limitation of type 1 fuel injection system.

[theKbStockpiler]

I'm planning on using a pair of 1975 beetle fuel injector end manifolds for a cheap DIY fuel system. I'm going to cut the Y off and use individual runners but the IRs that run down to the heads are quite small. What is a sane expectation with these? Will they go to 5500 rpms with a 1776? What is the peak rpms a stock beetle fuel injection system will reach?

Thanks for your expertise!

[Jadewombat]

The best way to tell is to put those pieces on a flow bench and measure them. If you have stock heads, the IRs should be an OK match up to a point--but yeah they are tiny. I don't think there is a limit to RPMs according to the injection, it's based on air flow and deflection of the AFM flap and does not take into account the RPMs of the distributor or have a rev. limiter.

Your crank is always the limiting factor, most stock cranks are about 4000-4500, counterweights welded on a bit higher, then aftermarket forged cranks can go much higher in RPMs.

[Marc]

If you're planning on using an L-Jet system, be aware that you'll probably need to do some tweaking (but possibly no more than just increasing the tension on the spring in the AFM). The stock system on a 1.8L Bus engine is about done by ~4500RPM, but that's an airflow meter limitation, not due to the cyclic rate of the injectors. L-Jet was used on many other marques besides ACVWs so there are boneyard parts that might work better for you if you find that you need bigger injectors or a different AFM. Nissan used L-Jet on the 240SX, IIRC that was a 2.4L and spun up to 6500 or so.

[theKbStockpiler]

It would be easier to use the beetle end manifolds because the bends around the shroud are done for you. I could use type 3 manifolds but all the curves have to be re-done and then welded back onto the head mount flange. The inside diameter of a carbureted 1.6 end cap at the head flange is 1.2 inches and the same measurement for a fuel injected one is 1.1. I'm going to try a speed density system so a flap style bosche sensor is not going to be used. I thought I read where a german plenum style F.I. was used on a 2.0 liter which boggles my mind with the size of the stock IRs. The plan is to use a 914 1.7 plenum and throttle body.

[Marc]

The 1.7L 914 used D-Jet, not L-Jet. D-Jet requires auxiliary trigger points in the distributor and has two injection events per cycle, each delivering half the fuel needed while L-Jet triggers from the ignition points and has four ¼-sized squirts per cycle. I'm not saying that it can't be done, but I don't know that anyone's ever tried firing L-Jet injectors with a D-Jet system.
If the only thing you'll be using from a FI Type I is the endpieces of the manifold, I guess the question becomes "what's the maximum cyclic rate of a D-Jet injector?" and to be honest I don't know off the top of my head (or if they aren't all the same for that matter). HP peak on a 411 1679cc with D-Jet isn't until 5,000 RPM, though, and they still pull beyond that so 5,500 doesn't sound like it'll be a problem. The endpieces should flow all that a stock head should ever need.

[theKbStockpiler]

I'm just using donor parts from the engine head flange to the throttle body that are vw/porsche. All the sensors ;except for maybe the tps ,will be whatever is easily adaptable to as far as electronically. A GM MAP sensor is far simpler than a ford for example ,jeep tps if I had to. I am however going to build it like a vw/porsche system as in leaving the ignition 'stand alone'.

I guess I will have to look into the design of a stock beetle injector ;if flow up to maybe 5500 rpms is not an issue with the German style F.I. end manifolds ,and design around the injectors.

Thanks for the tips!

[Marc]

Just keep in mind that on a stock L-Jet there are 4 squirts for every cycle, so the injectosr are sized accordingly (small volume per squirt compared to other systems). If your control system will allow programming the pulsewidth to be wide enough to compensate for that, they should work.

[theKbStockpiler]

So L tronic injectors pulse for every crankshaft revelution for each cylinder ,sort of like a batch system right next to the intake valve?

[Marc]

...L-Jet triggers from the ignition points and has four ¼-sized squirts per cycle...

All four injectors fire simultaneously, so for every revolution of the crank each injector fires twice. Only one squirt occurs at each cylinder while it's on the intake stroke, the other three just "pile up" in the port.

Compare to D-Jet, which has a pair of dedicated contacts in the base of the distributor to generate the trigger signal. D-Jet injectors are fired in pairs, so two of the cylinders receive their entire compliment of fuel while on the intake stroke and the two companion cylinders get it early...turns out that it doesn't make much difference except at extremely low RPM so they were able to get away with half the circuitry this way. Each injector fires just once for every cycle (every two revolutions of the crank)...for the same total fuel volume delivered the D-Jet injector opens once compared to four times for the L-Jet.

If you cross the wires on D-Jet injectors you get a rough idle because all of the fuel is injected at the wrong time. On L-Jet it makes no difference since they all fire simultaneously anyway, and due to the smaller squirts at least some of the fuel arrives on time.

[Jadewombat]

With L-jet there is nothing to "chip" or reprogram. L stands for lucht or airflow or the deflection of the flap in this case. These are very good systems and very reliable and since you are just swapping from one engine to another it just has to be ballpark close what the original engine configuration was. There are basically three adjustments you can do with L-jet to adapt to another sized engine to get the enrichment right. The trim on the airflap (just like it sounds--trim), adding resistors to the Temp II sensor for enrichment, or adjusting the air flap (last resort).

L-jet does NOT like a lot of valve overlap. Period. What happens is there is not enough draw on the airflap to produce a consistent steady signal for the ECU. Ask me how I know...you can run either high(er) ratio rockers, a slightly hotter cam but NOT both. I had an Engle 110 cam and 1.25 rockers with a bus 2.0L system on my 1588. Didn't work so good. I had to dial the spring tension way down because there was not enough draw. The system would still be "searching" quite a bit at highway RPMs.

You could use a bus 1.8L L-jet system with the beetle manifolds on your 1776. That would be a good match as Marc alluded to. If you already have the beetle 1.6 system I would just try it and see what happens, then make small adjustments and do a few dyno. runs (it's $50 for three pulls). A bus, 914, etc. 1.8 or 2.0 system swap is plug and play. Injectors and sensors are the same.

I would not mess with D-jet injectors, there's really no point. All L-jet beetles, buses, T4s, and 914s used the same 110?cc injector 1.6-2.0 so you will not run out of injector on your 1776.

I would HIGHLY suggest welding in a bung to your exhaust and using a simple lean-rich meter. They are $80 from SDS. This will take a lot of guesswork out.

http://www.sdsefi.com/mmm.htm

[luftvagon]

LC-1 o2 Wideband sensor is $120... if you will spend $80, might as well spend 50% more and get 100% functionality.

[Marc]

...I'm going to try a speed density system so a flap style bosche sensor is not going to be used...The plan is to use a 914 1.7 plenum and throttle body...

This is the part I'm worried about. L-Jet injectors have a high cyclic rate, compared to D-Jet and others which deliver all of the fuel needed for a cycle in a single burst they are "buzzers" since they have to open four times as often to deliver the same amount of fuel. So, while stock L-Jet injectors would be fine if controlled by an L-Jet system, they probabably aren't going to be adequate on a system which only fires them once per cycle unless there's a way to increase the pulse width considerably wider than would be needed for a D-Jet type injector.