****PLEASE READ CAREFULLY***THIS SHOULD PUT AN END TO ALL THE ARGUING***

I've seen discussions like these over and over. What always happens is that people compare diesel and gasoline engines in different contexts and the diesel usually wins. However, you should understand that anyone who plunks down an extra $5,000 for a diesel will have a long list of justifications. In reality, compared head to head, the diesel pulls no better than the gasoline engine although it will last longer.

I've seen articles written time and again where someone insists that torque is much more important than horsepower. This is actually wrong. In fact, a simple comparison of the manufacturers specs clearly shows that a 190HP diesel with 420ftlbs of torque is nearly identical to the performance of a 195HP diesel with 555ftlbs of torque. If the torque theory were correct then the second engine should be much better; it isn't.

The second notion is that a diesel is strong enough to pull a big load up hills that a gasoline engine won't. This is wrong too. HP is always the deciding factor. Low HP is low HP whether it is with gasoline or diesel.

The reason these comparisons are typically wrong is that people overlook the gearing. A diesel develops torque at low rpm whereas gasoline engines rev higher. Yet, time and again people will compare a diesel and gasoline engine with nearly the same gear ratio. This is wrong. To get similar performance, the gasoline engine always has to be geared higher. If a diesel has a 3.7 axel then the gasoline engine will need 4.88 (not 3.9, 4.1 or 4.3). A gasoline engine with a 5.38 is about equal to a diesel with a 4.1. However, you will find that the gasoline engines are typically geared too low both because higher gearing will decrease gas mileage even further and also because higher gearing lowers acceleration. Don't compare a gasoline and diesel with the same gearing; the diesel will win everytime.

The second reason that these comparison fail is because diesels also have a more limited power range. This limited range forces the transmission to have more gears to cover the same speed range. However, this also gives an advantage to the diesel because it will always be running closer to its best torque. I had experience towing with a V8 gasoline engine with a 4 speed OD automatic where 2nd gear had more than enough power but 3rd didn't have enough when climbing hills. Don't compare a 4 speed gasoline with a 5 speed diesel or a 5 speed gasoline with a 6 speed diesel; the diesel will win. More gears are better.

Will the V10 pull your travel trailer? Yes, it will. Be sure to get these two options:

Transmission: HD 6-Speed Manual w/OD
Limited Slip w/5.38 Axle Ratio

The F550 V10 with 5.38 axel will tow a maximum of 18,500lbs which is the same as the diesel with 4.88 axel. The V10 with 4.88 axel tows 2,000lbs less.

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Now, let's get to the real issues and avoid the armchair engineering and ego based preferences.

Downhill drag. The gasoline engine wins easily. When going downhill, you can always shift down to get engine braking with a gasoline engine. Unfortunately, this doesn't work with diesel because diesels have much lower cranking resistance. The diesel requires an exhaust brake to match the downhill braking of a gasoline engine. Because downhill braking is trickier with a diesel, the 5 speed auto with tow haul is preferred to the 6 speed manual. For gasoline, the manual should be fine.

Long haul. A diesel lasts longer because it is built heavier and turns at a slower rpm. A gasoline engine is usually good for 100,000 whereas a diesel can easily last 300,000. If you are driving long distances and racking up miles, diesel is better. If you are driving to local parks and not using the truck for much else, gasoline is fine.

Mountains. A diesel is turbocharged and keeps higher power at altitude. If you will be driving at higher than 4,000 feet above sea level, the diesel will do better.

Mileage. A diesel gets better gas mileage. Figure 6-8mpg with the V10 when towing a heavy load whereas you'll get 10-12mpg with diesel. This is similar to wear. The more miles you put on your vehicle per year, the better diesel looks.

Cold weather starting. No comparison. The diesel requires an oil pan heater that is plugged into 110AC to keep the engine warm. This is only a factor if you will be parking in cold weather (below 20 degrees F) with no electricity.

Resale value. Diesel wins. The diesel retains more of its value when you sell. However, for 4 years/40,000 miles the diesel will still cost more. Longer than this or more miles tends to favor the diesel.

So, can the V10 pull your trailer. Yes. Will the V10 drive more like a regular pickup truck? Yes, if you get a 4.88 axel and 4 speed auto, however, it won't have the pulling power when going uphill. If you get the 5.83 axel and 6 speed OD manual then it will pull and pull well, but don't expect to win any drag races. Also check if you can get dual tanks for gasoline and try not to wince when you fill up.

Although the V10 5.83 is rated at 18,500lbs, this number is not quite as good as the diesel's 18,000. Basically, the gasoline engine won't last as long if run close to maximum rating. So, if you really plan to pull more than 16,000lbs, get the diesel. If you don't like to shift gears then definitely get the diesel with 5 speed auto and tow haul feature.

 

i kind of shot through you post, i am not in the mod to read it all right now. one thing that i noticed was you claimed a diesel needs to be plugged in to start under 20*. i personally started mine, not plugged in, and the temp on the overhead was -8*

 

You are right that you can't tell how strong a vehicle is just by the HP or Torque rating. You need the rpm of the ratings. A simple example is consider two trucks pulling up a hill at the same road speed. One has a diesel making 600 ftlbs of torque and geared to run at 1600 rpm. The other truck with a gas engine is geared to run at 3200 RPM. The gas engine only needs to make half the torque or 300 ftlbs to put equal torque to the rear wheels.

 

I usually don't reply to topics like this, but before it turns into a flame fest, I'd like to clarify a few things.

Torque is the rotating factor, producing rotation. Diesel engines are designed for more torque because of the longer stroke of the piston compared to that of a gas engine. You have more rotating power produced off the crank with a diesel than a gas engine. Looking at basic physics, this equates to more pulling power available at the rear wheels. Compare a V10 to a 6.0 or 7.3L PSD, and the torque numbers for both are extremely high which is why both engines pull very well (V10 gets power from its large displacement). Compare the 5.4L to the V10 or a diesel, and the numbers aren't even close. Which is why the lower output of a smaller gas or even a smaller or low power (non turbo) diesel cannot match in towing strengh. Take your 195 HP comparison and mate that to a 6 cylinder gas engine that produces 195 lbs of torque and then try and tow something. Now take a 6 cylinder Cummins (yes I said a dirty word) with loads more torque and you'll see why torque IS a determining factor when towing.

Take a second look at that. With higher gearing on a gas engine, the engine must work harder (higher rpm's) than a diesel to produce the same output. This results in less efficiency from a gas engine, and like you said "decrease gas milage even further".

More gears are better whether gas or diesel to keep the engine in the desired rpm range. You said that diesels have limited power range, but that is only because they run at much lower rpm limits than a gas engine. They run at lower rpm's because of the longer piston stroke, so this is not a limited power range when you look at the actual power curve. Gas engines have more of a peak, where as a diesel has a flat power curve. Diesels produce so much power at a low rpm range because of the longer stroke and the fact that diesel has more energy per gallon that gas.

And it does a very good job of it.

Exhaust braking is used as an option for some because it is a readily available kit for diesel engines. This spares the brakes and keeps them from overheating when going down long, steep grades. Diesels have a much higher compression ratio than a gas engine, and because of the longer stroke, they actually have a much higher cranking resistance. The longer the stroke, the more load on the crankshaft, piston, and connecting rod providing even more resistance. So in essence, diesels will actually "engine brake" better than a gas engine. I've tried this myself, and when I can smell the overheating brakes from Hondas and Buicks going downhill, while I hold gear and engine brake downhill, I get a nice grin on my face.

I'm laughing deep down inside.

Put a turbo or supercharger on a gas engine and you get the same effect. Diesels today are turbocharged to burn fuel more efficiently. They need large quantities of air to run efficiently, and natural aspiration is not enough. Air is metered differently in a gas engine compared to a diesel. When you turbocharge a gas engine, it requires more fuel or the air/fuel mixture runs too lean. A diesel can gulp much more air without requiring nearly as much fuel.

Diesels have no spark plugs. They require heat and compression. Also, you can crank below 0 degrees F without a block heater. Cold temps are not really much of a problem for most diesel owners. Just remember, in extremely cold climates, even gas engines have a hard time starting too.


I'm extremely tired writing this, and I can't believe I actually replied. I just wanted to clarify a few things in this post. I'm sure this thread will turn into some kind of flame fest. Have fun with it folks. But just remember, both gas and diesel engines do their jobs and do it well. One clatters, the other sucks down the dino juice.

 

Very well put "pocket". After driving an PSD for the Last 6 years, I don't have a problem at all with switching over to a V10.

 

Oh yeah, I just went back and looked at my post. I'm dead tired and I'm sure I left plenty of stuff out, and goofed up on my replies, BUT I'M TOO TIRED AND LAZY TO FIX IT. Have fun discussing.

 

My reason for going with a V10 gas (used)was simple. It was less expensive and I don't put much mileage on in a year. I use it to tow a horse trailer from time to time. I'll be lucky if I go 15k in a year. If I was putting 70-90k on a year, I believe a diesel would be better. Bottom line, if you're not putting alot of mileage on, gas is a better choice.

 

i guess it depends on you cash flow.i only put on 3,000 miles a year on my diesel 's. my work is not that far .i don't have a problem with cold starting. we get some serious snow here in buffalo it's nice to plow a pile of snow as high as my hood from a dead stop.the gas trucks are not even in the same ballpark.i will NEVER buy another gas truck again. at the very least i like the diesel smell and noise. as far as im concern diesel is the only way to go.

 

You forgot to mention the cost of maintaining a Diesel is higher as well as the cost of fuel. That being said, I will keep my PSD.

 

More torque doesnt matter? Someone better call CAT Cummins Detroit Navistar etc. etc., The engines they make that produce 400hp and 1800ft.lbs. of torque (for example) that are used to pull up to 80,000lbs. are are going about it all wrong because a cheaper gas motor can do that. ???????????????????????? Come back down to Earth
Exactly where did your truth come from?

 

A Diesel produces more torque, ergo, more power. James Watt (yeah, the steam engine dude) developed the formula for horsepower so laymen of the time could relate it to something they were familier with. HP= torque x rpm/5150. Horsepower is an imaginary value. He could have used torque x the mass of Jupiter/1776. Torque is the force of work being done. Just read a physics book. Sorry to shoot you down. I own a v-10, by the way.

 

THE TRUTH CAME FROM ME! lets keep the conversation on sd trucks not tractors and semis, that waht Im talking bout. The bottom line is that gears is what make the difference when i come to gas vs diesel. The analogy about the gasser lasting about 100,000 miles vs diesel 300,00 miles is asuming that you tow all day every day a huge load up and down hills. 100 degree weather -10 degree weather and so on. You come back down to earth and kepp the topic where its supposed to be . on sd trucks!! (v10 and PSD)

 

Yeh, nothin like that eye burning, lingering haze, choking smell of a freshly started diesel at 6:00 in the morning when it's 20 below just so you can drive it 10 mins to work with no load. oh yeh forgot about that wonderfull smell on your hands from fueling up at truck stops. Man do I love the diesel.

Amen to that - I'll Keep my gas suckin V10, especially for the 8,000 miles a year it actually gets used.

To all their own, drive what you like and what you want - lots of people drive chevy and dodge pickups not because they are better but its what they think they want in their dillusional head.

This will be the last time I post to one of these discussions - nothin gets solved and there were at least 5 threads started on this same topic within the last week. We all need somthing more productive to do; obviously.

Happy thanksgiving.

 

All of those old theories cant compare to todays technologies, things have changed quite a bit. As with anything time brings a change.

 

hmmm..........