Thanks MG for that extensive explanation! It'll take me a little time to
study it a bit. ;-)
Take care -
LarryT
91 300D
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--------------------------------------------------
From: "MG" <trainpain2...@yahoo.com>
Sent: Friday, October 23, 2009 9:34 AM
To: "Mercedes Discussion List" <mercedes@okiebenz.com>
Subject: Re: [MBZ] transmission options....
Larry,
The way it was explained to me once was;
The stall speed is the point at which the engine can't turn any faster
when the accelerator is pushed all the way down while the car is standing
still brakes on and the transmission is in drive. This is due to the sheer
strength of the oil and the space between the fins and number of fins etc.
in the fluid coupling which is what the torque converter is.
The reason the engine can't turn any faster is because at any RPM there is
only so much horse power and torque that that particular engine can
produce. This goes up as the engine speed increases till it hits a plateau
dependent on the cam, intake, fuel, valve size, compression and on and on.
Lots of different variables there. Then usually it goes back down to some
extent at a much higher RPM. When the produced power equals the amount of
drag produced by the torque converter and what it is connected to
obviously the engine won't turn any faster. In normal use of course the
car starts moving usually before the stall speed is reached and as it
moves the input into the transmission starts turning so the RPM of the
engine can go up by the same amount. As the RPM of the engine goes up it
is able to produce more power so the car accelerates faster and so on.
So the reason for a higher stall speed is that in situations where you
want to start accelerating faster or start a bigger load from a stop that
requires putting more power to the wheels. Since the engine makes more
power at a higher RPM you can either go to a lower gear ratio or allow the
engine to get to a higher RPM where it will produce more power. This is
the basis of the so called torque multiplying. Nothing is really
multiplied it is just that the engine is allowed to produce more usable
power at any road speed if called upon, compared to an engine that is
directly coupled through a clutch.
Bad part is that a higher stall speed is produced by reducing the fluid
coupling of the torque converter. This causes more slip at a steady speed
or actually at any power point. That in turn effects your fuel mileage
unless there is a lockup clutch in the torque converter which gets applied
usually in the highest gear to eliminate that slip and recover that loss
of mileage.
Anyway that's what I was told and I'm sticking to my story. I got to go
out and do some work now or get killed.
Manfred
Date: Thu, 22 Oct 2009 17:54:44 -0400
From: "LarryT" <l02tur...@comcast.net>
Subject: Re: [MBZ] transmission options....
They talk about a different stall speed improving performance - how does
that work?
Thx
LarryT
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_______________________________________
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