Trying to understand
Trying to understand I read pretty much every thread that comes up about converters, but none of them explain what you guys mean by a "loose converter", and "tightening it up with shorter gears", or something like that.
(To me) loose means, you press the gas more
and the RPMs go up, but you still don't go any
quicker (acceleration).
How "tightly" the converter is coupled depends
on the engine RPM and the RPM difference
between input and output. More input RPM
increases coupling. More input-output difference
produces torque multiplication, up to the quoted
STR (stall torque ratio) at stall speed with the
output shaft not turning. But at (say) 6000RPM
you are not still slipping by the stall amount, or
your (in)efficiency would be heinous.
If you have a higher gear ratio, at any given
road speed you will be at a higher RPM and
thus closer to the stall speed of the converter,
or at least further into the coupling slope.
The STR affects the perceived "tightness".
A lower STR "multiplies torque longer", or
at lower RPM relative to stall. A 3500/2.0
might give you some acceleration effort at
2000RPM while a 3500/2.5 might need the
RPM at 2500 to get the same thrust. The
trade is that at higher slip you get more
wheel torque with the higher STR (like you
could hook it up anyway).
Putting higher ratio gears in, might put you
at that 2500 instead of 2000 at your typical
road speed and then it won't "feel as loose".
True, neither would the 3500/2.0... but it's
about making the combination not bug you
as-driven.
High STRs are often chosen by people with low
rear end ratios to make up for that lower torque
multiplier. But this also contributes to the loose
feeling (low road speed / RPM with sharper / higher
stall). I observe the hard-core types going with
both higher rear end ratios (tighter@speed) and
lower STRs (tighter over range) but higher stall
speeds (w/ higher-centered power band).
Yank's site is the only one I've found that tries
to explain this, and you can probably gain a
better visualization / understanding from going
to their dyno pages & comparing the effect of
various stall speed / STR option combos.
and the RPMs go up, but you still don't go any
quicker (acceleration).
How "tightly" the converter is coupled depends
on the engine RPM and the RPM difference
between input and output. More input RPM
increases coupling. More input-output difference
produces torque multiplication, up to the quoted
STR (stall torque ratio) at stall speed with the
output shaft not turning. But at (say) 6000RPM
you are not still slipping by the stall amount, or
your (in)efficiency would be heinous.
If you have a higher gear ratio, at any given
road speed you will be at a higher RPM and
thus closer to the stall speed of the converter,
or at least further into the coupling slope.
The STR affects the perceived "tightness".
A lower STR "multiplies torque longer", or
at lower RPM relative to stall. A 3500/2.0
might give you some acceleration effort at
2000RPM while a 3500/2.5 might need the
RPM at 2500 to get the same thrust. The
trade is that at higher slip you get more
wheel torque with the higher STR (like you
could hook it up anyway).
Putting higher ratio gears in, might put you
at that 2500 instead of 2000 at your typical
road speed and then it won't "feel as loose".
True, neither would the 3500/2.0... but it's
about making the combination not bug you
as-driven.
High STRs are often chosen by people with low
rear end ratios to make up for that lower torque
multiplier. But this also contributes to the loose
feeling (low road speed / RPM with sharper / higher
stall). I observe the hard-core types going with
both higher rear end ratios (tighter@speed) and
lower STRs (tighter over range) but higher stall
speeds (w/ higher-centered power band).
Yank's site is the only one I've found that tries
to explain this, and you can probably gain a
better visualization / understanding from going
to their dyno pages & comparing the effect of
various stall speed / STR option combos.
11 Second Club
Joined: Feb 2003
Posts: 523
Likes: 0
From: WESLACO, TEXAS
what he said!!
Originally Posted by jimmyblue
(To me) loose means, you press the gas more
and the RPMs go up, but you still don't go any
quicker (acceleration).
How "tightly" the converter is coupled depends
on the engine RPM and the RPM difference
between input and output. More input RPM
increases coupling. More input-output difference
produces torque multiplication, up to the quoted
STR (stall torque ratio) at stall speed with the
output shaft not turning. But at (say) 6000RPM
you are not still slipping by the stall amount, or
your (in)efficiency would be heinous.
If you have a higher gear ratio, at any given
road speed you will be at a higher RPM and
thus closer to the stall speed of the converter,
or at least further into the coupling slope.
The STR affects the perceived "tightness".
A lower STR "multiplies torque longer", or
at lower RPM relative to stall. A 3500/2.0
might give you some acceleration effort at
2000RPM while a 3500/2.5 might need the
RPM at 2500 to get the same thrust. The
trade is that at higher slip you get more
wheel torque with the higher STR (like you
could hook it up anyway).
Putting higher ratio gears in, might put you
at that 2500 instead of 2000 at your typical
road speed and then it won't "feel as loose".
True, neither would the 3500/2.0... but it's
about making the combination not bug you
as-driven.
High STRs are often chosen by people with low
rear end ratios to make up for that lower torque
multiplier. But this also contributes to the loose
feeling (low road speed / RPM with sharper / higher
stall). I observe the hard-core types going with
both higher rear end ratios (tighter@speed) and
lower STRs (tighter over range) but higher stall
speeds (w/ higher-centered power band).
Yank's site is the only one I've found that tries
to explain this, and you can probably gain a
better visualization / understanding from going
to their dyno pages & comparing the effect of
various stall speed / STR option combos.
and the RPMs go up, but you still don't go any
quicker (acceleration).
How "tightly" the converter is coupled depends
on the engine RPM and the RPM difference
between input and output. More input RPM
increases coupling. More input-output difference
produces torque multiplication, up to the quoted
STR (stall torque ratio) at stall speed with the
output shaft not turning. But at (say) 6000RPM
you are not still slipping by the stall amount, or
your (in)efficiency would be heinous.
If you have a higher gear ratio, at any given
road speed you will be at a higher RPM and
thus closer to the stall speed of the converter,
or at least further into the coupling slope.
The STR affects the perceived "tightness".
A lower STR "multiplies torque longer", or
at lower RPM relative to stall. A 3500/2.0
might give you some acceleration effort at
2000RPM while a 3500/2.5 might need the
RPM at 2500 to get the same thrust. The
trade is that at higher slip you get more
wheel torque with the higher STR (like you
could hook it up anyway).
Putting higher ratio gears in, might put you
at that 2500 instead of 2000 at your typical
road speed and then it won't "feel as loose".
True, neither would the 3500/2.0... but it's
about making the combination not bug you
as-driven.
High STRs are often chosen by people with low
rear end ratios to make up for that lower torque
multiplier. But this also contributes to the loose
feeling (low road speed / RPM with sharper / higher
stall). I observe the hard-core types going with
both higher rear end ratios (tighter@speed) and
lower STRs (tighter over range) but higher stall
speeds (w/ higher-centered power band).
Yank's site is the only one I've found that tries
to explain this, and you can probably gain a
better visualization / understanding from going
to their dyno pages & comparing the effect of
various stall speed / STR option combos.
