Your example is a good one to show that the F22C will always have enough torque to produce the required horse power at 4K RPM's to produce 75MPH. The problem that the OP is concerned about is max power speed. This is where you will see significant differences based on atmospheric changes. The torque produced by the engine at 95F versus 9F is dramatic in this little engine. So the horsepower will be much lower at 8K RPM, and the car will be slower.

An AP2 example (real world) for my 04 would be with 4th gear, since I routinely use it for passing. On a 75F day I will reach 99-100MPH at 8K RPM. On a 105F day, it will reach 93MPH at 8K RPM's.

If you ever have a chance to watch Indycar qualifying, you will always see the drivers jockeying for position for optimum track conditions (cooler track temps predominently). Even though all of their cars rev to 10,300 RPM, they will produce more power and speed if it gets cooler without changing their setup.

If you ever have a chance to take a boat from Florida (sea level) to Atlanta (3000'MSL), the Florida boat that used to do 45MPH will now be lucky to do 40MPH. That's with the same gearbox, propeller and fuel in fresh water at max RPM. Less torque, less power, less speed.

If you ever have the chance to fly aircraft, you will become intimately familiar with engine performance charts.

If you ever take
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Well, my ap2 does 100 at 8k in 4th gear no matter what the damn temperature is. It just might take a while longer to get there. 8k rpm is still 8k rpm. Perhaps you're describing it wrong, but what I'm getting from your post is that more power = higher top speed in gear. By that logic a 400hp turboed s2k would go well past 150mph in 4th. It just won't happen. All adding or reducing power (from heat loss or atmospheric changes) does is make it faster/slower to climb the speed in that gear. The only reason a car would go any slower in a gear is if it didn't have the power to continue climbing up the rpm band, which would require less then 1/2 throttle in the S2k.

And every aircraft and boat I've EVER seen didn't have a transmission or gearbox, so if they lose power, then they can't rev as high, and won't go as fast.

 

Planes and boats are affected by wind speed and current. A plane flying into a headwind will fly much slower than a plane with a tailwind at the same RPM...same with boats. Not the same with cars, unless your clutch is slipping.

 

Your example is a good one to show that the F22C will always have enough torque to produce the required horse power at 4K RPM's to produce 75MPH. The problem that the OP is concerned about is max power speed. This is where you will see significant differences based on atmospheric changes. The torque produced by the engine at 95F versus 9F is dramatic in this little engine. So the horsepower will be much lower at 8K RPM, and the car will be slower.

An AP2 example (real world) for my 04 would be with 4th gear, since I routinely use it for passing. On a 75F day I will reach 99-100MPH at 8K RPM. On a 105F day, it will reach 93MPH at 8K RPM's.

If you ever have a chance to watch Indycar qualifying, you will always see the drivers jockeying for position for optimum track conditions (cooler track temps predominently). Even though all of their cars rev to 10,300 RPM, they will produce more power and speed if it gets cooler without changing their setup.

If you ever have a chance to take a boat from Florida (sea level) to Atlanta (3000'MSL), the Florida boat that used to do 45MPH will now be lucky to do 40MPH. That's with the same gearbox, propeller and fuel in fresh water at max RPM. Less torque, less power, less speed.

If you ever have the chance to fly aircraft, you will become intimately familiar with engine performance charts.

If you ever take
[/quote]

This makes ZERO sense with respect to cars. RPM @ speed is RPM @ speed, regardless of power.

Everything else being equal, a car (an S2000 let's say) with 100hp with be at the same RPM as a car with 200hp. Again, assuming gearing, tire size, etc, all stay the same. As others have said, you might get there slower when it's hotter out due to loss of power, but you will always turn the same RPM.

 

Horsepower=(torque x RPM)/5252. If torque (ability to do work) is lowered due to whatever reason (in this case atmospherics), horsepower will drop and the associated friction and drag inherent at high speeds will cause top speeds to be reduced. Here is a short, easy to read description of what happens with this equation:

http://www.nsxprime.com/FAQ/Miscella...queHPSpeed.htm

 

I understand frictional losses and losses due to atmospheric conditions. Again, YES, your top speeds and/or acceleration can be reduced...but your RPM's for a given speed/gear will ALWAYS be the same. This only changes if you change gearing/tire sizes. Horsepower and torque have nothing to do with that.

 

The article says nothing that supports your theory. It says top speed is reduced by friction, atmosphere etc...

That means the engine will not produce enough power to reach redline in the top gear. RPM's don't just magically disappear.

Ever use an online RPM calculator? They ask for gear ratios and tire diameters, that's all they need to determine speed. They don't ask how much power your engine makes because it's irrelevant.

 

INDYMAC-

This is a gear ratio/speed calculator for the S2000 (AP2 stock).

This does not change, no matter the weather, altitude, etc.

 

Thanks for the graph TrboLag. It is a useful ballpark tool, and is probably very accurate on a standard day. But reality is reality, and that's all I'm here to report about. Here is a dyno I did not too long after I bought my car. I had three pulls done in 4th gear to rev limiter. The car was completely stock with about 3K miles on it (still had OEM engine oil fill). At 8033 RPM it was doing 93 MPH. There was no fan blowing the engine cool in the garage, and I actually don't know which pull this was (but I think it was the 2nd pull with the highest horsepower number).

https://www.s2ki.com/s2000/gallery/image/379953-dyno-1/

This is the type of performance I see in the Texas heat with the AC on. But come fall and winter above 40F, I have no trouble reaching 99-100 MPH in 4th gear.

Trust me, I'm not trying to misdirect anyone here. I'm just trying to correlate some physics to the phenomenon expressed by the OP.

I also spent 24 years as a Naval Aviator flying P-3C Orions. I still have my NATOPS manual, so if anyone wants me plug in some numbers for aircraft performance, I'll see if I remeber how.

 

A shining beacon for the armed forces right here.

 

The relationship between the speed of the engine (RPM) and the speed of the vehicle (MPH) is constant is any specific gear and does not vary based on power output. You could turn the car off, put it in gear, and tow it to a specific speed, and the rpm/mph relationship would be the same.