engine management

[michel richard]

does anyone have hard data on what can be done on a 914 2.0 l with modern electronic engine management systems. Any power increase etc . . . In other words, how good is the d-jetronic and distribuor compared to the latest.
thanks


[Note: This message was edited by an administrator or moderator.]

[Dave at Pelican Parts]

I don't know anyone (yet) who has gone to an aftermarket system on a relatively-stock 2.0, so I can't answer you directly. Try me again in 2004, when my 74 2.0 is EXEMPT from smog testing...

However, there are a few things to remember about the D-jet FI system.

First, is uses manifold vaccuum as the primary measurement of how much fuel is needed. This is not hideously innaccurate, but it is not measuring exactly what is needed. To maintain a reasonable mixture, you need a certain mass of fuel that goes with a certain MASS of air. (About a 1:14 ratio.) Therefore, measuring the MASS of air coming into the system will tell you very accurately how much fuel you need.

Second, the D-jet system squirts fuel at two cylinders at a time. One of these cylinders has its intake valve opening at this time, while the other still has 1/2 of an engine revolution to go before its intake valve opens. This can't exactly be great for fuel atomization. Having a system that can squirt the fuel at each cylinder just before or just as its intake valve opens should result in a better burn. More power (probably *very* little!), less emissions.

Third, D-jet operates in an "open-loop" mode. The FI takes a guess at what the correct mixture might be, and delivers that much fuel. Modern FI sytems operate in "closed-loop" mode. The exhaust gases are sampled, and the FI uses that sample to determine if the mixture is too rich or too lean.

Fourth, most aftermarket systems let you tune and program arbitrarily. If you've got access to a dyno and a laptop, you can program the FI to give you the best power at all RPM and throttle settings. You can tune it until you drain your bank account, or until you decide the remaining power gains are too little to bother with, whichever comes first.

Finally, some of the higher-end aftermarket EFI systems also include ingition control. They are real DME systems. Most have inputs for knock sensors, some of them have inputs for one per cylinder and can control timing on a per-cylinder basis. This means that you can have more advance on spark timing, giving you more power. The DME will retard timing if it senses knocking, thus keeping the motor from blowing itself up. And again, this is all very programmable, thus allowing you to eat up copious amounts of dyno time getting the last couple of HP our of your motor.

The short answer: They can do quite a bit, but it'll cost a lot!

--DD

[michel richard]

Dave,

If I understand correctly, you are saying that power can probably be gained
by replacing the fuel injection but, also, that there might be cheaper ways
of getting extra power.

Would you be able to make suggestions? What would be an easy way to get a
few extra horses; I would like to retain the displacement and have already
gone to euro-spec pistons and cylinders. Higher compression still? Is
there any way of pushing the redline up to get more power out there? Other
suggestions?

I am not highly experienced in these matters - the first time I ever took
an engine apart was last summer when I rebuilt my motor. Any guidance
would be most welcome!

Kindest regards

[Wayne 962]

Dave has been kind enough to document what he thinks are the best performance increases in the other post on the this BBS, titled 2.0L Performance Upgrades...

-Wayne

[J Noonan]

Before you fiddle with the D-Jet read "D-Jetronic Fuel Injection for the Porsche 914" on www.estinc.com/porsche/djet,html. It tells you some ways to adjust and rebuild the D-Jet for "free" horsepower. One other thing I've run into on 1.8 litre engines is that the L-Jet has been swaped for a D-Jet at some point. One friend of mine had a 2.0L '73 ECU with a 1.7 pressure sensor and injectors that probably came from a bus or 411 sedan. So make sure you have what you think you have first. This can be done with many of the "glossy" Porsche parts catalouges or ask Dave Darling were his parts cross reference is posted and check your part numbers( sometimes you have to use Bosch sometimes VW p/n). I have heard of a "complete" E.F.I. aftermarket unit that sold for $800-$900, I think it was in Excellence. but the money could by spent elsewhere with much more reward.

[michel richard]

You suggest, at the end of your note, that other can be done to improve the
2.0Liter power that more would be more cost efficient than fooling around
with the D-jetronic.

I have not checked yet, but I am confident that my D-jetronic is all
original. I am only the second owner and the car was looked after by a
very capable fellow before I started fooling around with it.

In any event, if you could detail some of your thoughts on what can be done
to improve power, while keeping the engine tractable, I would apprieciate.
I guess my goal would be to have something like the power the original
sixes had.

I realize this discussion might be better suited in the other posting concerning 2.0 Liter engines generally, but Mr. Noonan posted here so I did too.

Thank you kindly.

[michel richard]

Dear J,

Also, I was not able to log on to the site you describe. Did I miss something?

Thank you once again.

[J Noonan]

Sorry about the address. I'm new at this or just not very good. The site is Tim's 914 fan web page go to the estinc site and some where on the page is a link the the Porsche stuff. It also can be reached through Reagade Porsche club links under Brians fan web page and Tims fan web page. As for this forum I'm not sure that it is that stuctured. It was my understanding that it is an open forum but you have a point we should keep things in certain catagoried. Any thoughts from Wayne?
At the end of my message what I meant was that you will not get a great benifit from switching a stock 2.0L to a aftermarket F.I. only if you have a radical cam or large displacement that the stock D-Jet couldn't handle would it make sense to upgrade the F.I. The money would be better spent on D-Jet compatable performance cam, adjusting the D-Jet ( read that article ) and a complete tune-up. While swaping cams it is a good time to rebuild the whole engine. Euro pistons, a three angle valve job, new springs and adjuster nuts will give you more power. Also the 914 is not about the stoplight grand prix, it will benifit from sway bars in front and back if you don't already have them, and better tires etc.

[Wayne 962]

Great, no continue the discussion here. Here's the url that you wanted:
www.estinc.com/porsche/djet.html

Thanks,

Wayne

[michel richard]

Allright,

I have rebuilt the engine although I don't think I managed to put more than 5 miles on it before I had to put tha car away for the winter. (We get a lot of the white stuff around here).

I did use euro piston & cylinders but I may have been trying to go a little fast when I got around to the heads.

The machinist told me the springs were OK but htey may have been a little tired. His basis was simply that the spring were all still close to each other. Also, I did not bother replacing the adjusters.

Guess I might pull the heads and redo these. They were ported a little although the machinist told me they were pretty nice to start with. The exhaust valves were replaced and ground, the intake were just reground.

When putting things back together, at the very end, I broke a couple of the exhaust studs. Down came the engine, off came the heads, back to the trusty machinist who fixed my beginner's mistakes.

So I now have a little more experience at removing heads. By the way, how often can those sealing rings be reused.

I might actually get the courage to go back down to the camshaft to replace it at it was slightly worn.

Wayne, can you tell me about D-jetronic compatible cams; and gasket sets.

Cheers !

[Wayne 962]

There are a number of aftermarket cams (Webcam) that will increase your HP slightly over the original cam. Some of these may make a car run out of smog legal range though, so think twice about putting a high performance cam in your car. You should always replace the lifters as well. This I believe is to induce a uniform wear pattern with respect to the cam and the lifters.

We don't recommend hydraulic lifters unless you want minivan type performance at higher RPMs.

The gasket sets for 2.0L motors are not complete. You might need to replace the seals on your windage tray (only found in oil sump of 2.0L motors). These are no longer made. There are a few other things missing (flywheel seal, I think), but I can't remember them off the top of my head.

-Wayne

[JJ Slowik]

To add to the discussion about gasket sets...

I've done a top-end rebuild twice, and in one case I recieved the plastic "blocks" that are sandwiched between the intake runners and heads. In the other case, I didn't. Also, when you ask about reusing the "sealing rings", which ones are you talking about? I suppose you might be able to pull off reusing the cylinder base gaskets, but I wouldn't reuse any of the others... especially the copper gaskets used to seal the heat exchangers to the heads. I tried, and until I finally replaced them, the car backfired continuously.

[michel richard]

I was referring to the rings between the case and the cyls as well as those between the latter and the heads.

regards