Quote:
Originally Posted by aardvarcus
There are 5 and 6 speed transmissions that have very wide gear spread already. The modified NV4500 I have in my Suburban has the following ratios: 5.61-3.04-1.67-1.00-0.643 which is a 8.72 gear spread.
With 4.10's first is unnecessary for a torque down low engine, so I take off in second. Thus the vehicle could support a much taller rear end ratio and still take off fine in first, to the point that the overdrive ratio could be pushed to the limit of the engine's torque curve versus road load. For example, with 235/85R16 tires and relatively common 3.42 gears I would be turning 1208 rpm at 55 MPH. All with only one transmission and no auxiliary devices. With 3.08 gears this would be 1088 RPM. This is probably beyond the reasonably limit of most engines without drag and weight reduction to reduce the road load.
For 2wd applications there is the Tremec 6060 with 2.97 first and 0.50 overdrive. Less gear spread but more intermediate gears.
So given there are existing single transmissions with such spreads, I don't see the point in using multiple boxes outside of specialized use cases (e.g. rock crawling).
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My problem is I am very happy with both the Ford and Chevy power.
The part I am NOT happy with is the gas millage, 23MPG highway for the Ford and 14MPG highway for the Van.
The Ford is all set up and other than a few minor improvements I do not expect to find big MPG improvements in it.
The Chevy needs a better injection system and PCM changes.
Your talking about transmissions I cannot use in either of my cars. If I did they would cost a lot to convert. As much as my idea to convert to the 6 speeds and 8 speed transmissions.
The idea of adding a over drive seems like the lowest cost and biggest change for better MPG.
It stops my search for those rare low ratio rear end gears, same search for those 6/8 speeds transmissions and fittings, and saves the costs of rebuilding the two rear ends, the costs of shifter and computer controls for those new transmissions.
All I need do is mount the B&W over drive to the transmissions, it is cable and electrically controlled, simple to set up and use.
With the van I also think the gear splitting will help find a best fit of power-RPMs-speed in hill climes.
Rich