Well since it's commonly asked which trans, what diff ratio, etc. etc. I thought I would do a brief write up of what I've come up with for my personal uses.
I don't like overly tall gearing, it bores me, I like closer ratio's, I don't like dropping out of my power band, I don't like having to downshift constantly to pass or move around once I'm cruising etc.
Background: I have an 87 325, originally an eta, converted fully to 325is drivetrain, and then boosted to hell. Everyone said to get a 2.93, I got one, tried it, don't care for it. The only advantages are "quicker spool up" which is neglegable as you're downing the axle ratio and that drops the rate at which you accelerate, and that you don't have to shift into 4th in a quarter mile pass unless you trap over 130mph at 7200rpm or so.
Let's begin with the fact though, I offer up an in depth comparisson of a getrag 260 with either a 3.73 or 2.93 rear end, and a zf320 with a 2.93 rear end, however I can provide the same information for any given gear box (if you provide me gear ratio's) with any given rear end, and your tire size, and desired redline.
For the purpose of all of the following discussed, the "red line" is the point I'm shifting at, and that is 7,200rpm. The overall diameter of the rolling stock I am on is 24.9".
---------------------------------------------------------------------------
Getrag 260 - 3.73 rear end: 1st gear 37mph, shift to second 4,100rpm up to 65mph, shift to third 4600rpm up to 102, shift to fourth 5150rpm up to 143mph, shift to 5th 5800rpm up to 176mph
5th gear cruising speeds: 60mph 2450rpm, 70mph 2850rpm, 80mph 3300rpm
-----------------------------------------------------------------------------
Getrag 260 - 2.93 rear end: 1st gear 47mph, 2nd gear 4600rpm, 3rd gear 130mph, 4th gear 182mph, 5th gear 225mph
Shift points remain the same as actual egar ratio's remain unchanged, only final drive ratio change means only road speeds change in relation to shift points.
5th gear cruising speeds: 60mph 1900rpm, 70mph 2300rpm, 80mph 2600rpm
------------------------------------------------------------------------------
ZF 320 - 2.93 rear end: 1st gear 43mph, shift to 2nd 4,200rpm up to 73mph, shift to 3rd 4,800rpm up to 110mph, shift to 4th 5,400rpm up to 147, shift to 5th 5,800rpm up to 176mph
5th gear cruising speeds: 60mph 2400rpm, 70mph 2700rpm, 80mph 3100rpm
------------------------------------------------------------------------------
What does any of this mean? Well for me it mean I strongly disagree witht he notion that a 2.93 should be used on a turbo m20, as I always have, and I find that a ZF320 would provide even more favorable gearing in any situation to a getrag 260 w/3.73, and even with it's 1:1 5th it is better highway cruising.
If you would like any other combinations done post them up, just need gear ratio's of the transmission you are interested in, and which diff you'd like to see put behind it, I can plug in my vehicle specs from there or use yours if you'd like it custom tailored, but will probably post all results based on mine so all results in this first post are directly showing only differenes in trans/diff's, and don't reflect changes based on tire sizes and engine rpm.
I don't like overly tall gearing, it bores me, I like closer ratio's, I don't like dropping out of my power band, I don't like having to downshift constantly to pass or move around once I'm cruising etc.
Background: I have an 87 325, originally an eta, converted fully to 325is drivetrain, and then boosted to hell. Everyone said to get a 2.93, I got one, tried it, don't care for it. The only advantages are "quicker spool up" which is neglegable as you're downing the axle ratio and that drops the rate at which you accelerate, and that you don't have to shift into 4th in a quarter mile pass unless you trap over 130mph at 7200rpm or so.
Let's begin with the fact though, I offer up an in depth comparisson of a getrag 260 with either a 3.73 or 2.93 rear end, and a zf320 with a 2.93 rear end, however I can provide the same information for any given gear box (if you provide me gear ratio's) with any given rear end, and your tire size, and desired redline.
For the purpose of all of the following discussed, the "red line" is the point I'm shifting at, and that is 7,200rpm. The overall diameter of the rolling stock I am on is 24.9".
---------------------------------------------------------------------------
Getrag 260 - 3.73 rear end: 1st gear 37mph, shift to second 4,100rpm up to 65mph, shift to third 4600rpm up to 102, shift to fourth 5150rpm up to 143mph, shift to 5th 5800rpm up to 176mph
5th gear cruising speeds: 60mph 2450rpm, 70mph 2850rpm, 80mph 3300rpm
-----------------------------------------------------------------------------
Getrag 260 - 2.93 rear end: 1st gear 47mph, 2nd gear 4600rpm, 3rd gear 130mph, 4th gear 182mph, 5th gear 225mph
Shift points remain the same as actual egar ratio's remain unchanged, only final drive ratio change means only road speeds change in relation to shift points.
5th gear cruising speeds: 60mph 1900rpm, 70mph 2300rpm, 80mph 2600rpm
------------------------------------------------------------------------------
ZF 320 - 2.93 rear end: 1st gear 43mph, shift to 2nd 4,200rpm up to 73mph, shift to 3rd 4,800rpm up to 110mph, shift to 4th 5,400rpm up to 147, shift to 5th 5,800rpm up to 176mph
5th gear cruising speeds: 60mph 2400rpm, 70mph 2700rpm, 80mph 3100rpm
------------------------------------------------------------------------------
What does any of this mean? Well for me it mean I strongly disagree witht he notion that a 2.93 should be used on a turbo m20, as I always have, and I find that a ZF320 would provide even more favorable gearing in any situation to a getrag 260 w/3.73, and even with it's 1:1 5th it is better highway cruising.
If you would like any other combinations done post them up, just need gear ratio's of the transmission you are interested in, and which diff you'd like to see put behind it, I can plug in my vehicle specs from there or use yours if you'd like it custom tailored, but will probably post all results based on mine so all results in this first post are directly showing only differenes in trans/diff's, and don't reflect changes based on tire sizes and engine rpm.
Comment