Ford Mustang Forum - View Single Post - Underdriver pulleys
View Single Post
post #9 of (permalink) Old 02-20-2006
kscoyote
SHELBY GT 500 Member
V6 Member
 
kscoyote's Avatar
 
Joined: Aug 2002
Location: Topeka
Posts: 11,432
 
Quote:
Originally Posted by fast66
No, there is NO RWHP increase by changing rear gears. This is exactly the same as saying "my car has more HP in first gear than in second gear"
This is NOT the case.
If you put you car on a dyno, and run it in first you will get a certain HP reading. Then run it in second you will get the SAME reading.
Now put your car on the dyno with a 2.8 rear gear and take your HP reading, then swap the rear gear for a 3.75, your HP will be exactly the same and at exactly the same engine revs. It will show max HP at a lower road speed but it will be the same figure.
(there is potentially slightly different friction between different rear gears, but this would be so small as to be ignored)
again, you are correct, the engine hp is the same.

but mathematically, if you measured the power at the wheels, using only torque to compute hp, the mathematical illusion is that there is more hp, as you're deriving hp from measured torque.

The dyno corrects this to measure engine hp. by using the RPM and engine measurements and computing dyno acceleration.

Does this make more sense?

Woe to him who builds his palace by unrighteousness,his upper rooms by injustice,making his countrymen work for nothing...Does it make you a king to have more and more cedar?Did not your father have food and drink?He did what was right and just,so all went well with him. He defended the cause of the poor and needy,and so all went well...But your eyes and your heart are set only on dishonest gain,on shedding innocent blood and on oppression and extortion. Jer 22:13, 15-17
kscoyote is offline  
 
 
For the best viewing experience please update your browser to Google Chrome