HP/Torque, Formulas/Acceleration ?
Thread Starter
Heel & Toe
Joined: Sep 2004
Posts: 17
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From: Dayton OH
HP/Torque, Formulas/Acceleration ?
What would be useable formula for calculating effect on acceleration for any given HP/Torque.
My specific example: Car A & Car B making acceleration run, identical in every respect (weight, axle ratio, gear ratios), EXCEPT, that Car A, at given moment is putting out 260HP, 240ft# torque, Car B is putting out 240HP, 260ft#torque. Would both cars accelerate the same throughout the sprint, OR would superiority in 1 factor trump superiority in other factor? Thanks
My specific example: Car A & Car B making acceleration run, identical in every respect (weight, axle ratio, gear ratios), EXCEPT, that Car A, at given moment is putting out 260HP, 240ft# torque, Car B is putting out 240HP, 260ft#torque. Would both cars accelerate the same throughout the sprint, OR would superiority in 1 factor trump superiority in other factor? Thanks
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Car A will win.
At any particular moment, the rate of acceleration is determined by the torque, gear ratio, and weight of the car.
Since HP = TQ x RPM / 5252, Car A is obviously running at a higher rpm at that instant. So with your equal gear ratios, it has to be going faster right?
Or if we assume both cars are going the same speed, Car A would have 17% shorter gearing. It's torque is 8% less, but multiplied by 17% more. So it puts down more torque at the wheels than Car B, and therefore accelerates faster.
Short answer, the car making the most average HP will always accelerate faster between the shift points.
At any particular moment, the rate of acceleration is determined by the torque, gear ratio, and weight of the car.
Since HP = TQ x RPM / 5252, Car A is obviously running at a higher rpm at that instant. So with your equal gear ratios, it has to be going faster right?
Or if we assume both cars are going the same speed, Car A would have 17% shorter gearing. It's torque is 8% less, but multiplied by 17% more. So it puts down more torque at the wheels than Car B, and therefore accelerates faster.
Short answer, the car making the most average HP will always accelerate faster between the shift points.
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Safety Car
Joined: Sep 2000
Posts: 3,524
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From: Hinckley Ohio
There is one and only one thing that accelerates a car and that is the force the rear (drive) wheels exerts against the pavement.....the most direct measurement of this force is rear wheel torque
So what the heck is an automatons........
because rear wheel torque IS everything....
Safety Car
Joined: Sep 2000
Posts: 3,524
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From: Hinckley Ohio
Car A will win!!!!
Horsepower with proper gearing is king!!!
BTW this is consistant with saying RWTQ is the most important thing.....horsepower and rear wheel torque go hand in hand with proper gear and shift points
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by CentralCoaster
Or if we assume both cars are going the same speed, Car A would have 17% shorter gearing. It's torque is 8% less, but multiplied by 17% more. So it puts down more torque at the wheels than Car B, and therefore accelerates faster.
Originally Posted by pro6sp
My specific example: Car A & Car B making acceleration run, identical in every respect (weight, axle ratio, gear ratios), EXCEPT, that Car A, at given moment is putting out 260HP, 240ft# torque, Car B is putting out 240HP, 260ft#torque.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Read my entire post again. Paragraph 2. The rest was just taking it a step further than he asked for.
You guys can try and talk about TQ and HP as if they're unrelated concepts but they're not. I tried to explain it using torque which is easier to understand but I shouldn't have.
The main difference is, you can't determine what accelerates faster based on engine TQ alone. But you can based on HP without knowing anything about the gearing. This is the reverse of how all those datalogger/accelerometers/Gtechs work. You input your weight, it measures acceleration and determines your average and instantaneous HP.
Weight, Acceleration, Horsepower. Nothing more.
With equal weights, the car producing the most engine HP at any particular speed will ALWAYS be accelerating faster. (Please let's not talk about parasitic losses. )
You guys can try and talk about TQ and HP as if they're unrelated concepts but they're not. I tried to explain it using torque which is easier to understand but I shouldn't have.
The main difference is, you can't determine what accelerates faster based on engine TQ alone. But you can based on HP without knowing anything about the gearing. This is the reverse of how all those datalogger/accelerometers/Gtechs work. You input your weight, it measures acceleration and determines your average and instantaneous HP.
Weight, Acceleration, Horsepower. Nothing more.
With equal weights, the car producing the most engine HP at any particular speed will ALWAYS be accelerating faster. (Please let's not talk about parasitic losses.
)
Last edited by CentralCoaster; Nov 2, 2007 at 12:39 PM.
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Safety Car
Joined: May 2006
Posts: 4,290
Likes: 140
From: Salem NH
Read my entire post again. Paragraph 2. The rest was just taking it a step further than he asked for.
You guys can try and talk about TQ and HP as if they're unrelated concepts but they're not. I tried to explain it using torque which is easier to understand but I shouldn't have.
The main difference is, you can't determine what accelerates faster based on engine TQ alone. But you can based on HP without knowing anything about the gearing. This is the reverse of how all those datalogger/accelerometers/Gtechs work. You input your weight, it measures acceleration and determines your average and instantaneous HP.
Weight, Acceleration, Horsepower. Nothing more.
With equal weights, the car producing the most engine HP at any particular speed will ALWAYS be accelerating faster. (Please let's not talk about parasitic losses. )
You guys can try and talk about TQ and HP as if they're unrelated concepts but they're not. I tried to explain it using torque which is easier to understand but I shouldn't have.
The main difference is, you can't determine what accelerates faster based on engine TQ alone. But you can based on HP without knowing anything about the gearing. This is the reverse of how all those datalogger/accelerometers/Gtechs work. You input your weight, it measures acceleration and determines your average and instantaneous HP.
Weight, Acceleration, Horsepower. Nothing more.
With equal weights, the car producing the most engine HP at any particular speed will ALWAYS be accelerating faster. (Please let's not talk about parasitic losses.
)
-- Joe
Melting Slicks
Joined: May 2007
Posts: 2,382
Likes: 2
From: Kathleen FL
Sorry about hijacking this thread but I just put up my stock 88 up against a bolt-on modded Honda S2000; it was an embarrassing day for the Honda to say the least. He also knew I was a few hundred lbs heavier despite the fact that we both came with the same hp from the factory. S2000s weigh in at about 2800 lbs from the factory. My fat *** automatic 88 weighs about 3300 lbs from the factory. Add 160 lbs to each as the weight of the driver.
My new ALL TIME BEST 1/8th mile time yesterday: 8.713 @ 79.765 mph, 1.892 60' from 315/35 BFG drag radials.
His: 9.635 @ 78.260 mph, 2.178 60'.
Perhaps the S2000 isn't as optimally geared as it should be. His back tires were Falken Azenis drag radials.
My new ALL TIME BEST 1/8th mile time yesterday: 8.713 @ 79.765 mph, 1.892 60' from 315/35 BFG drag radials.
His: 9.635 @ 78.260 mph, 2.178 60'.
Perhaps the S2000 isn't as optimally geared as it should be. His back tires were Falken Azenis drag radials.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
It will also have way less power than you starting out when it's below the power curve in 1st gear, and will lose time there. If they had a torque converter, or some race tires or some other way to keep it in the powerband off launch, they'd fare better. But anyhow that's why they all want to race from a roll.
I beat up on those 276 hp imports all the time in my slow 85. I think they rate them at 276 because the Japanese goverment limits them, but they usually make more power than that.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Stock 85 motor with a high flow cat, mufflers removed, and some intake porting.That S2000 driver sucks. I wish some of those ricers would trade keys with me so I could see what difference their poor driving has. 1/8th mile doesn't give any room for error.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Obviously we can't tell who's further ahead because we don't know the HP put down during launch and up to that point. Car A could be behind and catching up, or ahead and pulling away.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Safety Car
Joined: May 2006
Posts: 4,290
Likes: 140
From: Salem NH
I used to go up on street nights to play. On a cold night, with horrible traction on street tires i'd run like.. 13.0.. at 120mph..
Yet the guy Who ran 12.99 at 108 screams "I beat you!"..
-- Joe
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
For starters we don't know at what rpms the peak torques and horsepowers occur plus we don't know how the shapes of the dyno curves compare......
Since the gear ratios of the two vehicles are the same, one thing we can say is that in each gear the vehicle with the higher torque will have a higher max acceleration point than the vehicle with the lower torque.......
Note: in each gear the torque mulitplication to the rear wheels would be the same so more motor torque must mean more rear wheel torque which means more acceleration....The acceleration peaks would occur at different speeds for the two vehicles (We know this, because if the torque peaks occured at the same rpm the higher torque engine would also have the highest horsepower)
This is pretty significant fact because this is why the L98 feels so strong......it is also why so many think motor torque is more significant than horsepower....
Horsepower is king, but you have to have matched gearing....
Some factual food for thought...
