The gasserization of the Diesel engine -- PSD, DMX

[Hohn]

Seeing the threads on the PS Fords and the Duramax GMs, I feel that I have to comment on their power ratings, and therefore on HP in general. I will use some generalizations that there are, no doubt, many exceptions to.

The trend that GM and Ford are clearly following (if not leading) is towards a higher-rpm, more gasser-like diesel engine. Rumor has it that Mercedes is working on a diesel that revs easily to 4000 rpm as a passcar motor. That is also the trend in diesels in general as they look at ways to use a diesel in cars to increase efficiency.

The biggest obstacles to marketing a diesel engine are pretty easy to name: noise, smell, and power delivery characteristics. The latter I will term the "fun to drive" factor, based on the marketing dogma that higher rpm means more driver enjoyment.
Manufacturers have addressed the noise and smell, as modern diesels are cleaner than ever. Yet, the sales and demand just aren't there. To wit: the VW TDI. The TDi gets fantastic mileage and has pretty good durability, but sales are still lackluster. Why? It's because it revs slow, and not very high. That means it doesn't feel as much fun to drive (so the marketeers believe).

A dyno does NOT measure HP, it measure torque. Hp is calculated. Tq is what moves the load. How fast you can move it is HP. Said another way, Hp is related to time AND force, while torque is just force. Torque can be multiplied by gearing; HP cannot.

Look at is this way, if I could take the torque of my BONE STOCK ETH up to 4000 rpm, it would make 385 hp!! At 6000 rpm it would be 576 HP!! The only real test of “horsepower” is how fast something can accelerate a known load from pt A to pt B. No, the highest rated HP motor doesn’t always win. There is a flaw in the way HP is measured. By existing standards, you can “gain” hp just by using a lighter flywheel or doing something that lets the motor build revs faster.

Or consider this: if you bombed a 24v motor, and a 12v motor to the exact same HP level, the 12V would have more torque because it generally won't rev as high.

This is why the Diesels from Gm and Ford are V8s. Not only because they can market the 8cylinder engine as an advantage, but because having more cylinders of smaller individual displacement is more appropriate for higher rpm. This is why Formula 1 Engines often have 10 or 12 cylinders even though they are less than 3.5 liters displacement. Those tiny pistons will rev forever into the 12K rpm range and up. BUT they have little power down low—launching the car is tricky without killing it.

A high-rpm, V8 diesel is a step in that direction, although not nearly as extreme. Unfortunately, as you move that direction, you give up some of the main benefits of a diesel to begin with—more low rpm grunt, etc. As Larry Widmer (best gasser engine man I know of—smokey yunick learns from him) likes to say RPM= Ruins People’s Motors.

The way I see it, Ford and Gm aren’t trying to build a better diesel. They are trying to build a better gasser, and using diesel technology to do it. A diesel excels when used on long stroke, big cylinder, lower rpm engine designs (think OTR diesels from Cat, Cummins, and others, as well as RR diesels). The PS and DM motors are running higher RPM and being whipped like a horse on the home stretch. They are moving towards being a racehorse/showhorse. I want a draft horse. The Cummins is just that. It can loaf all day doing the work that the others are giving 100% to do.

If you want to see performance, wait until they mate a high-torque diesel to an Electronic Continuously Variable Transmission (ECVT). It’s a transmission that has a high and low limit for gear ratios, but can achieve any ratio in between.

Until then, I keep my draft horse fed and groomed, knowing he will be good in the long haul.
HOHN


(PS-- I know I talk out my butt sometimes, and will admit wrong when corrected)