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



## Pcoz88 (Dec 20, 2007)

Or is it just a myth?? Why should I buy a diesel?How about maintance?:jawdrop: :jawdrop:


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## wood4heat (Dec 20, 2007)

They turn half the rpm's, hold three times the oil and are built far heavier but cost twice as much to replace or fix. With the price of diesel right now I'm not sure they're a bargain anyway, unless of course you have something substantial to pull.


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## DarylB (Dec 21, 2007)

Maintenance costs are a bit higher due to that fact that you MUST change the fuel filter on a regular basis, unlike a gasser. They usually hold 2x or 3x as much oil per change, but you can go 2-3 times longer between changes so the oil change is a moot point for comparason reasons. 

Diesel usually costs more up front on new vehicles but pay for themselves over time. I'm on my 2nd diesel pickup and will never go back to gasoline for a truck application - real world mileage for me is nearly 50% better with a diesel in a 7000lb pickup. Like Wood4Heat said above, they turn lower RPMS and are designed for Heavy Duty usage which is why their longevity is greater than a gasser.


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## romeo (Dec 21, 2007)

Another reason is that they generate far less heat, even when turbo charged. Plus a slower explosion rate in the combustion chamber.


I often wonder why they don't have more diesel choices in cars.


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## wood4heat (Dec 21, 2007)

romeo said:


> Another reason is that they generate far less heat, even when turbo charged. Plus a slower explosion rate in the combustion chamber.



I thought diesel burned hot.


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## Freakingstang (Dec 21, 2007)

wood4heat said:


> I thought diesel burned hot.



The combustion temp is hot, as it has to ignite, because there is no secondary force to burn the fuel (spark), but overall they run cooler.

They also have a lot more material in the castings to disapate heat better. A typical 3/4 ton or 1 ton diesel engine weighs 800-1000lbs more than a gas counterpart.

They are built to work, the older powerstrokes and cummins don't like being baby'd around, they need worked to run efficiently.


The lower rpm applies to the older school diesels, but the newer stuff is turning more RPM than any diesels of older vintage. Look at the Duramax, it spins quite a bit higher (almost 2 times a cummins)


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## Peacock (Dec 21, 2007)

Get ready for a diesel Honda Accord next year.

Diesels are for the most part quite a bit more fuel efficient than gassers. The newest wave of light duty diesels are saddled with some pretty invasive emission equipment. Particulate filters, EGR valves and coolers, oxygen sensors and cats.


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## spacemule (Dec 21, 2007)

romeo said:


> I often wonder why they don't have more diesel choices in cars.



Emissions. Also, I think Americans weren't formerly interested in diesels cause we've had cheap gas for so long. Efficiency was not a priority in the 90's.


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## DarylB (Dec 21, 2007)

spacemule said:


> Emissions. Also, I think Americans weren't formerly interested in diesels cause we've had cheap gas for so long. Efficiency was not a priority in the 90's.



QFT. The new honda diesel will be nice. EGR valves on a diesel is just pure ignorance. It's just something to make you have to change your oil sooner b/c of the soot.


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## DarylB (Dec 21, 2007)

Freakingstang said:


> The lower rpm applies to the older school diesels, but the newer stuff is turning more RPM than any diesels of older vintage. Look at the Duramax, it spins quite a bit higher (almost 2 times a cummins)



Not true necessarily. Most of the older cummins were goverend @2500rpms, but capable up to 4000 if you change the governor spring. Most of the ligh-truck diesels now spin up to +3k. The Kodiak's etc are still goverend @ aro9und 2500RPM's on the D-max. The Big cummins' and Semi-Tractor engines run at even less rpms since they have many, many more gears than a regular pickup.


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## Peacock (Dec 21, 2007)

DarylB said:


> QFT. The new honda diesel will be nice. EGR valves on a diesel is just pure ignorance. It's just something to make you have to change your oil sooner b/c of the soot.



EGR is one of the only ways to get the NOX emissions down to a reasonable level. They even use EGR cooler to lower the temp of the inert gas further.

The soot levels of modern diesels are pretty low. As far as I know, all the current new diesels call for low ash oil and using anything else will clog the DPF in short order.

I've got a diesel myself, even if it isn't a truck. It uses far less fuel than the competitors gas engines and it's a Kubota, so it should be running for a long time.


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## TDunk (Dec 21, 2007)

The combustion temp. is far hotter than a gasser because they use compression to ignite the fuel. Most gassers have a 8.5:1 comp. ratio, most "small block" diesels are anywhere from 17-22:1, that's alot of heat, but they HATE heat. Hence the larger radiator,large coolant passages,oil cooler,oil capcity,piston coolers,etc. With diesels, they really don't care about weight, so they over build them to take the abuse. If your pulling alot of weight or driving real far i might consider a diesel. But if you drive 5 min. to work then no i'd stay with a gasser. Diesels don't like short trips. Maintance defintely costs more. The filters cost more, the oil costs more and you have to do it just as often as a gasser. If you have the nead for a diesel, don't hesitate. If you not sure if you nead one, then i'd prolly stick with gas.


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## TDunk (Dec 21, 2007)

DarylB said:


> Not true necessarily. Most of the older cummins were goverend @2500rpms, but capable up to 4000 if you change the governor spring.



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.


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## Peacock (Dec 21, 2007)

TDunk said:


> 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.



I'd be willing to bet it was pretty inefficient at that rpm. The biggest reason why diesels don't turn more rpm is because there simply enough time to heat the fuel to the point of combustion.

I've talked to a few of Honda's engineers and they are completely against diesels. It goes against Honda's long line of lightweight, high revving, quiet gassers. They spent quite awhile trying to get the things to rev beyond 5k with any efficiency, but they couldn't. I guess the gains in fuel economy are worth it though....


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## wood4heat (Dec 21, 2007)

TDunk said:


> 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.



Holy [email protected]!!! What sort of stroke has a cummins got? I wonder what the piston speed would be at 6500 rpm. 

I have a buddy that built a Honda CRX drag car. He's running a Honda B-16 V-Tech four cylinder with 28lbs boost on a stock crank. Runs low 10's in the 1/4 at 140mph. He also runs two fuel pumps.


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## wood4heat (Dec 21, 2007)

Peacock said:


> I'd be willing to bet it was pretty inefficient at that rpm. The biggest reason why diesels don't turn more rpm is because there simply enough time to heat the fuel to the point of combustion.
> 
> I've talked to a few of Honda's engineers and they are completely against diesels. It goes against Honda's long line of lightweight, high revving, quiet gassers. They spent quite awhile trying to get the things to rev beyond 5k with any efficiency, but they couldn't. I guess the gains in fuel economy are worth it though....



I wonder if multiple glow plugs or some sort of auxiliary ignition source would have improved things. How did you come to talk with Honda engineers?

edit: never mind that last part, I just looked at your profile.


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## Peacock (Dec 21, 2007)

wood4heat said:


> I wonder if multiple glow plugs or some sort of auxiliary ignition source would have improved things. How did you come to talk with Honda engineers?
> 
> edit: never mind that last part, I just looked at your profile.



I don't think glow plugs would help at all. The piston is likely hotter at that point than the glow plugs anyways. The problem is that the cool fuel is coming so fast that there just isn't time to heat the fuel to the point of combustion. You gotta figure that at 5000rpm each cylinder is firing at the rate of roughly 40 times per second.


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## wood4heat (Dec 21, 2007)

Peacock said:


> I don't think glow plugs would help at all. The piston is likely hotter at that point than the glow plugs anyways. The problem is that the cool fuel is coming so fast that there just isn't time to heat the fuel to the point of combustion. You gotta figure that at 5000rpm each cylinder is firing at the rate of roughly 40 times per second.



Ok how about an inline preheater? I know Honda probably already figured all this out I'm just curious.


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## Peacock (Dec 21, 2007)

wood4heat said:


> Ok how about an inline preheater? I know Honda probably already figured all this out I'm just curious.




Like a fuel heater? Ford used these on the old 7.3 and 6.9. Only used for cold start. I guess the Big 3 never had a reason for a high revving diesel, so they never tried it. 

Most diesels have no reason to rev high. They produce so much torque at low rpm that they don't need to rev high. Most pullers only run so much rpm to build as much energy before releasing the clutch. I've got friends that tractor pull with a small block Deere and they leave the line a good 2,000 rpm more than the run during the pull.


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## DarylB (Dec 21, 2007)

TDunk said:


> 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.



I'll buy the 5k and dual pumps, but not 6500rpms... Stock internals? I dont think so Tim.


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## DarylB (Dec 21, 2007)

Peacock said:


> EGR is one of the only ways to get the NOX emissions down to a reasonable level. They even use EGR cooler to lower the temp of the inert gas further.
> 
> The soot levels of modern diesels are pretty low. As far as I know, all the current new diesels call for low ash oil and using anything else will clog the DPF in short order.
> 
> I've got a diesel myself, even if it isn't a truck. It uses far less fuel than the competitors gas engines and it's a Kubota, so it should be running for a long time.




Slick ride. Lots of those things down in my area, but I've never seen a Kubota. Mostly Polaris rangers, Yamaha Grizzlys, Kawasaki mules. 

My truck has EGR but no DPF (2006 engine, 2007 chassis). The oil turns black in a week with the EGR. After 5k miles on the old non-egr truck the oil would still be brown. As soon as I can afford an ECM Tune, the EGR valve will cease to exist (operate).


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## Peacock (Dec 21, 2007)

DarylB said:


> Slick ride. Lots of those things down in my area, but I've never seen a Kubota. Mostly Polaris rangers, Yamaha Grizzlys, Kawasaki mules.
> 
> My truck has EGR but no DPF (2006 engine, 2007 chassis). The oil turns black in a week with the EGR. After 5k miles on the old non-egr truck the oil would still be brown. As soon as I can afford an ECM Tune, the EGR valve will cease to exist (operate).



Try to find some low ash oil if you can. It seems to help.


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## spacemule (Dec 21, 2007)

DarylB said:


> I'll buy the 5k and dual pumps, but not 6500rpms... Stock internals? I dont think so Tim.



My thoughts exactly. 

Have you ever noticed that diesels sound like they're spinning much faster at a given rpm than a gas engine? I suppose that's because they run much longer strokes to get the greater compression ratios necessary and therefore the piston speed is faster at a given rpm than a gas motor. Probably why they take so much more power to crank as well.


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## DarylB (Dec 21, 2007)

Peacock said:


> Try to find some low ash oil if you can. It seems to help.



Running Shell Rotella, not sure if it was low ash or not. (i'm due for the 2nd oil change anyway). As one guy put it - I dont like my engine eating its on poo, which is basically what an EGR does.


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## DarylB (Dec 21, 2007)

spacemule said:


> My thoughts exactly.
> 
> Have you ever noticed that diesels sound like they're spinning much faster at a given rpm than a gas engine? I suppose that's because they run much longer strokes to get the greater compression ratios necessary and therefore the piston speed is faster at a given rpm than a gas motor. Probably why they take so much more power to crank as well.



Yep. The high compression is what makes em harder to crank. It is a "compression ignition" engine ya know


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## spacemule (Dec 21, 2007)

DarylB said:


> Yep. The high compression is what makes em harder to crank. It is a "compression ignition" engine ya know



Yeah, but I think that's only part of it. Consider the extra leverage against the crank from equal amount of downward force on the piston because of the longer stroke. Given equal compression pressures, the diesel would still be harder to crank.


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## wood4heat (Dec 21, 2007)

Peacock said:


> Like a fuel heater? Ford used these on the old 7.3 and 6.9. Only used for cold start. I guess the Big 3 never had a reason for a high revving diesel, so they never tried it.
> 
> Most diesels have no reason to rev high. They produce so much torque at low rpm that they don't need to rev high. Most pullers only run so much rpm to build as much energy before releasing the clutch. I've got friends that tractor pull with a small block Deere and they leave the line a good 2,000 rpm more than the run during the pull.



I realize it's not practical to run a diesel at high rpms I'm just curious about the technical aspects of doing it. Sounds like Honda played with the idea so I wondered where they wound up with it and how they got there. You already learned me something about what limits rpm, I thought it was just piston speed.


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## spacemule (Dec 21, 2007)

wood4heat said:


> You already learned me something about what limits rpm, I thought it was just piston speed.



I'm talking out my ass here, as most of you know, but seems to me if piston speed were the only limiting factor, it would be easy to overcome. You could achieve the much higher compression ratios with a shorter stroke by using a very small chamber area above the piston.


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## wood4heat (Dec 21, 2007)

spacemule said:


> I'm talking out my ass here, as most of you know, but seems to me if piston speed were the only limiting factor, it would be easy to overcome. You could achieve the much higher compression ratios with a shorter stroke by using a very small chamber area above the piston.



But as you pointed out in a previous post the longer stroke gives more leverage on the crank. This is part of where they get all the torque. Then again if we're pushing the rpm limits we'll probably throw some torque out the window anyway.

Anyone know what sort of rpm a volkswagon Jetta TDI turns?


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## Peacock (Dec 21, 2007)

spacemule said:


> I'm talking out my ass here, as most of you know, but seems to me if piston speed were the only limiting factor, it would be easy to overcome. You could achieve the much higher compression ratios with a shorter stroke by using a very small chamber area above the piston.



The head is flat. The valves generally protrude into the bore. Usually the piston is a bit under deck height. The combustion chamber is usually in the piston itself. This style of piston is called 'mexican hat'. They have a point in the middle that lines up with the injector in order to properly distribute the fuel throughout the piston.


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## woodchuck361 (Dec 21, 2007)

stroke has nothing to do with the compression ratio. (
You can have long strokes with low or high compression and you can have short strokes with low or high compression. 
Compression is determined by how small a space the fuel mixture is squeezed into. 
The length usually determines the amount of torque. longer stroke engines usually produce more torque and are slow to rev up./lower max rpm due to more rotating mass. while short stroke motors produce more h.p. and are fast to rev. up

There are many variables and some exception but for the most part this holds true.


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## dpcutter (Dec 21, 2007)

Diesel engines also last longer then gasoline engines because the fuel acts as a lubricant. During cold starts, there is always some blow-by, in a gas engine, this is a solvent not a lube and will damage engine parts if excessive amounts enter into the engine. On a diesel, blow-by is a concern, but the diesel fuel itself is a lubricant, unlike gasoline, which is a solvent.


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## DarylB (Dec 21, 2007)

wood4heat said:


> Anyone know what sort of rpm a volkswagon Jetta TDI turns?



Here's some specs on the 1.9 (1998 model). They phased this motor out in 2006 due to emissions. I think the new engine is 126hp and more torque
Horsepower:
90 bhp @ 4000 rpm (~147 bhp @3500 rpm)

Torque:
149 lb/ft @ 1900 rpm (~311 lb/ft @2200 rpm)

4 grand isn't out of the question, it's a smaller engine. Bigger cubes generally mean less RPM's (in a diesel)


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## TDunk (Dec 21, 2007)

Well i'll tell ya what DarylB. Go onto Woodruffdiesel.com. You'll see a blue reg. cab long bed dodge on there (not sure what links to click) But i know for a fact that truck will turn 6500 rpm, believe it or not.


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## Frank Boyer (Dec 23, 2007)

Look for a bunch of new diesel cars and light trucks in the next few years. Ford has a 1/2 ton pickup, Honda a car or two, Toyota a pickup etc, etc.


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## 55chevyparts (Dec 23, 2007)

As far as the 1.9 TDI, red line on tach is 4600 and I haven't found any reason to push it above 4000. The reason I have it is for the mileage, average about 50 per gallon. With a 5-speed it turns about 2000 at 60mph and 2600 at 70.


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## DarylB (Dec 23, 2007)

TDunk said:


> Well i'll tell ya what DarylB. Go onto Woodruffdiesel.com. You'll see a blue reg. cab long bed dodge on there (not sure what links to click) But i know for a fact that truck will turn 6500 rpm, believe it or not.



But with the stock bottom end and stock internals?:deadhorse: I doubt it. That was your original post said. Most hopped up trucks at least run a stud kit to keep the head from blowing off due to the abnormally high boost pressures. Even wastedgated turbos are going to crank out a lot of boost @6500rpms


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## TDunk (Dec 24, 2007)

DarylB said:


> But with the stock bottom end and stock internals?:deadhorse: I doubt it. That was your original post said. Most hopped up trucks at least run a stud kit to keep the head from blowing off due to the abnormally high boost pressures. Even wastedgated turbos are going to crank out a lot of boost @6500rpms



I said the engine block and internals were stock, nothing about the head. I know that Dan and Luke said that the rotating assm. was stock. It had all been balanced and the pistons lightened (not sure if they lightened the crank and rods or not) And i think the mains were studded,diff. caps, and something was modified for the oil pick-up. Now the head on the other hand, yeah that's pretty wicked. The turbo on it is so big that they had to custom make an exhaust manifold to get it away from the block. I'll try and post some pics. of it if i can find them.


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## SWI Don (Jan 28, 2008)

Around 6000 rpm is what I have been told is about the max rpm for med sized diesels (7-9L) used in tractor pulling. I'm not saying that some guys aren't running faster but diesel can only support a flame front that is only so fast. To run those kind of rpms it requires lots of custom parts to have them hold together for long.

Don


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## Jumper (Jan 29, 2008)

Frank Boyer said:


> Look for a bunch of new diesel cars and light trucks in the next few years. Ford has a 1/2 ton pickup, Honda a car or two, Toyota a pickup etc, etc.




How bout a Dodge Dakota with the 3.2 Mercedes diesel they put in the Grand Cherokee. I'd buy one tomorrow.


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## IndyIan (Feb 1, 2008)

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


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## 460magnumMOD (May 12, 2008)

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.


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## pdqdl (May 13, 2008)

*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!


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## glenn31792 (May 22, 2008)

_w4h
Holy [email protected]!!! 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


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## motoroilmccall (May 22, 2008)

TDunk said:


> 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.


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