I LOVE my 3.90's. Night and day difference over stock gears. And I've still been getting 18.5 mpg around town.
Do gears really make a big difference?
- Thread starter GT00STANG17
- Start date
Week old post, but I'll throw in my $.02 anyway.
I think a lot of people really misunderstand gears. They do multiply the torque and make the car go faster, but at the expense of vehicle speed. So while the car will pull harder, it will do so for a shorter amount of time. All in all, the gears do make the car faster, but not as fast as it feels.
I made a calculator in Excel that will allow you to compare two cars using their rear wheel torque numbers, and their gearing setup. You can also compare the same car, just with different gear setups.
Here's what a stock 2-valve PI GT looks like. It is calculating the torque on the wheels (which is what ACCELERATES the car) at any given speed. The blue car has stock 3.27 gears, while the red car has 3.73s.
As you can see, 1st gear pulls MUCH harder with the 3.73s, which is why most people are all "ZOMG GEARS MADE MY CAR SO MUCH FASTER!!!11!!!1!". However, this extra torque comes at the price of a slower vehicle speed. If you look closely, the 3.73 car has to shift to 2nd gear about 5 mph sooner than the 3.27 car; when it shifts, it looses the extra mechanical advantage of 1st gear that the 3.27 car still has, and for this time, the 3.27 car will actually accelerate faster. BUT, when the 3.27 car shifts to 2nd, the 3.73 car takes the advantage again. This flip-flop continues through all the gears until the top gear, where the steeper geared car will retain the advantage until it runs out of gear.
It is because of that flip-flop that the gears don't gain as much as many people like to make them seem. YES, in the same gear at any given RPM, the geared car will pull harder. But at any given speed, with the car in the proper transmission gear, the geared car may or may not pull harder.
BUT, that isn't to say that gears aren't worth it. My calculator also calculates the MPH difference in the 1/4 mile, and I've found it to be quite accurate over the course of comparing actual timeslips. On a stock 2-valve PI GT, 5-speed, you would gain about 1.5 mph with 3.73s over 3.27s. 4.10s would result in another 1 mph. The more power the car makes, the more pronounced the gain. On a full bolt-on, cammed Bullitt, it gains 2.5 mph going from 3.27s to 3.90s. On my supercharged auto Mustang (325 rwhp), it should theoretically gain almost 3 mph in the 1/4 mile going to 3.27s to 3.73s (which I plan to test later this year). A 3 mph gain with no increase in power is significant!
Actual ET gains at the track will be much more dependent on traction. Going from 3.27s to 4.10s on a 5-speed car is going to make it MUCH harder to hook up.
I think a lot of people really misunderstand gears. They do multiply the torque and make the car go faster, but at the expense of vehicle speed. So while the car will pull harder, it will do so for a shorter amount of time. All in all, the gears do make the car faster, but not as fast as it feels.
I made a calculator in Excel that will allow you to compare two cars using their rear wheel torque numbers, and their gearing setup. You can also compare the same car, just with different gear setups.
Here's what a stock 2-valve PI GT looks like. It is calculating the torque on the wheels (which is what ACCELERATES the car) at any given speed. The blue car has stock 3.27 gears, while the red car has 3.73s.
As you can see, 1st gear pulls MUCH harder with the 3.73s, which is why most people are all "ZOMG GEARS MADE MY CAR SO MUCH FASTER!!!11!!!1!". However, this extra torque comes at the price of a slower vehicle speed. If you look closely, the 3.73 car has to shift to 2nd gear about 5 mph sooner than the 3.27 car; when it shifts, it looses the extra mechanical advantage of 1st gear that the 3.27 car still has, and for this time, the 3.27 car will actually accelerate faster. BUT, when the 3.27 car shifts to 2nd, the 3.73 car takes the advantage again. This flip-flop continues through all the gears until the top gear, where the steeper geared car will retain the advantage until it runs out of gear.
It is because of that flip-flop that the gears don't gain as much as many people like to make them seem. YES, in the same gear at any given RPM, the geared car will pull harder. But at any given speed, with the car in the proper transmission gear, the geared car may or may not pull harder.
BUT, that isn't to say that gears aren't worth it. My calculator also calculates the MPH difference in the 1/4 mile, and I've found it to be quite accurate over the course of comparing actual timeslips. On a stock 2-valve PI GT, 5-speed, you would gain about 1.5 mph with 3.73s over 3.27s. 4.10s would result in another 1 mph. The more power the car makes, the more pronounced the gain. On a full bolt-on, cammed Bullitt, it gains 2.5 mph going from 3.27s to 3.90s. On my supercharged auto Mustang (325 rwhp), it should theoretically gain almost 3 mph in the 1/4 mile going to 3.27s to 3.73s (which I plan to test later this year). A 3 mph gain with no increase in power is significant!
Actual ET gains at the track will be much more dependent on traction. Going from 3.27s to 4.10s on a 5-speed car is going to make it MUCH harder to hook up.
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