Probably another dumb question

[Motorhead350]

I was wondering if our cars (or cars in general) always make their peak horsepower when they reach full RPMs. For example when we go down the 1/4 mile track we give it WOT and go through the gears and we know we have got 456RWHP going on.

Now if I'm just going outta a toll way with half throttle, but the RPMs still go all the way to 6,000 or maybe 4,000 before a shift, did I actually use all the horsepower dispite that it wasn't WOT, BUT I went though the RPMs anyway?

I know on a dyno it'll say our peak is around 5,000 give or take, but is that only under WOT? I guess that's the best way to break down my question.

[03blackmerc]

i would say you would have to be at WOT to make the peak Horse power. i know in like 5.0 liters the peak horsepower is at 5200 RPM and redline is 6000. so no real point to rev it all the way to redline. i understand what you mean because in my MM i dont have to be to the floor to see the tach go to Red line.

[Joe Walsh]

Measuring Horsepower:
If you want to know the horsepower of an engine, you hook the engine up to a dynamometer. A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load.

Torque:
Imagine that you have a big socket wrench with a 2-foot-long handle on it, and you apply 50 pounds of force to that 2-foot handle. What you are doing is applying a torque, or turning force, of 100 pound-feet (50 pounds to a 2-foot-long handle) to the bolt. You could get the same 100 pound-feet of torque by applying 1 pound of force to the end of a 100-foot handle or 100 pounds of force to a 1-foot handle.
Similarly, if you attach a shaft to an engine, the engine can apply torque to the shaft. A dynamometer measures this torque. You can easily convert torque to horsepower by multiplying torque by rpm/5,252.

You can get an idea of how a dynamometer works in the following way: Imagine that you turn on a car engine, put it in neutral and floor it. The engine would run so fast it would explode. That's no good, so on a dynamometer you apply a load to the floored engine and measure the load the engine can handle at different engine speeds. You might hook an engine to a dynamometer, floor it and use the dynamometer to apply enough of a load to the engine to keep it at, say, 7,000 rpm. You record how much load the engine can handle. Then you apply additional load to knock the engine speed down to 6,500 rpm and record the load there. Then you apply additional load to get it down to 6,000 rpm, and so on. You can do the same thing starting down at 500 or 1,000 rpm and working your way up. What dynamometers actually measure is torque (in pound-feet), and to convert torque to horsepower you simply multiply torque by rpm/5,252.

Graphing Horsepower:
If you plot the horsepower versus the rpm values for the engine, what you end up with is a horsepower curve for the engine. A typical horsepower curve for a high-performance engine might look like this (this happens to be the curve for the 300-horsepower engine in the Mitsubishi 3000 twin-turbo):
http://i984.photobucket.com/albums/ae326/JoeJWalsh/horsepower2.gif

What a graph like this points out is that any engine has a peak horsepower -- an rpm value at which the power available from the engine is at its maximum. An engine also has a peak torque at a specific rpm. You will often see this expressed in a brochure or a review in a magazine as "320 HP @ 6500 rpm, 290 lb-ft torque @ 5000 rpm" (the figures for the 1999 Shelby Series 1). When people say an engine has "lots of low-end torque," what they mean is that the peak torque occurs at a fairly low rpm value, like 2,000 or 3,000 rpm.

Another thing you can see from a car's horsepower curve is the place where the engine has maximum power. When you are trying to accelerate quickly, you want to try to keep the engine close to its maximum horsepower point on the curve. That is why you often downshift to accelerate -- by downshifting, you increase engine rpm, which typically moves you closer to the peak horsepower point on the curve. If you want to "launch" your car from a traffic light, you would typically rev the engine to get the engine right at its peak horsepower rpm and then release the clutch to dump maximum power to the tires.

Dom, you can learn a lot of things from the internet!
I just found this site called 'Google' !!!!

[MrBluGruv]

It is definately only at WOT, frankly I kind of think this is a silly question.

The logical way to look at it is that your dyno sheet shows you the power produced at WOT at a given RPM, if you wanted to know what 75% throttle makes at 5000 RPM, then take the power number from your dyno sheet at the RPM and scale it to 75% of that number.

[Haggis]

Dom, you can learn a lot of things from the internet!
I just found this site called 'AskJoe' !!!!

I would rather ask Joe myself then try to find it on the internet. By the way did you hear the inventor of the Internet is getting divorced?

[Egon Spengler]

I would rather ask Joe myself then try to find it on the internet. By the way did you hear the inventor of the Internet is getting divorced?
I heard that! Too funny! Tipper and Al no more!

[Joe Walsh]

I would rather ask Joe myself then try to find it on the internet.

By the way did you hear the inventor of the Internet is getting divorced?

I try to help fellow members whenever I can...especially really confused members!....:P


I heard that! Too funny! Tipper and Al no more!

After 40 years? What's the point?
I guess that Al-Tipper liplock that was on the national news was all for show.

Al must have met some young hottie from Greenpeace and they are discussing each other's carbon footprints....:rolleyes:

[Egon Spengler]

I try to help fellow members whenever I can...especially really confused members!....:P



After 40 years? What's the point?
I guess that Al-Tipper liplock that was on the national news was all for show.

Al must have met some young hottie from Greenpeace and they are discussing each other's carbon footprints....:rolleyes:
Al invented the internet and the easy accessibility of porn on there tore them apart. He would spend countless hours locked in his room stroking his ego for inventing the internet and then stroking something else to what was on his creation!

[Motorhead350]

I didn't exactly know how to phrase this question. It's not like pregnancy.

[SpartaPerformance]

I was wondering if our cars (or cars in general) always make their peak horsepower when they reach full RPMs. For example when we go down the 1/4 mile track we give it WOT and go through the gears and we know we have got 456RWHP going on.

Now if I'm just going outta a toll way with half throttle, but the RPMs still go all the way to 6,000 or maybe 4,000 before a shift, did I actually use all the horsepower dispite that it wasn't WOT, BUT I went though the RPMs anyway?

I know on a dyno it'll say our peak is around 5,000 give or take, but is that only under WOT? I guess that's the best way to break down my question.

No. Dyno HP numbers are at wide open throttle so you're not going to make that figure grannying out of a toll booth. LOL HP is a function of torque. HP = (Trq * RPM)/5250 so your car maybe at 6,000 rpm but if you're only making 100 trq due to 1/4 throttle then your HP is 114.28. At 1/4 throttle you have less air and fuel then WOT.