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Old 04-17-2007, 10:17 PM   #11
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I thought that you were saying that the increase in back-pressure from a turbo would harm mileage, in which case something like a larger or chopped off muffler would solve, or at least help the problem.
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Old 04-17-2007, 10:27 PM   #12
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How does the turbo leech power? The only thing I can think of is the extra power to pump the oil to the turbo, and that's minimal.

Exhaust gas energy is wasted in a car, and that's all that the turbo taps into. A well designed exhaust for a turbo has no back pressure at all, so the turbo doesn't push against that....

How is it not free power?
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Old 04-17-2007, 10:51 PM   #13
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Originally Posted by repete86 View Post
I thought that you were saying that the increase in back-pressure from a turbo would harm mileage, in which case something like a larger or chopped off muffler would solve, or at least help the problem.

It should (I mean, there is tuning involved for scavenging and such but a turbo is significant).... but the back pressure is coming from the turbo itself, not the muffler or other components. Reducing inefficiency from other parts of the exhaust system will help, but you still have that turbo in the way :P
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Old 04-17-2007, 11:01 PM   #14
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It's kinda iffy either way. A turbo does impose a restriction, and has a narrow band where at optimum efficiency, so it will reduce the volumetric efficiency of the engine at some combination of engine/turbo speed. Otoh, a turbocharged engine can make the equivalent amount of power that a larger displacement NA engine could, w/o the increase in pumping losses, gearing/car being equal. So, it's more powerful than a NA engine of the same size, but more efficient than a NA engine making the same power, kind of a compromise, but it's still less efficient on average than a NA version of the same car/engine/etc...

For instance, the 95' 2G Eclipse came in 2L turbo and NA flavors, and the turbocharged versions had a little less in the way of EPA highway efficiency, even though they had slightly taller gearing. By twincharging, a manufacturer can get better fuel efficiency, while still maintaining a supposed acceptable power level for the consumer. But, I'm pretty sure a 1.4L NA engine would get better mileage than the twincharged version all things being equal. This is just for gas engines, and diesels tend to see some significant efficiency increases imle, especially from variable vane turbocharging.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 04-17-2007, 11:11 PM   #15
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^^ that pretty much sums it up

I just wanted to make sure that it wasn't assumed a turbo was "free" - it takes energy to compress a gas (luckily, a good deal would have been wasted) :P
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Old 04-18-2007, 08:25 AM   #16
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isn't VW's TSI engine a direct injection gas engine? from what I was reading about a while back that was part of what made it more efficent, and why it's taken this long for it to be made, that direct injection of gasoline in to a combustion chamber has it's own set of problems.
I think it would be great if someone like honda came out with something like a 1 liter turbo charged v-tec engine to compeat what VW is doing.
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Old 04-18-2007, 03:10 PM   #17
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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
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Old 04-18-2007, 03:16 PM   #18
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Quote:
Originally Posted by Ryland View Post
isn't VW's TSI engine a direct injection gas engine? from what I was reading about a while back that was part of what made it more efficent, and why it's taken this long for it to be made, that direct injection of gasoline in to a combustion chamber has it's own set of problems.
I think it would be great if someone like honda came out with something like a 1 liter turbo charged v-tec engine to compeat what VW is doing.
Honda is reluctant to use turbos for a few reasons, the main one seeming to be that they make engine well enough without them (which is something I wouldn't be able to say about VW).

It is hard to compare honda and vw for a few reasons. Honda builds hybrids where VW doesn't. VW just doesn't want to, . 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).

But, more importantly, Honda does build the kind of small car that you're thinking of. However, like VW, it won't release it in the US,
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Old 04-18-2007, 03:45 PM   #19
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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.

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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?
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 04-18-2007, 06:58 PM   #20
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Quote:
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
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