I've been thinking this over, and at one point I couldn't see it working harder in 4th as opposed to 1st at 4000 rpm's. An engine running at 4000 rpm's is an engine running at 4000 rpm's right? Why or How would it function any different? But then I got to thinking. A car running in 1st at a certain rpm has a certain drag due to air resistance. As speed increases that resistance increases also. So in 4th gear at that same rpm the resistance has increased. Assuming you can hold a constant motor speed in both instances which would result in a constant vehicle speed....do a free body diagram with all forces equal to zero for both instances. Using F=ma, Force=Mass x Acceleration. Where A=0 (acceleration) therefore F=0. F being the net force on the body (car).
This means due to the increase in drag there must be an increase in power from the motor to maintain that speed and compensate for the increased drag, also fulfilling the equation. The physics is simple, the motor works harder to maintain a higher speed. I think what we aren't putting into consideration is gearing, which may answer the question, how does an engine output two different powers at the same rpm in a different gear?

Just something to think about.

 

 

"working as hard" = "making as much power" in my opinion. Perhaps wantone meant it differently than that, dunno, I'm not a mind reader. I also threw in the assumption that we're talking about full throttle. Because if we're at 10% throttle in 1st gear, and 50% throttle in 6th gear, obviously the engine will be making more power (ie, working harder) with the larger throttle opening.

 

on a dyno, is there a particular gear that you measure peak HP/TQ?

I think that a moving car in 1st gear and a moving car in 4th gear at 4000 RPM the engine is doing the same work.

take the tranny off and the engine will never know.

Dave

 

how about if you're riding a bike and your feet are turning the pedals at 50 RPM. you're covering a fair amount of ground. then have two people pick the bike up off the ground while your feet are still pedaling the same speed. are you still doing the same amount of work?

 

There's a difference between steady state and acceleration - Just as friction and gravity are constant, work to offset them is. When you're driving at 4,000 rpm in 4th gear, you're actually constantly accelerating against friction. Friction is different between 1st and 4th gears at 4,000 rpm, as is acceleration. Barring friction, 4,000 rpm is 4,000 rpm no matter the gear.

 

baring friction? what? we live in an imaginary world?

My friend asked me if I can slam dunk from the free throw line. I told him I could, baring gravity.

 

how does outside air resistance (drag) relate with the speed of the motor? isn't it an enclosed system? i would imagine 4k RPMs in 1st is the same work as 4k RPMs in 4th.

as far as drag goes, wouldn't that change how fast (velocity) you are moving from those 4k RPMs in the same gear?


edit: nevermind, didn't mean enclosed system. air in, air out. i meant like, drag works on the car, not on the engine...right?

 

lol. good call. in real world, is 4k rpm in neutral the same as 4k rpm in 1st during WOT the same as 4k rpm cruising at 74 mph? no.

 

Obviously we don't but you can't seem to seperate the principles from each other. Go back and read my description of the car driving down hill, and that should satisfy your real-world requirements.