4 Wheel & Off Road - - CONTENTS - Tren­ton McGee BY ED­I­[email protected] PHO­TOG­RA­PHY TREN­TON MCGEE

Right­ing the Gen­eral’s wrong by delet­ing dis­place­ment on de­mand.

LS SWAPS ALL THE RAGE THESE DAYS. IT DOESN’T MAT­ter whether it’s a street rod, a mus­cle car, or a 4x4. GM LS en­gines are find­ing their way un­der the hoods of ev­ery­thing. They’re plen­ti­ful, re­li­able as a ham­mer, nearly bul­let­proof, rel­a­tively in­ex­pen­sive, and can be built to make stupid amounts of power. The most de­sir­able non-Corvette/Camaro LS swap can­di­dates are in 1999-2006 GM ve­hi­cles, but find­ing low-mileage ex­am­ples is get­ting dif­fi­cult (though it’s im­pres­sive that you can find good-run­ning LS en­gines with over 300,00 miles on them). In re­sponse to in­creas­ingly re­stric­tive fuel econ­omy stan­dards, Gen­eral Mo­tors in­tro­duced Dis­place­ment on De­mand (mar­keted as Ac­tive Fuel Man­age­ment) in Gen IV small-block LS en­gines in 2005, and by 2007 most GM cars and trucks were equipped with DOD. These sys­tems greatly in­creased the com­plex­ity of the en­gine man­age­ment sys­tems, and they also hurt the leg­endary dura­bil­ity these en­gines were fa­mous for. It’s cer­tainly pos­si­ble to swap DOD en­gines, and a few af­ter­mar­ket en­gine man­age­ment sys­tems even sup­port the sys­tem, but with so many well-known me­chan­i­cal prob­lems, why not just get rid of the trou­ble­some sys­tem?

The good news is that it’s pos­si­ble to elim­i­nate all traces of DOD/ AFM, but the bad news is that it re­quires in­ter­nal en­gine work. Delet­ing the DOD sys­tem the right way in­volves pulling the heads and in­stalling a new camshaft and lifters, a new en­gine val­ley cover, and much more.

We found our­selves with a cheap 5.3L LH6 out of a Trail­blazer, and we thought about tack­ling the delete our­selves un­til we re­al­ized the ex­tent of the in­ter­nal en­gine work. Our en­gine skills are pretty rusty, so we took our 5.3L to the LS gu­rus at Tilden Mo­tor­sports to ex­or­cise the DOD demons. The com­pany of­fers ev­ery­thing from DOD delete pack­ages and per­for­mance mod­i­fi­ca­tions all the

way up to turnkey, ready-to-run en­gine pack­ages. The DOD delete pro­ce­dure is ba­si­cally the same on all Gen IV LS en­gines, though there are a few more steps if the en­gine is equipped with both DOD and Vari­able Valve Tim­ing. Since we had to re­place the cam any­way, we opted to go with some­thing a lit­tle hot­ter than stock with a Tilden Street Rod cam.

While we didn’t dyno the en­gine when we were done, Tilden con­sis­tently sees horse­power and torque num­bers in the 400 range with our ex­act com­bi­na­tion. Check out what it takes to elim­i­nate Dis­place­ment on De­mand and up­grade an LS en­gine the right way.

1 2 1The re­cip­i­ent of the up­grades was an al­la­lu­minum 5.3L LH6 we plucked from a very wrecked 2008 Trail­blazer with 125,000 miles. Power num­bers vary by source, but it makes around 310 hp and 330 lb-ft of torque. We were able to run the en­gine be­fore we pulled it and no­ticed it had a fairly pro­nounced tick. This led us to do some re­search on the Dis­place­ment on De­mand (DOD) sys­tem, which in turn helped make up our minds to delete it. Step one at Tilden Mo­tor­sports was pres­sure-wash­ing the en­gine. A clean ex­te­rior helps en­sure no con­tam­i­na­tion once the en­gine is opened up.2Truth be told, this was the author’s first foray into an LS en­gine, which is dif­fer­ent in al­most ev­ery way to a con­ven­tional GM small-block. We put the en­gine in the ca­pa­ble hands of LS guru Kevin Stearns at Tilden Mo­tor­sports. The com­pany has de­vel­oped a rep­u­ta­tion as the source for ev­ery­thing from take-out en­gines to high­per­for­mance LS-based en­gine builds.3 On LS en­gines, ac­cess­ing the lifters re­quires re­mov­ing the heads, so the in­take man­i­fold, valve cov­ers, rocker as­sem­bly, and val­ley pan all must be re­moved. Note the cathe­dral-shaped in­take run­ners; LH6 en­gines are equipped with de­sir­able 799 cast­ing alu­minum heads that are re­puted to be one of the bet­ter pro­duc­tion heads avail­able. Also note the elec­tri­cal plug on the rear edge of the en­gine val­ley cover. That plug is the 3 best ex­ter­nal sign that an en­gine has AFM/DOD.

4Uh-oh! Stearns noted this bent pushrod on No. 7 when pre­par­ing to pull the head. Usu­ally in­dica­tive of very se­ri­ous prob­lems, such as a hy­draulic event in a cylin­der, it turned out that one of the lifters for that cylin­der was frozen. For­tu­nately the pushrod was the only dam­age. Stearns found that the bleed hole for the lifter must have clogged with oil con­tam­i­nants, which is very com­mon. 4

5 5 The un­der­side of the val­ley cover on a DODe­quipped en­gine has the so­le­noids that con­trol the oil flow to the DOD cylin­ders. The raised bosses cast into the block below the val­ley cover sup­ply oil pres­sure to those so­le­noids. All Gen III and Gen IV blocks have those bosses, but pre-DOD val­ley cov­ers seal them off. Part of a DOD delete is in­stalling an ear­lier, non-DOD val­ley cover. Note that the in­side of the en­gine was very clean, in­di­cat­ing that the oil was changed reg­u­larly and that the owner stayed on top of main­te­nance.

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