What makes cars fuel efficient?

[Hateful]

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.

[dkjones96]

Originally Posted by Hateful

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).

[VetteOwner]

Originally Posted by dkjones96

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).

lol exactly, i was hauling around about 400 lbs of dirt + me and another adult around in my 2.2L s-10 and acceleration was no different. sure its only got like 96 HP at the wheels but it has a buttload of torque

chevette engine specs1.6L all iron everything)

bore and stroke: 3.228 x 2.980
82.0 x 75.7 mm

compression ratio: 8.5:1

net HP/@rpm: 70 @ 5200

max torque@rpm: 82 @ 2400

i belive 0-60 was in the 17 second range

[monroe74]

"From my observations what makes these vehicles so fuel efficient? 1) Lower HP"

This shouldn't be oversimplified. For example, compare the VX and CX ('92-'95). The VX has 31% more power, and still gets 13% better mpg. Why? Because the CX was built to be cheap to buy, and the VX was built to use less gas.

The VX has a bunch of subtle tricks to boost FE, like roller cam followers to reduce engine friction.

A good technical listing of various VX FE ingredients is in this pdf.

"i own a civic VX and I have to say its not that bad."

The VX has 18% more torque (and the same weight) as the Fiat 124 Spyder I used to drive. That was considered a sports car. What's happened is that our expectations have changed. Trouble is, we can't really afford our new expectations.

[StorminMatt]

Originally Posted by monroe74

"From my observations what makes these vehicles so fuel efficient? 1) Lower HP"

This shouldn't be oversimplified. For example, compare the VX and CX ('92-'95). The VX has 31% more power, and still gets 13% better mpg. Why? Because the CX was built to be cheap to buy, and the VX was built to use less gas.

The VX has a bunch of subtle tricks to boost FE, like roller cam followers to reduce engine friction.

A good technical listing of various VX FE ingredients is in this pdf.

"i own a civic VX and I have to say its not that bad."

The VX has 18% more torque (and the same weight) as the Fiat 124 Spyder I used to drive. That was considered a sports car. What's happened is that our expectations have changed. Trouble is, we can't really afford our new expectations.

I think that performance/acceleration is not really the issue. The REAL issue is WEIGHT. Someone before mentioned the Rabbit. Now the Rabbit may be considered to be a small car. BUT, this 'small car' happens to weigh a whopping 3000 pounds! 15-20 years ago, even a midsized car like a Honda Accord or Ford Taurus didn't weigh THIS much. HP is simply high because it NEEDS to be. 170HP sounds like alot for a small car. And, as anyone who has ever swapped a GSR motor into a CRX can tell you, it IS - if the small car only weighs around 2000 pounds. But a 3000 pound car needs this kind of HP just to be able to accelerate somewhat decently. The same goes for most any car out there. Although HP has skyrocketed, it has really not outpaced weight by very much over the years. And, once again, as anyone who has done a GSR swap on a CRX can tell you, mileage did not suffer as a result of the swap. This suggests that WEIGHT is a bigger problem than HP.

One more thing. Someone mentioned drag. This is another problem, ESPECIALLY with small cars (which tend to be MUCH less sleek these days than larger offerings). If you look at a 15-20 year old small car vs a new one, the new one is guaranteed to be taller and chunkier than an offering from the late 1980s or early 1990s. Perhaps the extreme example of this is the CRX, which was known for its GREAT mileage (especially in HF form). But even a VX looks sleek and aerodynamic compared to the overly tall small cars you see today. THIS is probably a big reason why small cars are just not very economical these days. And, because small cars tend to be MUCH less sleek these days than larger offerings, this is probably also a major reason why so many small cars just can't beat the fuel economy numbers of (much sleeker) midsized sedans by much of a margin these days.