Loss of power at 6,000 RPM 2025 GT
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LouG
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Not sure of peak torque rpm for the v8, but all engines drop from that point, it's the increase in rpm that keeps power increasing.
Junkyard Dog
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No, power should not be dropping off at 6,000 rpm on your car, not even slightly.
Why do you say it is dropping off? Do you have a dyno graph? Is this a feeling when driving on the street?
It should be pulling hard right up to red line. Shifting at 6000 rpm or below should result in less acceleration than running it up to the red line.
Why do you say it is dropping off? Do you have a dyno graph? Is this a feeling when driving on the street?
It should be pulling hard right up to red line. Shifting at 6000 rpm or below should result in less acceleration than running it up to the red line.
Cz_Ziemniak
Well-Known Member
It might be pulling timing. Are you using 87 or 93? I'm pretty certain that peak power isn't made with 87, even though the car can run that octane without issues
Cz_Ziemniak
Well-Known Member
Okay, so its def not that. Keep this updated for sure, curious what you end up finding
Junkyard Dog
Well-Known Member
This is just a function of how engines work. Torque is being measured, and horsepower is a function of math. This is why you always see the torque and horsepower figures cross at the exact same point, 5,252 rpm. This means torque is always going to be lower than horsepower after that rpm. It is just math.
Torque is the force being exerted, and horsepower is the work performed, which has to take into account the rpm (speed).
Here is the formula:
"Mathematically, horsepower equals torque multiplied by rpm. H = T x rpm/5252, where H is horsepower, T is pound-feet, rpm is how fast the engine is spinning, and 5252 is a constant that makes the units jibe."
https://www.caranddriver.com/news/a15347872/horsepower-vs-torque-whats-the-difference/#
With that background out of the way, let's turn to the S650 GT engine's dyno graph.
As you note, the torque is "dropping off" at higher rpm. Note that the figures for horsepower and torque cross at 5252 rpm (see the formula above where 5252 is a constant in the formula, so this is always true for every engine). See, however, the horsepower, which is the work being performed (moving your car), is still climbing at that point and on to higher rpms, all the way up to about 7200 rpm.
If you take a look at some of the Whipple dyno graphs for the the Mustang, you will see that forcing more and more air into the engine at high rpm means that the horsepower figure continues to climb even after 7200 rpm.
Remember, torque is just a force. It may or may not be getting any work done. For example, when you torque down nuts, they are not doing any work, but that clamping force is there nevertheless. Horsepower is the work, which accelerates the car. Yes, it is a function of the torque (force) being produced, but it takes into account the work being done. This is why race cars are always operating at high rpm. They are not necessarily getting any more torque, but they are getting more work done (horsepower) at a higher rpm, and therefore moving the car (accelerating) more quickly.
Low rpm is important for a street car, so folks focus more on lower rpm torque, since we can't head off to work out of our subdivision at 6:00 a.m. at a constant 6,500-7,500 rpm.
Remember, too, that there is torque multiplication through transmission and rear end gears, and the higher your rpm, the more torque multiplication you are getting v. another car that shifts earlier and has less rpm.
Anyway, this is a long way of saying something is wrong with your car if you feel like power is falling off at 6000 rpm. My Dark Horse pulls hard at full throttle all the way up.
Junkyard Dog
Well-Known Member
I realized I may have left the false impression that torque always decreases after 5252 rpm. This is not true. For factory engines, however, the peak torque is almost always below that rpm, around 4000 or so. The Coyote engine is an outlier in having a torque peak that is at 4,900 rpm, higher than almost all other v-8s from the factory. This is because cars produced to be driven on the street need to operate at lower rpms.
Pure race engines may have torque peaks at much higher rpms. They still, however, will have horsepower and torque cross at 5252 rpm. Both lines may still be climbing after that point, but horsepower will always be higher after that point.
Formula 1 engines may make peak torque around 10,000 rpm and peak horsepower around 18,000 rpm.
Compare that to the Coyote in the S650, in which those peaks are 4,900 and 7150 (unless you have a Dark Horse, in which case it is 7250).
Pure race engines may have torque peaks at much higher rpms. They still, however, will have horsepower and torque cross at 5252 rpm. Both lines may still be climbing after that point, but horsepower will always be higher after that point.
Formula 1 engines may make peak torque around 10,000 rpm and peak horsepower around 18,000 rpm.
Compare that to the Coyote in the S650, in which those peaks are 4,900 and 7150 (unless you have a Dark Horse, in which case it is 7250).
Cz_Ziemniak
Well-Known Member
This is a really great explanation of how it all relates.
Horsepower is, more or less, just an imaginary number that represents the amount of work (torque) is being done. The more torque at a higher speed, the more power (theoretically).
Its why old Honda's with low torque were able to make such impressive power for the time. They simply did that work at such high engine speeds. Spin anything to 9,000 RPM and it'll impress. They're just doing a little work really really fast.
Junkyard Dog
Well-Known Member
So one could look at that dyno graph and say, Oh, no! The torque is dropping off after 10,000 rpm, but the reality is that the Formula 1 engine will be pulling hard up to 18,000 rpm.
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