Ecodiesel power derating as temps rise?

[CrazyCooter]

You guys keep talking about RPMs and backing out of the throttle to control the EGT's......sure these can make a difference, but the bottom line is that it takes a certain amount of HP to climb a hill at a given speed.......The result of HP output is heat. Back out of the throttle and you slow down even more? Then add in that the VGT is going to do it's thing regardless of your input for efficiency and emissions.........

Also axle gear ratio has little to do with the equation. Axle ratio does not make HP! Simply dropping to 7th from 8th is a 10% gear change.....Equivalent to 3.73 to 4.10. A shift from 7th to 6th is another 16% or the equivalent to 4.77? Then add that 6th gear is 1:1 direct, so now your trans is making less heat? This is why I have not changed the ratio yet as it seems to work great as is.

Doesn't matter much what axle ratio you have....Unless you are stuck in between gears, which with today's 8 and 10 speeds is not happening........Its just not going to make a huge difference in the diesel's narrow operating RPM band. Now if we had 3 speed trans like 20 years ago, the correct axle ratio would make a big difference.

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[cotnballs2000]

High EGTs are from a too rich conditon (happens under load). Higher gear ratio = higher RPMs = More air into the engine. A gear change from 3.73 to 4.1 raises the RPM by over 200@ 70mph on a JTD 8 Speed in 8th gear. Shifting from 8th to 7th even at 70mph is a difference of about 1000rpm and still under redline and can easily pull the gear at speed.

 

[CrazyCooter]

High EGTs are from a too rich conditon. Higher gear ratio = higher RPMs = More air into the engine. A gear change from 3.73 to 4.1 raises the RPM by over 200@ 70mph on a JTD 8 Speed in 8th gear. Shifting from 8th to 7th even at 70mph is a difference of about 1000rpm and still under redline and can easily pull the gear at speed.

How is this 1000rpm possible when the 7th gear ratio is 11% lower than 8th? Your math and observations are flawed. It's not 1000rpm when you downshift.....it's 11% above your cruising RPM......

 

[Glad_he_ate]

Changing axel ratios will lower the stress on the engine thus lowering heat production. Shit any kid with a ten speed bike knows that

 

[Glad_he_ate]

Personally I think they all should have come with 410s not a huge difference but I bet it would run cooler
Or at least 410s should have been included in the tow package

 

[CrazyCooter]

Changing axel ratios will lower the stress on the engine thus lowering heat production. Shit any kid with a ten speed bike knows that

Actually lower gear ratios only reduce stress on the driveshaft since it links the engine and then transmission to the axle.

Assuming the gears in the transmission are low enough, the transmission actually reduces the stress on the engine. In our 8 speeds, they are lower than most earlier transmissions.

Underdrive and overdrive gears produce heat through multiplication. This is why 6th gear would produce less heat. Why would you want to run a weaker lower r&p set that generates more heat in the axle so that you can run up hills in 7th and 8th generating more heat in the trans too? I would rather use 7th and 8th for light loads and fuel economy and save 6th for pulling the hills while towing.

Spinning the driveline at a higher rpm than needed is also a waste of energy which has its price in economy and other stresses.

 

[CrazyCooter]

Personally I think they all should have come with 410s not a huge difference but I bet it would run cooler
Or at least 410s should have been included in the tow package

I think the 3.73s are perfect for 37's and could benefit from 3.45s with smaller tires.

In my earlier posts on this thread, I swapped smaller tires on to test the gearing theory and there wasn't much difference and the small difference there was made up by the few degrees cooler temps.

I could easily swap 4.10s in for the cost of a crush sleeve and oil, but I choose to stay 3.73s since I don't tow 100% of the time.

 

[Glad_he_ate]

Not being argumentative just looking at the process less stress on the transmission output shaft regardless of gear selection in the transmission would without a doubt equal less stress on the input shaft in every gear under the same load. Ratios being constant and all. So that would in turn equal less stress on the output shaft of the engine. Assuming full lock of the torque converter.

 

[Glad_he_ate]

Just my backwards process lol.

 

[CrazyCooter]

Not being argumentative just looking at the process less stress on the transmission output shaft regardless of gear selection in the transmission would without a doubt equal less stress on the input shaft in every gear under the same load. Ratios being constant and all. So that would in turn equal less stress on the output shaft of the engine. Assuming full lock of the torque converter.

This is open discussion.......Im not taking it as arguing.

But doesn't the transmission always upshift to the highest gear possible for the load....yes? So no matter what ratio 4.10, 4,56, 6.17 etc......it will always upshift and od gears make more heat than direct?

 

[CrazyCooter]

Surely 0-60 times will improve with lower axle ratio effectively bringing the trans gears closer together....this is assuming the Ecodiesel can rev fast enough to take advantage.

I've been wanting to line up with my buddy in his gas JT on 35s and 4.10s. I suspect he will pull me in a drag race, but I pull him on the hills and at the gas station.......I was even towing a 1500lb trailer.

 

[Deleted member 22728]

Actually lower gear ratios only reduce stress on the driveshaft since it links the engine and then transmission to the axle.

Assuming the gears in the transmission are low enough, the transmission actually reduces the stress on the engine. In our 8 speeds, they are lower than most earlier transmissions.

Underdrive and overdrive gears produce heat through multiplication. This is why 6th gear would produce less heat. Why would you want to run a weaker lower r&p set that generates more heat in the axle so that you can run up hills in 7th and 8th generating more heat in the trans too? I would rather use 7th and 8th for light loads and fuel economy and save 6th for pulling the hills while towing.

Spinning the driveline at a higher rpm than needed is also a waste of energy which has its price in economy and other stresses.

Again, I speak from my experience, training, and personal ownership of multiple platforms in the WK, JL, and JT lines that reflect a POSITIVE outcome from: 1. ensuring that the powertrain conforms to the design parameters given the matched tire size and axle ratio; 2. reducing underhood temperatures for the 3.0. These are the easy solutions for making the platform more amenable for whatever the heck. It works.

 

[Glad_he_ate]

From my experience in industrial maintenance any time you lower final drive gears aka in our case the axel ratio then you see less stress on the motor. In my last career we would commonly change drive gears to match the product being made to the capability of the machine it needed to run on. If a motor was pulling too many amps then we would drop final drive gears to lower the load on the motor. Did it reduce final drive speed ? Absolutely! Did it also in turn lower the temperature of the motor ? Absolutely!! Everything in between had less load as well. 13 years as an industrial tech tells me if there is one way to lower motor stress it is to change the ratios of what it’s spinning assuming the load at the end can not be lessened. Obviously there are limits as to how far is reasonable to go lol.

 

[Vtur]

Diesel with 37s will definitely benifit with 4.10 gear. Mine 37s wheel/tire weighted in at 105lb each. The 3.73 gear can still pull it and see 8th gear as normal, but i can tell that it's lugging the motor a little bit while picking up speed.

Similar to motorcycle gearing. In the case of adding bigger rear wheel, i would up a few rear sprocket teeths or go lower to the front sprocket, depending on wheels diameter.

Eventually, i will be changing it out to 4.10 gears, just to get the pickup power back.

 

[CrazyCooter]

From my experience in industrial maintenance any time you lower final drive gears aka in our case the axel ratio then you see less stress on the motor. In my last career we would commonly change drive gears to match the product being made to the capability of the machine it needed to run on. If a motor was pulling too many amps then we would drop final drive gears to lower the load on the motor. Did it reduce final drive speed ? Absolutely! Did it also in turn lower the temperature of the motor ? Absolutely!! Everything in between had less load as well. 13 years as an industrial tech tells me if there is one way to lower motor stress it is to change the ratios of what it’s spinning assuming the load at the end can not be lessened. Obviously there are limits as to how far is reasonable to go lol.

Absolutely in this situation the final would solve the issue, but your industrial equipment doesn't have an 8 speed gear box in between the motor and the load to fine tune things?

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