1.8 and 2.0's....FI systems

[rallyman]

I accidentally posted this on the for sale board also....(hint, hint, please remove it?)

I can't help but ask the question, and I apologize if it has been asked before......
Stock FI, which is supposed to be the better system? D-Jet or L-Jet? Based on other types of FI systems (Ford late model stuff - sorry!) I know the later Mass Airflow (similar to L-Jet /AFC?) is supposed to be better than the other earlier Pressure type FI (similar to the D-Jet?). Supposedly better because it is more adaptable and tuneable to engine mods.

Then the question begs......if L-Jet is better, is it adaptable to the 2.0 or 1.7? If it is a matter of the computer ("brain") not being set up, perhaps there is a computer genius out there that can make the chips to modify signals like they have for later model cars, (or complete rebuilt "brains").......

Thanks in advance and thanks for listening....

Craig.
rallyman@cts.com

[MidMike]

As far as a 914 goes ,I would stay with the system that is original to the motor.....The L type injection still lives on ( just seen a 85 Alfa Spider with almost the same injection)so it must be the better of the two.

[Dave at Pelican Parts]

"Better", in what way?

They both have their good and bad points.

The D-jet is set up to work with the 1.7 and 2.0 motors, and can be adapted to the 1.8s with a bit of tweaking. It does not allow you to use cams that are more than a very little bit more aggressive than stock, or the idle will be VERY VERY rich. It is also somewhat restrictive. It doesn't react all that much to vacuum leaks or backfires. It is fairly complex.

The L-jet is set up to work with the 1.8 engine. It can be made to work with the 1.7 and 2.0 engines, but it seems to be tougher (particularly for the 2.0). The stock air flow meter "maxes out" at about 4500 RPM at WOT (Wide-Open Throttle). If you increase the airflow requirements of the engine, like by going to 2.0 displacement, it will max out earlier and the engine may run lean on the top end. Bad for the motor, bad for performance. It may deal with lumpy cams a bit better, but you can get into "reversion" where the pulses in the intake system start wobbling the vane in the meter around and confusing the FI.

The L-jet FI is not very tolerant of vacuum leaks, it makes the motor run lean. It also doesn't tolerate backfires too terribly well--violent ones can warp the vane in the air flow meter. It is a little bit simpler (particularly internally) than D-jet, and more precise because it actually measures the amount of air coming into the motor rather than just "guessing". The vane in the air flow meter is another flow restriction, on top of the already somewhat-restrictive intake manifold.

Finally, both FI systems on the 914 are run by primitive analog computers. There are no "chips" that can be programmed or swapped. So that pretty much means you'll have to mess with the inputs to the FI to tweak the FI.

You can go with a different air flow meter, as long as the pin-outs are the same, and see what that gives you. You can also mess with the spring tension of the vane, the fuel pressure, the injector flow rate, and some other things as well. But most of them involve swapping parts rather than just tweaking what is there.

--DD

[rallyman]

Ok, I forgot about the "latest" innovations in computer technology.....and the relative age of these 914 "computers"!! It appears that the L Jet is a bit more forgiveable in engine mods (same as the Ford Mass Air)but you need to get it to read the increased airflow somehow...by tweaking or replacing the stock airflow meter???

What is the opinion as far as overall performance? A moderately modified 2.0 (minor head work, cam, etc?)with D Jet (I think D Jet is out of the question...) or modified L Jet or Carbs? Or would I be better off and stop pulling my hair out and drop the big bucks for an aftermarket FI system? I'd like to have a motor that's better (ie more powerful - hp/torque) than stock, without the hassle/expense of a six conversion (at this time ). Thanks for the responses!

Craig.

[JP Noonan]

IMHO If you are building the motor from sratch, don't mind a lumpy cam, live in a warm climate so there are never any cold start-ups, don't have any emmisions concerns, have personal knowledge or know a shop who is and EXPERT on Webbers, and don't mind the slightly louder intake noise, I would go with carbs.

The key things are to buy a cam that works with the carb, buy the right sized carb, and have them tuned profesionally. The last point is the most over looked. Ask the cam and carb manufacture what size jets and such to START with but this will most likly only be close. To have a good running engine that isn't lean or fat anywhere in the RPM range is hard to do with carbs (actually impossible, but you can get close). The payoff is tha you can get more horsepower from a modified motor with carbs than with a factory FI.

If you want more HP than stock, good cold starts, lower emmisions, and a longer life to the motor, after market FI is the way to go.

my $.02

[This message has been edited by JP Noonan (edited 02-24-2001).]

[rallyman]

I like the loud induction noises so that's not a problem....do the aftermarket FI's have the loud induction noises (thinking of like the CB Performance kits - the throttle bodies are just like Webbers, sort of)?

Thanks for the info......so I suppose it's going to be carbs or if I can squeeze out the bucks (while the wife isn't watching!) maybe an aftermarket FI system.....

Thanks again,

Craig.
rallyman@cts.com