a technical discussion, engine efficiency Options

[messix]

i guess i can take all those p.o.s rubber hoses off my engine since theres no such thing as vaccum.

[Jake Raby]

So what the hell is this post????? With all the damn "engineers" in this place there should certainly be someone able to outperform my old trial and error methods of making efficiency!

IMHO- Anyone trying to base an engine design off or D or L jet is wasting their time- replace the ECU with an SDS and be done with the son of a bitch...

I've been sitting back watching the posts roll in and can certyainly say that some have made me smile, some have made me laugh...... Others make me realize just how proud I am to "DO" rather than "SAY".....

Like I said, buy a flowbench and a dyno and spend several thousand hours paying attention to them- Check back with me in 10 years and we'll see what you have to say-

[Brett W]

I am not a teacher, I build race cars. If you didn't want a technical answer why did you ask the question.

As far as screwing with D-jet, don't bother. That would be like going back to a "Lisa" (computer) to do CFD. You would never get it done. Don't waste your time with an analog EFI system. There are reasons that manufactures don't use that anymore. Digital is much more efficent and adaptable.

[messix]

i agree with Jake... quit trying to polish that turd d-jet.

for the price of replacement mps you have an state of the art tuneable system.

[r_towle]

well, I am looking for a stock appearance.

I agree that Jake has spent the time and has the knowledge enough to just stop messing with Djet.

I am trying to Do something here, just want to get some opinions on what would be the best place to work on it.

Again. the MPS is getting input from the manifold pressure/airflow.

It produces a certain signal, in a certain range that is fed to the computer.

Let me ask it this way. Has anyone done this, or has everyone basically thrown it out and set up a different system.

Rich

[lapuwali]

QUOTE (r_towle @ Aug 18 2005, 10:48 AM)

well, I am looking for a stock appearance. I agree that Jake has spent the time and has the knowledge enough to just stop messing with Djet. I am trying to Do something here, just want to get some opinions on what would be the best place to work on it. Again. the MPS is getting input from the manifold pressure/airflow. It produces a certain signal, in a certain range that is fed to the computer. Let me ask it this way. Has anyone done this, or has everyone basically thrown it out and set up a different system. Rich

Yes, all of the cars running aftermarket EFI are doing so without the MPS. They use a solid state manifold pressure sensor instead. There's nothing wrong with the "hard" parts of D-Jet, like the manifolds, injectors, plumbing. Only the electronics and the MPS are the "old school" parts everyone is bitching about. Replace the ECU and the MPS with a programmable aftermarket unit, and you've got a system that's as up to date and modern as systems fitted to car made in the 90s.

If you really had to have a system that looked completely stock, then it's very possible to gut the D-Jet ECU and house a programmable unit in the same box (Mark Henry did exactly this with his SDS install). You can gut an MPS housing and plumb in a modern MAP sensor. The system will look totally stock. I doubt anyone has gone to this length, but it's certainly doable. There are enough dead MPSes out there that finding one to gut for cheap shouldn't be all that hard.

[Jaiden]

Follow this link it will give you all the calculations for the various combustion and air cycles Otto, Lenoir, etc...

http://www.personal.utulsa.edu/~kenneth-we...on/chapter6.pdf

[Mueller]

QUOTE

Back to our topic. I believe that djet could be fooled

it can and has been...many times....up to 2.6...larger throttle body....biggest problem with the MPS is it not liking to get beat up by the fluctuation air inside the plenum...even a modern MAP system has issues with the air fluctuations, but they are easier to please...

[Brando]

QUOTE (lapuwali @ Aug 16 2005, 10:46 AM)

[...] Note that L-Jet doesn't have this problem, because it measures airflow directly.  Thus, it's possible to install a hotter cam in an L-Jet engine and it will work.  There's still a potential limit here, as the intake pulsations can confuse the L-Jet airflow meter, so very wild cams can't be used with L-Jet.  You can install L-Jet on a bigger engine and it should work just fine.  The limit here is the size and airflow capacity of the airflow meter itself.

I disagree. I believe L-Jet (Air-Flow Control Injection) has some of the same limitations as D-Jet. For instance, if you go with a wild cam there will be problems with fuel delivery. Like D-Jet and unlike CIS, the injectors only pulse for a certain amount of time. I'm not sure what that duration is, but someone more knowledged on the technicalities of L-Jet can elaborate.

If you have a wild cam with some overlap on intake, or more duration on intake, the injectors don't open up longer. So you end up running lean on your air-fuel mixture. Unless there is a way to change the duration the injectors are open. That's the only way I see a fix for using L-Jet on a larger engine (my first idea before buying carbs).

[r_towle]

On Ljet,
You can increase the fuel pressure and add bigger injectors.

I am only looking for a solution at 2.2-2.4 liters.

Not a huge motor, not a wild cam.

I thinking that there must be a good solid solution that has been developed for this.

It seems that there are alot of people like me who would like a bit more HP, but not alot less cash.

New valves etc are done with a normal rebuild, so that cost would be close to the same.

New pistons and cylinders, figure 98mm or 100mm.

A cam that breathes better, thats all.

I am not looking for proprietary information here. I dont want to build a monster motor, I just want to stretch what money I have to produce the best bang for the buck.

So, I would like to here is there are really any live people that have built a motor larger than 2056 with either ljet or djet,,,these people should still be alive, and the car hopefully is still in operation.

It seem that a solution like this would sell quite well to the type 4 community...those of us that cant spend the big bucks....

Rich

[Brando]

I understand your intentions Rich ... Mine are the same.

Unfortunately I don't believe L-Jet can accomodate the needs of a 2056 with 48mm intake valves and a Webcam 86a up around 7k. L-Jet leans out in the higher RPMS (5k++). If it could accommodate those specs I would sell my carbs to get 48mm intake runners and a much larger throttle body to go with L-Jet instead of weber 44 IDFs.

It just seems like if you're trying to push L-Jet that far into modern times, the cheaper and easier solution is to get a completely digital injection system that's programmable. In the end, you'll get more for your money and much more tunability. But I believe for a stock 2.0 it would be sufficient, nothing more.

[Mueller]

QUOTE

L-Jet leans out in the higher RPMS (5k++).

and where have you seen this???

[Brando]

With a snap-on ride-along flexible gas analyzer.

Believe it or not, some 914s have to pass smog here on the Left-Coast (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[r_towle]

I agree, ljet leans out in the higher rpm's.

Again...I am not looking to build a motor that would see those rpm,s

keep the power band under 5k, just like stock and ljet will handle it...

Plus, ljet has many airflow sensors out there...lots of larger ones...

But, with ljet, I dont think it would be needed till it hits 2.4 of above.

Again, I can get mercedes injectors for a 4.8/8..same size etc.

Raise the fuel rail pressure.

build a 2.2 with the 4.8 liter injectors, stock air flow sensor...and of course put a O2 sensor in to monitor it all...

Not a hig revving race motor, but a torquey street motor in the 140-160hp range....

Rich

[Mueller]

QUOTE (Brando @ Aug 18 2005, 06:27 PM)

With a snap-on ride-along flexible gas analyzer. Believe it or not, some 914s have to pass smog here on the Left-Coast (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

interesting, at the upper RPMs the fuel is based on RPM not airflow since the flapper should be WOT.....

I'm all for the aftermarket FI, it can be installed and look damn near bone stock...in fact my D-Jet MPS is still installed in the engine compartment....hooked up and looking pretty just collecting dust....

[Al Meredith]

I have read some on engine basics (no reguard to number of cylinders , configuration ETC) and the intake to exhaust ratio is +/- 75%. Try this on just about any stock engine and I think you will find its close. I also read that the theoreticle (spelling) limit for a 4 cylinder inline is 2.2 Liters. The pistons get to big and get "buzzy" at high rpm. Once again, think about it , how many four cylinder engines are bigger than 2.2 L ? Some are but they use balancing shafts.

[lapuwali]

Bondo, you're correct up to a point. A given L-Jet system WILL max out if you increase the power of the engine enough. Higher fuel pressure and/or bigger injectors will mean more fuel ALL of the time, even when you don't need it, which usually means running rich a low loads. There's a calibration curve of airflow to injector flow, which is basically tied to the size of the injectors and the fuel pressure, and this curve is built into the ECU. So, at some point, you'd need to recalibrate the ECU AND fit bigger injectors. You'd also have to fit a bigger airflow meter, so the easiest route is to just get a complete setup from a bigger engine and use that instead.

However, you have to pump the engine up quite a ways to hit this point. I've seen 150hp engines be served by their stock L-Jet systems up to 200hp after cam, exhaust, and compression changes, so at least for those systems, a 30% increase in power can be handled. How far the 1.8 L-Jet system can go, I have no idea, though I'd expect it to be pretty high. FIAT used L-Jet on the very last 124 Spyders, and US dealers offered turbo setups that only consisted of the turbo and plumbing. 80-ish hp to 120-ish hp, or a 50% increase, without touching the L-Jet.

[Mueller]

QUOTE (Al Meredith @ Aug 18 2005, 07:07 PM)

I have read some on engine basics (no reguard to number of cylinders , configuration ETC) and the intake to exhaust ratio is +/- 75%. Try this on just about any stock engine and I think you will find its close. I also read that the theoreticle (spelling) limit for a 4 cylinder inline is 2.2 Liters. The pistons get to big and get "buzzy" at high rpm. Once again, think about it , how many four cylinder engines are bigger than 2.2 L ? Some are but they use balancing shafts.

that has to be BS with regards to engine size and cylinder number......a chevy V8 350 cubic in motor has pistons the same size as a /4 motor

with that theroy, no V8s would be bigger than 4.4liter and the Chevy V8 has models up 454 cubic inches (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

plenty of inline 4 motors with 2.4, 2.5 displacment and larger....

[Mark Henry]

QUOTE (rhodyguy @ Aug 16 2005, 09:01 PM)

such A thing as vaccum? i beg to differ. my dad was so frugal you had to force a cent out of his pocket. he was very centafrugal and he existed. is that what you mean? a poor child (k)

What's the difference between a Harley and a Hoover vacuum?

The location of the dirtbag.

Ba-dum-dum (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

[lapuwali]

QUOTE (Al Meredith @ Aug 18 2005, 06:07 PM)

I have read some on engine basics (no reguard to number of cylinders , configuration ETC) and the intake to exhaust ratio is +/- 75%. Try this on just about any stock engine and I think you will find its close. I also read that the theoreticle (spelling) limit for a 4 cylinder inline is 2.2 Liters. The pistons get to big and get "buzzy" at high rpm. Once again, think about it , how many four cylinder engines are bigger than 2.2 L ? Some are but they use balancing shafts.

For a long time, the theoretical maximum was held to be 500cc per cylinder, which is why you see so many 2.0 fours. However, these rules were engraved in stone in the 1950s, when metallurgy was nowhere near as advanced as it is today. British designers, in particular, were convinced of the soundness of this rule. The key factor is partly down to balance, but mostly it's the sheer forces of stopping and starting a piston bigger than that as revs increase. The forces go up as the square of the engine speed, so they get very serious indeed.

That said, there have been a very large number of engines made with cylinders well over 500cc, including the ubiquitous 350cu in (5.7L) small-block Chevy, weighing in at 712cc per cylinder. There are 800-900cc single cylinder bike engines, too. Porsche themselves made 3.0 fours in the later 944s and 968s, at 750cc per cylinder. The balance factor on inline fours isn't very good, and Porsche did use balance shafts in these engines, mostly to keep them from shaking themselves and the occupants of the car to death. The balance factor on a flat engine is much better, so there's little reason to no go larger, and the 2.5 flat-4 Subaru engine is proof of that. The 3.2, 3.4, and 3.6 flat-6s in later 911s and Boxsters also thumb their noses at this "rule".