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what rpm's are you running at 72mph?

1990 Views 17 Replies 8 Participants Last post by  Himmelkat
I set my cruise at 72mph at 2000rpm my car is a m6 it's 2016 hellcat challenger with stock size tires
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72mph at 2000rpm? Nice gearing. They must have upgraded the final overdrive at some point. On mine it is around 2000 at 60mph or so, nothing particularly efficient. It should be about 1000 rpm at 60mph. That would make efficiency leap about 10 percent, at least, based on industry standards of mpg relation to rpm.
That's what it works out to on so it's normal
Thank you so much for this!!! this site just saved me a ton of math, ONE, and made me realize I have a 3.90 rearend, TWO. Now it becomes more obvious why this thing felt like it was trying to climb the sky in 3rd gear!

I guess I will have to check into that. Now I REALLY want a different set of ratios in the transmission. I'd rather have a 2.0 to 1 rearend ratio and run an eight-speed Lenco, TBQH, as the final final total drive of the 3.70 setup is 2.33:1, whereas with a 3.90 its even more revvy at 2.46:1
An eight-speed Lenco would be absolutely EPIC. One of the things I like about the Lenco is that you can shift with or without the clutch, depending on speed and wear you want, etc. And, it's so Olde Skule.

But, alas, Lencos can cost around 30hp (most likely max-effort wide-gear racing versions.) and I'd have to set my clutch for a certain degree of slip, like Pro racers used to do when they used Lencos. However, it WOULD mean a very, very small-diameter on-off switch style of clutch could be used...
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We could ostensibly put the 392 sixth gear on the Hellcat, then, and get lower revs.

I would think the torque would be no issue, as it is sixth gear, not first. Direct drive to the input shaft, then knocked down to 0.5, meaning the output is taking half of the torque of the input, as it is spinning twice as fast, so I think it may be doable.
That would be nice, for certain.
But, the Lenco is not clutchless. It operates like an automatic does in its gear actuation.

The Liberty and other brands say they are clutchless, I believe, but what it means by clutchless is that it does not have clutches in each section for each gear, which take the gear in that section from being planetary at whatever ratio to being locked and direct-drive, as does the Lenco. It's why the end result of a Lenco is always 1:1. It's also why a Lenco can be shifted in any order one wants, as each section is merely changing the ratio between the input in front of it and the output behind it, so you can shift 5, 2, 3, 4, 6 if you wish, depending on what ratio you want to go from X:1 to 1:1, depending on circumstances, as a Lenco's final drive is just a combination of all ratios currently engaged multiplied by each other:

As an example, supposing one were to be traveling up an extremely steep hill, and didn't want a large gap between gears to keep the power flow going, one could select whichever section had the smallest change in ratio (say, 1.3:1) between its input and its output on planetaries. However, if one were heading down a hill, one might be more inclined to grab a gear that had a larger ratio change from clutch-pack-disengaged to clutch-pack-engaged for that gear, (say, 1.8:1.)

I mean, it's not terribly likely, but just an option you have when you can grab whatever gear section you want at any time.

Lencos have been street driven. Other brands, I don't know the sequentials, etc have ever been on the street.
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