Horsepower required calculation?
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,638
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Horsepower required calculation?
I know there is a computer program out there that takes into account the frontal area of a car - and all of the other variables and does a calculation as to how much horsepower will be required to achieve a certain speed.
So we have an 82 that we are getting prepped to try and run 200mph on the Bonneville Salt Flats - and also we need to look at what we will need to achieve 225 mph.
we have a 2.73 rear end - and an overdrive gear of 0.64. With 15 inch tires it looks like we need to spin about 6000 RPM to make 225. The engine - a hopped up ZZ4 making about 343 HP is easily capable of revving that high - but can it do it pushing against the monstrous drag that will be produced at 200 MPH? But I have no way of accounting for wind resistance - drive train loss etc. - can anyone help?
So we have an 82 that we are getting prepped to try and run 200mph on the Bonneville Salt Flats - and also we need to look at what we will need to achieve 225 mph.
we have a 2.73 rear end - and an overdrive gear of 0.64. With 15 inch tires it looks like we need to spin about 6000 RPM to make 225. The engine - a hopped up ZZ4 making about 343 HP is easily capable of revving that high - but can it do it pushing against the monstrous drag that will be produced at 200 MPH? But I have no way of accounting for wind resistance - drive train loss etc. - can anyone help?
Race Director
Joined: Sep 2002
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From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by Carl Johansson
I know there is a computer program out there that takes into account the frontal area of a car - and all of the other variables and does a calculation as to how much horsepower will be required to achieve a certain speed.
So we have an 82 that we are getting prepped to try and run 200mph on the Bonneville Salt Flats - and also we need to look at what we will need to achieve 225 mph.
we have a 2.73 rear end - and an overdrive gear of 0.64. With 15 inch tires it looks like we need to spin about 6000 RPM to make 225. The engine - a hopped up ZZ4 making about 343 HP is easily capable of revving that high - but can it do it pushing against the monstrous drag that will be produced at 200 MPH? But I have no way of accounting for wind resistance - drive train loss etc. - can anyone help?
So we have an 82 that we are getting prepped to try and run 200mph on the Bonneville Salt Flats - and also we need to look at what we will need to achieve 225 mph.
we have a 2.73 rear end - and an overdrive gear of 0.64. With 15 inch tires it looks like we need to spin about 6000 RPM to make 225. The engine - a hopped up ZZ4 making about 343 HP is easily capable of revving that high - but can it do it pushing against the monstrous drag that will be produced at 200 MPH? But I have no way of accounting for wind resistance - drive train loss etc. - can anyone help?
Where do you get 15 inch tires with a Z speed rating? That's the first thing you need!
Thread Starter
Drifting
Joined: Sep 2004
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Originally Posted by BigBlockk
I have one of those programs. I did these cals about three years ago. If I remember right the C3 body takes about 650 hp (at the fly wheel) to get 200 mph.
BigBlockk
Later.....
BigBlockk
Later.....
Thread Starter
Drifting
Joined: Sep 2004
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Originally Posted by SanDiegoPaul
Where do you get 15 inch tires with a Z speed rating? That's the first thing you need!
Drifting
Joined: Feb 2002
Posts: 1,906
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From: Berlin
Assuming optimal gearing and neglecting drivetrain friction and so on, the amount of power needed to reach a certain speed is
1/2*C_D*rho*A*v^3
C_D is the drag coefficient (very roughly 0.4), rho is the air density (~1.2 kg/m^3), A is the frontal area of the car (~1.9 m^2), and v is the speed (200 mph=90 m/s). Plugging all that in gives you about 330,000 Watts = 440 hp at the wheels.
Plugging in 225 mph gives 630 hp. In reality, you will of course require more than this. An extra 50-80 hp is probably realistic. Also realize that the car has to be geared for this, which doesn't simply mean changing the final drive ratio until you can reach the desired speed without redlining.
The also assumes you don't end up lifting off the ground at some point. I hope you've done about that... You also need to take into account that lift-reducing modifications will change the drag coefficient, and could easily make it worse.
1/2*C_D*rho*A*v^3
C_D is the drag coefficient (very roughly 0.4), rho is the air density (~1.2 kg/m^3), A is the frontal area of the car (~1.9 m^2), and v is the speed (200 mph=90 m/s). Plugging all that in gives you about 330,000 Watts = 440 hp at the wheels.
Plugging in 225 mph gives 630 hp. In reality, you will of course require more than this. An extra 50-80 hp is probably realistic. Also realize that the car has to be geared for this, which doesn't simply mean changing the final drive ratio until you can reach the desired speed without redlining.
The also assumes you don't end up lifting off the ground at some point. I hope you've done about that... You also need to take into account that lift-reducing modifications will change the drag coefficient, and could easily make it worse.
Le Mans Master
Joined: Apr 2000
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From: B'Ville NY
Cruise-In III Veteran
St. Jude Donor '05
Gkull hangs out at these types of events. I thought I remember him saying we needed around 500+hp to go 200mph. Maybe he'll chime in 
And yes I believe the thinner tires are a better choice when high speeding it at the flats, the car floats less 
And yes I believe the thinner tires are a better choice when high speeding it at the flats, the car floats less
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Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Yup Gkull is the man you want to talk to when it comes to this sort of thing he will tell you what HP you need and how to get to 200+MPH in a C3 
Drifting
Joined: Sep 2004
Posts: 1,959
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From: North Bend Ohio
Ok, I ran some more tests on the programs I have. By the way I'm using Desktop Dyno for engine power data and Pat Bowlings Car Test 2000 for the speed simulation.
What I came up with is an '82 Vette with a 2.73 gear, 27" tall tires and a wide ratio 4 speed would require 535 hp to reach 200 mph. This car will do 0 to 60 in 4.21 sec, the quater mile in 12.34 sec at 124 mph and 201 mph at 6663 engine rpm. It is very important for the engine to produce maximum power at the same rpm as 200 mph.
By the way, from a standing start it takes about 30,000 ft for the car to reach maximum speed.
A fue years ago I ran this tests on a model that more closely resembled a '70 Corvette. That is where the 650 hp number came from in my other post.
Hope this helps.
BigBlockk
Later.....
What I came up with is an '82 Vette with a 2.73 gear, 27" tall tires and a wide ratio 4 speed would require 535 hp to reach 200 mph. This car will do 0 to 60 in 4.21 sec, the quater mile in 12.34 sec at 124 mph and 201 mph at 6663 engine rpm. It is very important for the engine to produce maximum power at the same rpm as 200 mph.
By the way, from a standing start it takes about 30,000 ft for the car to reach maximum speed.
A fue years ago I ran this tests on a model that more closely resembled a '70 Corvette. That is where the 650 hp number came from in my other post.
Hope this helps.
BigBlockk
Later.....
