so, I have been thinking (not always a good thing)
If an engine is basically an air pump, and the objective is to make it as close to 100 percent efficient, why is the exhaust valve so much smaller than the intake valve?

Forget emmisions, forget fuel delivery, just want to understand why this is so...it is so on most engines...

Rich

Cause on the exaust stroke there's a hard piston pushing gases out, while on the intake stroke there's only soft atmospheric pressure pushing the mixture in. I suppose the exaust valve is made smaller because larger is not needed, and would there fore be a waste. Plus there's a ton of other concerns such as gas speed etc . . . that I don't fully understand.

FWIW, my .02

Michel Richard

I thought that there is a vacuum sucking the mixture in...

To obtain maximum airpump efficiency, we are taught to open up the exhaust (that is what I am told is the real restriction on these motors)

So...why not design it from the start to be somewhat closer in size.....

Rich

......... Because that about 20% of the air fuel mixture is burned completely and the density of a burned mixture is MUCH less than one thats atomized with fuel...

I have built some awesome Turbo engines with the same size exhaust valves as intake, with a really modified cam to promote it... BUT don't ask them to run very well N/A

thanx for that reply Jake...as always you get to the point.

Rich

Rich,
The summary I made was very general... With some things like this I fully understand them, but lack the ability to put them into words.

Remember that bigger valves are heavier and actually "Get in the way" at certain valve lifts, especially @ full lift.... From what we have seen big huge valves are a certain way to kil the TIV powerband and power output.

It's ALL in the combo! Buy a flowbench and dyno and you'll see that daily.

the exhaust is at very high pressure after ignition, therefore not as big of valve or port is needed due to the high velocity of the hot gas. the intake can be larger to assist in better flow and velocity. there is a balance between the intake and exhaust that is about 80% of exhaust flow to intake flow. this is measured on what is called a flow bench, this draws air thru the desired port at a standard barametic pressure in inches of mercury and the measurement is given as "CFM" much air has moved thru the port in a give time. the higher the number the more air.

this is the general basic for n/a engines, when any type of forced induction is applied things get much different.

If you look at typical cam timings, the exhaust valve usually opens well before the piston has even reached BDC on the power stroke. By the time the piston has reached about 80% of the way down the stroke, no more energy is going to be transferred to the crank by the still-expanding mixture, mostly due to geometric reasons (the big end of the rod is now moving as much sideways as down), and for simple thermodynamic reasons. But, as stated, the pressure in the cylinder is still quite high, so opening the exhaust valve early helps to evacuate the cylinder that much faster.

With perfect timing (which, with any fixed valve timing, will only happen over a narrow rev range), you'll actually have a slight vacuum in the cylinder by the time the intake valve opens while the piston is still rising. The inertia of the exhaust gases will draw the pressure down below atmospheric, and will help to draw the incoming charge in through the intake valve. The additional vacuum created by the piston falling will help, as well, though the intake vacuum is still far smaller than the starting pressure of the exhaust gasses just before the exhaust valve opens.

Since the "force" pushing the intake mixture into the cylinder are so much less than the forces expelling the exhaust gasses, and since you have a limited amount of space to use for valves, you bias the valve sizes towards the intake side.

Again, when the timing works perfectly, the inertia of the incoming charge will allow the cylinder to be pressurised slightly ABOVE atmospheric pressure, and you can shut the intake valve at just the right time, before the charge reverses direction and tries to flow back out the intake valve. This is why you can get such big power gains with just the right cam, but only over a narrow powerband. At the very extreme ends of this were engines like the Honda RC115 4-stroke 50cc GP bike engine of 1965, which made as much as 17hp (340hp/liter, or more than a modern F1 engine), but had a powerband so narrow it required a 17-speed gearbox. Riders talked of needing to make 9 gearchanges in a simple chicane.

There is no vaccum in the cylinder. Nothing sucks air into the cylinder. There is a low pressure area created by piston movement. By forcing the air out of the cylinder on the exhaust stroke there is a low pressure area left when the piston moves back to BDC. This low pressure area is much lower than atmospheric pressure. When the intake valve opens pressure in the intake tract will force the mixture into the cylinder. Ram tuning occurs at certian rpms when the wave created by the opening an closing of the intake valve bounces back and forces more mixture into the cylinder. This only happens at certian rpms. Look at the old Chrysler manifolds from back in the 60s.

The NASCAR boys have done quite a bit of testing to deterimine valve sizes and such. They have been increasing the intake size and skrinking the exhaust until they can run the smallest exhaust valves possible.

Look at a diesel engine. They are perhaps the most efficent engines right now. The lack of a throttle plate of any kind makes for very low pumping losses. The high compression ratio helps also.

i guess that vacuum assist power brakes don't exist? and the vacuum gage used to tune carbs? the low pressure created by the engine on the intake manifold is referred to as vacuum. [not in the absolute term]

So, taking this knowledge, how can we apply it to analyse the current stock cam profile and how is effects the djet FI system..

Mainly, in a higher HP motor, there is more lift and more duration, and overlap.

I know its all in the combo....

But the question here is what is the true restriction on the cam in a stock FI system, and why.

Without a dyno in my garage, I would like to understand the settings of the FI cam and how they can be changed, and what will happen once these changes are made.

I understand that the MPS is looking at that vaccuum/pressure inside the plenum to determine how much fuel is needed,

With a different sized valve setup, and a different cam profile, it seems that you could maintain a proper Air Fuel ration while increasing the airflow through the system..

The trick is to keep the MPS happy and within range.

Lets say that the MPS is designed to read only a certain set of readings, anything outside that pre-determined set of numbers will make the car run lean or rich.

So if we increase head flow, the car will run lean,,,outside of range of the FI system...

But, if we increase airflow, and increase overlap, we might be able to maintain the same pressure inside the plenum...now the issue would be that the cylinders need more fuel....this could be done with larger injectors and increased fuel rail pressure.

Does this make sense...

I am trying to look at the cam profile, or a change to the cam profile...

Possibly a better flowing head, and or larger valves...

What are the effects, and where can the djet system be taken to...realistically.

Let me give an example, merceded has a 4.8 liter djet driven motor from the 70's....taking four injectors, one could in theory build a 2.4 liter and run it with the proper air fuel mixture.

The readings would be outside of the range of the MPS.
now, can we change the cam/valve size/head flow characteristics to bring the manifold pressure back into range, or is the pressure going to increase or decrease with more air (larger pistons or stroke...)

Rich

The cam in the stock engine was chosen more for emissions reasons than power reasons, so it's unnaturally restricted.

There are two problems with using D-Jet with a wild cam. One is that wild cams set up substantial intake pulses in the intake tract, which cause the manifold pressure to fluctuate wildly at small throttle settings. You'd have a very lumpy idle and very poor drivability at or near cruise. You can fix this to some extent by using a mechanical damper (some people use a fuel filter, others use a small restrictor in the vacuum line), at the cost of response. The other problem is the MPS isn't actually measuring airflow. It's estimating airflow based on manifold pressure, air temp, and engine speed.

Any engine (or air pump) does not pump with 100% efficiency. When the intake valves close, the charge pressure will be some percentage of one atmosphere (the volumetric efficiency, or VE). The actual amount will vary based on how far the throttle is open, the air pressure outside, the engine speed, the cam timing, the valve sizes, and the efficiency of the ports. The VE curve will be pretty much fixed for a given engine, so if you know some of the outside parameters and the VE curve, you can estimate airflow, and thus how much fuel you'll need.

Putting in a wilder cam, or cleaning up the ports, or installing bigger valves, or making the engine bigger, will change the VE curve. So, while you still know manifold pressure and engine speed, the VE curve in the D-Jet ECU is no longer correct, so the right amount of fuel isn't delivered. If you can change the VE curve programmed into the ECU, you can adjust this for the new engine.

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.

Brett nailed it, there really isn't such thing as vacuum. Same goes for centrifugal force.
They are terms that generically decribe a condition in layman's terms, but try and use them in front of a physics professor and get ready for a lecture. Ask me how I know that

Neither of those are actually physical properties.

IMHO, Brett didn't "nail" anything. Both of you are just being pedantic.

Yes, airflow will always move from a higher pressure to a lower pressure. Reducing the pressure in the cylinder below the pressure of the air in the atmosphere will induce flow from the outside, through the intake tract, into the cylinder.

In common use, "vacuum" is simply "pressure lower than atmospheric". The fact that pressure pushes rather than vacuum sucking is simply idle semantics, and makes zero difference to the actual operation of the engine. You may as well go around constantly correcting everyone who misuses the terms "torque" or "force" or "work".

Describing things in "layman's terms" is USEFUL, and was exactly what was asked for by the original poster. Indeed, if you can't sufficiently explain something in non-technical terms, either you don't really understand it, or you're an inarticulate Neaderthal (hey, would you like to beat me up on the them "Neaderthal" now?).

Neither one of you have actually added to the conversation. Brett's statement: "The NASCAR boys have done quite a bit of testing to deterimine valve sizes and such. They have been increasing the intake size and skrinking the exhaust until they can run the smallest exhaust valves possible." My response would be: fine, WHY? Things are the way they are because the NASCAR boys say so? What's the theory behind this?

Easy. Explain the technical terms first in layman's terms. This is the essence of teaching. Build on existing knowlege to add new knowlege. One also hardly needs to rely on exact terminology to understand something. Simply knowing terms is a fairly useless thing. Knowing the concepts those terms represent is the useful bit.

QUOTE (James Thomlinson @ Aug 16 2005, 07:32 PM)

Disregarding the automotive discussion for a moment, I think what you state in your second to last paragraph is incorrect and contradicted by what you said in your last paragraph. In science and engineering if you want to provide someone with a true understanding, you will have to "get technical". For example, how would you explain electricity and magnetism or light in non-technical terms?

electricity is like the waves of an ocean.
or the current flowing down a stream
The width of the stream is the voltage, the amount of water.
the speed of the water, the force, is the amperage.

Magnetism is the same thing as love or lust or the need to be close to someone.

Light is the opposite of dark.
Dark is black, light is white.

no electricity, eye can see no light, my big toe(flesh) is like a magnet to the foot of the bed(wood) . i try to limit my criticism to their, there, they're, where, wear, we're.

humorless electus (k)

Back to our topic.

I believe that djet could be fooled.

If the VE is hard coded, its saying that given air temp, air flow and throttle position, the system will pulse the injectors for a certain amount of time.

Break that down.
Air temp can be fooled with electronics.
Throttle position can be fooled.
The one that I am having a hard time with is how to fool the MPS.
there must be a way.

If you bump up the fuel pressure, and put in larger injectors, you could add more fuel for a given airflow..

Here is my driving question...I am not looking for a wild cam or huge valves or anything ridiculous.

I am thinking 2.2 liters, a bit more of a cam that will keep it drivable (this is where I need help)
And still retain the original one second start of the djet that I love.

I know that 2056 has been done just be adjusting the MPS....
Now, go to 2.2.
Change the electrical output from the MPS versus how it is reading its input, normalize it to its original output.

Port the heads, slightly larger valves possible (this would depend on the cam etc...)

Just look for 150 hp from the original djet,,,,I am sure that Jake could make a 2.2 liter get close to 200 hp, that is not the idea.

Djet took a certain motor and would run it contricted for both economy and long engine life...

I am trying to figure out how to do the same thing at the 2.2-2.4 liter range...run it conservatively..

A 2.2 or 2.4 liter making 150 hp could be a nice long life motor with a nice torque curve and good around the town fun.

I love the single turn to get djet going.
I have plenty of spare djet parts.

I also have two Ljets, and going to your last comment, I know I can do this with Ljet,,,,just not sure I want to go that way yet....I might...but I have not real world experience with ljet, what I have read it can be done, has been done, and is still being done...

Rich

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)

You can fool the MPS. Indeed, you can replace the MPS with an entirely modern solid-state unit that will outlast the tub. However, to do all of this, you require enough electronics that you're 80% of the way to an full fuel ECU. If you used (nearly) any aftermarket ECU, you can replace the stock ECU, the MPS, and use all the rest just as it sits. You'll have a fully programmable fuel curve that you can tweak to suit any Type IV you can dream up. It will also have the easy starting of the D-Jet system.

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

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-

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.

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.

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

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.

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

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...

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).

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

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.

QUOTE

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

and where have you seen this???

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

Believe it or not, some 914s have to pass smog here on the Left-Coast

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

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

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....

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.

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.

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

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

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

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".

QUOTE (lapuwali @ Aug 18 2005, 07:21 PM)

Bondo, you're correct up to a point.

What? Hmm? I didn't say anything.. I think you mean bRAndo.

The other fly in the onintment for this 2.2L is the supply of intake charge with the stock system. Several engineers have pointed out that if you get much bigger than a 2056cc you will have to enlarge the runners(one runner should be equal to the volume needed to fill the chamber) and the plenum(what size I can't answer other than bigger).

Large valves can get in the way of the intake charge slowing it down but smaller valves can benefit from a good cam timing.

I have always wanted to try to build a larger djet motor just to see what happens. Hmm, I still might get the chance.....if I can find all the time I have misplaced....

I don't get it, I mean I understand wanting to work with what you have, but damn. Even I understand futility when it slaps me in the face. For all the time and effort you put into to making the stock DJET or LJET work, you could have gone down to Pull-A-Part and snagged everything you need to convert to CIS. Or you could have gotten a job at night delivering pizza until you could pay cash for a nice standalond Fuel management system.

Djet can't handle anything more than controlling a gas leak into each cylinder. You can use a modern system and tune for big cams, huge motors, turbos, superchargers, nitrous, etc. They cost less than the great lengths you will go to to tweak an already marginal system.

Don't re-invent the wheel, just to do so. Now if you want to figure out how to make a stock engine run on E85 or french fry grease thats cool.

generally engines are most efficient at wide open throotle, and low rpms, Wide open throtle means less restriction on your "air pump", low rpms mean less momentum change energy losses, and heat losses.

That is way generally a smaller displacment motor gets better mileage, as it tends to be ran at wide open throttle all the time, add an overdirve gearing,a nd you get the rpms down low to help reduce friction type heat waste. (think of an old 1100cc 36 HP Bug motor, it is driven wide open throtle almost all the time, the larger 1600 cc engines got worse mileage, dispite more favorable gearing (more overdrive) in part because the engines did not need be at wide open throotle for cruising speed (ie 65 mph) also the later Bugs weighed more, but the engine was just plain bigger than needed to move the car at speed.

what you gain with the bigger engine is the ability to accelerate faster (thats when you do have it at wide open) but at a fixed speed or say 65 mph, the smaller engine should give better economy, all other things being equal.

QUOTE (Brett W @ Aug 18 2005, 11:30 PM)

I don't get it, I mean I understand wanting to work with what you have, but damn. Even I understand futility when it slaps me in the face. For all the time and effort you put into to making the stock DJET or LJET work, you could have gone down to Pull-A-Part and snagged everything you need to convert to CIS. Or you could have gotten a job at night delivering pizza until you could pay cash for a nice standalond Fuel management system. Djet can't handle anything more than controlling a gas leak into each cylinder. You can use a modern system and tune for big cams, huge motors, turbos, superchargers, nitrous, etc. They cost less than the great lengths you will go to to tweak an already marginal system. Don't re-invent the wheel, just to do so. Now if you want to figure out how to make a stock engine run on E85 or french fry grease thats cool.

Don't worry, I will be running a Haltech EFI system on the 2.4l motor. I said I just wanted to try it to see for myself once and for all what the problems are.

QUOTE

generally engines are most efficient at wide open throotle, and low rpms,

Engines are most efficient @ peak torque.... Thats the point where the most power is being made with the least amount of work or fuel. This can be clearly seen by measuring BSFC on the dyno. Keep in mind this is at WOT- part throttle conditions can vary peak torque due to manifold pressure and load.

Double post- OOPS!