How do they make smaller engines more powerful but still fuel efficient?

[Tobin S.]

I'm not much of a mechanic, but hopefully I'll make some sense here.

I used to have a 2002 Chevy S-10 that had a 4.3 liter V6 in it and a manual 5-speed transmission. It was capable of generating 190 horsepower and I could squeak 20 mpg out of it overall if I took it easy. I went out looking at cars recently and checked out a Honda Civic SI. It's a sporty version of the Civic. It has a 2.0 liter 4 cylinder motor that can generate 197 horsepower hooked up to a 6-speed manual transmission and it gets 24 mpg overall- half the motor, more horsepower, and better fuel mileage than my S-10.

How do they do that? I'm guessing the weight of the vehicle might have a little to do with it, but the S-10 isn't exactly the sumo wrestler of trucks.

[flvegan]

1. Tweak the hell out of them.

Actually, cars are generally getting heavier these days, what with all the safety and convenience equipment. While carbon fiber and aluminum is being used more on high end cars, something like the Civic won't come stock with anything like that anytime soon.

I know one of the big parts of the Si engine upgrade is upping the internals (compression is a couple points higher, IIRC) and tweaking spark, electrics, etc. Having an 8k rpm redline doesn't hurt performance, either (not that it makes horsepower). So much of it is computer related these days. Air flow, spark and fuel management, timing, and so on combined with a well-managed and thought out engine and exhaust.

When I was in high school I had a Corvette. Naturally it came with a 350 cubic inch V8, but stock had 180 or 190 horsepower. MIGHT have gotten 15 mpg. Today, I have a Mazdaspeed 3. 2.3 liter 4 cyl, factory turbocharged, 263 horsepower. I get well over 20 mpg while driving like a maniac.

We've come a long way.

[ceveritt]

5. rpm + hp

Pardon me, but how can you say an 8k redline doesn't make horsepower?

The most common equation for figuring horsepower is:

BHP = torque in lb./ft. X rpm divided by the constant 5252

Therefore horsepower is directly related to rpm.

If I'm missing or misunderstanding something from your post, I apologize.

As to how smaller-displacement engines can make more power and be more fuel-efficient than larger ones, there are a variety of answers. Primarily it's rpm. Smaller-displacement engines simply have to spin higher, as per the equation above. Smaller engines cannot produce the torque of larger ones, so rpm is the answer. On top of that, manufacturers spend a lot of time and money these days optimizing intake and exhaust systems; better breathing brings with it power and efficiency. Likewise, manufacturers also concentrate heavily on combustion chamber design, for the same reasons. Plus, many modern smaller-displacement engines also utilize variable cam/valve timing to optimize breathing—and therefore boost torque and ultimately horsepower, and efficiency. Lastly (for now; a more informed/educated person on the topic could go on at length) modern materials and friction-reducing formulas have also contributed to increased efficiency, although such things will work on all engines.

I hope I might have been some help here. If not, or someone sees I am in error, please correct me.

CE

[safeinOhio]

2. They've come a long way

My 1950 Buick has a Fireball straight 8. Huge, must weigh 600lbs and 4 feet long. Churns out a whopping 130 hp. About what my Sunfire has. I have a 8.1 Lt, 300 hp motor in my truck and it even looks small to me.
For some fun reading and to see how far we have come, try reading the maintenance schedule for a 1950 model.

[beevul]

3. Two words...

Forced induction.

[Blue_Tires]

4. direct injection will become more widespread in the future, too

and hopefully, (if the auto gods are listening), more lightweight technologies