49mpg possible from full size mechanical diesel?

[aerohead]

If you were to reduce the road load it would allow the engine to over-speed,and also move it's BSFC off it's original island of efficiency.
If,say you did some LRR tires and streamlining,if you didn't match the gearing to the new load,you could lose up to 40% of the mpg benefit by operating the engine in a less efficient domain.
The new gearing would slow the engine down to it's rated power rpm,while raising the terminal velocity to a drag-limited top speed.
Here are some graphics

[deejaaa]

Originally Posted by UFO

Some people I know with MS practice Tai Chi regularly and they say it greatly alleviates their symptoms. I've been doing it for 20 years and have never felt better, and I am 50 years old.

must have missed something.

[bondvagabond]

By far the most common type of ms is "relapsing remitting" @ about %80 of ms patients. Some of which have only one episode of symptoms their whole life. I have the rarest kind, primary progressive with relapses. This means I get symptom spikes like the %80 but my base line of symptoms is getting worse over time. M.s. Is weird in that depending on where in the brain the lesions form the symptoms can vary significantly. For me I have had steadily increasing fatigue/memory loss/cognitive function loss/bowel and bladder control loss since 2009 with a relapse of psychological catatonia in 2013 and another relapse of a fatigue/cognitive function loss spike in 2014. It's been a weird ride, going from backpacking 1000+ miles per year/ bike commuting to building my eventual wheel chair van. End thread high jack.

[oil pan 4]

Does this 7.3 not have a turbocharger?
If you are not going to install a turbo you are throwing away a 10% to 20% fuel economy increase.
Decreasing the final drive ratio on a non turbo diesel is going to increase exhaust gas temperature as you try to work the engine harder at lower RPM. You will just end up blowing more heat out the exhaust.

[bondvagabond]

Originally Posted by oil pan 4

Does this 7.3 not have a turbocharger?
If you are not going to install a turbo you are throwing away a 10% to 20% fuel economy increase.
Decreasing the final drive ratio on a non turbo diesel is going to increase exhaust gas temperature as you try to work the engine harder at lower RPM. You will just end up blowing more heat out the exhaust.

Have you found any specific data on this? I have always heard that turbo diesels were more efficient, but the only apples to apples comparison I can find that is not anecdotal is the 1.6 na and turbo vw diesels. All other examples I know of the turbo model has lower compression ratio, so more than one variable is being changed. In the vw diesels I mentioned the non turbo gets 9% better fuel economy on the EPA rating. Keep in mind the vw diesels and my pre powerstroke 7.3 are relatively high compression mechanical diesels. One of the guys with a 2007 cummins on here is pushing close to 60mpg which is insane. But is that the turbo? The computer controlled fuel system? To many variables for me to guess being only a shade tree engineer. Big orange truck is getting 38 mpg tanks with my motor and no turbo now that he got a zf5. And he actually hauls a lot more weight than me.

If you can prove to me a turbo will get me more mpgs in my application I would be stoked. Also, if you had a specific model of turbo to recommend that would be optimized for efficiency not power I would be very great full. My motor had plenty of power for me with the slipping auto trans, I'm sure with the manual I will be even more satisfied with current power.

[oil pan 4]

I saw a 2 to 2.5mpg improvement when I installed a turbocharger.
I put the turbocharger on my engine and changed nothing else beyond the intake and exhaust plumbing. I was also running hot boost.

You have a big high compression IDI kind of like my diesel with the same family of injectors and injector pump as my diesel.

Specific model of turbo for your application?
Big. The biggest cheapest turbo I can think of off the top of my head for your application would be a P-trim T76.
Do not use the OE turbo.

That is what everyone who has a big non turbo diesel says.
I was just like you 5 years ago. I thought my non turbo diesel had plenty of power and didn't think I had any needed for a turbo.
Then when I put the turbo on, I wish I would have done it in 2006 as my first mod.

Read the MPG improvement wiki, I put all my links about studies about turbo chargers increasing fuel mileage in there.

[bondvagabond]

Originally Posted by oil pan 4

I saw a 2 to 2.5mpg improvement when I installed a turbocharger.
I put the turbocharger on my engine and changed nothing else beyond the intake and exhaust plumbing. I was also running hot boost.

Read the MPG improvement wiki, I put all my links about studies about turbo chargers increasing fuel mileage in there.

Believe me, as a semi retired diesel mechanic and big rig driver I have heard similar experiences to yours a lot. I wonder if with the auto trans, the turbo gives it just a bit more pep to keep the torque converter locked up a bit more, you see how even just changing one variable like you did, could have allowed something else to increase the mpg. You did do the intake and exhaust at the same time too, making it even more complex.

What is your take on the EPA data showing a vw 1.6 na diesel getting 9% better mpg than the turbo 1.6? Both 23:1 compression mechanical diesels like ours. Drives me bonkers. Just want to be scientific about my mods, since I am too broke to try everything Edison style, and there is this contradictory data.

As far as progress today, clutch and brake pedals are hung, brake booster removed, so now my clutch mc will fit. I will be changing the factory pedal ratio from 3.18:1 to 5.5:1 to counteract the loss of power assist. Since this is the only thing run by my belt driven vacuum pump other than a vacuum pressure gauge, I will be pulling that as well. It only adds 1/2" to the belt removing the vacuum pump so hopefully the tensioner can take up the slack.

[oil pan 4]

I kept the intake manifold and upper plenum the same. I actually tried to change as little as possible in the change over.
Highway driving it stays in top gear with the converter locked. Not much change there.

Problem with turbo versus non turbo is the OEMs and their cookie cutter one size fits all turbodiesel applications.
The OEM is motivated to put on the smallest cheapest turbo that will get the vehicle sold off the lot. That's great for start stop city driving, bad for highway and towing.
The OEMs have a bad habit of poor execution of great ideas.
When GM started to turbo charge the 6.5L same thing. Fuel economy really didn't improve much. They used a small turbo and crappy intake and exhaust piping.
The only OE part I used for my turbo build was the N/A intake manifold that I altered slightly for use with big turbo piping. I determined that the nonEGR N/A intake manifold gave the best fuel economy after testing 2 of the OE turbo intake manifolds. Everything else was military surplus, aftermarket or stuff I made.

Lets pretend I do not know squat about the old VW diesel. Are we sure they didn't change anything else drive line or fuel injection pump wise?

The old VW diesel is the worse I have ever seen as far as turbo and fuel economy loss.

[bondvagabond]

Now we are getting somewhere. I could see where an aftermarket turbo could be different than a stock. The na 6.9 and 7.3 idi can only handle about 10 psi boost before starting to pop headgaskets from what I've heard. What boost are you running? Is your 6.5 electronic or full mechanical?

Also, someone familiar with these idi's can you confirm that the transmission control modual only controls the trans? The zf6 is not electric except for neutral and reverse sensors. So hopefully I can pull and sell my good e40d control modual if it does nothing else. I know my van has no ECM for the motor.

[oil pan 4]

I run full mechanical.
The block and crank belong to a turbo 6.5L. Everything else is from the old 6.2L.
I run up to 20psi when I go back down to sea level.