Overdrive or Taller Gears for Fuel Savings

[ilovetrains]

Check out this link: AAM



It looks like the 11. 5 AAM is available with anything from a 3. 54 on up to a 5. xx? I checked out Richmond Gear, and couldn't find anything, but AAM may? I haven't called them, but it's worth a try. I too have a new G56 w/3. 73's and want som more room on top... .

I have emailed AAM for some explanation. Dodge claims they do not exist and I have found zero online retailers that can get those gears.

 

[Bernie]

I have emailed AAM for some explanation. Dodge claims they do not exist and I have found zero online retailers that can get those gears.

I did as well, but nobody responded. I'm going to try calling next week.

 

[ilovetrains]

I did as well, but nobody responded. I'm going to try calling next week.

I got an automated out-of-office reply. Hopefully we get something more on this. I need to get together with a gear calculator and start doing the math. 3. 54 is only about 8% difference. I was hoping for more like 3. 42.

 

[GHarman]

Bernie, have you considered TALLER tires? You can run the math from your expected MPH through the engine RPM, expected gear ratio in the trans, your axle ratio( check the tag on the differential cover) to the tire circumference. Just a thought. Might not be so expensive. GregH

 

[Jrissler]

8% aint much!!



But that would help just a few RPMs. Maybe 5 MPH. less.

 

[ilovetrains]

In terms of RPM - at 75 going from 3. 73 to 3. 54 would net 130 less RPM. Not axactly the jump I was looking for.

 

[Bernie]

Bernie, have you considered TALLER tires? You can run the math from your expected MPH through the engine RPM, expected gear ratio in the trans, your axle ratio( check the tag on the differential cover) to the tire circumference. Just a thought. Might not be so expensive. GregH

Greg:



Thanks. Read some of my other posts. Not quite right form me.

 

[wsurf]

Bernie, have you decided yet? I have the same truck and if you go the GV way please let us know. As previously mentioned, I've had the GV unit on my 03 3500 DRW. Thanks.

 

[Bernie]

Bernie, have you decided yet? I have the same truck and if you go the GV way please let us know. As previously mentioned, I've had the GV unit on my 03 3500 DRW. Thanks.

Haven't decided yet. I think 3. 50 diffs would be the most economical option, but I like the idea of not giving up the low gearing I have for towing. I'll let you know.



Thanks

 

[Jrissler]

What would happen if you took a old style trans and put in the new truck??



Or don't they bolt up??



Just a thought.

 

[Bernie]

What would happen if you took a old style trans and put in the new truck??



Or don't they bolt up??

I'll have to find an NV5600 and take a look at it. If the economics work out, that might be OK. As I've read posts about NV5600 failing (and being hard to get parts for), I'd just keep my G56 in reserve.



Anybody with more transmission knowledge have a better idea about this?

 

[Posm]

Speed, not RPM is what is killing the mileage. I have driven nearly 400K miles in Cummins Ram since 2000 and can verify this. If you want to check this out, drive a full tank in 5th instead of 6th gear. You will see a small change in MPG, but not much. Speed hurts mileage because the wind resistance is squared with speed. Most people think that it is a linear response.



I have a steak dinner for the first person to prove me wrong. You can drive as fast as you want, but you will pay for cutting the wind at the higher speeds!



Bryan

 

[Bernie]

Speed, not RPM is what is killing the mileage. Speed hurts mileage because the wind resistance is squared with speed. Most people think that it is a linear response.



I have a steak dinner for the first person to prove me wrong. You can drive as fast as you want, but you will pay for cutting the wind at the higher speeds!

I agree that speed is part of the equation (and maybe the largest part of the equation), but it is not the only part.



I (unfortunately) have no control over the aerodynamics of my truck, and I want to move along with traffic at 75 MPH, so the only factor left to control is the engine speed.



Although I haven't had a chance to drive my Dodge with different gears, I can say I've seen about 3 MPG change from my car when it had different differentials, averaging about 75 MPH on the highway with both differentials. It is more aerodynamic than my truck, but there still is the wind factor so I have to believe I will see an increase in MPG from less RPMs.



Now before everyone gets all high and mighty with the "just slow down" posts, see my earlier posts in this tread. My only goal is to move along with traffic, at about 75 MPH. It is much safer to move with the traffic flow then to go slower and disrupt it.



And I'm not a big steak fan. I'll take lobster.

 

[cojhl2]

You are both not incorrect!!!



The single biggest power requirement is the vehicle moving thru the air stream. The force does increase with the square of speed, and since power requirement is directly related to force it takes more to run at faster speed, hence the lower fuel efficiency.



The question tho is: at that speed whatever it is what is the most efficient RPM. theoretically RPM should not be related to efficiency of fuel used. Power of the engine is RPMxtorque. RPM goes up Torque goes down.



However there is no engine built that has a flat efficiency curve over the power range it is capable of producing. All engines that I know of have a best place to run RPM and Torque.



So,, Bernie is trying to place the engine at the best RPM for the power he requires, regardless what it is. The power requirement is fixed.



I'm not sure where these Dodge engines get the best economy but for the bigger engines we want to run about 1700 with post EGT around 6-800 F.



Also one should think about piston miles. From my standpoint that is more important than a few MPG difference cause there are many variable affecting fuel economy The less miles I can put on the engine internals the better I like it.



my 03





edit: I thought I better go back and add that I wrote this thinking only of crusiing down the road. Obviously when power is required to either accelerate or take a load up a hill that could very quickly becomes the dominating power requirement.

 

[AKaiser]

Some of the old Mac's had 10 speeds by using a 5 with a 2 bolted on behind (2 sticks) but that was so long ago they have probably all been melted down by now.

No, I know where two of them are, and I've driven both, but never really had to use the low gear on the aux box. One was a 78 Mack RD with a dry fertilizer tender box, and the other was a similar DM with a liquid chemical tank on it at a local Cooperative I worked for about 8 year back. I'm pretty sure they are both still running somewhere.



On that note, we have a mid-late 70s IHC 1600 Loadstar w/392CID 5x4 (Granny Low, two road and an overdrive on the aux, and Granny Low, 3 road and an OD on the main) 20 ft grain dump. It's underpowered, but we still run it alongside an 89 Pete tractor w/CAT and 9 speed (I think) with a 28 ft East aluminum frame dump.



Oh, and I turn 34 in a week.

 

[LHirshman]

Try a Power Puck

I put in a Diablo Power Puck and use it in the high HP mode.

I have seen an increase of a 2-3MPG with it.

 

[Jrissler]

Yea I beleive both are right. Wind does kill!!



But I have 01 with 6spd. with 3:55 rears and I can run it 75-80 and get 18-20 MPG and I can run anyone of my dually with 4:10s that I've had at 65 and only get 15 tops!! That is taking off slow and not hitting it hard at all.



I can't beleive that the weight of the 2 extra wheels and the wind catching the hips cause that big of a diff.

 

[wbrown02]

In my 2005 with the 4. 10 gears and six speed ..... NV5600... . and the GearVendor overdrive my RPMs at 75 mph run about 1900..... fuel mileage does not increase much at that speed for me..... running at 65 mph the fuel savings is much greater. I am pleased with the GearVendor unit as this is the second one I have owned. While towing I sometimes use the overdrive in 5th which gives me a slightly greater rpm than the same speed in 6th gear for a little more pulling power. Hope this helps.

 

[FDrake]

try this instead........

I didn't read all the responses. I suggest you try another way. I used a Gear Vendor behind my transmission in my 1T Chev and it worked great. It took me from a 3. 73 to a 2. 96 when engaged, It cost (then) about $2400 installed but I felt it was worth it. If opens the 6 speed to ten speeds since you can use the overdrive between gears. Look into that and see how that fits your needs.

Frank

 

[Bernie]

I didn't read all the responses. I suggest you try another way. I used a Gear Vendor behind my transmission in my 1T Chev and it worked great. It took me from a 3. 73 to a 2. 96 when engaged, It cost (then) about $2400 installed but I felt it was worth it. If opens the 6 speed to ten speeds since you can use the overdrive between gears. Look into that and see how that fits your needs.

Frank

Frank,

Thanks. The point of my original post was to get input on an overdrive or taller diff gears to increase fuel milage. What did you see for fuel milage changes when you put your overdrive on?