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1. ## horsepower

so about how fast does a car go based on its horsepower. like about how fast would a 90hp car go, a 100hp, car, a 140hp car, a 150hp car, and a 180hp car go?

2. There is lots of variables involved with that.

Got this from horsepower dot com

Horsepower is a measure of the amount of power a car's engine is able to produce in order to move the car. Power is equal to energy per unit of time. Energy is measured by joules which in turn is equal to a watt for every second that joule is used. Horsepower is measured in watts. Actually horsepower is equal to 746 watts. So it is all intertwined, though it is very complicated.
How horsepower affects the performance of the car is all quite complicated, so it will have to be broken down.
How fast a car can go is directly affected by the car's horsepower. One horsepower is also equal to 550 foot*pounds/second. That means that 550 pounds can be moved one foot in one second. Most drag racing cars have at least of 500 horsepower, but some can have as much as 1000. When they run the quarter mile strip, it is horsepower produced by the engine that gets them to the finish line. But how fast they go is dependent on Newton's second law. (F=ma) You see, the faster they accelerate, the more force will be used, and therefore the car will finish faster.
The first person to work with horsepower was James Watt, who discovered the unit of it by measuring the amount of power a horse (surprise, surprise) could deliver. According to the Encyclopedia Britannica, Watt must've used an extremely strong horse, or only calculated it's power for a very short time, because the number is so high.
The calculation of horsepower is never actually taken from a running engine. It is actually estimated by taking torque and converting it to the units of horsepower. The device used to measure the torque of an engine and then subsequently find the horsepower is called a dynamometer. A dynamometer is any machine that measures mechanical force. A dynamometer is a device that has two spinning cylinders that can rotate in either direction. The car's drive wheels are placed on these rollers, then when the gas is applied, sensors can measure the amount of torque at any given rpm, and horsepower is calculated from there.

Horsepower = Torque x RPM devided by 5252

This equation is used because one foot pound of torque at 5252 rpm is equal to 33,000 foot pounds per minute of work, which is one horsepower. So through this equation you can see why you need to take the estimate from torque.
Some physicists might dare to say that no horsepower is needed to go a certain speed, because, based on Newton's first law, an object that is in motion tends to stay in motion unless it is acted upon by an external force. Horsepower seems to contradict this law. An automobile that is moving straight on a road on level ground is acted on by many forces that slow it down, mainly friction. Then the engine has to oppose these forces, using horsepower. Horsepower is a major reason why the car propells forward, and stops the forces on the car that would otherwise make the car go backwards.

3. what would be your estamate

4. anywhere between 90-150 mph... It depends on so many things, weight, torque. A Geo metro could probably do 90 mph if going downhill with a manual trans.

5. Well my wife's minivan has about 160 horsepower and would barely go 120 mph (estimated, I wouldn't want to go 120 in a minivan), my motorcycle has just over 160 horsepower and will easily do better than 180 mph. Weight, torque, and aerodynamics need to be established along with hp to estimate top speed, and then gearing can make a huge difference.
Last edited by Big; 12-26-2005 at 01:14 PM.

6. Too many other variables to determine the speed. Weight being the biggest. Areodynamics is another variable. Gear ratios, ect.

7. Originally Posted by roger24
so about how fast does a car go based on its horsepower. like about how fast would a 90hp car go, a 100hp, car, a 140hp car, a 150hp car, and a 180hp car go?
depends on the weight of the car..its condition,transmission,driver,cylinders,induction system
i have a maxima with manual transmission coming in @ 222 HP and its really fast on the highway and faster in the higher gears

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Forget all the fancy shit and guesswork guys. All it takes is a simple bit of mathematics. You use a cubed route formula.

All you do is

Cubed route of (Horsepower you want/Actual hp) x original MPH

So for my car with only 75hp, say I gave it 150. Its top speed is 115, so...

³√(150/75) x 115 = 144 mph

Notice now that I rapidly increase HP, the mph does not go through the roof

³√(300/75) x 115 = 182 mph

That is because the formula has taken into account the speed characteristics in the data you provide. Changes with each car as well. Some factors are not taken into account such as gear ratios, but you assume that these step up proportionally. Speed is directly related to wind resistance and power. Double the power, you can't double the speed because of wind resistance having a greater effect the faster you go. The cubed route formula works because this is the relationship between these three main factors
Last edited by Flexor; 12-26-2005 at 02:26 PM.

9. fast is cool but exceleration is king and torque and light weight equal exceleration

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Originally Posted by craneboy
fast is cool but exceleration is king and torque and light weight equal exceleration
think its spelled with an a craneboy... but ill agree with ya id take a car that got to 150mph fast over one that makes it to 200 but needs a 3 mile straight away

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Originally Posted by Flexor
Forget all the fancy shit and guesswork guys. All it takes is a simple bit of mathematics. You use a cubed route formula.

All you do is

Cubed route of (Horsepower you want/Actual hp) x original MPH

So for my car with only 75hp, say I gave it 150. Its top speed is 115, so...

³√(150/75) x 115 = 144 mph

Notice now that I rapidly increase HP, the mph does not go through the roof

³√(300/75) x 115 = 182 mph

That is because the formula has taken into account the speed characteristics in the data you provide. Changes with each car as well. Some factors are not taken into account such as gear ratios, but you assume that these step up proportionally. Speed is directly related to wind resistance and power. Double the power, you can't double the speed because of wind resistance having a greater effect the faster you go. The cubed route formula works because this is the relationship between these three main factors
This is crap, sounds like your an engineer not a mechanic.

12. Forget top speed racing. It's all about the drag race. I just want to race a 1/4 mile and get over a hundred. I just wish I could know the DA for that day I hit 12.47@109MPH. Then I could figure out what I would run at sea level on a perfect day and then extrapolate my HP from those numbers.

13. and do not forget speed govenors. I had a lincoln once that was pushin 290 horsepower but the govenor wouldnt let it go past 120 bunch of b.s. that was. needless to say it was at 120 alot.

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Originally Posted by Dalton5
This is crap, sounds like your an engineer not a mechanic.
Sounds like you're a loser. I guarantee you it works, you look at any car range that has identical bodies but different models have different engine sizes and horsepower. Although the bigger engines are slightly heavier, the formula will accurately calculate how much faster the car with more horsepower will go. You can go and do the sums and check them against the official data and you will see its close...

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Originally Posted by Dalton5
This is crap, sounds like your an engineer not a mechanic.
Erm, isn't it preferable to be an engineer rather than a mechanic?

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Originally Posted by Flexor
Sounds like you're a loser. I guarantee you it works, you look at any car range that has identical bodies but different models have different engine sizes and horsepower. Although the bigger engines are slightly heavier, the formula will accurately calculate how much faster the car with more horsepower will go. You can go and do the sums and check them against the official data and you will see its close...
Well ill give you that, I AM a loser.......anyway, the original question was how fast does a car go based on its horsepower; what i am saying is there are far too many variables for this to be summed up in a nice little mathematical equation. Stuff like weight, gear ratios, amount of torque etc. as mentioned above come into play. Take the grand national for example, you'd be doing good to get 300 hp out of one however with its insane amount of torque it was the fastest production car (domestic) in 87'.

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Originally Posted by NotSmall
Erm, isn't it preferable to be an engineer rather than a mechanic?
Whatever floats yur boat......if your interested in making a car run under 12 seconds in a quarter mile i think it would be better to do fancy work with a wrench as opposed to a calculator.

18. Originally Posted by Dalton5
Whatever floats yur boat......if your interested in making a car run under 12 seconds in a quarter mile i think it would be better to do fancy work with a wrench as opposed to a calculator.
But as an engineer you can just pay someone to wrench that will your disposable income

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Originally Posted by Dalton5
Whatever floats yur boat......if your interested in making a car run under 12 seconds in a quarter mile i think it would be better to do fancy work with a wrench as opposed to a calculator.
LOL! How about a Mech. Engineer who makes cars run 8's?

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Originally Posted by Blown_SC
LOL! How about a Mech. Engineer who makes cars run 8's?
best of both worlds

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Originally Posted by Blown_SC
LOL! How about a Mech. Engineer who makes cars run 8's?
I know, I know........Ill never have the money nor the knowhow to make a small block chevy go in 8 seconds, but for a back woods project where just as much money went into beer as into the car 11.8 ain't bad.

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peak horsepower ratings don't tell everything. (wheel dyno'd) its the entire torque curve that determines how powerful a car will be in a race.

Drivetrain loss (engine through transmission to axels to wheels) also is different for every car.

for exmaple I have a 2004 srt-4 and a 2004 Ford Lightning
the srt-4 dyno'd to the front wheels(FWD car) 236hp peak and 258ft/lbs of torque peak. My lightning dyno'd stock 356hp rear wheels and 426ft/lbs of torque.

the srt-4 is 3000lbs the lightning 4600lbs. the lightning may weigh more but has the same power to weight ratio =.078

the srt-4 is able to beat the lightning on a highway run 50-100+ but on the 1/4th dead stop up to 1/4th miles the lightning wins by a couple cars.

You can't tell which auto will beat another unless you know their dyno curve , weight, and drivers ability.