Why do diesel's last longer then a gasser????

[IndyIan]

Here's a link about Audi's diesel LeMans car. It runs about 5000rpm although that may be limited by the restricter plate. Pretty cool car though.
http://en.wikipedia.org/wiki/Audi_R10

I'm also with Jumper, a 2.5-3.0L diesel in a midsize pick up would be a no brainer for me as well.
Ian

 

[460magnumMOD]

Just figured I'd try and get this one going again. A diesel doesn't start paying you back until after 100,000 miles. Also they take longer to break in. you can notice an improvement in mileage, NOT a decline from 20,000 to 60 or 70,000 miles. When the miles gets up in a gasser the mpg usually starts a slow decline. When a diesel engine reaches top dead center the air temp in the cylinder is 1,000 degrees plus. The diesel is then injected in a fine mist where it combusts and does a slow burn, pushing the piston down rather than slapping the top of it like gas engines. Also the cylinder temp in a gas engine at ignition is about half of pre injection temp. in the diesel engine. Exhaust gas temp on a diesel is much higher than a gas because of that. That is also the main reason for turbos. Cramming in more cool dense air will lower egt's. And the 6500 rpm cummins with stock internals???? C'mon, that is about a far fetched as they come. I've seen connecting rods blow off oil pans 1000 rpm lower than that many times. I can however see that in a built powerstroke or dirtysmack. inlines just don't turn high number like that. The internals are just far too heavy. Diesels are just a long lasting, efficient workhorse. Torque is the main thing for diesels. That equals pulling power.

 

[pdqdl]

There seems to be some misunderstanding about why they are built the way they are.

The fundamental reason for a long stroke in a diesel is that the slow burning fuel needs time to burn to the bottom of the stroke. Having a long stroke makes it easier to engineer the engine for the necessary compression to cause ignition, and helps give it more efficient combustion.

One of the basic concepts to engine efficiency [thermodynamics] is that to increase efficiency of an engine, it is necessary to increase the temperature difference between the combustion temperature and the exhaust gas temperature. Modern gas engines are getting better fuel economy (among other methods) by making the engines run hotter, thereby increasing the difference between the combustion temperature and the exhaust gas temperature. The improvement in materials used in engines has made this possible without destroying the engines.

This is also the basis for using turbochargers and superchargers on engines: pack in more air, increase the amount of heat released by making the "burn" more efficient, then try to convert as much of the heat into engine horsepower as possible.

Back to diesels: by burning to the bottom of the long stroke, they capture more of the energy from the fuel, and get better power out of the available fuel; which incidentally, contains more heat-energy than does gasoline.

The higher torque that comes off a diesel is the result of engineering around a longer stroke: the only way to give a longer stroke (for any given piston size) is to give the crankshaft a longer throw. This translates directly to more leverage on the crank when the diesel explodes against the piston. That long stroke also requires a bit more sense about how fast to turn the engine: Turn it too fast, and the acceleration changes in the piston, rod, and crankshaft start to exceed the capacity of the metals to stay together. KLUNK! time for a new engine!

 

[glenn31792]

w4h
Holy cr@p!!! What sort of stroke has a cummins got? I wonder what the piston speed would be at 6500 rpm.


I thought the same thing S= 4.72 in

5000 rpm piston speed 3916
6000 rpm 4700
6500 rpm 5113

 

[motoroilmccall]

When i was in college, a kid there had a pulling truck with a 5.9 24 valve. The engine block and internals were all stock and it could turn 6500 rpm. Now i admit it had a HUGE turbo on it, injectors etc. That thing sucked so much fuel at 5000 rpm + that he had to run two fuel pumps on it to keep it from starving under a pull.

No stock Cummins can turn that many RPM's, doesn't matter how big a turbo, injectors, IP, or whatever he's running. Anywhere past 3300RPM you run the risk of floating valves. Anything over 4k will blow the valves without question. Anything over 5k and your talking full head studs, o-ringed head (much better off with fire-rings), fly cut pistons, main bearing cap studs, connecting rod studs (and billet wrist pins and connecting rods), timing in the 24-28* range, and a turbo so big you'd never get it to spool on the street.

If this was a street truck there's no point in spinning past 4k RPM, you just can't make efficient horsepower or torque above that. Even drag race Cummins engine don't spin to 6500RPM (About 6200 is the limit so far), there's just no point to it on the street.

On the track or sled pull lane, guys do turn 6000rpm, usually with a big single turbo, fly cut pistons, moly rods, heads so extreme you wouldn't recognize them, studded mains, caps, and heads, and a P-Pump... No 24v is gonna have enough injection pressure or flow capability to run over 5000k rpm, and they don't use governor springs either, they're all electronic. And WTF do you mean he had to run 2 fuel pumps on it? Lift Pumps? They'll feed enough fuel for it sure, but the Injector pump can't flow that much fuel, it can't even flow enough to spin past 5000 rpm. Was he running 2 IP's? Impossible, 24V truck (except CR's) use individual injector lines to the IP, so you can't piggyback 2 VP-44 pumps, unlike the CP3's the Common Rail Dodge and GM's use.

My old 12V spins up to 4k rpm, but I have governor springs in it, head studs, a marine headgasket, 60lb valve springs, and enough other parts to maintain durability at those extreme loads.