[kaisen]

Originally Posted by speeder

It would take 10 years for the diesel to pay for itself if you are going to own each one for 10 years and then drive them into a lake. In the real world, where people keep trucks for a few years and then sell them, you would get most or all of the increased cost back on resale and the only difference would be the money you had tied-up in the equipment while you owned it. I've more than gotten my money back on both of the diesel PU trucks I've owned, they were esentially free with all fuel burned free as well. Try that on an 8 liter gas truck that you drive x-country a couple times and then sell and let me know how it goes.

You know I love diesels (and I know you LOVE diesels), but you're painting with a mighty broad brush in your statements.

Originally Posted by speeder

Between the depreciation and difficulty in selling a HD gas truck, (you really have to give them away), and the massive monthly fuel bill if you tow and/or put miles on it, it's an expensive and joyless ownership experience.

Massive? Another commonly repeated fallacy. Let's assume that you "tow AND put miles on it" -- towing 1000 miles per month. Using Fred's numbers the gas pig at 10 mpg and the diesel at 14 mpg, you'd burn 100 gallons of gasoline (@$3.57 natl avg) and 72 gallons of diesel (@$3.78 natl avg). That's about an $85 difference. Hardly "massive". Yet you paid $10,000 more more to save it.

Again, when using that arguement when referring to hybrids most Pelicans would rip that scenario to shreds.....

Originally Posted by speeder

Torque #s are the only #s that matter on a truck. Diesel engines have deceptively low HP ratings, I'm surprised that you mention them as a comparison.

A very powerful semi engine with 1000 lbs. of torque might only have 350 HP. A Formula one engine has 750 HP. Which one do you think will pull a load of steel beams in a fully-loaded semi over a mountain better? The F-1 engine would probably not be able to move the truck empty on level ground. An extreme example to make my point, I know, but you know all too well that torque #s are the only ones that matter.

Really?

Not

Both horsepower AND torque are important for towing on the freeway. Why do you think a "very powerful semi" has 18 speeds? Think about it. Horsepower is a function of torque, they're related. That semi that makes 1000 lb-ft but only 350 hp only does so because it can't rev high enough to make more horsepower. So it needs lots of gears to keep it in its (relatively) narrow powerband. That's the way diesels work.

So it is with a 7.3L Powerstroke. They make peak torque at 1600 rpm and peak horsepower at 2700 rpm. Redline is 3200 rpm. From 1400 to 2200 rpm torque is strong, staying almost 500 lb-ft. After 2200 rpm they fall off very fast, Under 1200 rpm (no boost) and over 3000 rpm they make less than 400 lb-ft and less than 200hp. So their "effective" powerband is from 1250 rpm to 2550 rpm. Keep them there and they're happy.

Not true of a 8.1L gas motor. They make peak torque at 3200 rpm and peak horsepower at 4200 rpm. Full-throttle shift point is 5200 rpm and redline is 6000 rpm. From 1500 rpm to 3800 rpm torque is strong, staying above 400 lb-ft. After 5000 rpm, they've fallen below 300 lb-ft and a little over 300 horspower, which is why they shift at 4800-5200 rpm WOT. Their "effective" powerband is from 1250 rpm to 4450 rpm.

At 3000 rpm the 8.1L gasser is making 280 hp and 450 lb-ft where the 7.3L Powerstroke is making, well, nothing. It can't spin that fast. At 4000 rpm, the 8.1L is still making 330 hp and 420 lb-ft. By 5000 rpm, both hp/tq are around 300.

By 1500 rpm, the 8.1L gasser starts making more horsepower than the 7.3L PSD. By 2300 rpm it starts making both more torque and horsepower, and continues all the way until 5000 rpm.

What's my point?

It's the area under the curve that counts in a street motor. The breadth of a powerband from low rpm to high rpm, not just peak numbers. Its flexibility. It's ability to pull at both low and high rpms......because neither the Excursion nor Suburban have 18 speeds like a semi.

Getting a load moving and keeping a load moving at speed are two distinctly different things. One takes torque, the other takes horsepower. You can gear for it, but when you only have four gears to choose from an a powerband that's only 1300 rpm wide....

Here's an applied scenario:

Let's say you have a 2003 Suburban and a 2003 Excursion 7.3 PSD
Both trucks have 265/75-16 tires (31.5")
Both trucks have 3.73 differentials

The GM's 4L85E vs Ford's 4R100 transmissions:
1st .. 2.48 .. 2.71
2nd .. 1.48 .. 1.54
3rd .. 1.00 .. 1.00
4th .. .075 .. 0.71

At 70 mph in fourth gear, the Sub will be turning 2100 rpm and the Ex at 2000
At 70 mph in third gear, both will be 2800 rpm (way over PSD power peaks, near redline)
At 70 mph in second gear, the Sub will be 4100 rpm (near peak horsepower) and the Ex at 4300 rpm (WAY over redline -- not possible)

So if you encounter a steep grade while towing at 70 mph, one that requires the extra leverage of 2nd gear the Powerstroke would have to slow down to 50 mph to stay under redline. In 2nd gear the Sub could pull 90 mph and still stay under the 5200 rpm WOT shiftpoint. Really extreme load/hill? The Sub can do over 50 mph in first, where the PSD can't break 30mph.

Whether the Sub has to downshift because it makes less power is largely irrelevant. The point is that it CAN still do the work and maintain 70 mph where the Excursion may run out of steam. It's happiest under 2600 rpm (where it still makes good power)

Remember, at 70 mph (2800 rpm) in third gear the Sub is still making 260 hp and 440 lb-ft. The Excursion 7.3 PSD is only making 185 hp and 320 lb-ft......And it's trying to move an extra 1500 pounds.

Which makes a better tow rig? They can both do the work. The Sub can just do the work faster.

One answer is to add more gears. The "bad" 6.0L got one more gear in the 5R110 (TorqueShift). But wait, the top two gears are the same (1.00 and 0.71), it's the first two/three that vary.

Ah, but guess what? The 6.0L PSD also gained "breadth" to its powerband and a higher redline (4200 rpm fuel cutout).

6.0L PSD = more HORSEPOWER (not important, right Denis?), a little more torque, and 1000 rpm higher redline.... so it can make use of under-driven gears at higher speeds. It can do more work, faster. It's a much better competitor to the 8.1L gasser, as BSiple and Fred Cook pointed out.

Originally Posted by speeder

Driving a nice diesel is a joy in comparison and makes a lot more financial sense if you can afford the initial outlay and don't over-pay like an idiot for it.

^^THIS^^

My point is that some diesels are on the bubble right now.
A 2003 Excursion 7.3 Diesel for $20-30K??? You're overpaying. Period.
Resale-logic on a $1MM home in Las Vegas appeared to be a safe bet at one point too.
The ONLY reason Diesel Excursions are holding that ridiculous value is that they are the ONLY choice if you've talked yourself into a diesel. And people talk themselves into a diesel because they haven't really looked at the data. They simply regurgitate the anecdotal information from their buddies. They don't even look to see that a comparable gas-powered tow rig would be HALF the price.

You can keep your $20-30K Excursion 7.3s

If I were forced (or truly needed, somehow) a factory diesel SUV it would be a 2005 Excursion 6.0L PSD with the coil spring front axle.