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Old 04-29-2010, 07:57 AM
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Diesel VS gas power

OK, this ones for all the mechanical engineers that visit this board and share their education. What is the difference between diesel and gasoline fired engines and why are diesels seemingly more powerful. And of course anyone else that wishes to jump in .....
Bill

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Old 04-29-2010, 08:17 AM
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diesel power

diesel engines run at a higher compression ratio , arounfd 20 to one, and redline at 3000 to 4000 rpm, they produce their power at a lower Rpm and ideal for a truck or tractor. diesel 's run with no air restriction. speed and power are regulated by the fuel injectors vs a throttle on a carb Ps they are hard to start at colder temperatures, diesel is no longer cheaper than gas, even with the off road tax relief. I use the gas power stuff in the winter when I can on the farm, they are easier and you don't have to worry about something not starting when your are 5 miles from the house and it's 20 below.
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Old 04-29-2010, 08:33 AM
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diesels are more efficient which helps, BUT they also run very large amounts of boost. Almost every decent diesel engine made today is turbocharged, so you have more air volume and more static compression. Where they lack is in the burn rate. That is why they are restricted to lower RPM (that and their parts usually weigh significantly more). cylinder head, injection, and piston design are all advancing at a very rapid rate though and the results are what you are seeing with these very driver friendly smaller diesel engines.

15 years ago if you would have thought a 7,000 RPM redline was possible with a diesel people would look at you like you're out of your mind, now its very possible and done in some cases (still fairly rare).

RPM is an issue because as I've tried so hard to explain power is a product of both energy (tq) and the rate at which its applied. 600ftlbs at 2,000 RPM is actually less powerful (and slower) than 300 ftlbs at 6,000 RPM.
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Old 04-29-2010, 08:39 AM
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We all appreciate the efforts made on the thread about torque, this seemed a likely arena for another exchange. What do you suppose the average compression rate is in a diesel and more interesting is how is the fire started.
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Old 04-29-2010, 08:43 AM
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Diesels dominate the Lemans prototype class, especially Audi and lately Peugeot. Audi uses a twin turbo v12 direct injected.
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Old 04-29-2010, 09:28 AM
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diesel>>>>>>>>>>>>>>>>>>>>>gas

a diesel sounds better, smells better, lasts longer, more efficent etc. Its all a matter of opinion, but i love diesels. If i could, my trans am would have a nice powerstroke in it. The 7.3 in particular. They last longer also because the fuel is like a lubricant which is pretty much self explanatory.
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Old 04-29-2010, 09:30 AM
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Quote:
Originally Posted by stroker444
diesel>>>>>>>>>>>>>>>>>>>>>gas

a diesel sounds better, smells better, lasts longer, more efficent etc. Its all a matter of opinion, but i love diesels. If i could, my trans am would have a nice powerstroke in it. The 7.3 in particular. They last longer also because the fuel is like a lubricant which is pretty much self explanatory.
diesel is a solvent, not a lubricant... hence I, and many others, use it to clean parts.
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Old 04-29-2010, 09:33 AM
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Quote:
Originally Posted by ap72
diesel is a solvent, not a lubricant... hence I, and many others, use it to clean parts.
Ill have to disagree... diesel is like keroseen, its an oil basically therefore its a lubricant. Its got more lubricating properties than gasoline.
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Old 04-29-2010, 10:25 AM
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Back to Bill's question....my '02 Powerstroke has a 17:1 comp. ratio, most diesel engines are in the 15-20:1 range. In a nutshell...the compression is what fires the mixture, you mix diesel fuel/air and compress it with a pre-determined ratio, which in turn causes a LOT of heat and you get combustion.

The new Ford built "Scorpion" (Powerstroke) 6.7 is factory rated at 390 hp and 735 lb. ft. of torque.....the 2011 GM Duramax is supposed to have a rating of 395 hp and 760 lbs. ft. of torque. Either one is remarkable and very interesting engineering...to me anyway as they both pass very stringent emmision tests, are very quiet and will get DECENT (???) mileage...so they claim. Time will tell when the 5th wheel folks start using them.
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Old 04-29-2010, 10:28 AM
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Quote:
Originally Posted by stroker444
Ill have to disagree... diesel is like keroseen, its an oil basically therefore its a lubricant. Its got more lubricating properties than gasoline.

no one in their right mind would use either kerosene nor diesel as a lubricant, can you use it, sure, you can use any fluid. Should you? No. It actually dissolves most accepted lubricants (because it is a solvent).
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Old 04-29-2010, 10:38 AM
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Quote:
Originally Posted by ap72
no one in their right mind would use either kerosene nor diesel as a lubricant, can you use it, sure, you can use any fluid. Should you? No. It actually dissolves most accepted lubricants (because it is a solvent).
No one ever said to use the fuel as a lubricant. You have oil in your engine for that and other purposes. The fuel just happens to have lubricating properties which just add to the pluses of a diesel because of the increased longevity of cylinder walls/piston rings. Im not claiming to be a genius, this is just what ive picked up over the years. I had a 99 F250 6 speed for a good while and the fuel was always a slight bit oily. Its going down though because of sulfer reductions.
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Old 04-29-2010, 11:14 AM
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Diesel fuel is part lubricating the engine. Some people run 30% mix kero in extreme cold weather, that know what they are doing. But kerosene has no lubricating structure like diesel fuel.

I like my '99 powerstroke But the '96 460 gasser does good for me too. Its always more money to diagnose and repair diesel engines, drivabilty and electronics. On U.S. built pickup trucks that is.
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Old 04-29-2010, 11:17 AM
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Next question:

Diesel vs. Gas, what smells better at idle?

LOL

Diesel for me
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Old 04-29-2010, 11:35 AM
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Quote:
Originally Posted by stroker444
diesel>>>>>>>>>>>>>>>>>>>>>gas

a diesel sounds better, smells better, lasts longer, more efficent etc. Its all a matter of opinion, but i love diesels. If i could, my trans am would have a nice powerstroke in it. The 7.3 in particular. They last longer also because the fuel is like a lubricant which is pretty much self explanatory.
Duramax in a Chevelle, 950 hp and 1700 lb-ft of torque...and 32mpg.
http://www.popularhotrodding.com/fea...sel/index.html
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Old 04-29-2010, 12:22 PM
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Quote:
Originally Posted by stroker444
No one ever said to use the fuel as a lubricant. You have oil in your engine for that and other purposes. The fuel just happens to have lubricating properties which just add to the pluses of a diesel because of the increased longevity of cylinder walls/piston rings. Im not claiming to be a genius, this is just what ive picked up over the years. I had a 99 F250 6 speed for a good while and the fuel was always a slight bit oily. Its going down though because of sulfer reductions.

It does have lubricating properties, but so does water. If you really want to have upper cylinder lube, run MMO in your tank.
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