Find solution
How do down load 8.0 messnger?

If driving at 70mph puts a 80% load on an engine, how could 120mph place a 100% load?

  • These aren't actual calculations, but I was talking to someone who led me to believe this could be possible. I have had the understanding that while cruising an engine is mainly working to overcome air resistance. I have also thought air resistance increases with the square of velocity. This being said it seems to me that while driving at 70mph the engine would need to be under 50% load if a top speed of 120mph can possibly be achieved. I understand it would be time consuming to accelerate to this top speed, since little additional load would be available to dedicate to acceleration but I'm quite confused on how the numbers I mention in the question could even be conceivably possible. Thanks for any feedback!

  • Answer:

    The only way that numbers in that general range are possible is if you consider the following: At 70 mph, the engine is turning at about 58% of it's maximum rpm. For the speed the ENGINE is operating at, the HP it is making could be somewhat close to its maximum possible (maybe 70 or 80% of possible load at that RPM). Remember, to make full HP, the engine needs to be near redline RPM. So, at 120 mph, it is conceivable that there is a higher horsepower capability of the engine, given the higher RPMs. Measured against this potential, you could say the engine is near 100% loaded in this second case. This is more likely now with things like turbocharging, where extra boost is obtained only when the demand on the engine is the highest.

John at Yahoo! Answers Visit the source

Was this solution helpful to you?

Other answers

Air resistance varies with the square of the speed. One book I read said the energy lost to air resistance varied with the cube of the speed. I don't belive any engine that runs at 80% for 70mph could make it to 120 mph. On this I agree with you.

Paschal H

One thing we are assuming here that speed vs engine load has a linear relationship. Where as most things in nature, it may not be linear. So the numbers are possible.

Sandip P

One of the things you should always be querying is the accuracy of your sources of information. Congratulations on your perspicacity.

Numbat

The transmission system probably determines this.

Mr. Un-couth

HP is torque x rpm (divided by a constant). Peak HP usually occurs somewhere along the rpm band at a speed greater than the torque peak and lower than the "red-line" or max rpm as torque usually peaks at an rpm less than max speed(rpm). It is possible that the torque output at 70 mph ( i.e., a certain engine rpm) times that rpm equals a HP that is 70% of the torque output x the rpm required for 120 mph. A Mopar 426 "Hemi" V-8 (circa 1960's) had a torque curve that might have produced such characteristics.

wmkl99

Load implies percent of engine rated power output. Your car would make 75 or 80 max. Short of a nasty cheat (like going uphill for the cruise and downhill for the top speed test), it can't do 120. BTW, rolling resistance and aerodynamic drag are normally considered separately for autos. Aero drag force increases with the square of the speed, power for that drag with the cube, because Power = Force * speed (this is from Work = force * distance). Aero drag indeed dominates at highway speeds.

wingstwo

Related Q & A:

Just Added Q & A:

Find solution

For every problem there is a solution! Proved by Solucija.

  • Got an issue and looking for advice?

  • Ask Solucija to search every corner of the Web for help.

  • Get workable solutions and helpful tips in a moment.

Just ask Solucija about an issue you face and immediately get a list of ready solutions, answers and tips from other Internet users. We always provide the most suitable and complete answer to your question at the top, along with a few good alternatives below.