Gears vs. HP???

[fryingricecobra]

Can someone chime in here please.

I have always thought that changing gears (I am running 4.10's) doesn't affect hp. I don't see how it could.

However, recently I began wondering....if I am going through the gears quicker is there some hp in the motor thats not getting out b/c of redlining quicker....make sense?

Just wondering....

Still sore about my recent trip to the dyno where I lost almost 30rwhp/tq. Of course its alot hotter now than my last dyno so thats some of it.

So does running gears make your hp read different on a dyno? I know it won't add of subtract any actual hp but does it make it where you can't "get to all of it" so to speak.


Thanks for the input.

Nick

 

[SStupid]

Deep gears.

Yes, running deep gears does make your hp numbers plummet.

 

[fryingricecobra]

anyone else have opinions?

 

[fryingricecobra]

SStupid,

Can you explain why? I am having a heat "discussion" with someone about this.

 

[sambandit]

I'm not sure why but I know it's true. Drag radials or softer tires also affect numbers a little. Wish I had some answers for you!

 

[Shadowgray03]

Horsepower = (Torque*RPM)/5250, changing gears will affect torque and thus HP.

When you doa dyno pull you are supposed to do it with a 1:1 drive ratio. If you change tire size or gear ration you in essence change the gear ratio.

If you have 500ftlbs tq @ 5000rpm would give you 476hp. If you changed gears your peak tq would likely increase and also peak at a lower RPM. For arguements sake lets say changing gears made it jump to 525ftlbs at 4300rpm you would net only 430hp. These are just example numbers and it will vary greatly by the mods you have etc.

 

[fryingricecobra]

So can you correct this with the dyno software.

I want my numbers to be correct.

 

[jtfx6552]

This is a complicated subject.

It depends on the type of HP measurement. On an enertial load dyno, where the power is measured based on acceleration of the rear tires against a load, the higher numerical gears will have a negative effect of HP measured. In a Mustang during a 4th gear pull on a dynojet, the pull will be shorter, the higher numerical ratio of the rear. This means the tires and axles, the ring and the differential have to be accelerated from the start RPM to the end RPM in less time, which will make the driveline loss higher and the rwhp reading lower.

On a dyno that can measure while holding the engine at a fixed RPM (like an eddy current or water brake) the gears would not matter. Well they would a little since the more reduction will result in a very slight decrease in efficiency.

JT