Gear Dyno Difference
 

Just in case some are interested in how gears affect dyno number..here you go..these were done on the same dyno about 2 years apart

first dyno before and after getting tuned with stock 3.36 gears

http://i22.photobucket.com/albums/b3...d76c09a68a.jpg

second dyno is with 4.08 gears with all the same mods

http://i22.photobucket.com/albums/b3...New%20Dyno.jpg

I still don't understand why the power dropped so much

Your car automatic or manual? What gear were the runs done in?

7at both done in 4th gear...the load on the gears has change is what my tuner said...my 4th gear tops out at 102 and before the gears it was 130..we tried a 5th pull and that went out to about 150

20hp in drivetrain losses from an upward final drive change is a lot more than I would have expected.

the real question is... do you actually update your signature to a lower number???

The dyno is measuring torque (actually tractive effort which is not quite the same thing) and the gear box and final drive are "torque multiplication" devices and there making the gearing shorter will be default provide for less "torque multiplication" which affects the Nm measure and by direct implication the Kw number (or lbs/ft and hp for non-metric folks).

Biggest risk is that with lower gearing, you are seeing a bit more slip on the rollers which some might interpret as "transmission losses".

This is why I prefer to set my engine up on an engine dyno and get numbers from the crank, but that is a PITA for anything other than a race engine build.

I need some quiet time outside the orifice to figure out the equivalence factors so you can compare readings with different FD ratios.

yes once I get the headers on and retuned in October ill update my signature with the new numbers..i haven't seen anyone who has changed gear's do a redyno..here is a a pic of all the dynos with 4th and 5th gear pulls

http://i22.photobucket.com/albums/b3...e311/image.jpg

You never cease to amaze me. Lol. Wish I lived close to you so I could be a fly on the wall in your garage.

Dynojet inertia dynos actually measure horsepower and calculate for the torque! He geared from 3.3 to 4.0 which would increase torque multiplication and therefore increase power/torque to the drive wheels. But the dyno reads flywheel power minus drivetrain losses so you dont see the torque multiplication have a direct effect on the dyno graph... the difference in power you see from one transmission gear to another (or one final drive gear to another) should be the result of efficiency lost between the gearings the further you deviate from 1:1

correct me where im wrong!

I was just teasing about the signature!

I do see that there are 2 years between your dyno sessions... so that could possibly explain a few of the HP depending on mileage and maintenance. I would also expect that the installation of the ring and pinion could eat up a few HP depending on how its shimmed and the gear mesh?

I like potato salad to

it all has to do with load.. I ddn't get in to it fully with my tuner..difference in Milage is about 20k and Maintenance is performed every 3 months oil changes..i think that any who does a before and after dyno after gears will have the same result.. as my tuner said don't get hung up on numbers it just a before and after result with mods or tuning.true number are made at the track.. which is where im heading this winter..

And of course Charles (Phunk) is correct and I am wrong .... perfectly argued but precisely 180-degrees wrong ....... lower diff ratio will provide more leverage for engine torque at the tyre face .....

I stand corrected ....

Hmm. Do you have the ambient conditions?

If they aren't similar between runs, that will account for at least some of the difference -- no correction factor perfectly accounts for wildly different ambient conditions.

Sounds like fried brains. :icon17: