final drive gear vs HP numbers

[v8huntr]

gears do not change rwhp. i just wanted to share.

 

[Nexus-6]

Do people have proof that they lost hp with gears?

 

[joe117]

They do change RW torque. A higher ratio will give you more power to the ground and if you can hook up they will cause you to accelerate faster.
If you don't believe this, try starting in second gear.

 

[Torquemonster]

Joe117 is right - the bigger the number the rear ratio is - the more torque at the wheels... the dyno is supposed to correct for the gearing however to provide what amounts to - the amount of flywheel power that makes it to the wheels.

Otherwise - a stock SRT10 with say 525ft lbs torque at flywheel would be making well over 1600ft lbs in 4th gear due to gearing (which it would) - they correct for that to make the figures comparable to engine power.... otherwise people would dyno in first gear and come up with over 4000 ft lbs

 

[joe117]

"Joe117 is right"
I like that torquie. Let me try it on you.
torquie is right..... That wasn't so hard... this time. ;-)

 

[Nexus-6]

lol @ Joe.

Cool info both of ya's...I was not aware!

Thanks!

 

[carguy07]

Can't change torque but not HP. The lines will intersect at the same place every time. Correct me if I'm wrong, but you are changing when and how quick it gets to the wheels. Other than minor frictional losses, I can't figure that HP or torque would be changed at all, just the delivery of it per your speed. More torque at slower speeds. Right?

 

[Paolo Castellano]

Can't change torque but not HP. The lines will intersect at the same place every time. Correct me if I'm wrong, but you are changing when and how quick it gets to the wheels. Other than minor frictional losses, I can't figure that HP or torque would be changed at all, just the delivery of it per your speed. More torque at slower speeds. Right?

Carguy, I would have to agree with you. I think the statement of this post addresses the fact that changing rear end gears has no effect on the dyno's reading of the RWTQ or RWHP after correction for the gear.

Of course the numerically higher rear end gear will yield a higher HP and TQ # to the ground as it is: rear end gear X transmission gear ratio X RWHP or RWTQ = RWHP or RWTQ multiple.

 

[RX VIPER]

Ok, now I'm confused. You say that a rear end gear change will not effect the dyno reading of the rwhp AFTER correction for the gear.

Let's use my #'s for a specific example. My car at the club dyno which was set up for all the cars in 4th with the stock 3:07. I have the 3:55 and pulled 459 rwph with no correction. What is my actual rwhp? I was always told to adj. up with the 3:55's by 3% so I would have approx 473. Is this not correct? Thanks in advance.

 

[joe117]

The dyno get's its HP number by measuring the torque and the rpm of the wheel.

I don't think changing the rear to a higher ratio will give you different HP numbers at the wheel. You will have more torque but if you get it from gears, you will be turning the dyno slower.

You could have 500 ft/lb of torque at the end of a large wrench at the end of tightening a large bolt and you would have no horsepower.

Horsepower is torque delivered in a measured amount of time. Gears can multiply torque but not HP.

 

[Ulysses]

heh heh heh. We've had this discussion many times before with tons and tons of calculations and mathematical equations. So, instead of boring you all with all of that stuff, gears only change torque to the ground. Not HP (well, there is a small driveline loss). The dyno is not fooled by the final gear. It could care less about the final gear.

 

[Nexus-6]

Dynos are smart...

 

[joe117]

Hey, what about me, I'm smart too..

 

[Nexus-6]

lol! There are quite a few smarties 'round these parts...