The two-part question was a simple one. How much boost will a stock 5.3L short-block withstand before the proverbial Big Bang and what is the resulting power output? The web is chock-full of speculation, ranging from absurd to the insane. What will go first? Will the sleeves split in the block or will the power level simply push the crank out the bottom? The smart money is on the notoriously weak cast pistons and powdered metal connecting rods, since neither was designed by GM to withstand the rigors of boost. Rather than rely on viral videos or Internet banter, we decided to find out for ourselves. Having run a similar test for Hot Rod with a 4.8L, we decided to step up to the larger (and more popular) 5.3L LM7 truck motor. Just how tough is the 5.3L? The results of this test will amaze you and make you proud to own a 5.3L Chevy.
The procedure for our Big Bang test was equally simple. We purchased a used (supposedly running) 5.3L truck motor (circa 2003) from a dismantler in Ohio and had it shipped to Westech Performance. Rather than just pull it from the shipping crate and run it, we decided to do a little prep. The engine was first disassembled to ensure it was a worthy candidate. The last thing we wanted was an unusable core with rusty innards or a spun cam bearing. The motor was listed as having logged 160,000 miles, and looked liked frequent oil changes were not part of the maintenance schedule. In addition to checking out the internals, we also wanted to perform a little boost-prerequisite modification to the otherwise stock short-block. The real reason most stock motors fail under boost is insufficient ring gap. The rings heat up and expand until the ring gap is eliminated. Once this happens, the ring can momentarily stick in the bore and snap the ring land off the piston. Damage that is usually attributed to weak piston design is actually insufficient ring gap. Knowing we were going for broke, we gapped the rings aggressively—meaning over .035 for both top and second rings.
While performing the regap procedure on the original 160,000-mile rings (new rings would be cheating), we also addressed a couple issues with the stock pistons. The excessive mileage and (PCV-related) oil consumption left hardened sludge in the ring lands (behind the rings). This was cleaned using a pick, screwdriver and brake cleaner. Scuffed piston skirts were addressed with a little oil and Scotch brite pads. The one machining operation performed was to ball hone the block. Given the high-mileage rings and excessive ring gap, this was probably unnecessary, but we felt better giving the tired truck motor a little love before sending it to its doom. Once everything was cleaned, we reassembled the short-block using the original bearings. We did take the liberty of installing a new oil pump from Federal Mogul. Though we were tempted, we refrained from replacing the seals in the front, rear, and valley covers. Even the original oil pan gasket was deemed adequate for this destruction test. With the stock short-block now boost ready, it was time for some modifications.