a technical discussion, engine efficiency Options

[bondo]

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. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[Bleyseng]

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.... (IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif)
(IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

[Brett W]

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.

[dmenche914]

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.

[Bleyseng]

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.

[Jake Raby]

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.

[Jake Raby]

Double post- OOPS!