Fuel injection or dual webbers?

[911t Fanatic]

Which is better performing Stock fuel injection or dual webbers?

[Mike Bellis]

Factory Fi will work best with a FI cam. Webbers will work best with a Carb cam. What is in the the engine? Ready for a re-build? You could go with EFI. Megasquirt is common add on for the 914. Any after market EFI system will preform better than both Carbs or FI once dailed in. CB performance make a bolt on EFI kit that look like dual carbs. It make the conversion easy.

[kachemakian]

How much does a conversion from the 2.0 D Jetronic to Mega Squirt end up costing? Has anyone also been using the M S system for firing their ignition without a distributor? If so, what mpg on the highway does the system yield? How many of the factory sensors does it use? Does it use an O2 sensor? Factory fuel injectors and pressure regulation system? Also, are you mounting the computer inside the cab with laptop access? Leon

[Dave at Pelican Parts]

Almost everything in MS varies. Since MS is, at its core, just a circuit board and a bunch of components that you put together, and software that you can write yourself relatively easily, you can make it do ... well, just about anything!

That said, it would be really absurdly difficult to make anything but the stock injection work with the stock MPS; it uses a completely different type of electrical signal to represent the different pressures than anything actually in use today.

You could do a divide-by-two in the software so that the timing pulses could use the trigger points--or merely use one of the two sets of signals, which probably would be easier. You can use the stock temp sensors if you set up the internal tables to do so. You can use the stock vacuum-regulating bits (like the decel valve and the aux air valve), and so on. You can set it up to use an O2 sensor, or not. Of course, that would mean adding one to the exhaust...

--DD

[911t Fanatic]

I assume when the po rebuilt the engine he went with an FI cam since the FI was installed. The only way to know for sure would be tearing it down which would be kinda silly. Does megasquirt offer a bolt on kit for my 70 1.7? would it gain any performance?

[Mike Bellis]

If you want a bolt on kit without fabrication, you must go with the CB Performance kit. Any other system will require some fabrication and custom sensors. The CB kit would give you a mild performance increase. If you swapped the cam then the CB kit would give a greater increase.

[racer]

For driveability, I've enjoyed my stock FI systems. Carbs were always noisier.. and could be a pain in really cold or hot weather.. but they did "sound" much better.

How will you be using the car? If competitively, check a rulebook to see if a change from factory system is allowable.

[911t Fanatic]

No racing just pleasure. thanks for all the input.

[Dave at Pelican Parts]

If you're happier tinkering with carbs, and you have the cash to drop on the conversion, then go for it. They usually come with compromises in driveability and economy, but they are (generally, to those who are used to them) quite simple.

The stock injection works quite well when in good shape on a stock motor. It is "set and forget" as long as everything works and you don't violate its operating assumptions (e.g., with an aggressive cam grind).

MS is literally a handful of electrical pieces (resistors, capacitors, integrated circuit chips) and a board that you are supposed to put together. Then you hook it up to a laptop and program it. Then you figure out what sensors and such you are going to use (though they do include a solid-state manifold pressure sensor already for you), spec out and build the wiring harness, and hook it all up. Oh, and find or make an enclosure for it.

If you're not into soldering, wiring, learning about engine management, and at least light fabrication, you are not the intended customer for MS. There are places that will sell you assembled MS boards and possibly more, but as far as I know there is no "bolt on" kit for the Type IV engine.

Simple Digital Systems (Simple Digital Systems EM-4) makes a setup that is closer to plug-and-play. I am not that familiar with it, though. The adjustments are much simpler, but that means you have less control about the mixture at different RPM/load points.

--DD

[Jared at Pelican Parts]

Without changing the cam and distributor, dual Webers on an otherwise stock engine is pointless.

[larrym]

just install a big bore throttle body on the D-jet

I got mine from Ed Mazula - it was a 4mm overbore

it significantly increases mid-range performance

just google bigbore throttlebodies - plenty of folks can ream yours out for you

[Jared at Pelican Parts]

I can't see how putting larger throttle body on D-jet would add power without also addressing the fuel pressure, re-adjusting the pressure sensor, fuel injection timing, etc...

I would think that it would also decrease overall engine vacuum, which is how the system operates. Without also changing the diameter of the intake runners, I cant see it doing much of anything.

I CAN see this working on a larger displacement Type 4 with some tweaking..

[Tobra]

There are a lot of reasons they put FI on these things.

If you have a good running stock FI car, I encourage you to drive the piss out of it, save your money, then put a big four together with plenty of cam and good heads, bugsquirt or something. Once you get your FI right, it stays that way. Most systems will work much better than carbs, especially if you are dealing with changes in altitude or with temperature extremes.

[911t Fanatic]

stock FI it is. Thanks guys