I know that installing a lower rear end gear will multiply torque, but I have a "real life" question. Let's say you dyno your car with 2.73 gears and it registers let's say 300 ft/lb, then you install 4.10's and go back to the dyno the same day, will the torque number on the dyno be a lot higher? If it actually multiplies torque then it should, shouldn't it? I am just having trouble converting from concept to real life. I guess what I'm asking is how do lower gears affect the dyno read-out, if at all?

 

nope, doesn't affect the dyno for some reason
not really sure why though myself

 

Good question.

If you are talking an inertia dyno like a DynoJet, it's not really measuring torque like an engine dyno does. Rather it measures the power it takes to accelerate the heavy rolls. Knowing engine rpm, it then backs into the torque reading.

Now, more gear (4.10) causes a little more frictional loss, but the tires will be turning slower so there is less rolling resistance, and less inertia.

Bottom line is that you might see a little more hp and therefore a little more torque, but not a lot.

If the chassis dyno had a power absorbing brake and actually measured torque, it would know wheel rpm and engine rpm so it would back into fw torque from rw torque.

Clear as mud?

 

To illustrate the point above, when working with the Dynojet if the rpm signal is lost you lose the torque reading but still get a hp readout. It is measuring work over time (hp).

Rich