87 Honda CRX...how many HP needed???

[ZugyNA]

Wondering approx how many HP are needed to keep this car going down the road at 55 MPH? This would include air, drivetrain, and rolling resistance, etc.

[civic94]

maybe less than 15 hp cruising at highway speeds. you dont need much power on the highway, just acceleration in city driving. thats why alot of the newer suv's with v8's shuts off 4 cylinders when cruising

[Erik]

15hp sounds reasonable.

My 87 civic (not a CRX) only has 68 hp and no AC. On level ground I only need to press the throttle about 15% to do 55mph. It jumps to about 35% to do 70 mph. I don't know exactly how throttle translates into hp though since it depends on rpm.

If this was Kansas and there were no hills, a CRX could probably get by with a 30 hp engine (the extra 15hp would be needed for the interstate on ramps), but hills are a different story with my puny motor.

I have to downshift on hills that 99% of cars can climb without downshifting- even before my HF trans swap.

[usedgeo]

If you take an accurate weight of you and your car and time the deceleration from 60-50 you can calculate the average deceleration force. Form the force and the speed which is really time and distance you can calculate work and come up with a horsepower number. This is pretty simple physics and I should put the formulas out but I am afraid I will embarrass my self. Someone else will probably give the answer before I finish typing this but I think 15 hp sounds a bit high.

I am repenting. I googled this decent link.

http://yarchive.net/car/horsepower_measure.html

Of course all you need is the deceleration HP.

[Ryland]

Acording the the AutoRef book an engine that has 70ftpounds of torque at 2,000rpm is producing around 27HP, and that is as low as their chart goes, but I think it is pretty close to what the HF engine puts out, 68ftp @2,500rpm if I remember correctly.

[trebuchet03]

Originally Posted by Ryland

Acording the the AutoRef book an engine that has 70ftpounds of torque at 2,000rpm is producing around 27HP, and that is as low as their chart goes, but I think it is pretty close to what the HF engine puts out, 68ftp @2,500rpm if I remember correctly.

Wouldn't that be dependent on throttle position?

[Biffmeistro]

That would be at WOT, which is what all dynos are done at.

[ZugyNA]

An opinion:

http://www.crest.org/discussion/ev/199712/msg01031.html

>A nice thing about EVs is that it is easy to measure the amount of power
>actually needed to cruise at various speeds. What you find is that most
>cars really do need 10-30 HP (or more!) to cruise at 55 mph. A very small
>efficient EV conversion like a Geo Metro can get down to 50 amps at 144vdc
>(7.2kw or 10 HP) at 55 mph. Most EV conversions are more.