What's so evil about 3000+ RPM?

Depends on the engine.. In some cases, the engine running that fast at highway speeds may indicate the vehicle isn't geared as well as it could have been for highway fuel economy (ex: no overdrive gear on the automatic transmission)..

Not sure what you mean? Do you consider 3000 RPM too much or too little? Are you talking "grocery getters" or "performance" cars?

Also what SIZE 4 cyl? Percentage wise, they can vary quite a bit from the largest to the smallest.

The distance the piston travels is the same if comparing a 3" stroke at

The manufacturer know what they're doing when it comes to getting the best MPG out of a car. They would change engine speed and gearing if it resulted in an improvement in the design goals for that vehicle. It takes X horsepower to maintain highway speed and they are going to run the engine at the most efficient speed to do it. That's probably going to be in the general RPM range where the best torque is available.

Now if you are talking about "performance cars", there are different trade offs.

Nothing in and of itself, although higher revs may cause faster engine wear and certainly more noise. I used to have a 16V GTI that turned about 4K at 75-80ish... sold the car to a friend and she's still driving it...

nate

Shucks, and there I was thinking my 3krpm at 75mph was geared a little on the short side! In fact, it kinda is, given that the power peak happens at around 4.3k, but this does have the advantage of providing decent passing power at highway speeds. Turbo boost is always nice... :}

My geo metro runs about 4K at 75MPH which is where it cruises at on the freeway. 220K on the original unopened motor. 3cyl, 5 spd.

Bull s*it.

If you lug an engine with too low an rpm it will wear faster and use a lot more gas.

If I rev my Jeep at 2300 rpm on the highway at 65 mph, it purrs and I get 19 US mpg. If I use 5th gear and run at 1700 rpm at 65 mph, it makes bad noises or rattles on the hills and my mileage drops to 14 or less mpg.

Mike

stu wrote: