UPGRADING AN LS ENGINE
UPGRADING AN LS ENGINE & RIGHTING THE GENERAL’S WRONG
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.