Fuel economy discussion goes here

[mrmephistopheles]

Originally Posted by JRas

I thought 4.63 gears would be shorter, therefore the engine revs would climb more quickly?

I'm a bit confused please explain how this stuff works, Please

Thanks

Think of it like this - Let's say we're working with a button and a light, and 3:1 and 4:1 ratios.

3:1
Press the button 3 times, and the button lights up for one second.

Press the button 180 times and you've got light for a minute.

4:1
Press the button 4 times, and the button lights up for one second.

Press the button 240 times and you've got light for a minute.


You can see there's a difference of sixty button pushes between the ratios. Consider that as a difference in how much an engine has to work.

Let's change the button presses to revs/min (rpm) and increase by a factor of 10.

1800rpm for a minute will get you a mile, or 2400 rpm for a minute will get you a mile.

Seeing the difference here?

4.36 or 4.6 gearing makes the engine work harder throughout the range of speeds.

Off-the-cuff example (not accurate by any means - just an example).

60mph

4.08:1 (stock) = 3500rpm
4.36:1 (some Silvias) = 3850rpm
4.6x:1 (something) = 4200 rpm
3.69:1 (S15 SpecR) = 3200rpm

That's messing only with final drive ratio, not tire/wheel sizing or transmission gearing.

As you can see, the engine has to spin more, work harder and burn more gas to do the same amount of work.