Quote:
Originally Posted by Piotrsko
Could you ever get a perfect gear ratio? Everything I've ever seen is a compromised compromise
|
Yes, you choose which you want power OR MPG.
But I will now have 8 gears, with the second OD it can be engaged in all four gears, AND thanks to adding a .80 over drive TO a .75 4th gear is comes out to a .56 into my rear end gear, SO I can have a very great compromise.
A second over drive is the ONLY way to reach a .56 ratio.
And yes I will need to control it manually, which is a little more complex that a 8L80E full automatic.
But again there is NO .56 over drive:
4L60 4L80 6l80 8L80 Gears
1St 2nd 3rd 4th 5th 6th 7th 8th
4L60 3.06 1.63 1.00 .70
4L80 2.48 1.48 1.00 .75
6L80 4.03 2.36 1.53 1.15 .85 .67
8L80 4.56 2.97 2.08 1.69 1.27 1.00 .85 .65
Yes a .65 is very close, but to switch to a 8L80 will cost me at best $2000.00 to $3000.00, this set up is only costing $1000.00
Possible stock GM Gear ratios: 2.73 In aftermarket only
2:73 3.08 3.23 3.42 3.73 3.90 4.11
RPMS and MPH: calcuator;
https://www.blocklayer.com/rpm-gear.aspx
So as in my 93 running a stock:
So a 4L60 at 70MPH with a 3.42 would be running 2100 RPMs
So a 4L80 at 70MPH with a 3.42 would be running 2065 RPMs
So a 6L60 at 70MPH with a 3.42 would be running 1690RPMs
So a 8L80 at 70MPH with a 3.42 would be running 1710RPMs
OMG I just figured out how great all this set up will be.
This combo of a 4L80E heavy duty transmission and the heavy duty US gear overdrive will mean I can TOW a trailer with this van with the front transmission in 3rd and the US Gear in overdrive.
So running in 3rd and US Gear OD I would be able to run at 70MPH and be pulling 2310 RPMs, not super MPG but still low and right at what should be near my torque peak. This is great.
My old layout of the weak 4L60e and an old Borg Warner OD was too weak to consider towing anything, I figured it was barely strong enough to handle the van.
If I was richer I would go with the 8L80...
Rich