acceleration is also determined by gearing.

if you swapped the oem wheel of an s2k, and mounted 5 inch wheels (and maintained drivable ride height)...

your acceleration will be a LOT slower.

the logic is the same with changing the gearing...it will affect acceleration.

 

You can change the torque at the wheels, though. That's what gears do, generally speaking. What you can't change (at the wheels or the engine) is power.

Power = Force * Speed

Perfect gearing changes the relationship between the force and the speed, but doesn't change the overall result. (Real world gearing has inefficiencies that suck away some of the power.)

If the dyno is directly connected to the engine, then obviously there is no gearing involved. If the dyno is connected to rollers that the car's drive wheels are spinning, then yes, you would have to correct for gearing in order to measure engine torque. however, they don't actually measure engine torque. They measure power, and then use the RPMs to calculate engine torque.

 

i've read otherwise...

thus, my understanding contradicts your explanation...

therefore, i'm confused at this point.

 

Yes, of course. But that's the whole point. Saying "acceleration is better with lower gearing" ignores the real world constraint that the engine can only deliver maximum power at certain RPMs. At any given speed the car is going, there is a perfect gear ratio that allows the engine to be operating at maximum power. Whatever keeps you closest to that over the range of speeds you care about is the optimum gearing solution.

Ideally a continuously variable transmission would be best, because you could keep the engine running at maximum power all the time and just let the gearing adjust for the speed of the car.

 

so hypothetically speaking...

if someone bought a USED s2k, with 4.77 gears...and dyno'd the car without adjusting for the gearing...

they would get a SUBSTANTIALLY higher power/torque dyno reading?

and say...holy shit, i have 265hp??

the next question would be, "has anyone got a torque/power dyno readout without adjusting for gearing change that measures the CHANGE in torque with new gears, just for comparison purposes?"

i don't think so...because i still believe that a gearing does not change the torque measured by a dyno...

 

Sigh. Physics again.

F=M*A so A=F/M

P=F*V so F=P/V

Thus, A=P/(V*M)

Acceleration is proportional to power and inversely proportional to speed and mass. Gearing and/or torque doesn't directly enter into it all. The function of the gearing is only to allow the engine to operate as close as possible to the peak power as the velocity changes. Torque is just a byproduct. (There are some real world constraints, though, such as aero drag, wheel spin, power loss in the drivetrain, etc.)

 

No.

The dyno could measure the force on the rollers and the speed of the rollers. That gives a power. (Or the dyno could measure power directly, by a variety of possible techniques.) Either way, you get a power.

Then the engine RPM is used to calculate engine torque from the power. The gear ratio of the car is not actually needed at all. An assumption can be made about what percentage of the power is lost to inefficiency, and the power (and thus engine torque) numbers can be adjusted for that if desired.

 

to me, it appears that you have contradictory statements.

 

^
this is what i understand and agree with.

 

The difference is between directly measuring engine torque versus directly measuring power output and calculating engine torque. To do the former you would need to know the gearing. To do the latter (which is what is actually done), you don't.