Does Lower Final Drive Change Dyno Numbers?

**barefootbonzai** · 21-09-2006 08:29 AM

So yeah, my question is does lower final drive affect power read outs on the dyno. From my understanding FD is kind of a torque multiplier, so does this affect the power reading or not?

For Example.

Same CAR

Run on Dyno with EK4 box - 4.4 FD
vs
Run on Dyno with EK4 box - 4.9 FD

Would the power figures change?

**DynoDave** · 21-09-2006 08:45 AM

Originally Posted by barefootbonzai

So yeah, my question is does lower final drive affect power read outs on the dyno. From my understanding FD is kind of a torque multiplier, so does this affect the power reading or not?

For Example.

Same CAR

Run on Dyno with EK4 box - 4.4 FD
vs
Run on Dyno with EK4 box - 4.9 FD

Would the power figures change?

Torque makes HP so you answered your own question,so it will change the dyno figures by a small margin.
Regards Dyno Dave

**aaronng** · 21-09-2006 08:54 AM

Is it true that certain dyno software require you to enter your FD ratio, otherwise the dyno is plotted as power vs road speed?

**barefootbonzai** · 21-09-2006 09:06 AM

bugger, it's because i got more power than my mates car with similar setup. Must be because of the final drive, *shattered* my engine probably doesn't make as much power as i thought after all.

**STOCK** · 21-09-2006 11:18 AM

how much more did your mate car make compared to yours?

**barefootbonzai** · 21-09-2006 12:10 PM

I made 10kw's more. But it's kinda hard to compare now that i think about it, our setup's ain't really similar at all. Just both running B18CR's, mine AUDM and his J-SPEC but different combination of bolt ones.

**string** · 21-09-2006 05:04 PM

The car with the shorter final drive will most likely give a smaller read-out.

Inertial loads will require more power to accelerate as you shorten the run time. By increasing relative wheel torque (to your friend for example) you will shorten the run time, thus increasing angular acceleration on all rotating parts in the engine, incuring a greater (engine) torque loss.

Conclusion: Dyno figures are a very general measure of power output. Don't take them to heart, since in this case, the car with the lowest 'read-out' will be quicker in most likely, every situation (all else equal).

**barefootbonzai** · 21-09-2006 05:32 PM

Originally Posted by string

The car with the shorter final drive will most likely give a smaller read-out.

Inertial loads will require more power to accelerate as you shorten the run time. By increasing relative wheel torque (to your friend for example) you will shorten the run time, thus increasing angular acceleration on all rotating parts in the engine, incuring a greater (engine) torque loss.

Conclusion: Dyno figures are a very general measure of power output. Don't take them to heart, since in this case, the car with the lowest 'read-out' will be quicker in most likely, every situation (all else equal).

lol, i think you're totally off the mark mate.

**kayot1k** · 21-09-2006 05:33 PM

lol, say no to drugs

**string** · 21-09-2006 05:38 PM

Well you're welcome to prove me wrong, just saying "you're wrong" doesn't really do much for your case however...

And, giving examples of dyno figures is not proof; we all know exactally how static they are.

**barefootbonzai** · 21-09-2006 05:47 PM

If you didn't notice, dyno dave gave me the answer i was looking for. And just so you understand.

My car made MORE Power with the 4.9 Final Drive then my friends car. Our Dyno numbers where run 5 mins after each other on the same dyno. So there's nothing to proof, i just wanted to know if my FD helped me in pulling a bigger figure than he did - and it did. Not sure what you're on about.

**string** · 21-09-2006 05:53 PM

DynoDave's answer in no way helps anyone who has any genuine intrest in knowing exactally how a final drive will relate to outputted power figures.

Were both motors identical in every way? Were both run conditions identical in every way? Were both cars identical in every way? (wheels, drive-train i'd especially like to know). Did you dyno test both cars with the same final drive, and find them producing the exact same power? Until you can answer yes to all of these questions, your point is moot.

There are so many variables in this type of real world dyno testing that you can never rarely compare two outputs, unless you are simply comparing, 'figures'.

Realistically, a final drive will increase wheel torque, i.e. available power, at every car speed. If you measure power output on a non-intertial dyno, it will not change (disregarding inconsistencies), and as a bonus, you'll get higher figures to gawk at!