BREAK­ING POINT: FORD

How much power can the Power Stroke han­dle?

Ultimate Diesel Builder's Guide - - Contents -

ISure, some en­gines sur­vive higher horse­power just fine. But then 100-per­cent stock en­gines let loose for no ap­par­ent rea­son once in a great while, too. So, for the pur­pose of this ar­ti­cle, we’re bas­ing our es­ti­mates off of what we’ve seen over the years through­out the diesel in­dus­try, and when (as a gen­eral rule of thumb) you can con­sider your­self near the break­ing point.

f you’re look­ing to more than dou­ble the horse­power your Power Stroke brings to the ta­ble, we’ve got you cov­ered. But first and fore­most, we have to be clear: Any knowl­edge­able diesel en­thu­si­ast will tell you it’s not any one cer­tain horse­power num­ber that kills fac­tory con­nect­ing rods, it’s the en­gine’s over­all setup—and that is cor­rect. Things like in­jec­tion tim­ing, EGT, oil­ing ca­pa­bil­ity at high rpm, boost, drive pres­sure, and how much low-end torque you’re deal­ing with all dic­tate how long (or short) a stock rod en­gine will live at higher horse­power.

7.3L POWER STROKE DAN­GER ZONE (forged rods): 600-650 RWHP DAN­GER ZONE (pow­dered metal): 500 RWHP

When it comes to the weak­est rods found in a Power Stroke en­gine, we have to start with the first mill of­fered: the 7.3L. But, it’s not nearly as bad as it used to be. Over the last decade, we’ve seen im­prove­ments in leaps and bounds in the 7.3L af­ter­mar­ket. Thanks to hy­brid in­jec­tors, more re­fined tun­ing, and bet­ter tur­bocharger tech­nol­ogy, you no longer need a built en­gine to have a 500-plus-hp ’94.5-03 Ford.

How­ever, there were two types of rods of­fered in the 7.3L, forged steel and pow­dered metal, which makes all the dif­fer­ence in the world when it comes to how far you should at­tempt to push things. If you own a ’94.5-99 7.3L Power Stroke, you’re in the clear, as all of those en­gines fea­ture forged rods. How­ever, pow­dered metal rods—known to be con­sid­er­ably weaker—be­gan to make their way into pro­duc­tion on late ’00 build date en­gines (start­ing with se­rial num­ber 1425747). How­ever, to run out the stock of forged rods, they were in­stalled once more be­gin- ning with se­rial num­ber 1440713 and go­ing to 1498318. From there on out, pow­dered metal units got the nod, mean­ing most ’01-03 model year en­gines have them.

As for forged rod en­gines, 600-650 rwhp is the gen­eral con­sen­sus, as long as spot-on, well-tai­lored PCM cal­i­brat­ing is be­hind it. This means a progressive ramp-up in in­jec­tion tim­ing through the low rpm range so as not to “over-torque” the en­gine. Stock rods are at their most vul­ner­a­ble at low en­gine speeds (2,500 rpm or less) when cylin­der pres­sure and torque is high, so pour­ing on the fuel at higher rpm keeps the rods out of dan­ger. The one trade-off is that the torque num­ber won’t be huge (say 1,000 lb-ft made at 2,600 rpm on a 600rwhp setup, as op­posed to 1,200 lb-ft be­ing made at 2,000 rpm). The same tun­ing method­ol­ogy ap­plies with pow­dered metal rod en­gines, but en­thu­si­asts are highly ad­vised to draw the line at the 500rwhp mark.

“I GET ASKED ALL THE TIME HOW MY FORGED ROD 7.3L IS STILL TO­GETHER, BUT PEO­PLE FOR­GET THAT I DID (EVEN­TU­ALLY) BEND THE NUM­BER 8 ROD IN THE ORIG­I­NAL EN­GINE, SO ANY­THING CAN HAP­PEN.” —Matt Maier of Irate Diesel Per­for­mance

6.0L POWER STROKE DAN­GER ZONE: 800 RWHP

Go­ing be­yond the fact that a lack of fasteners in the block led to the in­evitable head gas­ket fail­ures plaguing the 6.0L en­gine (or the lack of head bolt di­am­e­ter, or the torque-to-yield head bolts, etc.), it is one heck of a tough en­gine. Hard part-wise, it’s tough to beat, es­pe­cially when you con­sider the rods found in the LB7 and LLY Duramax en­gines of the same era be­came a prob­lem around the 600hp mark, if not sooner.

Like the late 7.3L rod, the 6.0L comes with pow­dered metal rods, but its rods have proven ca­pa­ble of han­dling much more power. And thanks to the uti­liza­tion of a bed­plate, the bot­tom end is ex­tremely rigid, and the main caps don’t walk around un­der big horse­power and torque like they do on the 7.3L. In our opin­ion, the short block side of a 6.0L is a great start­ing point for adding horse­power.

The 6.0L Power Stroke’s small bore, four-valve de­sign lends it­self to the higher rpm range, which means peak torque is achieved higher as well. This keeps the rev-happy 365ci mill rel­a­tively clear of ex­ces­sive cylin­der pres­sure and big torque down low—pro­vided ap­pro­pri­ate cus­tom tun­ing is be­ing em­ployed. Even a decade ago, be­fore PCM tun­ing was any­where near as re­fined as it is now, sev­eral 6.0L own­ers proved the 6.0L’s bot­tom end could with­stand 700 rwhp. To­day, a lot of se­ri­ous en­thu­si­asts con­clude that the 800hp range gets you into un­char­tered wa­ters with a 6.0L. 6.4L POWER STROKE DAN­GER ZONE: 1,000+ RWHP

In the early days of the 6.4L’s pro­duc­tion run, no one knew how well this se­quen­tial tur­bocharged mill would re­spond to power adders, nor how durable it would be at el­e­vated horse­power and torque lev­els. But once en­thu­si­asts dis­cov­ered how far you could push them, high horse­power builds sprang up everywhere. To this day, the bot­tom end on the 6.4L con­tin­ues to im­press us with its abil­ity to han­dle four-digit horse­power. We’ve seen a slew of ‘08-10 Fords make north of 900 rwhp on the fac­tory ro­tat­ing assem­bly. We’ve also wit­nessed our fair share of trucks churn out well over 1,000 rwhp, run 10s in the quar­ter-mile, and live to fight another day.

“GO­ING BE­YOND THE FACT THAT A LACK OF FASTENERS IN THE BLOCK LED TO THE IN­EVITABLE HEAD GAS­KET FAIL­URES PLAGUING THE 6.0L (OR THE LACK OF SUF­FI­CIENT HEAD BOLT DI­AM­E­TER, TORQUE-TO-YIELD HEAD BOLTS, ETC.), IT IS ONE HECK OF A TOUGH EN­GINE.”

The weak­est link on the 6.4L’s bot­tom end seems to be the pis­tons, but it’s not as cut and dried as you might think. While some crack un­der ex­treme power con­di­tions, most fail­ures oc­cur due to age, and it can even hap­pen on stock or “tune-only” trucks. From what we’ve gath­ered af­ter speak­ing to mul­ti­ple high-end 6.4L shops across the coun­try, it’s a toss-up on whether a stock piston will let go due to high horse­power or sim­ply due to age or abuse.

Some gu­rus be­lieve that piston fail­ures hap­pen more of­ten on trucks that still uti­lize the fac­tory com­pound turbo ar­range­ment. The mul­ti­pli­ca­tion of quick spool-up (lots of low-end torque), ag­gres­sive tun­ing, high drive pres­sure, and the fac­tory piston’s de­sign can all con­trib­ute to its fail­ure. To some ex­tent, we agree with this the­ory based on what we’ve seen, and the fact that large sin­gle-turbo 6.4Ls tend to sur­vive higher horse­power for longer pe­ri­ods of time.

“I HAD STOCK PIS­TONS IN MY 6.4L FOR 60,000 MILES WITH FIVE DIFFERENTSETUPS—FROMSTOCKTURBOS WITH A WASTEGATE AND SPRAY TO BIG COMPOUNDSWITHADDEDFUEL—AND NEVER HAD ANY PISTON IS­SUES.” —Mike Cor­silli of Mary­land Per­for­mance

6.7L POWER STROKE DAN­GER ZONE: 700 RWHP

While Ford’s ini­tial plans for the 6.7L Power Stroke en­tailed the en­gine get­ting forged con­nect­ing rods, pow­dered metal units ended up get­ting the nod (most likely to keep pro­duc­tion costs down). It’s clear that light­en­ing up the ro­tat­ing assem­bly was one of Ford’s goals with this en­gine, as the rods are con­sid­er­ably smaller than what was used in the 6.4L (not to men­tion also be­ing smaller than 6.0L rods).

The add-a-turbo craze, which is an af­ford­able way to have com­pound tur­bos un­der the hood on Duramax and Cum­mins-pow­ered trucks, was not lost on the 6.7L-pow­ered Ford crowd. How­ever, this is where rod fail­ures be­gan to sur­face on ’11-14 Su­per Du­ties. The sin­gle se­quen­tial, dual-in­ducer Gar­rett turbo proved to be a ma­jor re­stric­tion in mak­ing more power. Soon af­ter S400 framed tur­bos were be­ing in­stalled in front of the stock charger in the val­ley, ex­treme drive pres­sure was present and a host of en­gines bent rods in or around the 600rwhp mark.

This prob­lem was al­le­vi­ated once a freer flow­ing val­ley charger was uti­lized and tun­ing be­came more and more re­fined. Now, with the right cus­tom tun­ing, a sec­ond high-pres­sure fuel pump, and a turbo(s) that doesn’t pro­duce a ton of ex­cess drive pres­sure, the stock rods can eas­ily han­dle 650-700 rwhp. UDBG

“We ad­vise 6.7L cus­tomers go­ing over 700 hp that they are in the dan­ger zone, as we’ve seen two mo­tors let go be­tween 725-750 hp.” —Mike Dille­hay of No Limit Diesel

A tell­tale sign you’re look­ing at: a pow­dered metal vs. forged steel 7.3L con­nect­ing rod lies in the rod bolts. Forged rods uti­lize studs and nuts to se­cure the cap, while pow­dered metal units use bolts.

Matt Maier has been at the fore­front of push­ing the lim­its of forged rod 7.3L en­gines over the last few years. His 1997 F-250 has cleared well over 600 rwhp on a chas­sis dyno (fuel only), and a whop­ping 926 rwhp on ni­trous—not to men­tion run­ning bot­tom 11s in the quar­ter mile. To be sure, he has had his share of fail­ures, as the pre­vi­ous (and orig­i­nal) en­gine was pushed to the brink and bent the num­ber 8 rod.

Here you get an idea what hap­pens to 7.3L pow­dered metal rods at high horse­power. While they can be made to live in the 500rwhp range with ad­e­quate PCM tun­ing, this im­age ac­tu­ally speaks to how im­por­tant cus­tom tun­ing is on an en­gine equipped with big­ger in­jec­tors. The owner was run­ning a set of 238/100 hy­brids, which is fine, but an off-the-shelf pro­gram­mer was be­ing used for tun­ing. The added tim­ing and pulse width that’s ideal (and needed to make power) on trucks equipped with stock in­jec­tors is way overkill when the injector size has more than dou­bled.

We’ve all seen this im­age play out plenty of times at the lo­cal diesel shop: the cab be­ing re­moved from the frame of an ’03-07 Su­per Duty. But don’t let the 6.0L en­gine’s top-end prob­lems fool you; the ro­tat­ing assem­bly is quite stout, with a bed­plate, rods ca­pa­ble of han­dling up to 800 rwhp, and cast-alu­minum pis­tons that are known to hang in there just as long.

While cracked pis­tons aren’t a com­mon­al­ity with 6.0L mills, noth­ing is off the ta­ble when added horse­power is in play. Be­lieve it or not, ag­gres­sive tun­ing cracked the piston in this stock-injector Su­per Duty af­ter just 15,000 miles of use.

This is the hard way to find out how much power the 6.0L’s bot­tom end will take. Shortly af­ter clear­ing a lit­tle over 800-rwhp on the dyno, this en­gine ejected one of the fac­tory rods at the track.

It took plenty of fuel, two stages of ni­trous (a 0.136 jet and a .093 jet), and more than 1,100 rwhp to bend this 6.4L con­nect­ing rod. And upon tear­down, the owner of the truck dis­cov­ered the rod wasn’t even the prob­lem. He told us that too much spray and not enough wastegate took out a valve, which was the ac­tual cul­prit that led to all of this may­hem.

As is the case with any en­gine, un­ex­pected fail­ures can oc­cur with a lead­footed driver, a big load in tow, and the pro­gram­mer set on kill. This 6.4L came in with a dead cylin­der due to the afore­men­tioned sce­nario. Also, like most other piston fail­ures, no­tice the crack formed along the cen­ter­line of the wrist pin.

Be­cause the 6.4L’s rods have proven so ca­pa­ble of han­dling big horse­power, a lot of en­thu­si­asts fo­cus their at­ten­tion else­where when build­ing an en­gine. To rule out piston fail­ure, a large sum of folks set­tle on Maxxforce 7 pis­tons from In­ter­na­tional that fea­ture a more de­sir­able style lip that’s bet­ter suited for high per­for­mance. The Maxxforce 7 is the sis­ter en­gine to the 6.4L, so these pis­tons are easy to come by and can be had for a very af­ford­able price tag—hence their pop­u­lar­ity. The Maxxforce 7 piston shown here came from River City Diesel and fea­tures the com­pany’s ther­mal bar­rier coat­ing. The valve re­liefs are an added op­tion for those putting all-out com­pe­ti­tion style en­gines to­gether.

The 6.4L rod and piston assem­bly is big­ger than the 6.0L hard­ware in al­most ev­ery imag­in­able way—which is one rea­son it lends it­self to a bit more dura­bil­ity and be­ing able to sur­vive higher horse­power and torque lev­els. No­tice the larger di­am­e­ter wrist pin here, not to men­tion the beefier con­nect­ing rod used in the 6.4L.

Thanks to great R&D work among the premier tun­ing com­pa­nies in the in­dus­try, the 6.7L’s stock rods are hold­ing up well cur­rently. How­ever, if you’re think­ing about bridg­ing the 700hp range with your Su­per Duty, you may want to con­sider a set of Car­rillo’s H-beam con­nect­ing rods for peace of mind. These rods were re­leased very early on af­ter the ’11 trucks de­buted. We think Car­rillo prob­a­bly knew the lighter, smaller rods in the 6.7L might not be enough for power hun­gry own­ers.

Back when the 6.7L was equipped with the sin­gle se­quen­tial turbo (’11-14 model years), rod fail­ures were def­i­nitely more preva­lent than they are to­day. The 43mm dual com­pres­sor wheeled Gar­rett was great for low-end, tow­ing grunt, but when left in the val­ley with a low-pres­sure charger feed­ing it, way too much torque was pro­duced down low to keep the fac­tory rods safe. Once out of its map, the tiny charger pro­duced crazy high drive pres­sure as well—a recipe for dis­as­ter just wait­ing to hap­pen.

By and large, the gen­eral con­sen­sus is a max­i­mum of roughly 700 rwhp on the 6.7L Power Stroke. While it’s not as high as what you can po­ten­tially get out of the 6.4L it re­placed, it’s a ma­jor im­prove­ment over the early years of this mill’s ten­ure—when a host of stock rod fail­ures sur­faced with ag­gres­sive tun­ing and an at­mo­spheric turbo added to the mix.

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