Two overdrives?

[cleanspeed1]

Not in this lifetime. I think the problem has always been trying to make machinery do things it was not meant to do without looking at the total picture.

I never said it couldn't be done, it's just that folks think one thing alone will change the outcome.

[Frank Lee]

Originally Posted by cleanspeed1

Not in this lifetime. I think the problem has always been trying to make machinery do things it was not meant to do without looking at the total picture.

I never said it couldn't be done, it's just that folks think one thing alone will change the outcome.

Seems to be a common affliction i.e. trying to make pickups be sportscars.

[cleanspeed1]

Or Jeeps into Metros.

[t vago]

Hey, if you don't like what we want to do with our property, with our money, on our own time, then you don't have to comment on it.

Especially you, Frank, and after complaining about me making cutsey remarks, too. Get the hell out of my thread if you don't have anything constructive to say.

[cleanspeed1]

Woah, easy now, there's no need to get hostile. There are rules you know.

[t vago]

Originally Posted by cleanspeed1

Woah, easy now, there's no need to get hostile. There are rules you know.

Rules, such as taking a thread off-topic?

Besides that, your theory is really nice to read and all, but it neglects real-world experience.

For instance, I consider my own setup to be pretty similar to Duner (the other guy with the Dakota with the installed fuel rail cooling mod). Therefore, I consider my engine's output to be similar to his.

I had a 45RFE transmission installed as original equipment, and I did some research into adding an overdrive back in 2009. After doing some research, and realizing that the physical 45RFE transmission was identical to the 545RFE transmission offered on later model Dakotas, I changed out the transmission computer in November of 2009 to electronically upgrade my transmission into a 545RFE. Mainly, what it did was add a 5th gear (2nd overdrive) to the transmission via software control of the planetaries inside the transmission itself. That had the effect of dropping my crusing RPM by about 300 RPM. That had the effect of raising my gas mileage from 14 MPG to 15 MPG, and that was back when my truck was getting relatively lousy gas mileage.

If I could drop that operating RPM even further, while maintaining the same speed as before, then my FE will go up. And, no, it's not an option to go 55 down an interstate with a 65 MPH speed limit.

[Big Dave]

I have the GV overdrive in my F-350 although with a stick shift. The GV’s 0.78:1 ratio combined with the ZF’s 0.71 ratio gives me an 0.554:1 overall ratio.

The double overdrive does improve MPG by about 1.25 MPG for me. With OEM-size rubber, I am turning 1310 RPM at 70 MPH. 1125 at 60 MPH. My big diesel turns this with insouciant ease. I kinda have to use the GV because there are no commercially available alternatives without sacrificing the capabilities of my truck, which I am not prepared to do.

Couple of caveats about a GV setup. Have your automatic worked on by a really good performance transmission builder. Tell him about the GV.You will be slowing the torque converter down a lot and heat is gonna be a problem.

Secondly, GVs are very heavy-duty pieces of machinery (originally built for Bedford military deuce-and-a-halfs) and are priced accordingly. It would be cheaper for t_vago to get a T-56 and do the “sex change operation” to convert his truck to a manual and he’s still have enough money left over to pay bondo to make him a very slick über-quality aerolid. Then he’d have a 0.5:1 top overdrive and only have to overcome the losses of one gear mesh. The T-56 gets around the frailties of the automatic altogether.

The optimum driveline would be a manual transmission with a straight-through (1:1) top gear and an appropriate gear ratio (about a 1.5:1). Numerically low ratios are getting hard to find. 3.08s and occasionally 2.73s are about it (and thise take some looking) unless you have an outstanding junk yard at your disposal. The OEMs are under governmental pressure over NOx. High load generates more NOx than light load. NOx emission is fairly RPM-neutral. So the OEMs tend to use 3.73s to keep load down and RPM up.

To me the optimum MPG driveline for my truck (considerably heavier than t_vago’s truck, obviously) is to have a custom rear axle made with a 13:20 (1.56:1) ring and pinion and ditch my ZF6-650 and GV for a Spicer seven-gear with 1:1 top gear.

[cleanspeed1]

Let me explain real world experience to you. It's called 20+ years driving, fixing, maintaining and making money with vehicles that most people just use to go back and forth to work. I have owned or driven every type of roadgoing vehicle for commercial use that you can think of, and have clocked more miles in that time than most people would do in a lifetime. Whether gas or diesel, been there, done that. But I never lost my curiosity, which makes me want to learn more about why vehicles are not operating to their maximum mpg, because for me, it's my livelihood as well as my hobby.

Having said that, given the variables that you are working with and the fact that you drive a big, heavy, high powered, high drag vehicle with high frictional losses in the driveline and high road friction because of the tires, along with a propensity for high speed, you are not going to win an mpg contest. The laws of physics and thermodynamics are working against you, and unless you have figured out a way to take a 28 percent efficient gas motor to well past 50 percent your gains will be incremental at best and nonexistent at worst with the stock set up you have. No amount of overdrive is going to change that and that was the point.

[cleanspeed1]

Originally Posted by Big Dave

I have the GV overdrive in my F-350 although with a stick shift. The GV’s 0.78:1 ratio combined with the ZF’s 0.71 ratio gives me an 0.554:1 overall ratio.

The double overdrive does improve MPG by about 1.25 MPG for me. With OEM-size rubber, I am turning 1310 RPM at 70 MPH. 1125 at 60 MPH. My big diesel turns this with insouciant ease. I kinda have to use the GV because there are no commercially available alternatives without sacrificing the capabilities of my truck, which I am not prepared to do.

Couple of caveats about a GV setup. Have your automatic worked on by a really good performance transmission builder. Tell him about the GV.You will be slowing the torque converter down a lot and heat is gonna be a problem.

Secondly, GVs are very heavy-duty pieces of machinery (originally built for Bedford military deuce-and-a-halfs) and are priced accordingly. It would be cheaper for t_vago to get a T-56 and do the “sex change operation” to convert his truck to a manual and he’s still have enough money left over to pay bondo to make him a very slick über-quality aerolid. Then he’d have a 0.5:1 top overdrive and only have to overcome the losses of one gear mesh. The T-56 gets around the frailties of the automatic altogether.

The optimum driveline would be a manual transmission with a straight-through (1:1) top gear and an appropriate gear ratio (about a 1.5:1). Numerically low ratios are getting hard to find. 3.08s and occasionally 2.73s are about it (and thise take some looking) unless you have an outstanding junk yard at your disposal. The OEMs are under governmental pressure over NOx. High load generates more NOx than light load. NOx emission is fairly RPM-neutral. So the OEMs tend to use 3.73s to keep load down and RPM up.

To me the optimum MPG driveline for my truck (considerably heavier than t_vago’s truck, obviously) is to have a custom rear axle made with a 13:20 (1.56:1) ring and pinion and ditch my ZF6-650 and GV for a Spicer seven-gear with 1:1 top gear.

You are my new hero. You own what I have been explaining. Thank you.

If the fuel were of a higher quality, then a spark ignited engine can pull off something similiar to a diesel, but that will not happen because the mpg would skyrocket and someone will get cut out of the money.

[womprat]

I have heard of lotus 7 replica owners using a two ratio box inline with a conventional gearbox. Lets them have a hope of getting the best out of a car on track, and being managable on the road. Popular in the UK with bike engine cars that have a need for a reversing gearbox.

I guess when you have a car that weighs about half or a third of the original machine wrapped around the engine, you don't need short low gears (traction issues), but too taller rear end and you won't be able to make use the higher gears (3-4-5 maybe a 6) with their closer ratio spacing - but you'll be doing 4000rpm on the highway. Know a guy here in NZ who says he doesn't get out of 2nd or 3rd in a hill climb race in his 1800c engined Fraser. Obviously in need of something like this.

Some them dudes known to get 40-50mpg going back and forth from a track meet.