wts the relation between (engine CC & HP & acceleration) ??

25

Asked by Feb 08, 2010 at 09:23 AM

Question type: General

i notice tht many cars hv low HP can accelerate faster than other cars which hv a good HP, and i c many cars have a large engine capacity (3000 CC or more) like Cherokee can't accelerate fastly , if there is an equation have these parameters??

5 Answers

65

Engines are measured in C.I., or Cubic Inches generally, only smaller engines such as motorcycles four-wheelers are measured in C.C.'s. Usually. Torque is the reason that some cars accelerate well while they seems to have no horsepower. A pretty general quote is "Torque gets you there while horsepower keeps you there." In the case of a Jeep Cherokee they have several things to consider such as the size of the vehicle, versus which engine it's using, also they are 4 wheel drive which takes more power away from the wheels. There is no "Equation" per se, unless you really want to talk physics, and i'm not the one for that. Jeeps engines generally have more torque then horsepower because they are made for towing, and offroad use. Low end power is much better then horsepower for such uses. There is a reason Diesel engines will often have approximately 250hp, while having double that in torque. Or Honda's often have no torque, but decent horsepower. Bad acceleration, but good higher end speed. Hope this makes sense.

1 out of 1 people think this is helpful.
7,515

There is no direct comparison between the three. However, strictly speaking F=M*A is the closest you're going to get. F, the force, is related the amount of push the car puts to the pavement which is more or less a function of torque. (Horsepower is a function of torque and engine speed. so that's the closest you're going to get to horsepower) Torque, as the engine produces it, is a function of the force on the piston head multiplied by several other factors. That force on the piston is the products of the pressure exerted on it times the area of the piston. So to get more torque, everything else held equal, you can either increase the piston size (get a bigger area) or increase the pressure (This is where things like turbos, superchargers, high compression, high volumetric efficiency, and other factors come into play). That increasing of area will increase the displacement which is what cc's measure. (FYI cc's are cubic centimeters, there are 1000 of them in a liter, so when you see a 3.0L engine there are about 3000cc... These are both metric measurements while cubic inches (c.i.) are a American measurement (Imperial, B.S., or B.G. if you prefer)... The measurements aren't used based on size of the motor but more accurately are just used based on what the maker prefers to use.) So that's how that 'F' comes into play. The 'M' stands for mass or how heavy the vehicle is and 'A' is the acceleration. So if you have two vehicles with the same amount of power/torque (The 'F'), but one weighs twice as much, then the lighter one will accelerate twice as fast. Now it get more complicated because that F also has to account for all of the drag forces on the vehicles (like aerodynamic drag, frictional drag, rolling resistance, ect...) So lets try and put this in one equation for you.... ('k' will be put in place of coefficients that are unit dependent, and torque will be assumed to be in ft-lbs) F~Torque-Drag= Torque=(Horsepower*5252/RPM)=k*[Pressure]*[Area]*[Lever]=k*[Pressure]*([Displacement]/[Stroke])*[Lever] Horsepower= M~Mass A~Acceleration So... k*((5252*[Horsepower]/RPM))-[DRAG]=[MASS]*[ACCELERATION] or k*[Pressure]*([Displacement]/[Stroke])*[Lever]-[DRAG]=[MASS]*[ACCELERATION] This is a gross simplification, and that 'k' stands for a hell of a lot of factors not even mentioned here. If you have anymore questions just reply with them. I'm not the best at explaining things like this since they are a bit complex, but I'll do my best.

6 out of 6 people think this is helpful.

adam, i was wondering, are you a teacher or are you a high tech car nerd?

7,515

Engineering major, had a couple of years toward a mechanical engineering degree (with the intent of becoming an automotive engineer), but switch to a civil engineering program (decided I'd like the option of working somewhere warm and I'd like to keep cars a hobby... I think working on them all day would keep me out of my own garage at night). On top of that I worked in a shop for a number of years as well as on my own cars....

thats good to hear and that explaines why when ever you post its like a book. so youre like a high car nut.

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