optimal shift points
optimal shift points Something I have searched for on here and don't see much of are optimal shift point calculators. Anyone have any info on optimal shift points on an automatic transmission?
I don't have any calculations for you but what I observed on
my car, using an accelerometer, is that you should stay in
gear until the motor is fixing to blow up. Even my stocker
was accelerating more at 6000 in 2nd, than shift-to in 3rd.
And by a fair bit too.
Autos with a higher than stock stall speed converter, this
becomes even more true; their efficiency keeps going up
with RPM and the only reason to shift, is engine safety.
Maybe if you had a wheezer of a setup there might be a
different story but even stock, these motors breathe too
well to give up early. And it only gets better with airflow
mods.
my car, using an accelerometer, is that you should stay in
gear until the motor is fixing to blow up. Even my stocker
was accelerating more at 6000 in 2nd, than shift-to in 3rd.
And by a fair bit too.
Autos with a higher than stock stall speed converter, this
becomes even more true; their efficiency keeps going up
with RPM and the only reason to shift, is engine safety.
Maybe if you had a wheezer of a setup there might be a
different story but even stock, these motors breathe too
well to give up early. And it only gets better with airflow
mods.
TECH Junkie
Joined: Dec 2005
Posts: 3,092
Likes: 11
IMHO you would need a dyno graph of your car. That way you can see where the peak horsepower is and select a shift point at some rpm higher to get the most hp under the curve. Or you can experiment at the track with different shift points and compare times.
Teching In
Joined: Dec 2006
Posts: 15
Likes: 0
From: Crown Point, IN
Here is how to figure it out.
We all know that forward acceleration is what we are after.
Forward acceleration is a factor of:
1. Engine torque @ current rpm
2. Drivetrain torque mutiplicaiton (i.e. gear ratios, both trans and final)
3. Tire diameter
4. Tractive effort (normal load x coefficient of friction)
5. Many other factors that can be neglectied for main calculation (drag, drivetrain friction, torque converter.. etc)
There are 2 reasons to shift
1. Maximum engine RPM (redline)
OR
2. Torque curve falls off drastically. i.e. your acceleration will be greater in the next higher gear. Just remeber, next higher gear gives less torque multiplication, so your torque must drop off dramatically for this to be beneficial.
We all know that forward acceleration is what we are after.
Forward acceleration is a factor of:
1. Engine torque @ current rpm
2. Drivetrain torque mutiplicaiton (i.e. gear ratios, both trans and final)
3. Tire diameter
4. Tractive effort (normal load x coefficient of friction)
5. Many other factors that can be neglectied for main calculation (drag, drivetrain friction, torque converter.. etc)
There are 2 reasons to shift
1. Maximum engine RPM (redline)
OR
2. Torque curve falls off drastically. i.e. your acceleration will be greater in the next higher gear. Just remeber, next higher gear gives less torque multiplication, so your torque must drop off dramatically for this to be beneficial.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
The problem with most automatics is that the gear ratios are widely spaced...
This means that any upshift will put the engine RPM at the very low end of the torque band or even outside of it;
To keep the RPM well inside the torque band, the upshifts need to be at the highest RPM that the engine can get away with (...valve train limitations...).
This means that any upshift will put the engine RPM at the very low end of the torque band or even outside of it;
To keep the RPM well inside the torque band, the upshifts need to be at the highest RPM that the engine can get away with (...valve train limitations...).
That all depends on the motor. From what I see in dyno sheets,
LS1s near stock have a fading torque curve and a flat HP curve,
while modded you get to a flat torque & rising HP profile.
I dug up this accelerometer data 'sheet I had from the logging.
You can see on my car the fading torque (acceleration) even
in 1st where air drag is negligible. Looks like 1st wants to stay
in it to about 6500 or so (extrapolated lines intersect), 2nd
might want to shift by 6000. Of course as soon as you change
you'll see a new bottom-of-next-gear point and maybe want
to retweak a time or two.
LS1s near stock have a fading torque curve and a flat HP curve,
while modded you get to a flat torque & rising HP profile.
I dug up this accelerometer data 'sheet I had from the logging.
You can see on my car the fading torque (acceleration) even
in 1st where air drag is negligible. Looks like 1st wants to stay
in it to about 6500 or so (extrapolated lines intersect), 2nd
might want to shift by 6000. Of course as soon as you change
you'll see a new bottom-of-next-gear point and maybe want
to retweak a time or two.
Trending Topics
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
Originally Posted by joecar
The problem with most automatics is that the gear ratios are widely spaced... This means that any upshift will put the engine RPM at the very low end of the torque band or even outside of it; to keep the RPM well inside the torque band, the upshifts need to be at the highest RPM that the engine can get away with (...valve train limitations...).
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