One for the true Diesel Nerds.

[CRSmith]

There was a post in the competition forum having to do w/ reliability and power. I was wondering if we could quantify and predict the life expectancy of the cummins in scientific units. Maybe the Joule or Watt. For example, consider 2 engines. Engine 1 is stock. Engine 2 is twinned, comp box, big injectors, propane, nitrous, etc. Engine 1 lasts for 400,000 miles at an output of 240hp. Engine 2 lasts for 100,000 miles at an output of 800hp. Based on mileage, engine 1 clearly has more longevity. Based on energy output over its lifetime, however, the comparison is less clear. Maybe both have ouput roughly the same amount of energy over their respecive mileages. For example, engine 1 may power a generator that lights a lightbulb for 20 years before blowing up. Engine 2 may power a generator that powers a town for 1 day before blowing up. Lets say the 20 year energy requirement for the lightbulb is the same as the 1 day requirement for the town. They will both have provided the same energy over their lifetime. If we could determine the energy ouput of a cummins before blowup, we could (very, very, very roughly) approximate the lifetime of our motors with respect to hp output. A rhetorical question to chew on.

 

[skobylenski]

My brian hurts, it's too early to be thinking like this. #ad




I'm sure someone can work this out, though.

 

[esommer2500]

From the front cover of my physics book:



1 Joule = 0. 738 ft-lb or 1 ft-lb = 1. 36 Joules



1 Watt = 1 Joule/sec. = 0. 738 ft-lb/sec



1 hp = 550 ft-lb/sec = 746 Watts



Somebody else can try it from here, I have to do enough of this stuff during the week.



Eric

 

[Steve G]

It depends on which transmisson upgrades you have. :-laf :-laf :-laf

 

[RustyJC]

Smokey Yunick (the NASCAR genius) was once asked a question like this when someone asked about hopping up a stock engine. His response, paraphrased, was that a given engine design has a given number of horsepower-hours built into it. You can take it out as a little bit of horsepower for a long time (stock engine), or a lot of horsepower for a little bit of time (racing engine).



Try BHP-hours as a measurement standard. See how it works out.



Bear in mind, however, that this rule of thumb is based on the produced, not necessarily the maximum instantaneous BHP. You could have a BOMBed Cummins that dynoed at 490 BHP, but that doesn't mean that it would last half as long as a 245 BHP ETH if both were used for the same service at the same produced BHP. On the other hand, put them both on an engine dyno and run them at their maximum BHPs until each fails, and the halved life expectancy for the engine with doubled maximum BHP would probably be closer to true.



By the way, I think the relationship will be more exponential or logarithmic than linear. Remember the estimates we see quoted for automatic transmission life at various fluid temperatures? I think the engine life measurements at produced BHP levels will probably look more like that than a purely linear relationship between BHP and operating hours.



The above is my 2 cents' worth of s4!thouse philosophy for this morning.



Rusty

 

[Hohn]

What Rusty said^^^^



Dang, I am gonna have to get faster and beat him to the punch.



I think it would be exponential too. Like, you double the power, you get 1/4 the engine life. Also true as to what is being demanded of the engine. An engine could last almost forever if all it had to do was idle.



Let me phrase this as another advantage for the Dodge/Cummins combo. In our trucks, this engine is loafing (unless you always tow) compared to the loads it was intended for. I could drive with the pedal to the floor all the time, but the load of pulling my 6800 pound truck in 6th is STILL less than what it was designed for. I would slip the clutch before I would hurt the engine.



Hohn

 

[BV]

Wait a minute

Okay - Now I added just enough power to my 99 that it didn't work hard - but it worked smarter so I believe that the life expectancy was extended out to around 500k - This assumes that the wife didn't drive it pedal to the metal all the way to the store.





EDIT: So I think to sum it up - It like that gun saying "Guns don't kill - People kill". Now apply this here "Power doesn't Kill - Power Heals"

 

[jmtandem]

engine life vs. power

reduaram,



This is an excellent forum. I suspect that there is data on how to begin to answer the questions with Cummins. the racing community, or high performance general aviation piston engines. Many piston airplane engines are limited to five minutes takeoff power to keep stresses down. A tangential issue is when will the stresses exceed the design loads for the Cummins as more and more power is added to the point of component failure or excessive heat buildup destroys the engine.

 

[jcbrown]

MTBF...

Mean Time Before Failure.

 

[JLEONARD]

IMO engine life is more a matter of duty cycle and how much you actually use the available horsepower.

In the marine applications Cummins (and all diesel engine manufacturers) are very specific about duty cycle and longevity.

They also commonly use the total amount of fuel burned thru an engine to predict longevity.

Just another point to consider.

 

[Diesel Freak]

chew on this one!

Effective Full Power Hours: a term used to describe how old a nuclear reactor core is. It is used to track a core from initial criticality to end of life (EOL)



An ISB 275 is waranteed for 10000 hours. This 10000 hours would most likely be spent in an industrial application where the engine runs at rated speed and load for the entire 10000 hours. If this engine were in a Dodge truck with an average speed of 35 MPH, it would travel... 350000 miles.



Where am I going with this? People have been asking what BOMBing does to the life expectancy of these engines. Before you read any farther keep in mind that the engines will be running at full load and horsepower for their entire lifetime in this discussion.



If the engine is maintained perfectly it should last at least 10000 hours of operation at rated load and speed. 10000 hours at 275 HP gives us 2750000 effective full power hours for an ISB275.



Say for instance we BOMB an ISB to 350 rear wheel horsepower in a truck with a manual transmission. What we actually have is a 402 horsepower engine under the hood. If the engine is designed to last 2750000 EFPH, the life expectancy of the BOMBed engine is now 6840 hours if it were run at rated load and speed for its entire life.



Running a BOMBed CTD powered Dodge at full power for it's entire life is absurd. The truck would fall apart in the process. Since we can not measure the EFPH of the engine effectively once it has been bombed, the only way to measure life expectancy would be to measure the ammount of fuel the engine uses over its entire life.



An engine can only burn so much fuel before overhaul. If we raise the power level of the engine but not use the power... (or extra fuel) the engine if maintained perfectly should last over 10000 hours. Once we start using the added power (fuel) we start to reduce the lifespan of the engine.

 

[15w40]

I think Diesel Freak is on the right track.



275 HP = 700K BTU/Hr



If the engine lasts for 10K hours then the total energy converted, diesel fuel-to-motion and heat, is 7 billion BTU.



If diesel fuel contains 146. 5K BTU/Gallon then after you burn 47,770 Gallons of fuel you will need an engine rebuild. At 10 MPG when making 275 HP, that is 477,700 miles. (Maybe a little high. )





Now if you are making 350 HP at the wheels or 402 engine horsepower, and working backwards;



Assuming 5 MPG and the same 47,770 gallons of fuel used, then you will rebuild your engine at 283,900 miles.



These numbers probably are not accurate but an old time diesel mechanic used fuel records to determine the rebuild interval on the fleet he serviced.



And who are you to call us nerds?

 

[drees1]

Engine manufacturers do exactly that, rate their engines for power*life. Typically, it is rated in terms of hours to first overhaul, usually defined by reaching an oil consumption limit. For example: 8000 hours, B10 life, 400Hp. The B10 life is where 90% would make it to the mark without failure. The 400Hp is continious, but can be expressed in duty cycle. Duty cycle is a percent of 100% power that is equivilent to an actual application. Over the road truck, 50% - 75% duty cycle, max. A prime power generator, 100% duty cycle. Our engines in the Dodge, towing, probably 25% duty cycle, empty, maybe 5%.



Typically, hot rodding an industrial engine like ours will probably be a near linear function with wear and tear up to a 2x power increase or more. As long as we can carry away the heat, and there is decent oil film, then wear will be roughly linear to power. And remember much wear occurs during starting, at least in the ring belt area.



Super extreme power increases blurr the life expectancy prediction because breakage, not wear, enters the picture.



Engine manufactures balance duty cycle against power rating to make sure the engine lasts in it's intended application. Take the same basic engine with several scenarios. CAT 3126: Marine, 475?Hp, RV and Ambulance, 330HP, On highway truck, 210 - 250 hp. Industrial prime power, 190 or less. The relation ship is how hard and how long do you work it. The marine engine has a 45 SECOND rating, get the boat on plane and back off in 45 seconds or less. Same with the RV and ambulance, get it rolling or do some passing and back off. The truck has to work more. Also, manufacturers try to price their engines according to Hp. 425Hp costs more than 190 in the same family. Although the engine does cost a little more to build a higher HP, much of that extra revenue supports increased warranty claims.



I think you find with our engines, we load them so little, that even hot shot drivers that tow 100% daily get the same life as the rest of us.



I heard, a long time ago, Navistar dynoed Cummins B, Navistar 7. 3, and GM 6. 2 at full nameplate load and speed to destruction. The Cummins was pulled off at over 1000 hours and still running, the Navistars made it to 400hours or better, which was their goal, and the GM 6. 2 went 200 hours, some less than 100 hours.



Sorry for all the rambling, but interesting subject.



Doug Rees