Need a straight answer.....

not that simple, i'm afraid

well, actual top speed to the mph is probably impossible to tell. Not all GTs off the same production line will have EXACTLY the same top speed to start with. Then, figure in road surface and conditions, and it varies mile to mile. all comparison is purely theoretical and subject to too many variables to be at all useful. bottom line: it's a little lower. Do you need to go 147 instead of 132?

As for gas useage, it will be theoretically equal to the percentage increase in RPMs at a given speed. This, in turn, is a direct mathematical relation to the change in gearing. works like this:
(4.10-3.55)/3.55 = % of gearing increase = % increase in rpms for a given mph. It also more or less = the % increase in fuel consumption. "More or less" because effective load on the engine will differ because of the gearing change. Also, throttle mapping across the RPM spectrum differs, so fuel delivery is slightly different. If you reflash a custom tune to account for the gears, all this goes right out the window. All of this is null and void unless you drive PRECISELY the same way. I'd bet a big part of the declining mileage you will experience is the sudden fondness of the gas pedal for the floor board.:hihi: :hihi:

having said all that, if you go from 3.55 to 4.10, and were getting 17.5 mpg, you will then get 14.8 mpg. In a mathmatically perfect, theoretical world.:shigrin

bottom line: mileage is worse. Do the gears and enjoy the heck out of it.

clubt said:

Looking to change gears to 4.10 in an o5 gt vert:

How much will I lose in top speed? For instance If the car goes to 143 with the speed limiter will the car only go 120 now?

Click to expand...

clubt,
This may help.

http://www.f-body.org/gears/

GT Five-speed manual (Tremec 3650)
1st: 3.34
2nd: 2.00
3rd: 1.32
4th: 1.00
5th: 0.68
axle ratio: 3.55

V6 Five-speed manual (Tremec T-5)
1st: 3.75
2nd: 2.19
3rd: 1.41
4th: 1.00
5th: 0.72
axle ratio: 3.31

GT & V6 Five-speed automatic (5R55S)
1st: 3.25
2nd: 2.44
3rd: 1.55
4th: 1.00
5th: 0.75
axle ratio: 3.31

ultraclyde said:

As for gas useage, it will be theoretically equal to the percentage increase in RPMs at a given speed. This, in turn, is a direct mathematical relation to the change in gearing. works like this:
(4.10-3.55)/3.55 = % of gearing increase = % increase in rpms for a given mph. It also more or less = the % increase in fuel consumption. "More or less" because effective load on the engine will differ because of the gearing change. Also, throttle mapping across the RPM spectrum differs, so fuel delivery is slightly different. If you reflash a custom tune to account for the gears, all this goes right out the window. All of this is null and void unless you drive PRECISELY the same way. I'd bet a big part of the declining mileage you will experience is the sudden fondness of the gas pedal for the floor board.:hihi: :hihi:

having said all that, if you go from 3.55 to 4.10, and were getting 17.5 mpg, you will then get 14.8 mpg. In a mathmatically perfect, theoretical world.:shigrin

bottom line: mileage is worse. Do the gears and enjoy the heck out of it.

Click to expand...

Ultracyde, good thinking, but it's the wrong concept. I thought the same way until someone explained this to me, and it makes a lot of sense! Gas consumption is indirectly related to RPMS and Torque, it is directly related to horsepower. Since horsepower is effectively torque x RPM, in theory with different gears, there would be less torque, but proportionally more RPM, thus using the same amount of horsepower (gas) to move the car at a given speed. This is in a perfect world, but in reality, more RPMs through the tranny generate more heat, more resistance in the engine itself, so it should be slightly worse, but not a huge difference.

Consider this: with a full tank, most cars will idle about 30 hours without running out of gas, this is about 7-800 RPM. So, using that logic, cruising down the highway at 1600 RPM, the car should run for 15 hours, right? No, because when idling, it's both not spinning fast, but putting out almost no torque, meaning it's producing very little horsepower and only burning enough gas to overcome internal resistance in the engine.