo
www.instagram.com/garagecedric/

[morghen]

The old cis has served us well for decades but fewer cars stay running as they should every year and less people really know and have the proper tools to sort out cis properly.
EFI is a necessary thing sooner or later for all our cars.

Buying a bolt-on, already tuned and ready to drive EFI kit from me is always an alternative. You can play lego with the kit, and pick up an already running “game” where if you wish you can fine detail tune it for your specific engine or you can just drive it as is as the tunes have evolved and been improved by people like Vaughan for the 931 and some general aspects that apply to the NA as well.
The upside of this kit, appart from being pretty straightforward to install, is the fact that you still use some of the CIS parts and the engine bay looks nearly identical to the original.
If you go Microsquirt or something else, the engine bay will look totally different from the original. To me thats an important aspect, i dont like seeing modern stuff like fuel rails and other modern arangements in the 924 engine bay.
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Supercharger and EFI kits
https://www.the924.com

[Raize]

[safe]

I bought a 931 8 years ago, it ran fine apparently at least.

It needed some, quite a lot, of restoration. I'm now trying to move it to another garage on by its own power.
I tried getting it started on the k-jet, that was a dead end. Piston stuck to the level of using a hammer to get it out.
Then I borrowed another fuel distributor, didn't work... now the WUR was acting up control pressure showed 0 psi all the time, it worked before I changed FD.
The air meter plate would not move, later found out the hose between the turbo and air meter was cracked (disintegrated to be fair).

I really think the k-jet is ingenious, for its time, and as long as its being used it chugs along pretty good. But getting a system working after its been of the road for a long time.
Yeah, that can be challenging. The parts are not cheap, if you need to pay someone to fix it, its going to be expensive and probably not be good anyway.

I'm fitting Ciprians system on it right now. Its going a bit slow, which is my fault not having enough time and also needing to fix other stuff on the car (changing clutch master cylinder is not something I would like to do again).

I got it started for a few seconds the other day, but it ran crap because I forgot to fix a few vacuum leaks... Rectifying that this weekend hopefully.

Just need to weld up holes in the roof (antenna) and the fenders (indicators and rust) and then i can drive.....out of the garage onto a trailer....
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

[Beartooth]

It's such an irony that my position ten years ago leaned towards ditching K/KE-jet when I had the time and money to switch to EFI. Now, however, I have no plans to retrofit any of my three K/KE-jet engines. On my 560SEL, I plan to swap an M104 I have access to, and the first move will be to take that M117 apart and see if I can get the cams re-ground. port the heads, maybe upgrade the valves (although possibly just the intake - the exhaust valves are sodium-filled and would probably be a big benefit in a turbocharged application) - mostly with the goal of pushing past 300HP in my 560SEC. Down the road, I want to turbocharge the now-spare M117, keeping KE-jet, but probably using FrankenCIS to give me control over it. I don't remember the exact numbers, but >500HP comes to mind for how much HP/fuel output the 8-port FD will support.

I'm not sure if I've just been lucky or too hard-headed to give up, but I didn't find getting my car going to be that bad, and I had a worst-case scenario: whoever last owned the car had something go wrong they were trying to fix (might have had something to do with the bodged turbo), and had left the line at the fuel filter un-done. As a result, the gas had all evaporated, leaving a film everywhere and a stuck fuel plunger. Leaving out the fuel pump, filter, and some random bits, the only injection-related cost to get it running was $100ish for a FD rebuild kit. Original injectors, WUR, fuel lines, frequency valve, cold start valve, electrical components, yada yada yada. It took some time to figure out the nuances, but someone comfortable with the system probably could have got the injection issues sorted out in a day. Now, it did throw me for a loop because it took a couple cycles of removing and cleaning the WUR - it ran well for a bit, then didn't want to run right. I discovered the control pressure was jumping - turns out it was crud breaking free and blocking the screen in the WUR. The only other big problem initially was that the frequency valve wasn't getting a signal: maybe a bad ground or something.

I'd think one liability is the ancient control units, but mine works fine. A microsquirt can replace that, gives you tuning capability, and ignition options. I wish @Fasteddie was around - I know he's done the Microsquirt setup that I'm talking about, and for @Cedric, it sounds like that would give you everything you want: fuel control, ignition timing, ability to run coil packs, etc. And for $325 (plus $25-50, depending on harness options). If you're happy with the basic function of your K-jet setup but want more power and tuning options, I don't know what you'd gain choosing EFI that would be worth the cost, unless you've got a big budget.

I don't know of any part that's NLA or can't be rebuilt. That could change, but the good news is, not much is actually bespoke to the 924, and there are plenty of high-dollar collector cars (911s obviously, but also Ferraris) that share components. Obviously, it's not as future-proof as EFI, but hardly a reason to abandon K-jet until it's legitimately difficult to get needed replacement parts.

Now, I'm not arguing there's no advantage to EFI - not even over a properly-sorted K-jet system. On a 931 in particular, someone unfamiliar with the system is likely to develop a problem over time that could shell out a motor. My experience mirror's @Cedrics: K-jet works as well for me as EFI would. Probably a REALLY GOOD setup (like Crispain's, given the reports - and installed by someone of his skill) will have some noticeable improvements side-by-side, but K-jet is pretty amazing for being so archaic. Another aspect is HP headroom - you'll hit a wall at some point with K-jet; for me, all I "need" is a solid 200HP, and it seems that's well covered. But EFI has it's pitfalls too - mostly in that how well it works depends on the quality of the kit, the install, and the tune. K-jet will probably have some noticeable idiosyncrasies, but the only big one I've got is hot starts - and I'm sure that's partly leaky injectors. Otherwise, even with a very tired engine, it always starts (minus the stupid fuel pump power supply issues), and driveability is pretty good. The transmission is much more of a problem than K-jet.

Finally, I just have to mention I've worked on several Ford products. My current Fords: a '64 Fairlane (first car - put 75,000 miles on it), my tough as nails '97 F250 Powerstroke, and I'm currently working on getting a salvage auction '94 Explorer going. In the family, that I've wrenched on to some degree, are a '62 F100, a '90 E150, an '89 Aerostar (the only one I'd say definitely avoid), and an '03 F250 6.0 Powerstroke (not as trouble-free as my 7.3, but it's got over 400,000 miles on it). No, I don't do it for a living, so I can choose the better ones, but I the other two of the big three have laid plenty of eggs. I can also point to solid vehicles from all three - nothing to compare to the quality of pre-90ish Mercedes, but you did have to pay good money to get that.
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1980 931 diamond in the rough

[Beartooth]

Well, I recently had another break-down (just a no-start situation at home). I'd noticed some cracking on the boot between the air box and the turbo, but it wasn't misbehaving in particular and I thought I could just get to it at my leisure. After first suspecting the fuel pump or relay, then eliminating that variable, I decided to fix what I knew was broken.



The cracking was worse than I initially saw - two areas where it's cracked through. That could enough cause enough of an air leak to be trouble, especially at idle and low throttle. It seems these are wildly NLA, unfortunately. Even if that weren't the case, I figure it's worth a try to fix it, so I pulled out some epoxy.



I of course scrubbed it with the strongest de-greaser I could find, and flushed it out with brake cleaner, then blew it out with compressed air. That epoxy should stick better than glue to anything that's NOT oily... Now I just hope the rubber isn't too impregnated with oil. I also wonder how the epoxy stands up to oil - there's plenty of oil coating the inside of the intake track, so if it can't take it, I'll find out sooner rather than later. It took some cranking to start; I think the plugs were getting a little oil fowled, but I'm not sure. It seems pretty clear that the reason for the no-start was it was leaking enough air that it wasn't moving the plate enough to get any significant fuel flow. This was a "cold" start on a warm day - I think another part of the equation is that for a while it's always been cold enough to trigger the cold start valve. Cold starts have not been a problem, but warm ones have been pretty bad. I can't say I've noticed much worse just recently: they've just been bad for a while, so maybe this will help with that.

On another note, this arrived in the mail:



That would be the fuel distributor and air flow meter assembly off a 2.2L Mercedes M102. KE-jet, or CIS-E as Mercedes prefers. The good news is, it looks like it'll physically fit without too much trouble. One of the mounting flanges will have to be cut off, most likely, but the inlet is exactly the same size, so it'll play easily with the original air cleaner assembly and boot (although, like the turbo boot, that's seen better days and is NLA...). I had wondered if maybe I could just put the top half on the lower half of the 931 box, but the bolt pattern and shape have significant differences. Anything's possible, but that seems like the more extreme measure unless I run into real issues. The plate itself is slightly larger.

I need to get my hands on some surplus KE-jet fuel lines next, and a Microsquirt. I'm reading that with the injector outputs can be programmed to control the EHA - you just need a resistor or two to get the power applied to the EHA down in the 100 milliamp range (maximum - it's usually much lower). I'm not sure what FrankenCIS's interface does, but from what I'm reading, it's nothing elaborate. I wish FastEddie313 was on - I know he's done some pretty impressive stuff, using a V8 KE-jet FD. That's probably overkill for what I have in mind. I've heard the V8 FDs will flow enough for 500 HP easily (and that may be without even pushing the control pressure down more aggressively than stock).

Rather than use an expensive (new anyway), fixed-pressure OE fuel pressure regulator, my thought would be to use an aftermarket rising rate FPR (using a one-way valve and bleed to ensure it only "sees" boost - since K(E)-jet fuel pressures aren't referenced to manifold pressure). I may be in highly experimental territory since I don't know of a boosted factory KE-jet application. I'd hope a one-to-one rise in fuel pressure would give somewhat adequate boost enrichment just so there's kind of a fail safe. But that's something I'll have to experiment carefully with.

Ultimately, I want to keep K-jet but have the most modern version and full control over it. I'd also like to incorporate the air shrouded setup, but that could be a big challenge and maybe require machining. Obviously, there are plenty of ways this could go wrong, but now's the time to do it, risking a dodgy engine in need of a rebuild instead of trying to do it after it's rebuilt. It's going to be another steep learning curve, I think, but it'll help in other areas since I can apply what I learn to my Mercedes, and I have thoughts of a boosted M117, or M119. I don't foresee pushing 800 HP (along the lines of the C9), but I've got to wonder how much that forged bottom end can take. Going back to the 931, I've got 250 HP as my vague target. That's probably a "I won't be happy until I hit that" figure, but it should be possible, and maybe a lot more. Obviously there are a lot more supporting mods before I start pushing anywhere near that. The goal for now is just to make it work right at stock power levels.
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1980 931 diamond in the rough

[safe]

You can use a 60 mm ( 2,375´´) 25 degree silicon bend.

I did on mine.
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe