Interstate Driving
#11
03-12-2008, 06:24 PM
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#12
03-13-2008, 07:24 AM
RE: Interstate Driving
first learn the basics
of torque, hp, hill climbing, aerodynamics, and tire rolling resistance:
http://www.etrucker.com/content/downloads/ccj0302.pdf
the above article is written for 18 wheel truckers
but applies to all vehicles
your overdrive top gear was designed by Chrysler engineers
to be used on
'a lightly loaded truck'
on flat/downhill highways at modest (below 75 mph) speeds
Fourth gear (which is the more efficient 1:1 ratio)
is meant for climbing hills
going fast
or towing heavy loads (and here ATF pump rpm in the trans is crucial)
Best fuel economy will be found when the trans ratios are set up
so that you HAVE TO downshift to climb any hill steep than about 2% grade
or are travelling into a strong head wind
or are carrying heavy load in the truck.
18 wheel truckers who speed up on downhills using engine horsepower produced at lower rpms are following a MPG improvement strategy that works even though it is unsafe to other vehicles on the road.
Later when climbing hills they are using 'stored kinetic energy' to overcome hills 'potential energy' requirement...and they are doing it without increasing engine rpms to levels where more fuel is needed to overcome increased friction inside the engine...mainly piston ring friction against the bore walls.
If you find that you can't climb steep hills in overdrive gear on a Ram truck...you are not supposed to be doing that.
If you find that when in 4th gear 1:1 ratio the rpms seem a bit too high with a 3.55 diff while climbing those hills....you are right. Dodge has set 4th gear a bit to high because 'its better to be safe than sorry'.
You actually can still climb nearly all those hills at lower rpm with a 3.21 differential
and the 3.21 diff will give about 1 MPG better than a 3.55 on flats and downhill sections of the highway.....but this is influenced by tires, both diameter and rolling resistance. This is especially true of the high torque 5.7 V8. It will be even more true of the even higher torque 2009 model year 5.7 V8 with its new mods. This is why 3.42 (American Axle) and 3.21 gearsets options will be available to knowledgeable buyers.
What about the 4.56 crowd that exists on forums?
They are trying to turn overdrive into 4th gear.
They seem to want their truck never to downshift for a hill....they think this is a 'strong' truck and that transmissions that downshift are 'wimpy'.
The primary thing a 4.56 diff gearset does is allow easy breaking loose of tire traction so that these children can do 'burnouts' at will.
If you understand quartermile racing
you will have a different idea...that you want a combined system of
differential gearset/tires/suspension
that will allow you to do a maximum torque launch
(on a 5.7 V8 that is 4000 rpm full throttle)
with just a little wheelspin
to get the best 60 foot time.
Try holding your brake,
raising the rpms to 4000 rpms
and launching while going to
full throttle and letting off the brake at the same time.
What happens?
Severe wheel hop and traction loss.
Do this in a safe place like a drag strip.
There is an old saying:
"A picture is worth a thousand words"
You understand transmission and differential gear ratios
when you understand the two small graphs
on page 737 of the Bosch Automotive Handbook, 6th edition
of torque, hp, hill climbing, aerodynamics, and tire rolling resistance:
http://www.etrucker.com/content/downloads/ccj0302.pdf
the above article is written for 18 wheel truckers
but applies to all vehicles
your overdrive top gear was designed by Chrysler engineers
to be used on
'a lightly loaded truck'
on flat/downhill highways at modest (below 75 mph) speeds
Fourth gear (which is the more efficient 1:1 ratio)
is meant for climbing hills
going fast
or towing heavy loads (and here ATF pump rpm in the trans is crucial)
Best fuel economy will be found when the trans ratios are set up
so that you HAVE TO downshift to climb any hill steep than about 2% grade
or are travelling into a strong head wind
or are carrying heavy load in the truck.
18 wheel truckers who speed up on downhills using engine horsepower produced at lower rpms are following a MPG improvement strategy that works even though it is unsafe to other vehicles on the road.
Later when climbing hills they are using 'stored kinetic energy' to overcome hills 'potential energy' requirement...and they are doing it without increasing engine rpms to levels where more fuel is needed to overcome increased friction inside the engine...mainly piston ring friction against the bore walls.
If you find that you can't climb steep hills in overdrive gear on a Ram truck...you are not supposed to be doing that.
If you find that when in 4th gear 1:1 ratio the rpms seem a bit too high with a 3.55 diff while climbing those hills....you are right. Dodge has set 4th gear a bit to high because 'its better to be safe than sorry'.
You actually can still climb nearly all those hills at lower rpm with a 3.21 differential
and the 3.21 diff will give about 1 MPG better than a 3.55 on flats and downhill sections of the highway.....but this is influenced by tires, both diameter and rolling resistance. This is especially true of the high torque 5.7 V8. It will be even more true of the even higher torque 2009 model year 5.7 V8 with its new mods. This is why 3.42 (American Axle) and 3.21 gearsets options will be available to knowledgeable buyers.
What about the 4.56 crowd that exists on forums?
They are trying to turn overdrive into 4th gear.
They seem to want their truck never to downshift for a hill....they think this is a 'strong' truck and that transmissions that downshift are 'wimpy'.
The primary thing a 4.56 diff gearset does is allow easy breaking loose of tire traction so that these children can do 'burnouts' at will.
If you understand quartermile racing
you will have a different idea...that you want a combined system of
differential gearset/tires/suspension
that will allow you to do a maximum torque launch
(on a 5.7 V8 that is 4000 rpm full throttle)
with just a little wheelspin
to get the best 60 foot time.
Try holding your brake,
raising the rpms to 4000 rpms
and launching while going to
full throttle and letting off the brake at the same time.
What happens?
Severe wheel hop and traction loss.
Do this in a safe place like a drag strip.
There is an old saying:
"A picture is worth a thousand words"
You understand transmission and differential gear ratios
when you understand the two small graphs
on page 737 of the Bosch Automotive Handbook, 6th edition
#13
03-13-2008, 08:50 AM
RE: Interstate Driving
What about the 4.56 crowd that exists on forums?
They are trying to turn overdrive into 4th gear.
They seem to want their truck never to downshift for a hill....they think this is a 'strong' truck and that transmissions that downshift are 'wimpy'.
They are trying to turn overdrive into 4th gear.
They seem to want their truck never to downshift for a hill....they think this is a 'strong' truck and that transmissions that downshift are 'wimpy'.
#14
03-13-2008, 09:43 AM
RE: Interstate Driving
ORIGINAL: HankL
first learn the basics
of torque, hp, hill climbing, aerodynamics, and tire rolling resistance:
http://www.etrucker.com/content/downloads/ccj0302.pdf
the above article is written for 18 wheel truckers
but applies to all vehicles
your overdrive top gear was designed by Chrysler engineers
to be used on
'a lightly loaded truck'
on flat/downhill highways at modest (below 75 mph) speeds
Fourth gear (which is the more efficient 1:1 ratio)
is meant for climbing hills
going fast
or towing heavy loads (and here ATF pump rpm in the trans is crucial)
Best fuel economy will be found when the trans ratios are set up
so that you HAVE TO downshift to climb any hill steep than about 2% grade
or are travelling into a strong head wind
or are carrying heavy load in the truck.
18 wheel truckers who speed up on downhills using engine horsepower produced at lower rpms are following a MPG improvement strategy that works even though it is unsafe to other vehicles on the road.
Later when climbing hills they are using 'stored kinetic energy' to overcome hills 'potential energy' requirement...and they are doing it without increasing engine rpms to levels where more fuel is needed to overcome increased friction inside the engine...mainly piston ring friction against the bore walls.
If you find that you can't climb steep hills in overdrive gear on a Ram truck...you are not supposed to be doing that.
If you find that when in 4th gear 1:1 ratio the rpms seem a bit too high with a 3.55 diff while climbing those hills....you are right. Dodge has set 4th gear a bit to high because 'its better to be safe than sorry'.
You actually can still climb nearly all those hills at lower rpm with a 3.21 differential
and the 3.21 diff will give about 1 MPG better than a 3.55 on flats and downhill sections of the highway.....but this is influenced by tires, both diameter and rolling resistance. This is especially true of the high torque 5.7 V8. It will be even more true of the even higher torque 2009 model year 5.7 V8 with its new mods. This is why 3.42 (American Axle) and 3.21 gearsets options will be available to knowledgeable buyers.
What about the 4.56 crowd that exists on forums?
They are trying to turn overdrive into 4th gear.
They seem to want their truck never to downshift for a hill....they think this is a 'strong' truck and that transmissions that downshift are 'wimpy'.
The primary thing a 4.56 diff gearset does is allow easy breaking loose of tire traction so that these children can do 'burnouts' at will.
If you understand quartermile racing
you will have a different idea...that you want a combined system of
differential gearset/tires/suspension
that will allow you to do a maximum torque launch
(on a 5.7 V8 that is 4000 rpm full throttle)
with just a little wheelspin
to get the best 60 foot time.
Try holding your brake,
raising the rpms to 4000 rpms
and launching while going to
full throttle and letting off the brake at the same time.
What happens?
Severe wheel hop and traction loss.
Do this in a safe place like a drag strip.
There is an old saying:
"A picture is worth a thousand words"
You understand transmission and differential gear ratios
when you understand the two small graphs
on page 737 of the Bosch Automotive Handbook, 6th edition
first learn the basics
of torque, hp, hill climbing, aerodynamics, and tire rolling resistance:
http://www.etrucker.com/content/downloads/ccj0302.pdf
the above article is written for 18 wheel truckers
but applies to all vehicles
your overdrive top gear was designed by Chrysler engineers
to be used on
'a lightly loaded truck'
on flat/downhill highways at modest (below 75 mph) speeds
Fourth gear (which is the more efficient 1:1 ratio)
is meant for climbing hills
going fast
or towing heavy loads (and here ATF pump rpm in the trans is crucial)
Best fuel economy will be found when the trans ratios are set up
so that you HAVE TO downshift to climb any hill steep than about 2% grade
or are travelling into a strong head wind
or are carrying heavy load in the truck.
18 wheel truckers who speed up on downhills using engine horsepower produced at lower rpms are following a MPG improvement strategy that works even though it is unsafe to other vehicles on the road.
Later when climbing hills they are using 'stored kinetic energy' to overcome hills 'potential energy' requirement...and they are doing it without increasing engine rpms to levels where more fuel is needed to overcome increased friction inside the engine...mainly piston ring friction against the bore walls.
If you find that you can't climb steep hills in overdrive gear on a Ram truck...you are not supposed to be doing that.
If you find that when in 4th gear 1:1 ratio the rpms seem a bit too high with a 3.55 diff while climbing those hills....you are right. Dodge has set 4th gear a bit to high because 'its better to be safe than sorry'.
You actually can still climb nearly all those hills at lower rpm with a 3.21 differential
and the 3.21 diff will give about 1 MPG better than a 3.55 on flats and downhill sections of the highway.....but this is influenced by tires, both diameter and rolling resistance. This is especially true of the high torque 5.7 V8. It will be even more true of the even higher torque 2009 model year 5.7 V8 with its new mods. This is why 3.42 (American Axle) and 3.21 gearsets options will be available to knowledgeable buyers.
What about the 4.56 crowd that exists on forums?
They are trying to turn overdrive into 4th gear.
They seem to want their truck never to downshift for a hill....they think this is a 'strong' truck and that transmissions that downshift are 'wimpy'.
The primary thing a 4.56 diff gearset does is allow easy breaking loose of tire traction so that these children can do 'burnouts' at will.
If you understand quartermile racing
you will have a different idea...that you want a combined system of
differential gearset/tires/suspension
that will allow you to do a maximum torque launch
(on a 5.7 V8 that is 4000 rpm full throttle)
with just a little wheelspin
to get the best 60 foot time.
Try holding your brake,
raising the rpms to 4000 rpms
and launching while going to
full throttle and letting off the brake at the same time.
What happens?
Severe wheel hop and traction loss.
Do this in a safe place like a drag strip.
There is an old saying:
"A picture is worth a thousand words"
You understand transmission and differential gear ratios
when you understand the two small graphs
on page 737 of the Bosch Automotive Handbook, 6th edition
#15
03-13-2008, 10:29 AM
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#16
03-13-2008, 01:10 PM
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RE: Interstate Driving
ORIGINAL: TheForce55555
Those mods should help a little but not much, The best thing to do is upgrade to 3.92 or 4.10 gear ratio to make the O/D more useful
2000 RPM seems to be have a good power and decent gas mileage, and you can pull most hills without losing speed
Those mods should help a little but not much, The best thing to do is upgrade to 3.92 or 4.10 gear ratio to make the O/D more useful
2000 RPM seems to be have a good power and decent gas mileage, and you can pull most hills without losing speed
#17
03-13-2008, 01:28 PM
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RE: Interstate Driving
I read that long post but I'm still not sure which way is better for the transmission. I realize that it is going to have to drop to a lower gear up steep hills one way or another. That is just the way it is.
When having to do so is it better to A) leave the truck alone on cruise in OD and let it downshift by itself or B) manually take it out of OD while on cruise and put it back in once the road is flat again?
Now that that part is out of the way, what about the little wimpy uphill climbs that it keeps downshifting on? Will a CAI, HPPIII with properly calibrated speedometer, and a cat-back solve this problem?
Here is a perfect example of the kind of "hill" I'm talking about. Even on a tiny hill like this, the truck (when it was 100% stock with the speedometer needing to be calibrated) would seem to bog down in OD at 2,000 RPM at an indicated 75-78 MPH and it would downshift to maintain speed. It would sometimes do this 2-3 times on the same hill, depending on how long the hill was. Hopefully this pic will give you a clear idea of the kind of tiny hills I'm talking about.
When having to do so is it better to A) leave the truck alone on cruise in OD and let it downshift by itself or B) manually take it out of OD while on cruise and put it back in once the road is flat again?
Now that that part is out of the way, what about the little wimpy uphill climbs that it keeps downshifting on? Will a CAI, HPPIII with properly calibrated speedometer, and a cat-back solve this problem?
Here is a perfect example of the kind of "hill" I'm talking about. Even on a tiny hill like this, the truck (when it was 100% stock with the speedometer needing to be calibrated) would seem to bog down in OD at 2,000 RPM at an indicated 75-78 MPH and it would downshift to maintain speed. It would sometimes do this 2-3 times on the same hill, depending on how long the hill was. Hopefully this pic will give you a clear idea of the kind of tiny hills I'm talking about.
#19
03-13-2008, 03:13 PM
#20
03-13-2008, 03:25 PM
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RE: Interstate Driving
[blockquote]quote:
ORIGINAL: TheForce55555
Those mods should help a little but not much, The best thing to do is upgrade to 3.92 or 4.10 gear ratio to make the O/D more useful
2000 RPM seems to be have a good power and decent gas mileage, and you can pull most hills without losing speed
[/blockquote]
.
I meant 2000 RPM at 60 MPH
ORIGINAL: TheForce55555
Those mods should help a little but not much, The best thing to do is upgrade to 3.92 or 4.10 gear ratio to make the O/D more useful
2000 RPM seems to be have a good power and decent gas mileage, and you can pull most hills without losing speed
[/blockquote]
Not in this truck, LOL. 2,000 RPM = downshifting out of OD even on the smallest little uphill grade. I'm talkin' just a little bit above what would be considered a flat surface. I've never had or witnessedthis problem in any other V8 truck I've been in. Steep hills? Sure. But not little ones
I meant 2000 RPM at 60 MPH