I took my car down the track for the first time and did ok for being a driver and not anything special as far as engine/trans/rear end goes. It's a 1970 Monte Carlo with a 327 and TH350. Someone asked what gear I had in the rear end. I have no clue, but it gets decent mileage, doesn't wind at highway speed, and is slow off the line. I figured I would try to figure it out. It's not a posi because one tire turns one way and the other turns the other way. What I did was put it on blocks, blocked one wheel, counted the tire spins to the driveshaft spins. I rotated the tire 10 times and the shaft rotated about 12.75 times. Then took the formula I found online (shaft spins times 2, divide by 10) to get 2.55. The closest ratio to that is 2.56 for a GM. Did this formula and numbers look correct?
If it were a 4.10 ratio the tire would turn 10 times and the shaft 20.5 times according to the formula. If both a 2.56 and 4.10 were running the same RPM's, which tire would turn faster? I'm assuming the tire that turns faster would be faster off the line and thus be the 4.10, correct?
Would a 2.56 or 4.10 get better:
Gas mileage
launch on the line
lower RPM's going 65mph
They may be stupid questions to some, but my mind was wondering and thought I'd ask here.
This may have been stated but just in case.
The 2.56 gears would turn the tires faster at the same engine speed but the car would accelerate slower. Torque is the turning force an engine makes. When accelerating, the car engine uses it's torque to turn the tires.
Gear ratios can act like a torque multiplier. Gears take the energy from the number of turns and convert it to torque or turning force. The higher the number of turns in to the gears verses number of turns out, the greater the turning torque.
It's kind of like leverage.
Imagine a wrench that is 2.56 foot long and another that is 4.10 foot long. When turning a big bolt the 4 foot wrench has more leverage and can turn the bolt more easily. Replace the bolt with a tire and the same thing.
The 4.10 gears can turn the tires more easily than a 2.56 gear, so the car accelerates more quickly since the tires can turn more easily. Over simplified and a physics teacher would cringe but you get the point.
As for the gas mileage lots of things go into consideration but with 2.56 rear end gears and the transmission in 3rd gear (1 to 1 ratio), every time the engine turns 2.56 times the rear wheels turn 1 time.
with 4.10 rear end gears and the transmission in 3rd gear (1 to 1 ratio) the every time the engine turns 4.10 times the rear wheels turn 1 time.
Either way the tire moves the car the same distance with one tire turn but the number of times the engine turns is different.
Every time that engine makes 1 more rotation it uses more gas so the 4.10 gears cause the engine to turn more times and use more gas.
I hope that was helpful and didn't come across insulting. Sometimes I overthink the question.
