M6 Speed in Gears vs Diff Gears
Thread Starter
Racer
Joined: Oct 2001
Posts: 442
Likes: 2
From: San Clemente CA
M6 Speed in Gears vs Diff Gears
Hi,
This is the companion set of curves to the popular "A4 Speed in Gear vs Diff" Curves. It was buried in a previous post. I think I need a set of 3.90's!
Have fun,
Steve :seeya
[Modified by SNW Vette, 3:25 AM 2/4/2002]
This is the companion set of curves to the popular "A4 Speed in Gear vs Diff" Curves. It was buried in a previous post. I think I need a set of 3.90's!
Have fun,
Steve :seeya
[Modified by SNW Vette, 3:25 AM 2/4/2002]
Thread Starter
Racer
Joined: Oct 2001
Posts: 442
Likes: 2
From: San Clemente CA
Re: M6 Speed in Gears vs Diff Gears (Iboomalot)
Hi,
The graph of transmission drops is the % the RPM will decreased when you shift into the next gear.
Example: When shifting from 1st into 2nd @ 6000 rpm the rpm when you engage the clutch in 2nd will be:
M12 = 4200 (near peak torque rpm)
MN6 = 4000 (near peak torque rpm)
A4 = 3200 (a BIG drop in gearing but the torque converter helps. A higher stall speed can help here.)
In designing a transmission, the usual practice is to reduce the % drop as you go to the higher gears. This is shown in the MN6 1st through 4th gear and in the A4. This is because the drag is lower at low speeds so there are fewer penalties to a big drop when the acceleration is high. At high speeds, a big drop can stop you in your tracks if you fall off the power curve.
The total gearing in a manual shift Vette uses the first four gears to run the 1/4-mile. Chevy choose to change the trans gear rather than use a steep diff gear (3.90) in the Z06 to get the total gearing they were looking for. 4th gear is what is called "straight through" because the power is transmitted straight from the input shaft directly to the output shaft without going through a set of gears. This is why the total gear ratio has that bump in it on the Z06 curve. This also forced Chevy to accept higher gear drops in the 2-3 and 3-4 shifts. This is balanced by the much reduced drop into 5th gear, which is a good thing at high speeds.
I hope this helps,
Steve :seeya
[Modified by SNW Vette, 11:21 AM 2/4/2002]
The graph of transmission drops is the % the RPM will decreased when you shift into the next gear.
Example: When shifting from 1st into 2nd @ 6000 rpm the rpm when you engage the clutch in 2nd will be:
M12 = 4200 (near peak torque rpm)
MN6 = 4000 (near peak torque rpm)
A4 = 3200 (a BIG drop in gearing but the torque converter helps. A higher stall speed can help here.)
In designing a transmission, the usual practice is to reduce the % drop as you go to the higher gears. This is shown in the MN6 1st through 4th gear and in the A4. This is because the drag is lower at low speeds so there are fewer penalties to a big drop when the acceleration is high. At high speeds, a big drop can stop you in your tracks if you fall off the power curve.
The total gearing in a manual shift Vette uses the first four gears to run the 1/4-mile. Chevy choose to change the trans gear rather than use a steep diff gear (3.90) in the Z06 to get the total gearing they were looking for. 4th gear is what is called "straight through" because the power is transmitted straight from the input shaft directly to the output shaft without going through a set of gears. This is why the total gear ratio has that bump in it on the Z06 curve. This also forced Chevy to accept higher gear drops in the 2-3 and 3-4 shifts. This is balanced by the much reduced drop into 5th gear, which is a good thing at high speeds.
I hope this helps,
Steve :seeya
[Modified by SNW Vette, 11:21 AM 2/4/2002]
Racer
Joined: Oct 2001
Posts: 294
Likes: 15
From: South Orange Co. CA
Re: M6 Speed in Gears vs Diff Gears (SNW Vette)
This was in another thread, thought it was appropriate here:
It’s curious to me that the Z06 designers changed gear ratios in the transmission rather than just change the differential ratio, especially since the changed ratios appear to be very similar to using the standard gear box with a 3.90 differential. Just specifying a different differential ratio seems to be a much cheaper way to go. But the answer may lie in the separate input and output torque ratings of the transmission and gear box, and the increased torque rating of the Z06 engine.
The spec sheet for the LS1 gear box and differential is a maximum input torque of 450 lb-ft. Using the 2.66 first gear, the maximum input to the differential is 1197 lb-ft of torque. Next, the maximum output torque of the differential is 1197 * 3.42 = 4094 lb-ft.
Going backwards from the maximum differential output torque to maximum input torque for the standard gear box with 3.90 ratio: (4094 / 3.90) / 2.66 = 395 lb-ft, which is too low for the 400 lb-ft torque of the Z06 engine. Going the other way, with 400 lb-ft for the Z06 engine and the 2.97 1st gear ratio: 400 * 2.97 = 1188, which is just under the maximum differential input torque. This helps to explain why the Z06 differential gears are shot peened, since the torque at the differential input is near its maximum rating.
The next question that I had was why several sources (including Getrag) think that the 3.73 is the only alternative to consider. Going backward from the maximum output torque:
4094/3.73 = 1097 / 2.66 = 412 lb-ft (high enough for Z06 engine)
4094/3.90 = 1050 / 2.66 = 395 lb-ft (not high enough for Z06 engine)
4094/4.10 = 999 / 2.66 = 376 lb-ft (2001/2002 LS1: 375 lb-ft, 2000 LS1 350 lb-ft)
From a simple torque rating point of view, any of these ratios should be OK for stock LS1’s. Of course, for any after market power additions, the potential is there to blow up the transmission or the differential (or clutch, etc.).
So which differential to choose? The 3.73 offers a 9% gear reduction, the 3.90, 14%, and the 4.10, 20%. To me, the 1st and 6th gears in the standard transmission are too tall. IMHO, the 3.73 doesn’t go far enough, while the 4.10 goes too far. This is borne out by the Z06 designers choosing overall ratios that are very similar to the 3.90 differential.
-Jim
It’s curious to me that the Z06 designers changed gear ratios in the transmission rather than just change the differential ratio, especially since the changed ratios appear to be very similar to using the standard gear box with a 3.90 differential. Just specifying a different differential ratio seems to be a much cheaper way to go. But the answer may lie in the separate input and output torque ratings of the transmission and gear box, and the increased torque rating of the Z06 engine.
The spec sheet for the LS1 gear box and differential is a maximum input torque of 450 lb-ft. Using the 2.66 first gear, the maximum input to the differential is 1197 lb-ft of torque. Next, the maximum output torque of the differential is 1197 * 3.42 = 4094 lb-ft.
Going backwards from the maximum differential output torque to maximum input torque for the standard gear box with 3.90 ratio: (4094 / 3.90) / 2.66 = 395 lb-ft, which is too low for the 400 lb-ft torque of the Z06 engine. Going the other way, with 400 lb-ft for the Z06 engine and the 2.97 1st gear ratio: 400 * 2.97 = 1188, which is just under the maximum differential input torque. This helps to explain why the Z06 differential gears are shot peened, since the torque at the differential input is near its maximum rating.
The next question that I had was why several sources (including Getrag) think that the 3.73 is the only alternative to consider. Going backward from the maximum output torque:
4094/3.73 = 1097 / 2.66 = 412 lb-ft (high enough for Z06 engine)
4094/3.90 = 1050 / 2.66 = 395 lb-ft (not high enough for Z06 engine)
4094/4.10 = 999 / 2.66 = 376 lb-ft (2001/2002 LS1: 375 lb-ft, 2000 LS1 350 lb-ft)
From a simple torque rating point of view, any of these ratios should be OK for stock LS1’s. Of course, for any after market power additions, the potential is there to blow up the transmission or the differential (or clutch, etc.).
So which differential to choose? The 3.73 offers a 9% gear reduction, the 3.90, 14%, and the 4.10, 20%. To me, the 1st and 6th gears in the standard transmission are too tall. IMHO, the 3.73 doesn’t go far enough, while the 4.10 goes too far. This is borne out by the Z06 designers choosing overall ratios that are very similar to the 3.90 differential.
-Jim
