This article originally published in Issue 61 of the Turbo Diesel Register.

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Technical Topics

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IT'S ABOUT THE (fuel) ECONOMY STUPID! (page 2)

by Robert Patton, Editor TDR

Been There, Done That; Got Lots of Spare Parts

As much as I would like to pretend that I am a diesel engineer and offer you a magic fuel economy fix-all, the reality is that as a group we have already been there and done that. So much for the sensational title line that I could splash on the outside cover, “Writer Dude Discovers 25% Greater Fuel Economy for His Dodge/Cummins Turbo Diesel.”

Back to the task at hand, can you increase the fuel economy of your truck? Oddly enough Issue 51 was the second article in Scott Dalgleish’s quest to improve the mileage on his ’05 Turbo Diesel 2500, 4x4, Quad Cab with the G56 six-speed transmission and 3.73 rear differential ratio.

Rather than send you back to your archives to gather the information, I’ve assembled a brief summary of each of his articles.

Read the summaries and let’s see if we reach the same conclusion(s) at the end.

Issue 50 Baseline MPG 15.8 city; 9.8 towing.
Added TST PowerMax CR, Amsoil synthetic lubricants, Mag-Hytec differential cover, gauges, fresh air box with aFe Proguard 7 filter. Notes: Playing with different timing settings the TST PowerMax CR showed an increase of up to 13% better mileage.

Issue 51 Added Gear Vendors overdrive, Banks High Ram inlet, Banks intercooler, Banks Monster exhaust. The combined effect of the aftermarket products thus far: up to 17% better.

Issue 52 Added BFGoodrich 285/70/17 tires which reduced engine’s rpm by 100. Experimented with pre-production Banks Six-Gun Tuner and Power PDA. The combined effect is still in the 16-17% range with the power setting on the Banks unit at “2.”

This comment caught my eye: “Power settings above 2 provide marked performance increases along with an equal increase of driving fun. But the fun has a cost and decreased fuel economy is the price.”

Scott is about to “go over to the dark side,” “fall off the wagon”; choose your cliche. This article was written in the May 2006 time frame when the pre-Katrina fuel price is at a stable $2.25.

Issue 53 No report.

Issue 54 Recap of baseline at 15.8mpg. Noted increase of mileage to 18.7mpg. Added Industrial Injection Super Phat Shaft 62 turbocharger and PDR camshaft. Scott noted that the turbocharger neither hurt nor helped fuel economy.

I told you Scott had moved to the dark side. Notice the emphasis on performance: “The setting of the Banks Speed Loader was 6 and the 0-60mph time dropped from 10.2 seconds to 8.9 seconds.

In the Issue 54 article Scott noted that the PDR camshaft had a dramatic effect on economy—approximately 2.1 mpg. Great news! But, why didn’t the Cummins engineers think of that?

They did.

Scott’s explanation from Issue 54: “If obtaining better fuel economy can be found from a different cam grind, why didn’t Cummins do it?” The answer is Cummins Inc. can provide camshaft grinds for better fuel economy. But, as I stated earlier, Cummins has to abide by a different set of standards, which are primarily emissions driven. (Editor’s note: Sounds familiar, doesn’t it?) In order to meet current NOX standards, combustion cylinder pressures must be lowered. One way to accomplish this goal is to retard injection timing, reducing cylinder pressure and thereby reducing NOX. The Catch 22 is that it takes more fuel to operate the engine in this manner. The engineer has to certify clean exhaust emissions, often at the cost of fuel economy. So will the cam offered by PDR meet EPA emission standards? To our knowledge it has not been tested for EPA compliance and probably would not pass. Would it pass a local emissions test as administered (snap idle)? Probably.”

Issue 55 Scott is to the point: “In my review of some of the back issues I realized I have made a transgression. I have once again, fallen to the temptation of more power. While it is true we are close to accomplishing our goal of 20% better fuel economy across the board, the alluring power increases have blinded me like a moth drawn to a bright light. I now believe that it is possible to obtain the 20% fuel economy goal AND increase horsepower to the 500-rwhp mark. Along with this revised goal I had to accept the reality that was true for me way back in Issue 23, the financial impact of all of these fuel mileage and performance goodies will never be offset by the 20% economy I may someday achieve.”

Further, Scott writes, “This isn’t to say I have forsaken the fuel economy project. Currently we are averaging about 18.1 mpg. That is approximately a 15% increase across the board (solo, towing, city and highway). We have produced as much as 18.8 mpg driving solo combined city and highway, which is a 19% increase! But we have shifted from some of the original stated criteria. Most notably, ‘to remain emission compliant and to maintain the factory warranty.’ Some of the parts we have tried may not be emissions compliant (no current emissions testing data is available) and their effect on warranty is subject to debate.

“Knowing this up front, you are faced with a dilemma. Will you a) live with the fuel economy offered by the current HPCR engine’s configuration; b) make some of the changes which provide some fuel economy improvement and leave the engine warranty intact, or c) become your own warranty station and move in the direction which will provide the best fuel economy and performance available?

“On the topic of emissions compliance: most, if not all, of the products tested to date will pass the current snap-idle emissions testing which is performed in some states today. Would these products pass the current Federal standards? Probably not. We do not have access to the test equipment nor is there a standard procedure for such testing after a product is sold to the end user. Since no testing of the Federal emissions standard (EPA or CARB) is currently in place (the exception being for manufacturers), it is a moot point.".

TDR members, if you reference Issue 60, pages 50-52, you will likely conclude that parts testing for emissions certification for the ’03-’07 HPCR engine is still a moot point.

Issue 56 Noted a decrease in mileage of 7% that was attributed to the required ULSD fuel (January ’07). Added DDP injectors and mileage checks in at 18.9 mpg.

Issue 57 Added Leer truck cap, but noted no difference in economy.

Issue 58 Changed turbocharger to a Turbo Re-Source unit. Mileage is 19.1 using Scott’s combination solo runs on the short and long track.

Issue 59 A higher performance set of DDP injectors (DDP90) and an emphasis on horsepower. Fuel economy went down 6%. Overall economy is better by 14%

Issue 60 No report.

Issue 61 See Scotts turbocharger write-up on page 92.

Conclusion(s)

Credit to Scott—in his adventure seeking fuel economy and performance, he took the time to address three important concerns: Why didn’t the factory engineer for fuel economy? What happens to emissions compliance? What are the effects to the factory warranty?

As I looked back at his findings, there was one modification where I could see a cost justification and two nice-to-have modifications.

The item that can be cost justified: The use of a performance box that modifies the timing of the fuel injection event. Cost: $800. Number of gallons that you would need to save (@$4/gallon) to payback the $800 ($800 ÷ $4 = 200 gallons). From his Issue 50 Scott found that the mileage increased by 13% or 15.8 x 1.13 = 17.8 mpg.

Drive 30,000 miles ÷ 15.8 mpg = 1,898 gallons used
Drive 30,000 miles ÷ 17.8 mpg = 1,685 gallons used
213 gallons saved

Okay…drive the truck 30,000 miles and you’ve paid for the performance/timing box. The nice-to-have modifications: The camshaft and the overdrive unit. From Issue 54 Scott noted the cost of the cam and installation was $1600. He noted a 2 mpg increase. Yet the 2 mpg was lost (the numbers should have gone up to 19.8 mpg) in his quest for power. But, for the sake of argument, let’s assume another 2 mpg improvement. At $1600 ÷ $4 gallon you need to save 400 gallons of fuel to pay for the camshaft. This would take 60,000 miles. And the nice-to-have overdrive? Writer Loren Bengston covered the payback for his overdrive unit back in Issue 47, page 162. In Scott’s case insufficient data exist to do a calculation.

Bottom Line

It seems simple to me…

• As we learned from Joe Donnelly and Issue 47, operate the engine at the BSFC rpm that corresponds to the engine’s sweet spot. Unfortunately, highway speeds don’t allow you to go that slow without impeding traffic, so slow down as much as possible.

• Change the engine’s timing. Scott’s findings and the article by Joe Donnelly on page 98 confirm that this modification is applicable for all years of the Turbo Diesel truck. Be careful of the cause and effect and realize that the payback could take a while. • All of the other modifications are discretionary.

P.S. Wal-Mart is still out of stock on the fuel magnets and the tornado thing still has not been released for our intake size.

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