well i guess i'm having trouble with the idea of mechanical advantage vs increased torque. in many cases it seems like they are one in the same...

with my shorter final drive (4.785) i can certainly feel the difference...now are you saying that the mechanical advantage is having more of an affect...and the engine is actually losing torque(if it were measured on a dyno)? to me, it seems like there is a contradiction...

 

Yeah...its a mind boggler. Did you read the link?

The gears do give more mechanical advantage to the drive wheels. This in turn allows the engine to spin up much quicker through its normal rpm range. The faster the engine spins up...the more energy is consumed acclerating its own components which results in less work done at the wheels...more done at the motor(crank,pistons,flywheel,rods,etc)

Thats why its very important to choose the correct gear, taking both concepts into account. Otherwise, if higher gear always = more power..we would just get the steepest gear available. Try to think of it in its extremes. What would happen if a stang went from a 3.73 gear to a 20.73 gear. Yes...mechanical advatage would be incredible...for pulling stumps. But for accelerating the car it would be horrible, The engine would rev so fast...most of the energy produced would be consumed to accelerate the engines rotating components. Not much would be used at the wheels.

 

Scott...with the dynojet the torqueload on the motor is the weight of the drums, which as you say is unchanged regardless of the cars gears. However...put the 4.10 in the rear in place of the 3.42 and it will spin up through the engine rpms faster due to mechanical advantage. So with 4.10s you would see that the car goes from say 3000 rpm to 6000 rpm in say 8 seconds. Which would be faster than the say 8.5 spin up with 3.42s. However...look at the dynojet readouts for mph of the drums. You would see that the the time to accelerate from X mph to Y mph will be less for the 3.42 gears

So you would see what looks like two conflicting stories until you seperate them.

Time to accelerate the 3.42s from 3000-6000 rpm= 8.5 seconds
Time to accelerate the 4.10s from 3000-6000 rpm= 8.0 seconds

it looks as though the 4.10s are better..untill you compare that to something that will better show the work done at the wheels. It may look something like this

Same dyno runs as above...just reading time to MPH instead

with 3.42s in 8.5 seconds went from 40-140 mph
with 4.10s in 8.0 seconds went from 38-119 mph

if you did the math you would see that with 3.42s your accelerating at an avg speed of 11.76 mph per sec
and with 4.10s it would be 10.1 mph per sec

More work done at the wheels with 3.42s, means more tq/ hp applied to the rollers of the dynojet.

This could easily be tested on Johns dyno. But I believe its right.

 

youre right hybridss
lets remember that the dyno measures the work done, or the horsepower.

it only calculates the torque from the rpm signal however. this is how you can have a smooth horsepowercurve but a missing holein your hoespower /torque curve.
so in actuality although it gets confusing

 

My question is as follows: Does a different stall converter affect torque? From personal experiance, I have seen that it does. Is there any concrete evidence of this? It's always baffled me...whacky ass automatics.

 

thanks guys, i understand the points made by hybridss and "shane roberts."

this isn't as straight forward as you would think...

 

Al, I knew the basic gearing laws but now reading this post it's brought up a few questions. Case in point. I went from 4.10 to 4.56 gear. Went to Tune Tec and had the car dynoed. My hp/tq levels basically stated the same. But when I went to the track my mph did suffer about 1-3 mph. Now I thought bigger gears would yield higher mph due to the gears help put the engine in it's powerband quicker and longer during the run. But yes my 60ft and 1/8 times are faster(et wise)but the mph is alittle lower. So your saying that if I were to 4.10's back in I would gain the mph but lose the et. I understand that, but wouldn't a higher mph offset(well almost) for slower acceleration? Or would it be better to go with a larger diameter tire than opposed to a lower gear ratio? -Mark

 

as goofy as this sounds, I have personaly whitnessed it.
If you take the tach signal out, the dynojet will still give you hp numbers but no torque, if it truly measured torque and calculates hp, how does it pull that off?

My best guess is the dynojet software measures acceleration over time to calculate hp and then calculates torque from that using the tach signal.

again I have done NO research, this is just what I have seen with my own eyes watching cars on a dynojet.