Horsepower vs Torque?
Racer
Joined: Dec 2017
Posts: 331
Likes: 74
From: Florida
Read carefully "starting force" and "starting power" (ie combustion strength or force) You're not increasing the strength of the combustion process in the cylinder by adding leverage to the equation. You do increase torque in the end result, but I meant to split hairs here.
I'm not talking about resulting power from RPM. Of course that can have the ability to go up.
We need to look at it from the instant the force happens in an engine
Torque is force X distance. When you change the gearing ratio, it changes the distance but not the starting force (ie. combustion)
This is torque manipulation through gearing.
Does this end up in better acceleration and power? Sometimes. That depends on peak power
And more torque does not mean better acceleration.
My example from earlier:
Car A with 100 hp and 200 tq and car B with 200hp and 100tq
Car B (although down on torque) will still give a higher top speed (more power = more work done, faster) and thus have more acceleration.
In the case of the Z06, gearing helps because the car can do 55 more HP of work. If you left the torque at 400TQ and 4800RPM without being able to do extra work (ie no extra HP), even with the added gearing, it would not accelerate faster.
Torque and HP are different units although are mathematically bound, but so are alot of things. It's certainly not in a linear fashion.
More of one doesn't mean more of another and you can manipulate this alot.
The graph says added power although this could be with or without torque change, not sure all what went on there. Not enough info
I'm not talking about resulting power from RPM. Of course that can have the ability to go up.
We need to look at it from the instant the force happens in an engine
Torque is force X distance. When you change the gearing ratio, it changes the distance but not the starting force (ie. combustion)
This is torque manipulation through gearing.
Does this end up in better acceleration and power? Sometimes. That depends on peak power
And more torque does not mean better acceleration.
My example from earlier:
Car A with 100 hp and 200 tq and car B with 200hp and 100tq
Car B (although down on torque) will still give a higher top speed (more power = more work done, faster) and thus have more acceleration.
In the case of the Z06, gearing helps because the car can do 55 more HP of work. If you left the torque at 400TQ and 4800RPM without being able to do extra work (ie no extra HP), even with the added gearing, it would not accelerate faster.
Torque and HP are different units although are mathematically bound, but so are alot of things. It's certainly not in a linear fashion.
More of one doesn't mean more of another and you can manipulate this alot.
The graph says added power although this could be with or without torque change, not sure all what went on there. Not enough info
Last edited by 02torchred; Aug 13, 2019 at 01:40 AM.
Racer
Joined: Dec 2017
Posts: 331
Likes: 74
From: Florida
Of course, but it can be often misused and misunderstood. You can make more power than torque, and vice versa. I discussed this in one of my posts dealing with engine design. (My above examples of car A and B still holds true in my previous post)
Lets say a diesel engine makes 500tq max at 1000RPM (industrial application) So 500 x 1000 / 5252 thats only 95 max Hp... We can see where this goes.
If that torque drops off to 100tq at 4000RPM so 100 x 4000 / 5252 thats only 76 Hp at that RPM level.
Conversely an opposite type of design exists in a gas engine that makes 150tq at 6000RPM, (max tq dropped off alot by then) so 150 x 6000 / 5252 thats 171Hp which is more than the particular torque that was made up there in that RPM
Of course if we drop the both the diesel and gas engine's first torque figures (500 for the diesel, to say 400 and the 150 for the gas to say 100), the HP will go down, but I'm using the above examples to illustrate a different way of thinking when it comes to motor design.
Lets say a diesel engine makes 500tq max at 1000RPM (industrial application) So 500 x 1000 / 5252 thats only 95 max Hp... We can see where this goes.
If that torque drops off to 100tq at 4000RPM so 100 x 4000 / 5252 thats only 76 Hp at that RPM level.
Conversely an opposite type of design exists in a gas engine that makes 150tq at 6000RPM, (max tq dropped off alot by then) so 150 x 6000 / 5252 thats 171Hp which is more than the particular torque that was made up there in that RPM
Of course if we drop the both the diesel and gas engine's first torque figures (500 for the diesel, to say 400 and the 150 for the gas to say 100), the HP will go down, but I'm using the above examples to illustrate a different way of thinking when it comes to motor design.
Last edited by 02torchred; Aug 13, 2019 at 01:46 AM.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
That table is a great example. Assuming 6600rpm is redline, it shows very clearly the car will accelerate faster by holding each gear all the way to redline than by shifting to the next gear at any earlier time. It doesn't really matter where in the torque curve the rpm's drop to either, holding to redline is faster. The exception being possibly 4th to 5th as you mentioned.
I wish there was shift ratios data included so we'd know where the rpm would drop when switching gears. Dropping no more than about 1500 rpm would work well though.
Cruising
Joined: May 2019
Posts: 13
Likes: 2
Horsepower is a measure of how much torque is available at the rear wheels through gearing.
NSFW made a couple very good posts in this thread. Torque at the wheels matters, but torque at the engine is largely meaningless. There's a reason why the online calculators for how fast a car will be in the quarter mile just ask for horsepower and weight. They don't ask for torque, because you can't tell how fast a vehicle will accelerate using an engine torque number. It's not enough information. Horsepower is the key measure of how an engine can make a car accelerate. Of course things like DCTs with lots of gears can help optimize acceleration, but still the power is the key.
NSFW made a couple very good posts in this thread. Torque at the wheels matters, but torque at the engine is largely meaningless. There's a reason why the online calculators for how fast a car will be in the quarter mile just ask for horsepower and weight. They don't ask for torque, because you can't tell how fast a vehicle will accelerate using an engine torque number. It's not enough information. Horsepower is the key measure of how an engine can make a car accelerate. Of course things like DCTs with lots of gears can help optimize acceleration, but still the power is the key.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
You'll generally have better results continuing beyond the power peak because torque at the wheels is what gives you acceleration and shifting reduces torque at the wheels. You'll accelerate fastest by shifting at the point where staying in gear would cost more torque than shifting will cost. Or until you hit the rev limiter, which may happen first.
If you're looking at the power curve to choose your shift point, you might get the right answer, but only by coincidence.
If you're looking at the power curve to choose your shift point, you might get the right answer, but only by coincidence.
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Racer
Joined: Dec 2017
Posts: 331
Likes: 74
From: Florida
When you shift gears, you usually want the RPM to fall (in the next gear) to where TQ is the greatest so the HP can build from that (the highest point of torque) and carry on to peak power and above until the next shift and repeat
Last edited by 02torchred; Aug 13, 2019 at 01:47 AM.
Drifting
Joined: Nov 2017
Posts: 1,392
Likes: 303
If TQ at the wheels is what gives you acceleration then why would you want to shift where the RPM's drop below peak TQ at shift ? If your engine makes max HP at 6000 RPM's and you shift at 6500 RPM's yes the drop in RPM's may be higher But it is Not at peak TQ- When the RPM's at shift point drop below peak TQ -- You are not gaining acceleration in your RPM range ------ Shifting when the RPM's drop above peak TQ or even below does not promote acceleration as the TQ is LESS in both senarios
If you don't plot the curves, you're only speculating. Why even bother?