What makes cars fuel efficient?

[dosco]

Originally Posted by Hateful

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.

OHV = OverHead Valve = pushrod directly actuates valves.

As opposed to OHC = OverHead Camshaft = cam directly actuates valves.

Wikipedia is your friend.

[Hateful]

Originally Posted by dosco

OHV = OverHead Valve = pushrod directly actuates valves.

As opposed to OHC = OverHead Camshaft = cam directly actuates valves.

Wikipedia is your friend.

I'd say I've got the OHV,then.

[jbmorse02]

Originally Posted by RoadWarrior

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. 1985...

I agree. My dad's 83 vw westy weighs a lot and has something like 84 horsepower. The only time this is a slow vehicle is when you start out on a steep hill. It's adequately powered and maintains 70mph easily.

People think they want power but they don't realize you don't need much. In Europe small cars can come with 1.2 liter engines. In the US, if you want a vw rabbit, you get a 2.5l 5 cylinder. Isn't this overkill?

[GasSavers_Ryland]

horse power is always peek horse power and that peek is around 5,500 - 6,000 rpm on most civic engines, the peek torque on the other hand ranges between 3,000-4,500rpm, the cars that get better mileage tend to have better torque and at lower engine speeds like the crx hf had peek torque at around 2,500rpm and because of that feels like a very powerful car even tho the peek horse power was around 60hp.

[67 Satellite]

Originally Posted by RoadWarrior

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.

Regardless of whether you have all the cams on one shaft,or an individual cam shaft for each valve,they need to turn at 1/2 the crankshaft r.p.m. in a 4 cycle engine to stay in time.That being said,reducing valve train mass does help efficiency.It will take less spring pressure to control valvetrain motion resulting in reduced friction, and fewer total parts.

[GasSavers_RoadWarrior]

Yeah, you know that made my brain itch when I typed it, read that somewhere recently, hadn't thought about it carefully. Maybe that's what it was, the reduced mass, due to driving pairs of valves off one lobe and needing less leverage or something.

[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.

[froggy81500]

Originally Posted by suprapsu

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?

The Aveo for fuel economy sucks. We had a rental Aveo for a month while our Ion was getting put back together after getting hit by a paving truck. For a car that size and a smaller motor, it should do better than that. My '06 Ion 2 manual has seen 2 tanks run to 37+ MPG. The Ion is bigger and heavier and also .6 Liters more displacement than the Aveo and yet gets better MPG.