Mistaken ideas about how a diesel engine works

Turtle n Peeps wrote:

ShinerBock wrote:

Adam R wrote:

RinconVTR wrote:
A C&D mag not long ago showed cars/trucks from 20 years ago compared to now. Time and time again, HP/TQ we vastly increased, and MPG was flat-lined.

Diesels pre-2006 we mostly true diesels and could deliver good power with good fuel economy. Today they deal with tough emission standards and have a scary and costly array of components to scrub and chemically clean what comes out the tail pipe. It's insane, and it doesn't result in loss of power exactly, it results in less fuel economy. They might beat gassers still, but the gap has closed drastically as I'm seeing real world towing reports that average only 10% better than gas, if that. Then enter the debate of cost to own.

Regarding MPG of various HP motors...first of all no one is using all available power unless they are WOT. Which SO many people are afraid to do, for fear they are hurting their motor. I am not afraid of WOT.

For more than 2 seasons each, I towed the very same aero shape TT weighing 4300lbs loaded, with a Honda Pilot and Toyota Sequoia.

The Pilot has a 3.5L V6 and the Sequoia a 5.7L V8. Roughly 250hp (Gen2 Pilot) vs 380hp.

They both returned the VERY SAME MPG AVERAGE while towing.

Not towing, I would commonly see 20-22mpg. The Sequoia I commonly see 15-16mpg.

Yep, good comparison and more inline with what I've been trying to get the point across. Comparing the 3.0 Eco to a modern 6.7, I would agree the 3.0 Eco would get slightly better mileage than the 6.7 in the same pickup if placed in a 3500 MC, until you put a huge load behind it. The 3.0 does not have any margin for carrying or moving loads at the upper end of a 3500's rated capabilities. The 3.0 is better optimized for smaller loads and commuting duties, but you cannot expect it to safely pull an 18,000 lb trailer which requires more HP, a heavier chassis, etc.

For another mileage comparison, I have a 1984 Toyota 2L (2.4L)diesel 4x4 pickup. It came NA and returned a whopping 20-21 mpg. I grafted a turbo and intercooler onto it, cranked up it's fuel screw and doubled it's rated hp output (21 lbs of boost) to achieve 28 mpg on the highway. This is 1984 technology mind you and since I've been driving it for 21 years, I'm pretty familiar with it. I now drive a 2007 Ford S-Max 1.725L turbo diesel and I get 40-42 mpg which is a little disappointing since the S-max is far lighter, smaller and much more aerodynamic than my clapped out Toyota. This all goes to say that other than exhaust cleaning advances, I would say the technology to burn fuel has not grown by leaps and bounds. A little yes, but not a lot.

Actually the loaded and unloaded testing of the two engines like RinconVTR is saying has already been done a few years ago by Truck Trend. They did a 500 mile test loop both unloaded with the Ecodiesel netting 28.47 mpg and the Cummins 19.97. That is in no way shape or form a slight difference in mpg.

Then they loaded up the same 7,020 lbs up to both trucks on a 260 mile test loop. The Ecodiesel did struggle a bit and lost speed going up a 7% grade, but it returned 19.46 mpg. The Cummins of course did not struggle one bit pulling it with ease, and it returned 15.82 mpg.

2014 Ram 1500 EcoDiesel vs. 2014 Ram 2500 - Sibling Rivalry

All of that energy (fuel) is being used up by the drive train. It takes a lot of energy to turn a super heavy crankshaft and torque converter and tranny internals and super big and heavy drive shaft and rear end gears and on it goes...........They need that super heavy crankshaft and everything in back of it to keep the duty cycle up. Can you make 450 HP from the 3.0? Sure! But the duty cycle would go to hell and it would no longer be a HD pickup.