Not to start a gear ratio debate on what is better, as god knows there are millions in the search directory. Just some info I thought I would share with everyone, as it took me a while to trying to calculate which gear I will be going with. Keep in mind your transmission gear ratios may differ depending on the year. Here is a link to the manual t5 gear ratios on 82-93 t5's and 84-93 aods.
http://www.mustanggt.org/89gt.htm
Anyways to compute I'm using the following tranny gear ratios
First-3.35
Second 1.99
Third-1.33
fourth1.00
fifth- 0.675
reverse 3.15
For computing purposes I decided on using a 225/60/15 tire to find my diameter of 25.6 inches
Now a few quick things
mph=(rpm x tire diameter) divided by (final gear ratio x 336)
and
engine rpm= (mph x final gear ratio x 336) divided by (tire diameter).
note: final gear ratio is calculated by multiplying tranny gear ratio by dif gear ratio
So lets begin
Lets say this is a race application and you are debating 3:73 or 4:10 gears.
Lets also assume you shift at the end of your 5.0L stock power band which I have not been able to find any stock dyno results. I found a spec that "CLAIMS" 225HP @ 4000 rpm. How true this is I can't say.. For my equasions I used the rpm power band starts @ 3400 RPM and drops off @ 4800 RPM..
Now I don't know if this rpm curve is correct-couldn't find any info.
lets say your thinking of a 3:73 gear your final drives would be
first-12.48
second-7.42
third-4.96
fourth-3.73
fifth 2.51
reverse--who in the hell cares?
again with 3:73 shifting @ 4800 rpm from every gear
first gear @ 4800 rpm =29.3 MPH
start second 29.3 MPH @ 2853 rpm shift @ 4800 rpm @ 49.28
third 3200 rpm @ 49.28 shift point 4800 @ 73.7 mph
Fourth start @ 3608 rpm---- shift 4800 @ 98 MPH
fifth start 3228 rpm by the time you hit 4800 in fifth gear you would be going 145 mph
now 4:10 gears final drive
first 13.73
second 8.16
third 5.45
fourth 4.1
fifth 2.77
first gear @ 4800 rpm- 26 mph
second @ 26 mph = 2784 rpm shift 4800 @ 44. 8 mph
third @ @ 44.8 mph= 2410 rpm 4800 @ 67.11
fourth @ 67.11 = 3600 rpm 4800 @ 89 mph
fifth @ 89 mph = 3235 rpms 4800 rpms @ 132
So as you can see with 3.73:1 gear, your shifting closer into the power range, from the end of the rpm power curve, also with the 3:73 you don't run out of engine until about 145 mph, where the 4:10 you run out around 132 mph.
I'm really tired and may have done some numbers wrong. But my point if you are trying to decide this could give you a reference point. The only negative I see for going 3.73:1 is I will have to wait longer to shift @ higher speeds as compared to 4.10:1. Which is almost offset by being closer to the rpm power curve after a shift.--theoratically cancelling out any positives and the taller gear has. There is no doubt looking at the comparisons that the 4.10 will take off the line, possibly slightly helping in over all 1/4 mile speed, depending greatly on where the power band is and how long it would take to get into the power curve @ 2400 rpm) Really a matter of opinion, and I'm not trying to start a debate. Just wanted to put this info out.
http://www.mustanggt.org/89gt.htm
Anyways to compute I'm using the following tranny gear ratios
First-3.35
Second 1.99
Third-1.33
fourth1.00
fifth- 0.675
reverse 3.15
For computing purposes I decided on using a 225/60/15 tire to find my diameter of 25.6 inches
Now a few quick things
mph=(rpm x tire diameter) divided by (final gear ratio x 336)
and
engine rpm= (mph x final gear ratio x 336) divided by (tire diameter).
note: final gear ratio is calculated by multiplying tranny gear ratio by dif gear ratio
So lets begin
Lets say this is a race application and you are debating 3:73 or 4:10 gears.
Lets also assume you shift at the end of your 5.0L stock power band which I have not been able to find any stock dyno results. I found a spec that "CLAIMS" 225HP @ 4000 rpm. How true this is I can't say.. For my equasions I used the rpm power band starts @ 3400 RPM and drops off @ 4800 RPM..
Now I don't know if this rpm curve is correct-couldn't find any info.
lets say your thinking of a 3:73 gear your final drives would be
first-12.48
second-7.42
third-4.96
fourth-3.73
fifth 2.51
reverse--who in the hell cares?
again with 3:73 shifting @ 4800 rpm from every gear
first gear @ 4800 rpm =29.3 MPH
start second 29.3 MPH @ 2853 rpm shift @ 4800 rpm @ 49.28
third 3200 rpm @ 49.28 shift point 4800 @ 73.7 mph
Fourth start @ 3608 rpm---- shift 4800 @ 98 MPH
fifth start 3228 rpm by the time you hit 4800 in fifth gear you would be going 145 mph
now 4:10 gears final drive
first 13.73
second 8.16
third 5.45
fourth 4.1
fifth 2.77
first gear @ 4800 rpm- 26 mph
second @ 26 mph = 2784 rpm shift 4800 @ 44. 8 mph
third @ @ 44.8 mph= 2410 rpm 4800 @ 67.11
fourth @ 67.11 = 3600 rpm 4800 @ 89 mph
fifth @ 89 mph = 3235 rpms 4800 rpms @ 132
So as you can see with 3.73:1 gear, your shifting closer into the power range, from the end of the rpm power curve, also with the 3:73 you don't run out of engine until about 145 mph, where the 4:10 you run out around 132 mph.
I'm really tired and may have done some numbers wrong. But my point if you are trying to decide this could give you a reference point. The only negative I see for going 3.73:1 is I will have to wait longer to shift @ higher speeds as compared to 4.10:1. Which is almost offset by being closer to the rpm power curve after a shift.--theoratically cancelling out any positives and the taller gear has. There is no doubt looking at the comparisons that the 4.10 will take off the line, possibly slightly helping in over all 1/4 mile speed, depending greatly on where the power band is and how long it would take to get into the power curve @ 2400 rpm) Really a matter of opinion, and I'm not trying to start a debate. Just wanted to put this info out.
