Diesel Power - - Contents - Words and Pho­tos by BRUCE W. SMITH

WEL­COME TO TOP TECH QUES­TIONS. One of our fa­vorite forms of reader com­mu­ni­ca­tion is tech ques­tions. Our Top Tech sec­tion is a place where you ask what’s on your mind, and we answer.

Send us an email at dieselpow­ertech@en­thu­si­ast­net­ and ask away!


QUES­TION: Why is the pyrometer’s probe placed af­ter the tur­bocharger on a Class 8 trac­tor, and in the ex­haust man­i­fold (be­fore the turbo) on a pickup? Also, what are the safe oper­at­ing-tem­per­a­ture lim­its of both? Wayne Dil­lon via email

ANSWER: It’s com­mon­place for pry­ome­ter sys­tems to mea­sure ei­ther pre-turbo or post-turbo tem­per­a­tures. The lo­ca­tion of the probe de­pends on where a truck man­u­fac­turer’s en­gi­neers feel is best for the ap­pli­ca­tion. Their de­ci­sion takes into ac­count EGT ac­cu­racy, along with po­si­tion for ease of ser­vice and cost con­cerns. They all con­trib­ute to the rea­son for post­turbo pyro place­ment on Class 8 rigs. The pre­ferred lo­ca­tion for get­ting true EGT with the most ac­cu­racy is im­me­di­ately af­ter the ex­haust leaves the cylin­der head, so the probe is lo­cated in the ex­haust man­i­fold or in the in­let to the turbo. Once ex­haust hits the turbo, EGT can drop as much as 400 de­grees. That tem­per­a­ture re­duc­tion can eas­ily con­trib­ute to cracked heads, split pis­tons, or a de­stroyed turbo if it is not mon­i­tored. Pre-turbo EGT on daily driven trucks should be kept at less than 1,200 de­grees un­der full load. Ex­ceed­ing 1,300 de­grees (pre-turbo) for any ex­tended pe­riod of time is known to cause dam­age. What’s our sug­ges­tion for EGT “red­line?” Play it safe: 1,150 de­grees (pre-turbo), and 750 de­grees (post-turbo).


QUES­TION: I have an ’04 Ford Su­per Duty that has de­stroyed three flexplates. When I bought the truck back in 2016, it had 145,000 miles on it, and I just had the en­gine com­pletely re­built to take care of all the prob­lems that plague 6.0L Power Stroke engines. Since then, I’ve added an­other 20,000 miles, and I have had the trans­mis­sion out twice in that time to re­place the flexplates that have come apart in the cen­ter. The sec­ond time, I in­stalled a Ford flex­plate along with a re­built trans­mis­sion and a new torque cov­n­erter. Af­ter just 1,200 miles, that flex­plate also came apart. The truck has a 6-inch lift and 38-inch-tall tires. The en­gine and trans­mis­sion mounts are new, as are the drive­shafts. The only mod­i­fi­ca­tions to the en­gine are SCT ECM tun­ing and a Gar­rett Pow­erMax tur­bocharger. Ev­ery­thing else is stock. What am I miss­ing here? Jack Con­lee via email

ANSWER: There ap­pears to be some move­ment be­tween the en­gine and trans­mis­sion that’s caus­ing the flex­plate to flex way too much. In the process of in­stalling the dif­fer­ent flexplates, did you no­tice if the two align­ment dowel pins in the back of the block were worn or miss­ing? The dow­els are es­sen­tial for mak­ing sure the trans­mis­sion and en­gine align and are bolted to­gether prop­erly. If you’re in doubt, in­stall new ones. Go­ing in an­other di­rec­tion, if the prob­lem be­gan af­ter the re­built en­gine was in­stalled, it is worth­while for you to ask the builder if the end­play in the crank was checked be­fore the en­gine went back into the truck. Ken­neth Tripp at Tripp Trucks in North Carolina says Ford 6.0L spec­i­fi­ca­tions call for max­i­mum crank­shaft end­play of .020 inch (.508 mm). Aden McDon­nell at Au­to­matic Trans­mis­sion Spe­cial­ists in Liv­ingston, Mon­tana, says he has seen blown flexplates (and cracked trans­mis­sion cases and en­gine blocks) caused by har­mon­ics from drive­shafts that are at the wrong an­gle. Aden also says, “Ex­ces­sive shift pres­sure, harsh shifts, an in­cor­rectly tuned trans­mis­sion, or ex­treme con­verter lockup can all trans­fer more en­ergy than the stock flex­plate can with­stand. In­stalling a bil­let flex­plate for the 5R110 is a good idea.”

“Bill rec­om­mends hav­ing ARP 2000 cylin­der-head studs in­stalled to pre­vent head-gas­ket fail­ure due to higher com­bus­tion pres­sures. He also notes that in­stalling an AirDog II 4G DF165, FASS, or sim­i­lar lift pump air/fuel sep­a­ra­tion sys­tem will take some of the fuel-de­liv­ery load off the fac­tory CP3 in­jec­tion pump...”


QUES­TION: I own an ’06 Ram 2500 with a few mi­nor mods. The truck has 124,000 miles on it. My wife and I are plan­ning on buy­ing a fifth-wheel RV and do­ing a lot of trav­el­ing. For mul­ti­ple rea­sons, I am se­ri­ously think­ing of adding a sec­ond tur­bocharger to the stock unit. Noth­ing ex­treme, just some­thing to help keep EGT down and give it a lit­tle more grunt. I will prob­a­bly also add EFILive tun­ing. My ques­tion is: At what point do I need to worry about re­plac­ing head bolts with studs? I don’t plan on get­ting all wild and crazy with it and am on a lim­ited bud­get. Any ad­vice would be ap­pre­ci­ated. Mike Yates

via email ANSWER: When prop­erly tuned, com­pound tur­bocharg­ers are great for mak­ing power while keep­ing EGT in check. How­ever, there is a bet­ter way to do what you want with­out the ex­pense of set­ting up the en­gine to han­dle the high boost pres­sures you will ex­pe­ri­ence when tow­ing a fifth-wheel travel trailer. Bill Allen of Source Au­to­mo­tive says, “You can get the same power bang you will with com­pounds and stock fu­el­ing by go­ing with a sin­gle-turbo setup. But know­ing the av­er­age al­ti­tudes of ar­eas the truck will pri­mar­ily be used for tow­ing is vi­tal to se­lect­ing the cor­rect turbo. We make these mod­i­fi­ca­tions a lot at our shop (in Ore­gon) for com­mer­cial and RV cus­tomers. We rec­om­mend a High Tech Turbo–pre­pared 62/65/14 BorgWarner S300 turbo, Mads Smarty Jr. pro­gram­mer, and a Mishi­moto intercooler. That pack­age will drop EGT 300 to 400 de­grees, while in­creas­ing fuel mpg and im­prov­ing over­all drive­abil­ity by a ton!” Bill rec­om­mends hav­ing ARP 2000 cylin­der-head studs in­stalled to pre­vent head-gas­ket fail­ure due to higher com­bus­tion pres­sures. He also notes that in­stalling an AirDog II 4G DF165, FASS, or sim­i­lar lift pump air/fuel sep­a­ra­tion sys­tem will take some of the fu­elde­liv­ery load off the fac­tory CP3 in­jec­tion pump and pro­tect the in­jec­tors from wa­ter in­ad­ver­tently en­ter­ing the in­jec­tion sys­tem. With these mod­i­fi­ca­tions, you should be able to tow the RV with plenty of power (and safe EGT) for tack­ling big, long grades.


QUES­TION: I know most of the tech ques­tions you get are re­lated to power, engines, and trans­mis­sions, but I was hop­ing you might be able to give a few tips re­gard­ing tow­ing a trailer in sand. I’m a lit­tle ap­pre­hen­sive about get­ting our new 34-foot toy hauler stuck. Our tow pack­age is a stock ’16 Ram 3500 with the 6.7L Cum­mins. Jay Hawkins

via email ANSWER: When it comes to driv­ing in the sand, flota­tion and mo­men­tum are your two best al­lies. Those who love to “sand camp,” as you plan to do, air down their truck and trailer’s tires as low as pos­si­ble with­out bust­ing beads off the rims. The low air pres­sure cre­ates a wider foot­print, which gives bet­ter flota­tion in sand (and snow). A good start­ing point for trailer-tire air pres­sure when tow­ing in sand is 16 psi, with 15 psi for the rear tires of the truck, and 12 psi for the front, as they are car­ry­ing the light­est load. If that’s not low enough, drop an­other pound or two from the truck’s tires. It’s also pru­dent to run a tire/ wheel com­bi­na­tion that pro­vides enough tire side­wall to al­low the un­der-in­flated tires to flex with­out pop­ping off the bead. In this in­stance, 16-inch trailer rims and 17-inch truck rims are good choices. We also rec­om­mend hav­ing a good on­board air sys­tem to re­in­flate tires, along with six 4x2x8 wooden boards, and/or four emer­gency trac­tion mats such as those of­fered by Max­trax (, just in case the tires of the truck, trailer, or both be­gin to sink. The boards are also in­valu­able for help­ing keep the trailer stable on jacks once it’s parked on the sand. We also rec­om­mend hav­ing a strong winch (min­i­mum 12,000-pound ca­pac­ity) and heavy-duty winch bumper in­stalled on the tow rig, just in case self-re­cov­ery is needed. As for driv­ing tips, there’s re­ally only one: Keep a good amount of for­ward mo­men­tum while driv­ing over soft, dry sand when tow­ing in/out of your camp. When you take off in sand, roll lightly into the throt­tle un­til the truck is mov­ing for­ward, and then be more ag­gres­sive. If you feel the tires dig­ging down in­stead of rolling for­ward, get off the throt­tle and use the trac­tion mats or boards in­stead of bury­ing the tires. With aired-down tires and a lit­tle ju­di­cious weight on the right foot, you shouldn’t have to worry when tow­ing over rel­a­tively flat, sandy ter­rain.


QUES­TION: I haul build­ings rang­ing from 8x10 to 14x40 feet up to 15 feet tall and plan on buy­ing a ’19 F-550. Chas­sis cabs are de­tuned ap­prox­i­mately 100 hp. I’ve been told they have smaller tur­bocharg­ers so you can’t just use a pro­gram­mer on them. Also, I don’t in any way want to jeop­ar­dize longevity. (This is a haul­ing truck I use to make my liv­ing, on the high­way, moun­tains, dirt-log­ging roads, you name it—five days a week). So, what is your in­put? Is there a safe and not too ex­pen­sive way to at least match the power of a stock F-350? I would like a lit­tle more per­for­mance than the fac­tory of­fers. Thanks for the help! Brian Un­ruh

via email ANSWER: As you note, Ford in­creased horse­power and torque for the 6.7L Power Stroke en­gine in ’18 F-250 and F-350s to 450 hp and 935 lb-ft of torque. The same en­gine in chas­sis cabs is rated at 330 hp and 750 lb-ft torque. The power dif­fer­ence lies in the engines hav­ing dif­fer­ent tur­bocharg­ers and, ac­cord­ingly, unique ECM cal­i­bra­tions. The new­est “light-duty” F-Se­ries uses a dual-sided com­pres­sor wheel, also known as a sin­gle-se­quen­tial turbo, while the “medium-duty” F-Se­ries is de-tuned by us­ing a con­ven­tional fixed­vane turbo that flows less air. That ac­counts for a chunk of the chas­sis cabs’ power de­fi­ciency. As Ford’s “2017 Su­per Duty Chas­sis Cer­ti­fi­ca­tion vs. Dyno Cer­ti­fi­ca­tion” sheet notes, “The tur­bocharg­ers are not di­rectly in­ter­change­able. In ad­di­tion, the ex­pense to change the tur­bocharger would be ex­ces­sive and likely not worth the ef­fort, as the ve­hi­cle still re­quires a dyno cer­ti­fi­ca­tion, which will pro­duce lower rat­ings. Also, chang­ing the tur­bocharger in the chas­sis cab would likely cause the ve­hi­cle to fall out of fed­eral emis­sions com­pli­ance. Dam­ages caused by this kind of al­ter­ation may void the en­gine and EGR sys­tem war­ranties.” Ac­cord­ing to the en­gine cer­ti­fi­ca­tion sheet,

“All Su­per Duty pick­ups are chas­sis cer­ti­fied, which does not re­quire ex­haust gas re­cir­cu­la­tion at full power to pass the emis­sions test. Chas­sis cabs and medium-duty trucks are dyno cer­ti­fied, which does re­quire EGR in or­der to pass the emis­sions test.” EPA guide­lines al­low trucks with 10,000- to 14,000-pound GVW to be ei­ther chas­sis or dyno cer­ti­fied. That’s why Ford (and its com­peti­tors) uses chas­sis cer­ti­fi­ca­tion for trucks in this GVW range, thus al­low­ing them to show a 20 to 25 per­cent higher power rat­ing than what dyno cer­ti­fi­ca­tion (re­quired for trucks more than 14,000 pounds GVW) shows. So, short of run­ning afoul of the fed­eral smog laws, we’re afraid there aren’t many op­tions to get the same power as found in the smaller light-duty F-Se­ries pick­ups. Tun­ing that in­creases the flow of the piezo in­jec­tors might be the only way to stay smog-le­gal and get a bit more horse­power.


QUES­TION: I have an ’11 Ram. It’s stock with about 88,000 miles. I have only changed the airbox to an S&B Fil­ters cold-air in­take and Dy­na­trac lock­out hubs. I have made two round-trips from Illi­nois to the West Coast, cross­ing over the big hills, and find that from about 6,500 to 9,200 feet al­ti­tude fuel mileage in­creases from 17 to 21.4 mpg on the com­puter, which I ver­i­fied by the amount of fuel used and miles trav­eled. Do you have any ideas why there is a fuel-mileage dis­par­ity at higher al­ti­tude? Bob Houlne

via email ANSWER: Mul­ti­ple rea­sons for al­ti­tude af­fect­ing fuel econ­omy come to mind. The truck’s ECM could be pro­grammed to use less fuel at those higher al­ti­tudes, be­cause diesels op­er­ate with a wider air/fuel ra­tio range than gaso­line engines’ op­ti­mum 14.7:1. Diesels love cold, dry air, too, so the gain you see could be from a more ef­fi­cient fuel burn. Climb­ing moun­tains also means coast­ing down the other side. If you are rel­a­tively light on the throt­tle while climb­ing grades, the light use of throt­tle on the down­hill side could be enough to boost the over­all av­er­age to a higher mpg. How one drives has a huge ef­fect on fuel econ­omy. Drag also plays a role. At higher al­ti­tudes, the air has less drag on the ve­hi­cle, so it takes less power to main­tain a cer­tain speed at 6,000 feet el­e­va­tion than it would at sea level. Tire pres­sure also con­trib­utes to bet­ter mpg at al­ti­tude; as the el­e­va­tion climbs, so does tire pres­sure, which will be about 3 psi higher in that range of al­ti­tudes if am­bi­ent tem­per­a­ture is the same. The cu­mu­la­tive ef­fect of all these can con­trib­ute to a boost in ob­served fuel econ­omy.

The ideal place­ment for a pyrometer probe is in the ex­haust man­i­fold, where the EGT is the most rep­re­sen­ta­tive of what’s hap­pen­ing in the com­bus­tion cham­bers. It can be more than 400 de­grees cooler where the ex­haust ex­its the turbo.

Flex­plate fail­ure is usu­ally the re­sult of dam­ag­ing vi­bra­tions from the crank­shaft or driv­e­line, move­ment be­tween the en­gine and trans­mis­sion, or from high torque loads and hard shifts. Stock flexplates should be re­placed with bil­let-style units when fail­ures oc­cur.

Tow­ing in sandy ter­rain re­quires air­ing down trailer and tow-ve­hi­cle tires. For ex­am­ple, it’s com­mon for sandlov­ing ATVers in the Pa­cific North­west to lower toy-hauler tires to 15 psi and as lit­tle as 12 psi on their diesel tow rigs.

Ford uses the same ba­sic 6.7L Power Stroke en­gine ar­chi­tec­ture in all Su­per Du­tys. How­ever, chas­sis-cab F-450/-550s don’t get the sin­gle se­quen­tial tur­bocharger, nor can they be eas­ily up­graded to achieve the same power as the pick­ups—at least not legally.

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