594HP 5.3L Gen III Small Block for $3,252

GM has built millions of trucks and SUVs equipped with iron Gen III/IV small-blocks since

Hypothetically speaking, let’s say you had the wrenching skills necessary to build a 600hp Rat motor for $6,500. With the astounding airflow potential of today’s conventional, 24-degree, big-block Chevy cylinder heads and the multitude of dirt-cheap rotating assemblies cluttering up the Summit catalog, this caliber of horsepower-per-dollar heroism is certainly attainable-try hard and you could even do it with stock rec-port heads. Even though that would qualify as an impressive budget build by most standards, how many people have an extra $6,500 to throw around on anything, let alone an engine, these days? Since we’ve all had to recalibrate our affordability scale in recent years, it’s only prudent to pursue truly budget-friendly engine combos that most hot rodders can build without running up the credit cards.

While that concept is, like, so cliché, we’re serious about turning up the wick on dollar-stretching performance. How does a junkyard 5.3L Gen III small-block, boosted to 550 hp with a do-it-yourself turbo setup, built for $3,069, suit your fancy? That tally includes a tuned factory computer, a wiring harness, bigger fuel injectors, and every last nut, bolt, and U-bend to make it happen. If you’ve got another $183 to spend on a stock LS6 camshaft, the power jumps to 594 and the price tag to $3,252. We built it and you can, too, so let’s fire up the welder and throw some sparks.

Gen III truck exhaust manifolds flow extremely well, which, combined with their rugged, ca

The Dirtball Special
Throwing boost at a 5.3L Gen III small-block just makes too much sense. Secondhand OE hardware stockpiled in junkyards has always represented the pinnacle of cheap performance, and the LS-series small-block takes this universal truth to the extreme. Unlike in the early days of LS engine swaps, where hot rodders paid a big premium just for the cool factor, these motors are now just as cost effective to build as a Gen I small-block Chevy. Aluminum variants still command a premium-with plain-Jane, 5.7L, LS1 long-blocks costing upwards of $2,000-but their iron counterparts are much more plentiful and sell for a fraction of the cost. The hot ticket in the Vortec truck engine lineup is the 6.0L LQ9, which was originally installed in 3/4-ton trucks and SUVs. It packs an additional 18 ci over the 5.7L (364 versus 346) and comes equipped with aluminum, LS6-style cylinder heads. The LQ9’s 4.000-inch bores mean that it’s compatible with GM’s L92/LS3 rectangle-port head castings that flow a stunning 320 cfm out of the box. Matching them with a mild hydraulic roller cam nets an easy 550 hp for about $5,000, even after factoring in the cost of a single-plane intake manifold, a carb, an MSD ignition controller, and headers.

If the 6.0L is so great, then the obvious question is, why even bother building a 5.3L in the first place? The biggest downside to the 6.0L truck motor is scarcity, and some early ones had piston-slap issues. GM built way more 1/2-ton trucks and SUVs with 5.3L engines than it did 3/4-ton models with the 6.0L. Consequently, junkyard 5.3L motors can be had for $250, while their bigger brother fetches $1,000 to $1,500. For a naturally aspirated engine build, the 6.0L is a more appealing option due to its additional displacement and superior cylinder heads. On the other hand, what if you took the money saved by buying a 5.3L motor and put it toward a DIY turbo system? To make things more interesting and further drive down costs, let’s hang one of those Chinese eBay turbos off of the factory exhaust manifolds and see if it holds.

To complete the top portion of the merge collector assembly, one end of a short stub of 3-

On paper, a stock 5.3L small-block boosted to 7 to 14 psi seems to have the edge over a naturally aspirated 6.0L build in terms of horsepower per dollar. To put this bold theory to the test, we purchased a complete 5.3L LM7 engine plucked out of an ’01 GMC Yukon-complete with a matching computer and wiring harness-for $449 from a Houston junkyard. If you can’t find a 5.3L motor locally, there are tons of similar deals on eBay if you’re willing to dish out a couple hundred dollars for shipping. At this price point, expect a motor with lots of miles; our tester had 150,000 on the ticker. Even so, many of the junkyards we ran across offered some type of guarantee that their engines were in good working condition.

To pressurize our test subject, we put in a lowball bid on eBay for a 76mm turbo and won it for $425. The rest of our cobbled-up DIY turbo system included a Turbosmart wastegate, blow-off valve, and manual boost controller. To control the fuel and spark, we matched up a stock computer with HPTuners tuning software, Ford SVO 42 lb/hr fuel injectors, and a GM 2.5-bar MAP sensor off of a new Chevy Cobalt SS. The U-bends, flanges, and V-band clamps required to build the turbo piping were all supplied by Fastlane Inc. in Houston, which also stepped up to fabricate everything for us. Fastlane specializes in building custom turbo systems for LS-, Hemi-, and mod-motor-powered late-models, and was kind enough to rig us up a kit in no time. (As you’ll notice, the labor to fabricate the plumbing from the tubing we provided was not included in the total price. Anyone with a MIG welder should be able to build this setup, but if not, factor in several hundred dollars for the fab work.) From there, we hauled the motor down the street to the good folks at the School of Automotive Machinists for a merciless dyno thrash.

The first step in fabbing up a turbo system is figuring out where to mount the turbo in re

Boost
With the 5.3 strapped to SAM’s SuperFlow 902 engine dyno, our goal was to see how far we could push the stock long-block on 93-octane pump gas. For the baseline pulls, we set the wastegate at 8 psi of boost and dialed in a conservative 11.8:1 air/fuel ratio and 16 degrees of ignition timing. The wee 325ci mill responded with a respectable 532 hp at 5,300 rpm and 562 lb-ft of torque at 4,500 rpm. For the next round of testing, we increased the boost to 12 psi, and surprisingly, the motor lost between 10 and 15 hp from pull to pull with the power curve jumping up and down above 5,000 rpm.

Suspecting that the stock 150,000-mile valvesprings were the culprits, we swapped them out for a set of LS6 units. The simple fix did the trick, and horsepower and torque increased to 550 and 575, respectively. “On an engine with that many miles, it’s possible that the boost pressure was preventing the worn out valvesprings from closing the valves all the way,” explained Judson Massingill of SAM. With a junkyard build like this, it’s probably a good idea to replace the valvesprings no matter what.”

Perhaps the most challenging aspect of designing a single-turbo system is building the mer

Considering that the stock 5.3L motor is choked by a minuscule 191/190-at-0.050 cam with just 0.457/0.466-inch lift, the 550 hp our test mule produced thus far was even more impressive. Curious to see what dividends some extra duration and lift would yield, we installed a stock GM LS6 camshaft. The cam was PN 12560950, the ’01 LS unit. There’s much confusion online over the LS6 cam specs, so we had SAM get the real numbers on a Cam Doctor: 203.8/212.1 duration at 0.050, 0.523/0.522 lift, and a 115.9-degree LSA. The LS6 cam’s wide lobe-separation angle bolsters its boost-friendly credentials. Even so, we were shocked when output jumped to 594 hp and 588 lb-ft from a measly 13-degree increase in intake duration. Conventional wisdom says that stock camshafts work well in forced-induction applications, but when the cam in question is as small as the stock 5.3L LM7’s, conventional wisdom apparently doesn’t apply.

Breaking Down the Numbers
In retrospect, our DIY turbo 5.3L motor built on a working-man’s budget far exceeded every expectation. As much as we’d like to take credit for it, LS enthusiasts have been building similar budget turbo combos long before we took a crack at it. To our surprise, the factory long-block survived 27 dyno pulls without a hitch, the Chinese turbo didn’t self-destruct, and it came within six numbers of cracking the 600hp mark. Even at 594 hp, the Dirtball Special produced more than twice the output of a stock 285hp 5.3L LM7. That said, there’s definitely more left in this package considering that the motor picked up just 18 hp after cranking up the boost from 8 to 12 psi. To keep costs to a bare minimum, we passed on rigging up an intercooler, but our dyno figures clearly indicate that this decision sacrificed power during our high-boost pulls. “With an intercooler or methanol injection, this engine would easily make 650 hp,” SAM Head Instructor Chris Bennett opined.

Big-time power gains aside, the pressing question for anyone contemplating a similar buildup is how long a turbocharged, stock, 5.3L engine will last. Based on our dyno results, it’s a good idea to limit boost to 7 to 8 psi on pump gas in nonintercooled applications. Without a means of cooling the inlet air temperature, anything beyond that point yields negligible power gains while increasing the potential for detonation. Furthermore, infinite variations in fuel quality and a hot rodder’s engine tuning skills make it very difficult to put an exact figure on short-block longevity. A whole lot of stupidity can blow up a motor in not a lot of time, whereas some enthusiasts have reported tens of thousands of miles of reliable operation from their forced-induction LS motors. The great thing about the 5.3L small-block is that if you do indeed blow it up, a mere $250 will get you back on the road to boosted glory once again.

At the outset of this engine build, we wanted to find out if a junkyard 5.3L Gen III motor with a giant DIY turbo hanging off the stock exhaust manifolds could really make more power than a naturally aspirated 6.0L for less money. With the fab work and dyno testing complete, the answer is a resounding “yes.”

People’s Republic of Boost?
Although we managed to make some respectable horsepower numbers with a Chinese-made knockoff turbo, we can neither advocate them nor advise against them. On one hand, our unit performed very well during our test. Conversely, the experts at Fastlane have seen them go kaput with minimal mileage. That said, we can’t in good conscience recommend bolting one into a car with expectations that it will last tens of thousands of miles. It just so happens that HOT ROD is in the position to serve as a universal lab rat so you won’t have to spend your hard-earned money experimenting with a Chinese turbo on your own. Just like the reliability of offshore cranks and rods was questionable at best in the beginning, but improved substantially in the years that followed, it’s possible that Chinese turbos will follow a similar path. Even so, turbos are much more complex devices to reverse-engineer than cranks and rods, and for now, the higher cost of well-established, American, name-brand turbos is well worth it. We’d like to pit our Chinese T76 against a Borg Warner T72 to see who comes out on top.