PSD vs IDI fuel economy

[Rusgo]

Been reading around about ways to improve fuel economy. Couple things I keep coming across.

Direct injection diesels are said to be 10% more efficient than indirect injection. Something about flame propagation spreading more evenly and completely during the combustion process.

Add in another 5% efficiency for modern fuel delivery metering strategies. No smoke or haziness makes for better economy.

Most guys in newer diesel trucks are getting 14 to 19 mpg, in 4wd platforms and depending on driving conditions.

They're getting 10 to 14 mpg when towing 10k to 15k pounds.

Seems about the same as a good running IDI?

Do the newer rigs just weigh so much that there is no improvement in how far they can drive?

Sent from my SM-G975U using Tapatalk

 

[Rusgo]

Possible way of solving the flame propagation issue in IDIs..
https://www.sciencedirect.com/science/article/pii/S0360319918310085

https://www.popularmechanics.com/cars/car-technology/amp19609371/ultra-low-emissions-diesel-hydrogen

Sent from my SM-G975U using Tapatalk

 

[riphip]

It will cost you more $$ than the extra mileage is worth + extra unwanted heat in the cylinders.

 

[Cubey]

More gears and OD makes a difference in MPG. Many, if not most, IDIs with A/T have the 3 speed C6 with no OD.

It seems that mid-2000s F350s (presumably F250s too) have 5 speed A/T. That's a HUGE difference when you think about the engine RPMs required to stay at highway speed in 3rd gear vs 4th or 5th gear.

 

[Rusgo]

35" tires cost me more than the mileage is worth too, haha. The time doing all these upgrades cost me a ton not working for somebody else. Sometimes its just about tinkering and making things tough and better. Even so, I think there is actual cost savings potential if setup right.

The guys doing these tests are not talking about a large percentage of hydrogen relative to diesel. Talking in terms of single litres per minute, which in gaseous form isn't much extra energy.

And extra fuel alway adds heat. Kinda the point? There are ways to offset it.

Sent from my SM-G975U using Tapatalk

 

[Rusgo]

More gears and OD makes a difference in MPG. Many, if not most, IDIs with A/T have the 3 speed C6 with no OD.

It seems that mid-2000s F350s (presumably F250s too) have 5 speed A/T. That's a HUGE difference when you think about the engine RPMs required to stay at highway speed in 3rd gear vs 4th or 5th gear.

That's what I'm saying, the modern stuff should get better gas mileage but it doesnt.

IDIs get 15 o 19 mpg all day long. Even some 2wd setups with a zf5 push into the mid 20s.

Sent from my SM-G975U using Tapatalk

 

[Cubey]

That's what I'm saying, the modern stuff should get better gas mileage but it doesnt.

IDIs get 15 o 19 mpg all day long. Even some 2wd setups with a zf5 push into the mid 20s.

Eh, my F250 gets about 15 max highway without towing with a C6 and 3.55.

The motorhome, with probably true 72k original miles (just hit 72k today) gets single digits with a C6 and 4.10. I say probably true 72k because it burns very little oil compared to the F250, which I'm sure is in the 200k range, but it could be 100k.

Maybe $1000 for a new IP and injectors would give a few more MPG but there is no guarantee of it either.

 

[Rusgo]

Yeah the C6 is an mpg killer ****. Put that in a super duty and see what mileage they get. So with a tranny and maintenance you're right there with newer diesels. I'm at 17 to 18 pretty regularly with the zf5.

Sent from my SM-G975U using Tapatalk

 

[nelstomlinson]

I have a crewcab '97 F350 powersmoke with the e4od, and a crewcab '94 F350 IDI with the e4od. They both have stock tires and both have the same 4.1 rear end. Same body style, same weight, same everything. They both get about 14 to 16 mpg. The '94 is pretty worn out, the '97 is just starting to burn a couple quarts between oil changes.

With the direct injection design, the fancy computer and the fancy electronic injection, the powersmoke should get significantly better mileage than the old, worn out IDI. It doesn't.

 

[u2slow]

I found a noticeable hit in economy going from 89-94 IDI 5spd trucks to PSDs (95 5spd & 97 auto).

Efficiency is often a red-herring. The context is usually the percentage of fuel burned (vs tailpipe soot), not about how little it uses.

 

[mexicanjoe]

Heck I get 15 mpg with a 5 speed ZF5 and 4.10 gears on flat West Texas desert roads.. often times with a either a headwind or tailwind......

 

[firehonomichl]

My 89 f250 with the ZF5 gets around 16-18 in town but I don’t drive it hard and I have my pump tuned.

 

[Golden Helmet]

This isn't so much for IDI vs PSD, just old diesel MPG vs new diesel MPG.

My theory for why the newer diesels get roughly the same MPG as ours is the power they make. Yeah, they're also heavier and they have the emissions BS added to them, but I don't think that matters as much, especially when you factor in the absurd amount of gears modern transmissions have.

Our IDI engines, new, made about what, 180 HP at the crank? The new 6.7's are making 450+. Same MPG, slightly lower displacement, but well over double the actual power. My line of thinking is if they de-tuned them down to our IDI's level, then you might be seeing 25+ MPG out of them.

That's my completely uneducated, bored-at-work theory, but i'm curious to find out why i'm wrong

 

[Garbage_Mechan]

Well I’m going to test that theory in reverse I guess.... my 7.3 Powerstroke used to get 16-19 mpg. The new engine going in was broken in on the dyno and pulled a smoke free 460 hp and 1,000 ft lbs, pretty much matching a new 6.7. Once we get used to it and settle down we will see if we can hit 20. It’s wind resistance, rolling resistance and friction loss plus accelerating mass that all add up. A lot of development in 20+ years

 

[kuskoal]

You need to also look at compression ratio under naturally aspirated conditions. Our engines have a super high 22.5:1 and came n/a for most of it's career. Off the turbo, these engines are designed to turn peak torque at 1400 rpm, 200 rpm lower than the 5.9 Cummins. Higher static compression can extract more power from the fuel, but we also kind of need it to run with the pre-chamber.

Direct injected diesels range from 17.5 to 14? In the new Duramax. As the compression ratio gets smaller, you can add more boost! Adding more boost cleans up NOx and other emissions related to Rudolf's original design of 50:1 compression.

With boost, comes fuel. The more air you got, the more fuel you can burn! The big 3 diesel engines rely 100% on boost to do anything. Where ours kind of putz around towing stuff. We don't have boost, we don't have electronics, we don't have high pressure injectors, we have compression!

Fwiw, the IDI was rated at higher HP and torque than the Cummins when it came out. Anecdotal evidence is the IDI is more powerful than the 7.3 PSD. My giant 4 door bronco on 37's and a gen 2 banks turbo out ran my dad's 2002 Excursion. We really scratched our heads at that when my pump was tuned to never even touch 1000* in Reno, which is about 4000' elevation.