HP vs Torque
Burning Brakes
Joined: Dec 2006
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From: Tyrone PA
The car making the most horsepower at any speed will always accelerate quicker. The car making the most rear wheel torque at any speed will always accelerate quicker. (Hint: you can't have one without the other.)
Again, do the math at 10 mph. Do the math at 50 mph:
Acceleration = Horsepower / Mass / Speed
Acceleration = (RWTQ / TireSize) / Mass
(keep TireSize equal otherwise we can't compare RWTQ)
In your example, Car 1 is turning 8200 rpm, Car 2 is turning 5500 rpm. Since speed is equal, Car 1 must be geared 50% shorter than Car 2, and therefore is getting 50% more torque multiplication through gearing, and even with less FWTQ, is putting down about 25% more RWTQ than Car 1. So you see that Car 1 is accelerating quicker, is making the most HP and the most RWTQ.
The car making the most horsepower at any speed will always accelerate quicker.
Again, do the math at 10 mph. Do the math at 50 mph:
Acceleration = Horsepower / Mass / Speed
Acceleration = (RWTQ / TireSize) / Mass
(keep TireSize equal otherwise we can't compare RWTQ)
In your example, Car 1 is turning 8200 rpm, Car 2 is turning 5500 rpm. Since speed is equal, Car 1 must be geared 50% shorter than Car 2, and therefore is getting 50% more torque multiplication through gearing, and even with less FWTQ, is putting down about 25% more RWTQ than Car 1. So you see that Car 1 is accelerating quicker, is making the most HP and the most RWTQ.
The car making the most horsepower at any speed will always accelerate quicker.
Last edited by dan0617; Dec 20, 2007 at 01:29 PM.
Safety Car
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From: Toronto ontario
To elaborate on this, maybe I should include these two graphs. Pictures always help me understand things better. The first one is HP versus velocity. The second is acceleration versus velocity. To CC's point- let's look at 58 mph as an example in the graphs below. How do you maximize acceleration at 58mph? You have the choice between 4 gears at this point (we're constrained to 2000rpm or above here). You pick the highest HP of the available gears at 58 mph- this means you stay in 1st gear. Now look at the other graph at 58 mph-you'll see this corresponds to maximum acceleration of your available 4 gear options.
So what does this really mean in the real world? For this hypothetical car, it means that if you want to accelerate fastest, you don't shift at the power peak in 1st gear, you run that baby all the way up to 7000rpm in this case. Even though HP falls off, you are still accelerating faster than if you shift to 2nd at the power peak. If you shift to 2nd at the HP peak, you lose about 0.16g acceleration, as shown in the second graph (0.76g vs 0.60g). In this particular example, you can see that you should run every gear out to 7000RPM (past the HP peak and WAY past the TQ peak), otherwise you are not moving as quickly as you could be. And as a side note: per CC's equation above, a car with more HP (and more RWTQ, by association) at a given mph will accelerate faster.
So what does this really mean in the real world? For this hypothetical car, it means that if you want to accelerate fastest, you don't shift at the power peak in 1st gear, you run that baby all the way up to 7000rpm in this case. Even though HP falls off, you are still accelerating faster than if you shift to 2nd at the power peak. If you shift to 2nd at the HP peak, you lose about 0.16g acceleration, as shown in the second graph (0.76g vs 0.60g). In this particular example, you can see that you should run every gear out to 7000RPM (past the HP peak and WAY past the TQ peak), otherwise you are not moving as quickly as you could be. And as a side note: per CC's equation above, a car with more HP (and more RWTQ, by association) at a given mph will accelerate faster.
Advanced
Joined: Dec 2007
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From: Raleigh North Carolina
In this link, the author makes a persuasive argument for torque:
http://www.vettenet.org/torquehp.html
http://www.vettenet.org/torquehp.html
Thread Starter
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From: Overland Park Kansas
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OK, here's a tougher example.
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI
) that peaks at 457HP peak @ 4,200 rpms?
Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI
) that peaks at 457HP peak @ 4,200 rpms?Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
Last edited by GREGGPENN; Dec 21, 2007 at 12:07 AM.
Safety Car
Joined: Jul 1999
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From: Marianna FL
OK, here's a tougher example.
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI ) that peaks at 457HP peak @ 4,200 rpms?
Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI
) that peaks at 457HP peak @ 4,200 rpms?Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
For a real world answer to your question: If both combinations are optimized for their setup, the one with the most HP under the curve over the operating range during the race would win. If they both have equal HP under the curve over the operating range during the race, they would theoretically tie.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
OK, here's a tougher example.
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI ) that peaks at 457HP peak @ 4,200 rpms?
Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI
) that peaks at 457HP peak @ 4,200 rpms?Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
In reality peak horspower numbers, peak torque numbers don't really mean much until you look at the entire picture......from the old days compare two identical vehicles one with wide ratio 4-speed and one with close ratio 4-speed.......yeh add the variable of rear end ratios
Hint: The reason it would be a dead even race is because you would have a constant 457 rwhp in both cars from start to finish...
Last edited by LT4BUD; Dec 21, 2007 at 10:35 AM.
Advanced
Joined: Dec 2007
Posts: 63
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From: Raleigh North Carolina
If you put a CVT set at 6k rpm in the 400 ft-lb car and a CVT set at 4200 rpm in the 570ft lb car and make everything else equal it would be a dead even race from start to finish!!!!!
In reality peak horspower numbers, peak torque numbers don't really mean much until you look at the entire picture......from the old days compare two identical vehicles one with wide ratio 4-speed and one with close ratio 4-speed.......yeh add the variable of rear end ratios
Hint: The reason it would be a dead even race is because you would have a constant 457 rwhp in both cars from start to finish...
In reality peak horspower numbers, peak torque numbers don't really mean much until you look at the entire picture......from the old days compare two identical vehicles one with wide ratio 4-speed and one with close ratio 4-speed.......yeh add the variable of rear end ratios
Hint: The reason it would be a dead even race is because you would have a constant 457 rwhp in both cars from start to finish...
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Safety Car
Joined: Sep 2000
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From: Hinckley Ohio
You are right that torque is what makes the car go forward, but equal rear wheel horsepower means equal rear wheel torque means equal acceleration....
I am certain, read correctly as I intended, my statements are absolutely true.......
Think about what you said....mostly correct BTW, but neither vehicle will have 570 ft-lbs at the wheels,
You are correct in acknowledging the significance of gear ratios.....I need to plot it out to be sure, but my intuition is a stock LT4 with 4.10 gears will out accelerate a L98 with stock 3.45 gears from start to finish even tho the L98 has a higher peak torque.....due to the higher torque multiplication of the gear ratio
So to reiterate peak horsepower & peak torque ratings are only a part of the puzzle........
Advanced
Joined: Dec 2007
Posts: 63
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From: Raleigh North Carolina
Do you know what I mean by CVT? Continuously Variable Transmission
You are right that torque is what makes the car go forward, but equal rear wheel horsepower means equal rear wheel torque means equal acceleration....
I am certain, read correctly as I intended, my statements are absolutely true.......
Think about what you said....mostly correct BTW, but neither vehicle will have 570 ft-lbs at the wheels,
You are correct in acknowledging the significance of gear ratios.....I need to plot it out to be sure, but my intuition is a stock LT4 with 4.10 gears will out accelerate a L98 with stock 3.45 gears from start to finish even tho the L98 has a higher peak torque.....due to the higher torque multiplication of the gear ratio
So to reiterate peak horsepower & peak torque ratings are only a part of the puzzle........
You are right that torque is what makes the car go forward, but equal rear wheel horsepower means equal rear wheel torque means equal acceleration....
I am certain, read correctly as I intended, my statements are absolutely true.......
Think about what you said....mostly correct BTW, but neither vehicle will have 570 ft-lbs at the wheels,
You are correct in acknowledging the significance of gear ratios.....I need to plot it out to be sure, but my intuition is a stock LT4 with 4.10 gears will out accelerate a L98 with stock 3.45 gears from start to finish even tho the L98 has a higher peak torque.....due to the higher torque multiplication of the gear ratio
So to reiterate peak horsepower & peak torque ratings are only a part of the puzzle........
Oh yeah, know what a CVT is and what the point was that you were trying to make. However, equal rear horsepower does not equate to equal rear torque, unless both cars' back tires are rotating at the same speed and the tires have the same rolling diameter, and ...
Safety Car
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From: Hinckley Ohio
The assumption of equal cars with different motors would include tires of equal diameters........so what is the "however" all about......my CVT illustration is absolutely true????
Thread Starter
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From: Overland Park Kansas
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Did I say anything about a CVT?
Did anyone really say which one would win -- and why?
Did anyone really say which one would win -- and why?
Racer
Joined: Jul 2002
Posts: 466
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OK, here's a tougher example.
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI ) that peaks at 457HP peak @ 4,200 rpms?
Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
What if a 400 ft-lb motor generating 457HP @ 6K races a 570 ft-lb motor (with a TPI
) that peaks at 457HP peak @ 4,200 rpms?Which to you prefer? Which is faster?
(Don't cheat and say put lower gears in the lower torque motor.... Ughh... and I know it needs a new intake!)
gp
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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If they were identical except the engines i think engine no 1 would win because engine b would be making 365ft-lb at 4200 and when it reaches that rpm it would need to shift and engine 1 would still have a bit more rpm to in any gear and therefore more time in its powerband.
Torque = HP*5252/RPM
571=457*5252/4200
Did I do something wrong?
Burning Brakes
Joined: Oct 2004
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From: fighter pilots make movies, bomber pilots make history
Exactly!
Take a Formula 1 car, they produce 850 hp at roughly 18000rpm.
They don't stop accelarating at those rpm's, to the contrary if it would be possible those engines would rev till 25,000 rpm and over.
I believe that torque is what gets you moving and horsepower is what keeps you accelarating after the torque starts dropping.
Take a Formula 1 car, they produce 850 hp at roughly 18000rpm.
They don't stop accelarating at those rpm's, to the contrary if it would be possible those engines would rev till 25,000 rpm and over.
I believe that torque is what gets you moving and horsepower is what keeps you accelarating after the torque starts dropping.
Safety Car
Joined: Jul 1999
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From: Marianna FL
Yes, someone did.
Two engines in cars making the same HP at different peaks is not enough information to predict who would win a race. Whether you want to believe it or whether you can understand it or not, the rest of the car makes a huge difference in which one will win the race.
You cannot simply say that because no one knows what gears you plan to compare these cars with or whether or not they are manual or automatic transmissions. All you said was that 'changing the gears would be cheating'. If they're both in stock automatics with stock convertors running 2.73 gears the engine making more torque down low would likely win a 1/4 mile race. If they're both 6 speeds with 3.45 gears, the higher RPM engine would likely win the 1/4 mile race.
Two engines in cars making the same HP at different peaks is not enough information to predict who would win a race. Whether you want to believe it or whether you can understand it or not, the rest of the car makes a huge difference in which one will win the race.
You cannot simply say that because no one knows what gears you plan to compare these cars with or whether or not they are manual or automatic transmissions. All you said was that 'changing the gears would be cheating'. If they're both in stock automatics with stock convertors running 2.73 gears the engine making more torque down low would likely win a 1/4 mile race. If they're both 6 speeds with 3.45 gears, the higher RPM engine would likely win the 1/4 mile race.
Thread Starter
Race Director
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From: Overland Park Kansas
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I get it...
This thread started as an effort to understand the changes I provided graphs for on page 1.
On a 383, I've super-imposed the graphs of stock, large TPI, and HSR setups. If you look at the area between the curves of the large TPI and HSR from 3000 to 5000 and compare it to the area between the curves above 5000, I'd have to assume the large TPI motor would win in most short races. In other words, it's a more powerful setup for street driving. (The HSR would likely squeak out in a 1/4 mile, but the other setup would feel stronger and play better around town).
My lastest example was designed to see if everyone is "stuck" on a high-revving motor.
When I said don't cheat, my point was to get an answer to the example given vs how to change the results toward the "ideal".
This thread started as an effort to understand the changes I provided graphs for on page 1.
On a 383, I've super-imposed the graphs of stock, large TPI, and HSR setups. If you look at the area between the curves of the large TPI and HSR from 3000 to 5000 and compare it to the area between the curves above 5000, I'd have to assume the large TPI motor would win in most short races. In other words, it's a more powerful setup for street driving. (The HSR would likely squeak out in a 1/4 mile, but the other setup would feel stronger and play better around town).
My lastest example was designed to see if everyone is "stuck" on a high-revving motor.
When I said don't cheat, my point was to get an answer to the example given vs how to change the results toward the "ideal".
Racer
Joined: Jul 2002
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while audi was making 650bhp/1050ft-lb of torque. Theirs a big difference in torque numbers between the two engines.
Get two engines 1 diesel and 1 petrol with the same performance as the petrol engine i just mentioned and see who would win(considering everything is the same on both cars). I bet my money on the petrol one cause of the higher rev range.
By the way the numbers are approximate.
Team Owner
Joined: Aug 2004
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From: Park City Utah
The real reason why the Audi won was becasue there isn't another car in that class. That makes a "win" pretty easy regardless of which type of fuel you're burning.
The Audi does have an advantage though, and that advantage is less fuel stops.
Although the Audi does produace more crank tq, it's already been shown in this thread, that any other like-hp'ed car can put just as much tq to the rear wheels (at the same speed) w/different gearing, since the engine can spin at a different speed too. And they do.
You were right that the Audi won LeMans. Unfortunately, your reasoning was wrong, and so was the use of the example.