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Re: [GMCnet] "six-speed" transmission [message #61570 is a reply to message #61556]

Sun, 25 October 2009 12:02

Gary Casey

Messages: 448
Registered: September 2009

Karma:

Senior Member

Emery,
I wish I had some of my old converter data, but I can't find anything on variable pitch units. In one position they increase the stall speed and stall torque ratio (useful for backing up a hill). That has a byproduct of reducing the load on the engine at idle, which can be an advantage with a carburetor(easier to get a smooth, no-stall idle). Then the other pitch extends the torque multiplication out further in the speed range at the price of a lower stall torque ratio. Unfortunately, that reduces the efficiency as well. So, at 25 to 35 mph up a grade do you want to run full throttle at 90% efficiency with a torque ratio of 1.1, or run part throttle at a slightly higher engine speed at a torque ratio of 1.48(second gear) and 97% efficiency? At the higher efficiency the engine will have to put out less torque to do the same work. The converter characteristic in that mode is very similar to modern cars with converter clutches. Quite often they will
be programmed to disconnect the converter clutch going up a hill to give a perceived performance increase, when most of the extra engine power is just going into heat. My car has a throttle-by-wire system and I swear they program the throttle to open when the converter clutch is disengaged, to make you think you are getting something for nothing. No free lunch, I'm afraid.
Gary

________________________________
From: Emery Stora <emerystora@mac.com>
To: "gmclist@temp.gmcnet.org" <gmclist@temp.gmcnet.org>
Sent: Sun, October 25, 2009 9:54:04 AM
Subject: Re: [GMCnet] "six-speed" transmission

On Oct 25, 2009, at 9:31 AM, Gary Casey <casey.gary@yahoo.com> wrote:

> I'd respectfully consider the variable pitch stator to make the 3-
> speed transmission into a "3 1/2 speed" transmission. Or maybe "3
> 1/4". As I said before, the low pitch might enable you to back out
> of a steep downhill parking spot, but that's about it. Just my
> opinion again.
> Gary
>
I find the main advantage of my switch pitch is the help it gives in
keeping up RPMs when going up hills. It allows one to pass that truck
that is slowing down in front instead of forcing you to drop behind
and slowing down to perhaps 25 mph where you loose all rpm and drop
way down on the torque curve.

Emery Stora
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		Re: [GMCnet] Horsepower and Torque Converter Efficiency By: Gary Casey on Sun, 25 October 2009 09:13
		[GMCnet] "six-speed" transmission By: Gary Casey on Sun, 25 October 2009 10:31
		Re: [GMCnet] "six-speed" transmission By: emerystora on Sun, 25 October 2009 10:54
		Re: [GMCnet] "six-speed" transmission By: Gary Casey on Sun, 25 October 2009 12:02
		Re: [GMCnet] "six-speed" transmission By: emerystora on Sun, 25 October 2009 13:39
		Re: [GMCnet] "six-speed" transmission By: Gary Casey on Mon, 26 October 2009 07:07
		Re: [GMCnet] "six-speed" transmission By: Gary Casey on Sun, 25 October 2009 12:04
		Re: [GMCnet] "six-speed" transmission By: comcast on Sun, 25 October 2009 12:21
		Re: [GMCnet] "six-speed" transmission By: emerystora on Sun, 25 October 2009 14:01
		Re: [GMCnet] Horsepower and Torque Converter Efficiency By: Tin Gerbil on Sun, 25 October 2009 10:59

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