cummins diesel efficiency

[MEby]

I have a simple question that might have a more complex answer. I you were to build a diesel (cummins) strictly for fuel efficiency with absolutely NO regard for emissions what would you have to change to our cummins? Anything?

 

[bmoeller]

Well, how you determine fuel efficiency will matter, too. Mileage isn't the true way to measure it. Although I'm sure most do, since you notice it more.



As an example-



My last gasser Ford had a 6. 6L (400V8)130hp engine, and got 11 mpg. A neighbor had a SD truck with the 310hp 6. 8L V-10, and it got 10mpg.



The V10 is more efficient since it is making more than twice the power with about the same amount of gas.



The Nebraska Tractor tests also uses horsepower hours per gallon. # of hp/# of gallons used per hour= hp hrs per gal.

 

[RustyJC]

The measure you're probably looking for is Brake Specific Fuel Consumption (BSFC). If you want to compare between fuels, this would best be measured in BTU/BHP-hour. If you're always going to be dealing with a diesel fuel of constant heat content, you could use lbs/BHP-hour.



More information is available HERE.



Rusty

 

[1stgen4evr]

I am thinking that you have the definition restricted to a truck application and right there you have multiple applications; big truck, little truck, no load, heavy load, big foot, light foot. But if you narrow the application to a single use, there would be little that NEEDS to be changed with the exception of how you apply the throtte. That will return the greatest efficiency of all. As with all combustion engines, the higher you run the heat, the higher you will achieve efficiency. The materials used are the best commercial grade available. Exotic ($$$$$) metals allowing higher heat will return higher efficiency. In the injection pump, higher pressures will return cleaner burning and greater efficiency.



I can remember when injection pressures were MUCH lower than is currently used.



So yes, the answer becomes quite complex.



James

 

[MEby]

to clarify a bit..... I guess I was thinking along the lines that emisions equiptment seems to be in direct opposition with power and fuel efficiency. right? Practically it seems like if you built an engine for efficiency and/or power forgeting about the epa we would be much farther off. So, how would you accomplish this? I mean on top of things like free flowing exhaust, cold air high flow intake, etc. or is that the route to go , different cam, turbo, port and polish the heck out the head, and reducing other air flow restrictions? What about different spray patterns and hole sizes in injectors? At what point do we hit maximum effieciency? Has anybody ever reached that point? I read the tdr articles Back in the Saddle by scott dalgliesh on his quest for fuel economy. any thoughts on that? one last thing, yes I think that "brake specific fuel consumption" is the "measure" i'm looking for. thanks guys.

 

[cojhl2]

The V10 is more efficient since it is making more than twice the power with about the same amount of gas.



The Nebraska Tractor tests also uses horsepower hours per gallon. # of hp/# of gallons used per hour= hp hrs per gal.

No, it's not making more power. It may be capable of it but it only is developing the necessary power to drive the vehicle.



That is why it is using about the same amount of fuel.

 

[bmoeller]

OK. A better anology.



2 JD tractors. 1 is a 7. 6L 200hp 8300 MFWD, and the other is a 4wd 9100 with a 280hp 8. 1L. The 8300 has the best power to weight ratio.



Both pulling the SAME piece of tillage equipment (5 shank subsoiler with 10" wide points and cover boards), at the same depth in wet, tight, heavy clay gumbo. Nasty ****.



8300 has enough power to only go 3mph. 9100 at 4. 5mph. 8300 using 1. 25 gal/acre and the 9100 is using 1 gal/acre.



So, now, which one is better?

 

[MR.K]

Yea ... much is in the timing ... Our motors are quite retarted and the newer the worst ... it is to reduce NoX . . The cam is also an issue. . the last couple of TDR mag. had some cam shaft changes to increase mileage . Also better intake & exhaust systems help too. . Generally any time you increase the effenicy of an engine you will increase mileage ... Gear ratios are also a factor ,use of a gear vendors or a US Gear box can help ... .

 

[cojhl2]

OK. A better anology.



2 JD tractors. 1 is a 7. 6L 200hp 8300 MFWD, and the other is a 4wd 9100 with a 280hp 8. 1L. The 8300 has the best power to weight ratio.



Both pulling the SAME piece of tillage equipment (5 shank subsoiler with 10" wide points and cover boards), at the same depth in wet, tight, heavy clay gumbo. Nasty ****.



8300 has enough power to only go 3mph. 9100 at 4. 5mph. 8300 using 1. 25 gal/acre and the 9100 is using 1 gal/acre.



So, now, which one is better?

Yes that is a good analogy. The key us the 9100 is producing 50% more power (same load but 50% faster) with ... oh oh,, still cant tell much cause you have mixed gal/acre with mi/hr. .



Anyway I get the point you are trying to make bmoeller. And you are probably right. The only point I was maiking is the engine capabilty is not related to the demand for power at any one time. Two different hp engines pulling the same load at the same speed are producing the same power.

 

[MEby]

Yea ... much is in the timing ... Our motors are quite retarted and the newer the worst ... it is to reduce NoX . . The cam is also an issue. . the last couple of TDR mag. had some cam shaft changes to increase mileage . Also better intake & exhaust systems help too. . Generally any time you increase the effenicy of an engine you will increase mileage ... Gear ratios are also a factor ,use of a gear vendors or a US Gear box can help ... .

so how many degrees should we advance the timing to obtain the best fuel efficiency? on the gear vendors or us gear box, does anybody have any if and how much you have improved mpg? also i've been wondering about when I cruise down the interstate at 75 mph my rpm is much higher than the "sweet spot" which is 1700-1800 according to the cummins data sheet in issue 55 pg. 17. I am running a nv4500 with 3:54 gears and stock tires. According to gear vendors web site, the overdrive reduces rpm by 22%. I think I am running around 2100 rpm ( tach dont work) at 75mph. overdrive would reduce my rpm to 1638 rpm @ 75 mph. the reason I ask is when I drive down the interstate I always drive that fast anyway, so why not reduce rpm to the sweet spot. for driveing around home I can use a lower gear to achieve the correct rpm. Anything wrong with this theory?

 

[Greenleaf]

8300 has enough power to only go 3mph. 9100 at 4. 5mph. 8300 using 1. 25 gal/acre and the 9100 is using 1 gal/acre.



So, now, which one is better?

Niether one. Use a John Deere 720 Diesel. It's fuel economy record stood for 40+ years I believe.



Not just that but the John Deere 720/820 tractors provide more smiles per acre too.

 

[bmoeller]

My neigbor owns THAT very tractor used in the test. Hooks a 4 bottom plow onto it once in a while to blow the cobwebs out of it. Haven't driven it, but it sure sounds great. He retired from Deere.

 

[Don Tanklage]

on the gear vendors or us gear box, does anybody have any if and how much you have improved mpg? also i've been wondering about when I cruise down the interstate at 75 mph my rpm is much higher than the "sweet spot" which is 1700-1800 according to the cummins data sheet in issue 55 pg. 17.

i dont know that the gv improved my mileage when loaded or towing (sure helped the thing get thru the gears tho!) but...



empty, keeping my leg outta it, and crusing at 1600 rpm in 5th over, i drove 150 miles on just over 7. 5 gallons of fuel



before installing the gv it would be at 2000 rpm and getting about 10 mpg



driving tech has a lot to do with mileage with these things



when you start to go up a slight grade if you just keep the throttle position the same and let the r's drop a little and the boost go up a little the grades dont seem to hurt the mileage hardly at all...



but if you increase throttle every time you hit a small grade to keep speed constant the mileage goes away



jmo

 

[KOG]

Don't expect any great increases in mileag by dropping rpm. You will see some improvement, but diesels are quite efficient at part load, unlike gasoline engines, so show nothing like the smae mileage improvement when you slow the engine.



I ran a Deere 70 diesel in the '50s. Interesting toys, but more work than I want to deal with these days. All of the large 2 cylinder Deeres were quite fuel efficient for their types, most ran at about 950-1100 rpm full speed. Got a Cat D82U (about 1950) that runs 900rpm full speed. Only 130HP, but will run at full power for decades at full load.

 

[bmoeller]

Got a Cat D82U (about 1950) that runs 900rpm full speed. Only 130HP, but will run at full power for decades at full load.

Could you start a thread with pics of the Cat?

 

[KOG]

Let me figure out what part of 1st gen a D8 is. It does have an inline 6. And a 5 speed. As well as 4 clutches, a flathead twin pony engine and 50,000lbs of ground hugging weight.



We discovered what the "8" means. Means that it will push over an 8" sweet gum. A 10" will stop it and spin the tracks in the summer when the GA red clay is like a brick.

 

[cojhl2]

Let me figure out what part of 1st gen a D8 is. It does have an inline 6. And a 5 speed. As well as 4 clutches, a flathead twin pony engine and 50,000lbs of ground hugging weight.



We discovered what the "8" means. Means that it will push over an 8" sweet gum. A 10" will stop it and spin the tracks in the summer when the GA red clay is like a brick.

Sure nice to hear someone old enough to know all that stuff.



I put many hours a a D69U. I love that tractor.



Also a signifcant hours on 3cyl cats.

 

[dpuckett]

Friend of mine has a 60-something D4D Cat that still has the original fuel system. Electric start, though.



Anyway, back on track. There are many things to consider when shooting for max MPGs. Injector spray pattern and atomization are two important things to consider. I think the reason many guys say they gain x MPG when going to PODs, 190s, etc, is that their stock injectors are not as good as they once were. So, even if they had rebuilt their stockers, they'd have seen an improvement. Not to knock the aftermarket, as they can focus on performance, but it often isnt an apples to apples comparison.



Also, turbo efficiency maps & exhaust housing sizes can affect MPGs and eficiency. The smaller housing may spool like greased lightning, but it may choke at higher RPMs and loads. Conversely, the 21 Lag queen may be just fine for 3. 07s and no OD, but would spool in town miserably, or smoke horribly. just becaus eyou are getting more boost into the engine doesnt necessarily mean you are running at peak efficiency. I had a 12cm and an 18 on my old 91, and it did better with the 18 than the 12. Spooled just a hiar slower than the 12 (I had ported the 18, so that helped), but I gained 1. 5MPg average by going back to it.



TIming is another issue that gets lots of attention. Too much can be detrimental to not only the stock head gasket, but fuel efficiency. I could see where the spray of my injectors had been outside the piston bowl (could also have been the . 060 washers vs the . 020 washers too), indicating the POSSIBILITY my timing was too advanced. Get the fuel charge in ther cylinder too soon, and the combustion event is trying to force the piston down while the crank is still trying to push it back up. Not a good scenario. Likewise, if the fuel charge gets there too late, it wont maximize the potential power production. How much is too much? That is hard to say. I have k nown guys to go up to 1. 9mm area with aftermarket injectors, and a certain turbo combination, and it gave them the performance thye wanted. I have also seen trucks go 500K on stock timing and still get really good MPGs and make decent power. General consenus on this board tends to be the 1. 4-1. 7mm range, depending on a myriad of factors.



So, to achieve maximum efficiency, I'd get a set of injectors that had a spray pattern and placement in the head to match my piston bowl shape, with 5-6 holes. I'd set the pump timing around 1. 45-1. 55mm @ TDC (once again, to complement the piston bowl designand get optimium spraying to maximize power pushing down on the piston). Turbo on the order of an HX35/16- good bottom end, yet spool well enough to not smoke anyone out. If you have enough fuelling and EGts get out of hand, you will need to get a bigger huffer, naturally. 4" exhuast, and a BHAF or reuseable filter that will actually FILTER the air coming into the engine. PSD or similar intercooler with 3" pipping, and a 2nd gen intake horn to flow better. Head porting and a cam would help with flow, as boost is nothing more than resistance to flow.



Daniel

 

[MEby]

dpuckett,

how do you like you dynomite injectors?



I have advanced my timing slightly, as of right now just enough that it cleared up the whitish haze at cold idle. I think I should try for more soon. I am not complaining about my fuel economy, 16 mpg average. I love lots of power but I'd like to try to build my power in conjuction with keeping or increasing mpg's, hence all the questions seeing like I said earlier that it seems like effieciency and power are in opposition with keeping emissions down.