Question on Gears
Champion
Joined: Aug 2010
Posts: 2,697
Likes: 3
From: Cape Carteret NC
Eff the 4.10's.. go 4.56 and don't look back.. you'll actually pick up some mpgs as counterintuitive as it seems.. gears are all about leverage, and the 5.9 planes off nicely around 1800 to 1950 rpms, and doesn't stress up until 24-2600 rpms.. you'll greatly reduce engine load as the leverage is almost perfect with that rigs transmission ratio, and power band (assuming you're running oe camshaft)..
I'd guess absolute perfection for that rig would be with an axle ratio somewhere around 4.4:1, but you can dial that in with tire diameter.. you will also find that the torque converter (again, assuming oe stall of 1800ish rpm) will lock up at highway speeds and stay there over the risers, which improves economy and keeps the heat off the trans, which in turn promotes transmission life..
I've often lamented that the three things mother mopar should have done with those rigs is offer a 408 from the factory, offered better steps in transmission ratios with better fluid flow through them, and lower ratio axle.. maybe, also, a less severe step to o/d would have been a good thing too..
Everyone is so afraid of rpm.. I don't get it.. it's only a partial reckoning about fuel consumption, and is based on a constant which is NEVER a constant.. engine load is a bigger factor and much more important.. reduce load, improve economy.. leverage through lower gears is the cheater bar of reducing load..
I'd guess absolute perfection for that rig would be with an axle ratio somewhere around 4.4:1, but you can dial that in with tire diameter.. you will also find that the torque converter (again, assuming oe stall of 1800ish rpm) will lock up at highway speeds and stay there over the risers, which improves economy and keeps the heat off the trans, which in turn promotes transmission life..
I've often lamented that the three things mother mopar should have done with those rigs is offer a 408 from the factory, offered better steps in transmission ratios with better fluid flow through them, and lower ratio axle.. maybe, also, a less severe step to o/d would have been a good thing too..
Everyone is so afraid of rpm.. I don't get it.. it's only a partial reckoning about fuel consumption, and is based on a constant which is NEVER a constant.. engine load is a bigger factor and much more important.. reduce load, improve economy.. leverage through lower gears is the cheater bar of reducing load..
Champion
Joined: Aug 2007
Posts: 4,702
Likes: 2
From: N. Florida
Engines are big air pumps. The faster they turn, the more air (and fuel) they use. At a steady 80 mph, my truck is turning 1,980 rpm. With the 265/70x17 tires, it was turning 2,020 rpm.
I tried an experiment recently: drove a day-trip with O/D off on the out-bound leg and got 14.3 mpg. On the return leg, O/D was on and it got 14.8 mpg and that included driving around a small town to try and locate the home of two dogs we found on the highway. Same route, same distance (excluding the search for the dogs' home). Don't know for sure, but I suspect the return mileage might have been 15. So, same speed, same route, at least 3.5% better mileage with the "taller" gear of O/D.
"Leverage" is torque? OK, but it doesn't take much torque to hold a steady speed, just enough power to push the Ram's big face through the air.
I tried an experiment recently: drove a day-trip with O/D off on the out-bound leg and got 14.3 mpg. On the return leg, O/D was on and it got 14.8 mpg and that included driving around a small town to try and locate the home of two dogs we found on the highway. Same route, same distance (excluding the search for the dogs' home). Don't know for sure, but I suspect the return mileage might have been 15. So, same speed, same route, at least 3.5% better mileage with the "taller" gear of O/D.
"Leverage" is torque? OK, but it doesn't take much torque to hold a steady speed, just enough power to push the Ram's big face through the air.
Thread Starter
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Registered User
Joined: Oct 2012
Posts: 20
Likes: 0
From: College Station
Eff the 4.10's.. go 4.56 and don't look back.. you'll actually pick up some mpgs as counterintuitive as it seems.. gears are all about leverage, and the 5.9 planes off nicely around 1800 to 1950 rpms, and doesn't stress up until 24-2600 rpms.. you'll greatly reduce engine load as the leverage is almost perfect with that rigs transmission ratio, and power band (assuming you're running oe camshaft)..
I'd guess absolute perfection for that rig would be with an axle ratio somewhere around 4.4:1, but you can dial that in with tire diameter.. you will also find that the torque converter (again, assuming oe stall of 1800ish rpm) will lock up at highway speeds and stay there over the risers, which improves economy and keeps the heat off the trans, which in turn promotes transmission life..
I've often lamented that the three things mother mopar should have done with those rigs is offer a 408 from the factory, offered better steps in transmission ratios with better fluid flow through them, and lower ratio axle.. maybe, also, a less severe step to o/d would have been a good thing too..
Everyone is so afraid of rpm.. I don't get it.. it's only a partial reckoning about fuel consumption, and is based on a constant which is NEVER a constant.. engine load is a bigger factor and much more important.. reduce load, improve economy.. leverage through lower gears is the cheater bar of reducing load..
I'd guess absolute perfection for that rig would be with an axle ratio somewhere around 4.4:1, but you can dial that in with tire diameter.. you will also find that the torque converter (again, assuming oe stall of 1800ish rpm) will lock up at highway speeds and stay there over the risers, which improves economy and keeps the heat off the trans, which in turn promotes transmission life..
I've often lamented that the three things mother mopar should have done with those rigs is offer a 408 from the factory, offered better steps in transmission ratios with better fluid flow through them, and lower ratio axle.. maybe, also, a less severe step to o/d would have been a good thing too..
Everyone is so afraid of rpm.. I don't get it.. it's only a partial reckoning about fuel consumption, and is based on a constant which is NEVER a constant.. engine load is a bigger factor and much more important.. reduce load, improve economy.. leverage through lower gears is the cheater bar of reducing load..
Champion
Joined: Aug 2010
Posts: 2,697
Likes: 3
From: Cape Carteret NC
Engines are big air pumps. The faster they turn, the more air (and fuel) they use. At a steady 80 mph, my truck is turning 1,980 rpm. With the 265/70x17 tires, it was turning 2,020 rpm.
I tried an experiment recently: drove a day-trip with O/D off on the out-bound leg and got 14.3 mpg. On the return leg, O/D was on and it got 14.8 mpg and that included driving around a small town to try and locate the home of two dogs we found on the highway. Same route, same distance (excluding the search for the dogs' home). Don't know for sure, but I suspect the return mileage might have been 15. So, same speed, same route, at least 3.5% better mileage with the "taller" gear of O/D.
"Leverage" is torque? OK, but it doesn't take much torque to hold a steady speed, just enough power to push the Ram's big face through the air.
I tried an experiment recently: drove a day-trip with O/D off on the out-bound leg and got 14.3 mpg. On the return leg, O/D was on and it got 14.8 mpg and that included driving around a small town to try and locate the home of two dogs we found on the highway. Same route, same distance (excluding the search for the dogs' home). Don't know for sure, but I suspect the return mileage might have been 15. So, same speed, same route, at least 3.5% better mileage with the "taller" gear of O/D.
"Leverage" is torque? OK, but it doesn't take much torque to hold a steady speed, just enough power to push the Ram's big face through the air.
Engines are big air pumps, without doubt. fuel is catalyst to ignite air.. in carb'd engines, the same gadget that regulated air intake also squirted fuel.. with injectors and pcm controlled fuel curve, o2 sensors, manifold absolute pressure sensors, and intake air temp sensors, the computer can squirt just the right amount of fuel to attempt to maintain stoichemetric ratios.. there is a problem with that though..
Torque is spinning power.. you leverage that at the fluid coupler which reduces it to create more torque through gears.. gears are the leverage mechanism.. gears of the trans and the diff... Gear also in a sense, at the fluid coupler itself (torque converter)...
The relationship between the engines output (crank) and leveraging (drivetrain) has a direct effect on how quickly an engine is allowed to spin up.. if you are in park and there is no load, you can, through the beauty of pcm controlled fi, maintain stoich while achieving a very fast spool when you rev it.. when the drivetrain is engaged, you don't spool as fast, because resistance is limiting you.. the engine is only pulling in the air the drivetrain and load allows, but to increase the rpm, the engine dumps fuel while it struggles for air.. it runs excessively rich, which wastes fuel..
If the leverage were to make that struggle easier, it decreases load, which decreases waste, and improves economy..
All within reason, though... There is a balance.. the engineers placate the epa, and field a rig that approximates what is needed, and use gears to do that. That costs us as often as it helps.. bigger heavier tires? Need better leverage... Hell, by my reckoning, all p/u trucks need better leverage, period.. if these things we're driven the exact same way everyday, it would be easy to dial it in.. they aren't, though..
OP: you'll appreciate the 4.56 s.. I wouldn't bother with 4.10's at all, if it were me.. it was me once, and I am glad i did the 4.56's..
Thread Starter
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Registered User
Joined: Oct 2012
Posts: 20
Likes: 0
From: College Station
Sounds like a plan
