Will a Diff gear change increase HP

[stockvs]

If you go from a 3.08 ratio to a 3.7 will your Horse Power rating increase.

Obviously HP at Flywheel will be the same, but will Rear Wheel HP increase.

I am assuming it will but just thought i will ask.

[Shounak]

No.. It will just affect how the HP is used by the Rear wheel..

[1991_Vn2nV]

No it wont...You will still have the same drivetrain loss as you would with normal diff gears..

[mattman]

Same power, just used differently, you will get a harder launch though.

[Adzzaman]

Doesnt it show on a dyno readout as more power though? I know its not making more power at the motor but dosent it multiply the power at the wheels?

[253@7k]

Doesnt it show on a dyno readout as more power though? I know its not making more power at the motor but dosent it multiply the power at the wheels?

Nope, if that was true I would just put 7:1 gears in my datsun 120y and take out horsepower heros around the country......

[Adzzaman]

cheers for the quick reply mate

[enhancedss]

changing diff gear ratio will not increase power figures at all, the only increase u will notice on a dyno is torque will be increased, i hope this clarifys a few things for people.

[Moredhel84]

^^ Wouldn't more torque actually be an advantage over the power? Torque being the pulling/spinning power behind it all, wouldn't this be a positive gain?

Not being a mechanic and all, I heard a while back that power is derived from torque over certain RPM ranges etc, so wouldn't increasing your torque also add gains to your overall KW as well? (Pure speculation on my behalf here)

Oh and one more thing, usually when changing gear ratios a lot of us would be thinking along the lines of getting a LSD/spool installed (if not already) at the same time, saving money. Wouldn't the added benefit of having more traction on the dyno (due to no more single spinner) also add marginally to your overall KW?

[enhancedss]

^^ Wouldn't more torque actually be an advantage over the power? Torque being the pulling/spinning power behind it all, wouldn't this be a positive gain?

Not being a mechanic and all, I heard a while back that power is derived from torque over certain RPM ranges etc, so wouldn't increasing your torque also add gains to your overall KW as well? (Pure speculation on my behalf here)

Oh and one more thing, usually when changing gear ratios a lot of us would be thinking along the lines of getting a LSD/spool installed (if not already) at the same time, saving money. Wouldn't the added benefit of having more traction on the dyno (due to no more single spinner) also add marginally to your overall KW?

Torque is twisting force, torque is actually what gets a vehicle of the line, so in drag racing, you take of from the line your using torque, then power takes over after torque fases out, change gears and it all happens again, every gear change. So if you can remeber it as torque gets u moving, power keeps you going.

A chassis dyno calculates on load vs speed, a car will make different power in different gears, due to driveline loss, nothing to do with changing ratios.

When diff ratios are changed torque is increased, so for eg. from 3.07 ratio to 3.9 ration there is a very large torque increase on the dyno. the engine wont produce any more torque, a dyno is caculating torque from load vs speed.

LSD's or spools are really a must when building a diff as the extra cost pays itself of very quickly, very very rarely a worn lsd will upset power figures on a dyno, as in straight driving the lsd isnt even working.

[Cane_It]

think of the diff ratio like leverage (tall ratio is like trying to do a bolt up tight with a short spanner, however with a short ratio its like trying to do up that bolt with a bigger spanner).
a 3.08 is relatively tall, takes a while for the car to get going, but a 4.11 will give you more mechanical advantage if your motor can rev hard enough and make torque and HP hig enough up the rev range to use it.
pure physics.

[greenfoam]

Changing the diff will help you get more torque and power onto the road more quickly, that's why you go faster but once you are out of first gear and up in the peak torque-power range there's not much difference, then again it takes along to time for the other guy with a bit more peak power but stock gearing to gain back that .3 of a second you pulled in front in 1st gear so it's a good thing.

Also power is calcualted from torque and time (revs)

Read this and you will know all about it

http://www.epi-eng.com/BAS-PwrTrq.htm

[Patrio7]

this is probably wrong but heck

torque is, as mentioned the twisting forge of the engine, where as power is the engines ability to keep accelerating under load?