The tricks up my sleeve... Methods I may implement for better FE.

[DrivenByNothing]

Yes, the VW motor uses DI, but one of the articles (may have been the one I linked to) they mentioned what little effect DI has in petrol motors. However, the addition of boost seems augment it quite nicely.

When comparing the mileage of factory N/A vehicles with factory forced induction vehicles, one must realize that cars are manufactured to appeal to a certain demographic of people. The group that buys sporty cars puts performance above fuel economy (for the most part).

In any event, automobile manufacturers have to come to a compromise on almost every aspect of a vehicle in order to attract the greatest number of consumers. The majority of these consumers want to buy a car, drive it, have the oil and tires changed, and fill the tank. We, however, are different.

The Civic I'm looking at will be between the years of 92 and 95. The VX is a wonderful car, but I don't think I want to spend the extra time and money to find one. I like a bit of a challenge anyway.

In my opinion, the Civic motors are small. I've never owned anything with less than 2.4L and the Jeep is 4L. I like the stock motors because everyone likes to swap them out in favor of something from Japan. If I blow a motor, I can get another quickly and for very cheap.

I could be completely wrong, so it's not that I'm blind to your critiques, but rather I'm stating my reasoning. I love this site already and you guys seem to know what you're talking about. Feel free to call BS on me if you see something that doesn't make a lick of sense.

Matt

[omgwtfbyobbq]

Originally Posted by DrivenByNothing

When comparing the mileage of factory N/A vehicles with factory forced induction vehicles, one must realize that cars are manufactured to appeal to a certain demographic of people. The group that buys sporty cars puts performance above fuel economy (for the most part).

That's the great part about the EPA highway test. It's consistent! So, given the same car, one with a NA engine, and another with a turbocharged version of the same engine and a taller transmission, on the same test. It's evident imo, that the turbocharged engine is less efficient than the NA engine if it gets worse mileage, because it's over the same test, in the same car, with the same engine, and a slightly more efficient transmission ratio. The only variable I can think of would be the ECU, but I'm pretty sure that's the same for both, since all cars have to keep the AFR at 14.7:1 during normal driving unless they're lean burn, diesel, or hybrid iirc. I'm not trying to knock your ideas. I'm just saying that imo, turbocharging a NA engine, designed for less power, and running it lean isn't the best for efficiency and reliability. It's cheaper to get a larger displacement engine and gear it down if you want power and efficiency at some speed. That way, you don't have to worry about replacing the engine in the first place.

Originally Posted by SVOboy

VW uses diesel where Honda is new to the market (but then VW's diesels are the dirtiest things on the road, and Honda's late entry into the diesel market should differ substantially on this point).

Both Honda and VW offer sedans that are in the Euro IV emissions category... How is this a substantial difference?

[trebuchet03]

It's evident imo, that the turbocharged engine is less efficient than the NA engine if it gets worse mileage,

Careful... that is quite easily a fallacy (slippery slope?)...

Thermal efficiency and fuel economy are very different things If you want to compare the efficiency of heat engines, compare the energy cost per kW

[omgwtfbyobbq]

Originally Posted by trebuchet03

Careful... that is quite easily a fallacy (slippery slope?)...

Thermal efficiency and fuel economy are very different things If you want to compare the efficiency of heat engines, compare the energy cost per kW

If the same test compares the same cars, over the same cycle, with the same engine, and (taller) gearing that's favorable in the turbocharged car for fuel efficiency, with the turbo car getting worse mileage than it's NA counterpart with shorter gearing. It's evident that the turbocharged engine is less efficient (over that cycle ) than the NA engine imo. I dunno what else to control for...

Originally Posted by landspeed

I would say two other reasons are, that turbo engines (at least mine) might enrich the fuel mixture at a lesser throttle than a NA engine, presumably because if you go on full boost, the engine heats up inside, and then cruise at part throttle, it might detonate due to the extra heat that you wouldn't get in a NA engine.

Also, turbo versions of engines generally have a lower compression ratio, again making the engine less efficient. Diesels have an extremely high compression ratio.

Yes. I don't think that's a problem at part load, since at most part load the turbo'ed engine probably still makes less power than the peak for the NA version. More throttle enrichment on WOT and peak might be present, but even then, the turbo Eclipses were intercooled to avoid that very problem. I think all things being equal, at part load, Mitsubishi still had to have the car at stoich.

Originally Posted by Snax

landspeed has it correct. It's about safety margins. While a higher compression motor can afford the random detonation here and there, a turbocharged motor is far less tolerant to it as cylinder pressure is increased. One good detonation event can literally blast the piston ring lands apart or worse. That simply doesn't happen with your average NA motor. So in the case of the turbo, they map extra fuel in to mitigate that possibility as well as reduce timing advance.

I would guess that tolerance to detonation has more to do with the power/L and engine speed where detonation occurs, than any inherent difference between a turbocharged and NA engine. In any turbocharged engine, they need to have more fuel, because they have more air, compared to aNA at the same speed. But, the engine is likely still at stoich for most driving conditions, due to emissions regulations. Any risk of detonation will likely be mitigated a bit by way of well designed intercooler. The turbocharged Eclipse motor put out ~100hp/L, which is what some NA motors can do, so it shouldn't be a matter of adding additional fuel and running the AFR richer than other manufacturers in a well designed system imo. I think you touched the point, different CRs, which imo is why the turbocharged motor was less efficient over the EPA highway cycle. There is probably some portion of the load map where the turbocharged engine is slightly more efficient due to higher peak cylinder pressure and turbocharger efficiency, but because of the supposed power requirements of today's vehicles, most drivers, and the EPA highway test, seldom see that portion. So, for most low load operation, the turbocharged engine will be less efficient than the NA engine imo, and this seems to be backed up by the EPA highway results with the same car/engine.

P.s. You sure that bike is 700 MPG Equivalent Energy?

Originally Posted by SVOboy

I am just saying that I think the diesels honda and toyota bring to the us in the next few years will beat VW in the emissions department, Im not saying that some of their cars aren't comparable.

EDIT: For example, the diesel released in the US will be a 50 state diesel, which no one else has right now: http://www.iht.com/articles/2006/05/...rg/sxhonda.php

Orly? Yarly! Honda, Toyota, or VW may have the cleanest 50 state diesel, but Honda's offering in Europe hasn't been very different, so I doubt it will be much different if/when released over here.

[trebuchet03]

Originally Posted by omgwtfbyobbq

If the same test compares the same cars, over the same cycle, with the same engine, and (taller) gearing that's favorable in the turbocharged car for fuel efficiency, with the turbo car getting worse mileage than it's NA counterpart with shorter gearing. It's evident that the turbocharged engine is less efficient (over that cycle ) than the NA engine imo. I dunno what else to control for...

That's what I'm getting at... the engine cycles are not the same -- "sameness" means the system model is the same -- turbo charging can be modeled as a reheat stage (something the NA system won't have). I'm not saying that particular setup is or isn't more efficient (because the design determines that and there are plenty of ways to design a turbocharger system) - I am saying that it is a fallacy to make that comparison as a statement of general (or possibly specific to this case) fact.


Hands down, I won't argue that the test shows different fuel economy results reliably. Simply, thermal efficiency is 1 - (heat out)/(heat in). Which is why comparing thermal efficiency of two engines VIA mileage can't happen for engines that have different power ratings (unless adjusted by the ratio of power generated - which is not linear).

[omgwtfbyobbq]

Originally Posted by trebuchet03

Which is why comparing thermal efficiency of two engines VIA mileage can't happen for engines that have different power ratings (unless adjusted by the ratio of power generated - which is not linear).

Semantics (or categorization theory ) aside, isn't that what the EPA test does? Provided the comparison is between the same cars with different engine configurations... All they do iirc is put the car on a dyno that simulates the force the car should experience driving over the cycle. So, shouldn't the same car, have the same dyno configuration, and require the same amount of power regardless of engine cycle? Which would then allow for a comparison of BTE of both engines during that cycle, vera?

[trebuchet03]

Originally Posted by omgwtfbyobbq

Semantics (or categorization theory ) aside...

and require the same amount of power regardless of engine cycle? Which would then allow for a comparison of BTE of both engines during that cycle, vera?

It's not semantics

Fuel Economy = The amount of fuel required to achieve the task at hand (that is, make power).
Thermal Efficiency = The amount of heat/energy (in this case chemical) required to achieve a certain amount of work.


While momentum, energy, force etc. are conserved - power is not conservative and therefore must be controlled when doing a comparison. A heat engine that is more efficient, but generates much more power is not expected to need less heat than a heat engine that makes less power and slightly less efficient. That is what I'm trying to get across.

I have a perfect example (complete with P-v T-s diagrams) from my thermodynamics text book on this very subject... Unfortunately - I think I left it at home (200 miles away) because it's not on the book shelf :/

Again, I'm not saying this particular case goes either way... I'm saying that the system models are different and thus comparing the systems is a fallacy.

If put a carb'd engine and a more powerful poorly tuned fuel injected engine (both with the same displacement) on a bench test we can't make the conclusion that carb'd engines have a higher thermal efficiency because the carb'd engine sipped less fuel

[SVOboy]

I am just saying that I think the diesels honda and toyota bring to the us in the next few years will beat VW in the emissions department, Im not saying that some of their cars aren't comparable.

EDIT: For example, the diesel released in the US will be a 50 state diesel, which no one else has right now: http://www.iht.com/articles/2006/05/...rg/sxhonda.php

[landspeed]

Originally Posted by omgwtfbyobbq

That's the great part about the EPA highway test. It's consistent! So, given the same car, one with a NA engine, and another with a turbocharged version of the same engine and a taller transmission, on the same test. It's evident imo, that the turbocharged engine is less efficient than the NA engine if it gets worse mileage, because it's over the same test, in the same car, with the same engine, and a slightly more efficient transmission ratio. The only variable I can think of would be the ECU, but I'm pretty sure that's the same for both, since all cars have to keep the AFR at 14.7:1 during normal driving unless they're lean burn, diesel, or hybrid iirc. .....

I would say two other reasons are, that turbo engines (at least mine) might enrich the fuel mixture at a lesser throttle than a NA engine, presumably because if you go on full boost, the engine heats up inside, and then cruise at part throttle, it might detonate due to the extra heat that you wouldn't get in a NA engine.

Also, turbo versions of engines generally have a lower compression ratio, again making the engine less efficient. Diesels have an extremely high compression ratio.

My car has a lot of torque at about 2000RPM, but, below 1400rpm, there is very little torque at all. The newer 2.0 16v high compression engine (mine is 1.8 8v low comp) is so different; if you just touch the accelerator slightly at 1000rpm, you can feel the power of the engine, and the car will begin to speed up if on a straight or slight downhill. Even the 1.0 Nissan Micra/March 16v engine is like this - a lot of torque low down. With my car, I need to keep the revs at 1500rpm minimum, in order to accelerate at all.

[Snax]

landspeed has it correct. It's about safety margins. While a higher compression motor can afford the random detonation here and there, a turbocharged motor is far less tolerant to it as cylinder pressure is increased. One good detonation event can literally blast the piston ring lands apart or worse. That simply doesn't happen with your average NA motor. So in the case of the turbo, they map extra fuel in to mitigate that possibility as well as reduce timing advance.