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Old 05-08-2008, 08:58 AM   #1
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What makes cars fuel efficient?

Cars back in the day were much more fuel efficient than todays cars.

For example.

The 1992 - 1995 Civic VX gets from 42 - 60 MPG
The Geo Metro Xfi gets from 40 - 65 MPG

From my observations what makes these vehicles so fuel efficient?
1) Lower HP
2) Light Weight

Now comparing to Compact cars today why can't we have gas efficient cars like these without the battery pack?

I think safety regulations play a big deal in part of this because there are certain guidelines to how much a vehicle has to weigh and there is a min. HP it has to have.

Even the new Chevy Aveo gets 24-34 MPG which I think its not that great when you factor it's 1.6liter engine and it's weight of 2300lbs. It should be getting at least 30 city and 40 HWY

Is there anyway to modify the Aveo's transmission so that it gets this kind of MPG?
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Old 05-08-2008, 09:06 AM   #2
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I also blame whiny barsteward auto hacks and reviewers who complain about 0-60 times being "poor" at 9 seconds.... back in the day anything doing better than 15 was a sports model. Least powerful motor you can buy in a compact these days? 105 HP I think... which was the most powerful motor you could get in a Chrysler minivan back in 1985...
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Old 05-08-2008, 09:12 AM   #3
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i own a civic VX and I have to say its not that bad. I get good FE and not have to sacrifice performance. I also had the geo metro and I have to say that its handling was pretty bad but its performance was okay to get by with.
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Old 05-08-2008, 09:52 AM   #4
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less efficient: more cams and valves. more moving parts, more friction parts (more valves=more pressure against cam, more resistance as they have to climb the lobes, more pressure on bearings). Emissions equipment and tuning, both noise and gaseous.

that's why the dinosaur of an engine in my truck gets 25 mpg mixed. 4 speed manual (no OD), 2.5l (big engine for this forum), and a computer that makes a pocket calculator feel good but OHV and a gear-driven cam. that and the springs are so light the valves float over 5k or so I've heard. hell it got 24 mpg going 65mph carrying 1000lbs
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Old 05-08-2008, 09:55 AM   #5
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It's a conspiracy I tell you.
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Car mods are overrated. Just gotta adjust that nut behind the wheel for best mpg.



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Old 05-08-2008, 10:28 AM   #6
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Was just looking up my drag coefficient (.36) and saw lots of bad reviews saying my Cavalier didn't have enough cam and valve stuff and only 115HP.I didn't see any complaint about the high drag or low EPA estimated MPG's.
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Old 05-08-2008, 10:43 AM   #7
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Theoretically, when you have one cam driving intakes, and one cam driving exhausts, you can have them turning half the speed with shallower ramped lobes. This means both that friction is reduced, because it increases with the square of RPM, so two 1500 RPM camshafts cause less frictional drag than one 3000 RPM camshaft at the same motor speed, additionally, because of the shallower ramps, I believe less powerful springs are required to keep the valve on profile and stop it skipping or floating, so there's less lossage there too.... however, they only get into premium engines that are tuned more for power because higher parts count means higher production and assembly costs, so it's not immediately obvious that twin cams=higher efficiency.
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Old 05-08-2008, 11:02 AM   #8
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I wouldn't call them effecient.

They waste most of the energy they consume.

Hypermiling demonstrates this perfectly.

To be effecient they need to be designed to hypermile naturally, without the driver having to be distracted from staying alive.

Every act it takes to hypermile could be programmed to perform automatically, which makes it a practical solution immediately.

The next step is to make it mandatory that every vehicle have a regenerative capacity so there is no need to use friction brakes. It's called a launch assist axle.

Then they need to be able to shut off and restart the engine rapidly with minimum fuss, to eliminate the totally wasted fuel consumed at idle.

Next you have to disconnect the engine from the accelerator pedal, by using the transmission for acceleration with the engine and some form of short term high output storage, enough for one acceleration cycle. I like flywheels or hydraulic storage for this becasue both systems are reaching the threshold of efficiency to make them the best system for great acceleration combined with the engine if necessary.

They will also be virtually maintenance free with 500K life expectancies, and actually take about 600 fewer parts per vehicle to build. Take a 1500 pound vehicle with a 1 liter turbocharged HCCI multifuel engine, connect it to an infinitely variable drivetrain with capacitive storage and you have the ingredients to make a vehicle that can maintain any speed while the engine does exactly the same thing as an engine off coast in hypermiling but the storage and transmission allow a constant vehicle speed.

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Old 05-08-2008, 11:02 AM   #9
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Quote:
Originally Posted by Hateful View Post
Was just looking up my drag coefficient (.36) and saw lots of bad reviews saying my Cavalier didn't have enough cam and valve stuff and only 115HP.I didn't see any complaint about the high drag or low EPA estimated MPG's.
OHV 2.2? Wonderful engine, doesn't rev well but down low it pulls great. Gotta say it's by far one of the best 4 bangers I've ever driven too. With the 36MPG freeway, a/c full blast and 80mph cruise speed I can't say I was unhappy with the mileage either. 219k miles and lost MAYBE 1/4th quart of oil between 5,000 mile changes. The only reason my 2.0 now even slightly holds its own against it is it's cammed to make peak torque at 3,000rpm and nothing past 4500 lol

As far as inefficiency, I'd say size is one factor but the engine is your biggest culprit. That 1.6 in the Aveo we actually ran some testing on yesterday, that poor little engine is so gutless down low I'm suprised it gets 24MPG driving around town as it is, probably the low displacement. It's the first car I've seen we had to redline to make it up a couple of the acceleration ramps on our fuel economy test. Engine inefficiencies is one of the things I hope to address when I start working R&D with an automaker (crossing fingers).
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Old 05-08-2008, 11:19 AM   #10
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it's a 2.2L, I don't know what OHV is. It's got 2200 SFI on the injector cover.I was relieved to find I have a timing chain rather than a belt at 85K miles.
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