MT-82 Transmission: V6 vs V8
3/10/22 | 03:47 PM
#22
Legacy TMS Member
Joined: February 2, 2004
Posts: 7,582
Likes: 670
From: Insane
Welcome to the forums! 
TL;DR: Your launches will be less spectacular, more sluggish, the rest will be about the same, and it looks like MPG will actually be negatively affected in 6th... I think?
A lot of this gets confusing, but I think that's right, or at least what my research told me. Read on if you wanna see the research, otherwise, there's your answer, hope it helps! 
---
Ok, I did the calculations for doing the swap on my '06 GT from the TR3650 to a Tremec T56XL with two different sets of gears available, as the shifting on the TR3650 is... well, it's fun. Thought maybe putting in the T56XL would be a move to make... but no, it turned out not really, and actually not so great in some respects. So I figure that might help me help you with this.
First, revisiting the original OP's post on the V6 and V8 ratios. Remember, higher number is lower gearing.
V6 / V8
1st: 4.236 / 3.66
2nd: 2.538 / 2.43
3rd: 1.665 / 1.69
4th: 1.238 / 1.32
5th: 1.00 / 1.00
6th: 0.70 / 0.65
Notice how the V6 has a lower first gear, slightly lower second, insignificantly higher third and fourth gears, 1:1 fifth, and a slightly lower sixth gear. Also be aware that the V6's axle is usually a taller gear, lower ratio number, for economy reasons. They then use the transmission to make up for some of the 'oomph' lost, yet still be as economical as possible, especially at cruise.
Now... on to my research on my situation, where I have the 3.55 gear in my axle. There was a calcumaputation device at Tremec at one time. I used it to compare my '06 GT's 3650 and 3.55 axle to what would happen if I put in a Tremec T56XL, of which there were two different gear sets available. I'll put the very rough 'document' I have on it and the conclusion at the bottom, which is comparable to your situation you're posting. Formatting is not my forte, I hope you can figure it out, but basically the same thing you're looking at is what I saw when I ran the numbers: lesser starts, ok middles, and loss of MPG at top (although mine was due to the RPMs being too low to be good for 6th, so I'd wind up in 5th a lot, not great compared to stock.... or at least, that's what I figured out.)
So there you go. The reasoning behind my statement. Have a good one, hope that helps!
TL;DR: Your launches will be less spectacular, more sluggish, the rest will be about the same, and it looks like MPG will actually be negatively affected in 6th... I think?
A lot of this gets confusing, but I think that's right, or at least what my research told me. Read on if you wanna see the research, otherwise, there's your answer, hope it helps! ---
Ok, I did the calculations for doing the swap on my '06 GT from the TR3650 to a Tremec T56XL with two different sets of gears available, as the shifting on the TR3650 is... well, it's fun. Thought maybe putting in the T56XL would be a move to make... but no, it turned out not really, and actually not so great in some respects. So I figure that might help me help you with this.
First, revisiting the original OP's post on the V6 and V8 ratios. Remember, higher number is lower gearing.
V6 / V8
1st: 4.236 / 3.66
2nd: 2.538 / 2.43
3rd: 1.665 / 1.69
4th: 1.238 / 1.32
5th: 1.00 / 1.00
6th: 0.70 / 0.65
Notice how the V6 has a lower first gear, slightly lower second, insignificantly higher third and fourth gears, 1:1 fifth, and a slightly lower sixth gear. Also be aware that the V6's axle is usually a taller gear, lower ratio number, for economy reasons. They then use the transmission to make up for some of the 'oomph' lost, yet still be as economical as possible, especially at cruise.
Now... on to my research on my situation, where I have the 3.55 gear in my axle. There was a calcumaputation device at Tremec at one time. I used it to compare my '06 GT's 3650 and 3.55 axle to what would happen if I put in a Tremec T56XL, of which there were two different gear sets available. I'll put the very rough 'document' I have on it and the conclusion at the bottom, which is comparable to your situation you're posting. Formatting is not my forte, I hope you can figure it out, but basically the same thing you're looking at is what I saw when I ran the numbers: lesser starts, ok middles, and loss of MPG at top (although mine was due to the RPMs being too low to be good for 6th, so I'd wind up in 5th a lot, not great compared to stock.... or at least, that's what I figured out.)
1 2 3 4 5 6
TR3650
3.38 2.0 1.32 1.0 0.675 N/A
MXL 1
2.66 1.78 1.30 1.00 .80 .63
MXL 2
2.97 2.10 1.46 1.00 .80 .63
Overall, the 2 is the closer one to use?
Ratio difference from TR3650
1 2 3 4 5 6
TR3650
3.38 2.0 1.32 1.0 0.675 N/A
MXL 1
2.66 1.78 1.30 1.00 .80 .63
-.72 -.22 -.02 0 +.125 -.045 over 5th.
MXL 2
2.97 2.10 1.46 1.00 .80 .63
-.41 +.1 +.14 0 +.125 -.045 over 5th.
Ratio between gears
1 2 3 4 5 6
TR3650
3.38 2.0 1.32 1.0 0.675 N/A
-1.38 -.68 -.32 -.325
MXL 1
2.66 1.78 1.30 1.00 .80 .63
-.88 -.48 -.3 -.2 -.17 (-.37 from 4th)
MXL 2
2.97 2.10 1.46 1.00 .80 .63
-.87 -.64 -.46 -.2 -.17 (-.37 from 4th)
---
Now, here's a cool thing.
http://www.tremec.com/calculadora.php
And here is the results for a TR3650 at 2250 RPM, 3.55 rear gear, 26.67 (my tires) speeds:
1 2 3 4 5 6
14.88 25.14 38.1 50.29 74.5 N/A
Seems right
MXL1
18.91 28.25 38.68 50.29 62.86 79.82
MXL2
16.93 23.95 34.44 50.29 62.86 79.82
So overall, the 2 is the one because it'll 'act' closer. What will happen, though, is launches will be less awesome, but you'll shift more, and you can cruise at a lower RPM in 6th... provided you're doin' 70+ otherwise you'll be in fifth... and probably using more gas.
Stick with the 3650. :|
TR3650
3.38 2.0 1.32 1.0 0.675 N/A
MXL 1
2.66 1.78 1.30 1.00 .80 .63
MXL 2
2.97 2.10 1.46 1.00 .80 .63
Overall, the 2 is the closer one to use?
Ratio difference from TR3650
1 2 3 4 5 6
TR3650
3.38 2.0 1.32 1.0 0.675 N/A
MXL 1
2.66 1.78 1.30 1.00 .80 .63
-.72 -.22 -.02 0 +.125 -.045 over 5th.
MXL 2
2.97 2.10 1.46 1.00 .80 .63
-.41 +.1 +.14 0 +.125 -.045 over 5th.
Ratio between gears
1 2 3 4 5 6
TR3650
3.38 2.0 1.32 1.0 0.675 N/A
-1.38 -.68 -.32 -.325
MXL 1
2.66 1.78 1.30 1.00 .80 .63
-.88 -.48 -.3 -.2 -.17 (-.37 from 4th)
MXL 2
2.97 2.10 1.46 1.00 .80 .63
-.87 -.64 -.46 -.2 -.17 (-.37 from 4th)
---
Now, here's a cool thing.
http://www.tremec.com/calculadora.php
And here is the results for a TR3650 at 2250 RPM, 3.55 rear gear, 26.67 (my tires) speeds:
1 2 3 4 5 6
14.88 25.14 38.1 50.29 74.5 N/A
Seems right
MXL1
18.91 28.25 38.68 50.29 62.86 79.82
MXL2
16.93 23.95 34.44 50.29 62.86 79.82
So overall, the 2 is the one because it'll 'act' closer. What will happen, though, is launches will be less awesome, but you'll shift more, and you can cruise at a lower RPM in 6th... provided you're doin' 70+ otherwise you'll be in fifth... and probably using more gas.
Stick with the 3650. :|
So there you go. The reasoning behind my statement. Have a good one, hope that helps!
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