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2003 Chevrolet Avalanche Supercharged Engine Build

Part 2: dropping the supercharged 408 LSX in the Chevy Avalanche and strapping it to the dyno

Scott Parker
Jul 17, 2015
Photographers: Scott Parker
In the first installment we detailed the build-up of Greg Lovell's 6.0L-based 408-cube LSx engine for his 2003 Chevy Avalanche. The purpose of the build was not only to make a fun daily driver, but something he could confidently tow customer cars as well as his own personal collection. To refresh you memory, the Avalanche had previously sported a nearly stock 5.3L LM7 V-8. However, the compatibility of the Gen III/IV small-block platform made upgrading quite simple. AntiVenom started with a fully machined 6.0L iron truck block from Summit Racing, added a Callies rotating assembly with Wiseco pistons, upgraded the valvetrain with Comp Cams full array, and topped off the motor with a set of CNC-ported LS3 heads.
While a naturally aspirated 408 LSx would have made plenty of steam on its own, Greg's plan was to make north of 750 horsepower on pump gas using a Magnuson TVS2300 supercharger. After all, it does have to keep pace with Corvettes. As a Magnacharger dealer, Greg knew all too well that the only direct-fit kits available used the smaller TVS1900 and the old MP112. Neither choice would be capable of supplying enough airflow for the stroker motor and its high-flowing heads. AntiVenom elected to use the Street Rod kit with a Corvette drive system, which would be retrofitted into the truck's roomy engine bay. This kit came with a 10-rib pulley sized for 16psi as well as a front-entry, rear drive supercharger casing. A carbon fiber jackshaft connects to the pulley, which meets a set of cogs in the rear of the blower to turn the rotors. The setup was completed with an ATI Corvette balancer and 10-rib accessory drive (PN 917348, 917034X). This would not only insure a slip-free belt setup, but it would also protect the engine from torsional vibrations and allow AntiVenom to pin the crank to the balancer.
To complete the powertrain overhaul, we needed to insure that the massive quantity of spent air and fuel could exit the LSx engine quickly and efficiently. Considering the level of performance expected from this engine, we didn't hesitate to call two of the best in the business for a little help. Kooks Custom Headers sent a gorgeous set of 304 stainless long-tube headers (PN 28502400) with 1 7/8-inch primaries and a 3-inch collector along with an accompanying 3-inch Y-pipe (PN 28513200). Though these headers were designed for 1500 Series Silverados and Sierras (1999-2013), we didn't anticipate any fitment issues on the Avalanche. Kooks uses state-of-the-art equipment from a CNC mandrel tubing bender to MIG and TIG welders, robotic welders, CMM 6-Axis Arm scanning, CAD, and precision made fixtures. Speaking of state-of-the-art, a Corsa Performance 3-inch stainless steel cat-back exhaust (PN 14250) was chosen to keep a lid on the raucous combustion events. Corsa uses Reflective Sound Cancellation (RSC) technology, rather than traditional perforated core and fiberglass, to "selectively eliminate resonate frequencies that cause drone." By reflecting certain sound waves out of phase, the engineers can tune the exhaust note to their liking while keeping flow at a premium. If you love a healthy sounding engine, but don't want to be punished for it – this is the exhaust for you.
With so many custom features to this build, the crew at AntiVenom had their work cut out for them. Your humble author is just glad he was only in charge of taking pictures. Follow along to see what I mean.
Photo 2/27   |   2003 Chevrolet Avalanche 408 Lsx Engine With Magnuson Supercharger
1-4 AntiVenom Racing is a dealer of Magnusson superchargers, and chose the TVS2300 as its weapon of choice for building a 750+hp Chevy Avalanche. This LS3 Street Rod kit came with a 10-rib Corvette-style drive system, fuel rails, and 60 lb/hr injectors. [A heat exchanger and valley cover is also included, though not pictured.] One downside to using this kit: since the '03 Avalanche had a Gen III V-8 from the factory, the provided Gen IV valley cover didn't have knock sensor provisions. AntiVenom used an LS6 valley cover instead (since it has the best PCV system), and removed material to fit under the blower. Greg prefers Magnacharger because they have proven extremely reliable and trouble-free, in addition to making excellent power when using the Twin Vortices Series (TVS) Eaton rotors.
Photo 6/27   |   2003 Chevrolet Avalanche 408 Lsx Engine Magnuson Supercharger Ati Super Damper
5 An ATI Super Damper is a great option on any engine build, as its patented design absorbs torsional crankshaft vibrations. In addition to exceeding SFI 18.1 specs, the ATI balancer allows you to pin the crank. Factory LSx balancers simply press on, and can spin (on the crankshaft instead of with) when driving a supercharger. The 10-rib option is essential with higher boost levels, as the smaller diameter blower pulley tends to slip. AntiVenom stuck with the stock diameter, but if more boost is required up to 10% overdrive is available. The Holley Performance accessory drive brackets (PN 20-135) are also pictured, which accommodate the Corvette drive setup. The belt routing was revised after this picture was taken.
Photo 7/27   |   2003 Chevrolet Avalanche Pulling Factory Lm7 V 8 Engine
6 Back at AntiVenom's skunkworks, Greg Lovell pulled the factory LM7 5.3L V-8 like a boss. The radiator and fans remained on the vehicle thanks to the truck's ample room. However, you'll notice that the engine is devoid of the accessories, exhaust manifolds, and intake manifold.
Photo 8/27   |   2003 Chevrolet Avalanche Degreasing Oil Pan And Windage Tray
7 After draining the oil from the stock LM7, Greg removed the oil pan and windage tray. A little degreaser was used to clean them off before installing on the new bullet. In case you are wondering, the deep skirted block design negates much of the effect of aftermarket oil pans and windage trays, so a stock pan is fine for most applications.
Photo 9/27   |   2003 Chevrolet Avalanche Openging Holes In Windage Tray
8 The windage tray needed to be modified slightly, though, for the main studs. In addition to opening up a few holes, Greg used spacers (from ARP) to clear the longer stroke.
Photo 10/27   |   2003 Chevrolet Avalanche Oil Pan Warning
9 GM actually cast this into the oil pan and it's no joke. Make sure you have the GM alignment tool and torque accordingly whenever you install an oil pan.
Photo 11/27   |   2003 Chevrolet Avalanche Cherry Picker Installing 408 Lsx Engine
10 Installing an engine into a late-model 1500 series GM truck requires a quality cherry picker with a long arm. Greg wound up having to retrieve this one from the main facility. Thankfully it is possible to install the engine with the hood, radiator, and fans intact.
Photo 12/27   |   2003 Chevrolet Avalanche 408 Lsx Engine Rivet Coolant Plugs
11 Here's another great tip from your friends at AntiVenom: forget about the old style coolant plugs. These rivet plugs are used on newer Gen IV engines and are super slick. They install with a pop rivet gun.
Photo 13/27   |   2003 Chevrolet Avalanche 408 Lsx Engine Dropping On Magnuson Supercharger
12 Greg dropped the supercharger on to the 408 – a task that requires a strong back and long arms.
Photo 14/27   |   2003 Chevrolet Avalanche 408 Lsx Engine Installing Corvette Style Accessory Drive System
13 Next Greg installed the Corvette style accessory drive system. Thankfully the F-body and Corvette style water pump are pretty much the same, and the Holley bracket allows use of the (cheaper) truck alternator. Once Greg revised the belt routing for maximum belt wrap (another key to eliminating belt slip), he had to order a new Kevlar belt. A few other modifications were required to accommodate the accessory drive system including a different thermostat housing, hoses, and Corvette A/C compressor. Greg also re-routed the wiring harness.
Photo 15/27   |   2003 Chevrolet Avalanche 408 Lsx Engine Magnuson Heat Exchanger
14 The large Magnusson heat exchanger had plenty of room sitting behind the bumper, while getting airflow across the bottom portion of the fins. At the same time it doesn't block the trans cooler or radiator.
Photo 16/27   |   Kooks Long Tube Headers
Photo 17/27   |   Inside Kooks Long Tube Headers
15 & 16 Kooks long-tube headers are constructed of 304 stainless steel. The 1 7/8-inch primaries are mandrel bent (as is the 3-inch Y-pipe), TIG welded to a 3/8-inch flange, and MIG welded to the 3-inch collector. The 4-into-1 style collector has a velocity spike MIG welded inside to smooth the transition of exhaust flow and prevent the swirling effect that can slow down exhaust pulses. The collector also has a ball and socket style flange, which makes installation a breeze. These headers are not 50-state legal, but are available with high-flow cats as seen here.
Photo 18/27   |   2003 Chevrolet Avalanche Installing Kooks Long Tube Headers From Bellow
17 Both headers are installed from below, and can even be done on a couple of a jack stands. Since these headers are designed for 1500 Series trucks, there was a slight fitment issue with the 4L80E. However, it was easily resolved by cutting off one of the ears on the bellhousing.
Photo 19/27   |   2003 Chevrolet Avalanche Removing Old Exhaust
Photo 20/27   |   2003 Chevrolet Avalanche Removing Old Exhaust
18 & 19 While Greg had his reciprocating saw out, why not use it to remove the old exhaust?
Photo 21/27   |   2003 Chevrolet Avalanche Kooks Y Pipe Bolted To Headers
20 With rusty old pipes out of the way, the Kooks Y-pipe was bolted up to the headers.
Photo 22/27   |   Corsa Performance Stainless Steel Exhaust System
21 Since Greg wanted his truck to sound as good as the Vettes he tows, we contacted Corsa Performance for a 3-inch stainless steel exhaust system. There is no other performance exhaust on the market that is as effective at eliminating drone thanks to the RSC technology and chambered design. The last thing you want when towing to a car out of state is an annoying drone on the highway. The rolled edge, double walled tips are a great touch as well.
Photo 23/27   |   2003 Chevrolet Avalanche Bolting 3 Inch Exhaust Pipe To Kooks Flange
22 The 3-inch pipe bolted up to the Kooks flange just like OEM, and the massive muffler slipped onto the pipe and into the hanger without issue.
Photo 24/27   |   2003 Chevrolet Avalanche Installing Tailpipe
Photo 25/27   |   2003 Chevrolet Avalanche Installing Tailpipe
23 & 24 The tailpipe went over the axle like factory, slipped into the muffler, and was clamped tight. Again, there was no issue sliding the system together or attaching to the hangers. [To hear this beast go to: http://goo.gl/unOECH.]
Photo 26/27   |   2003 Chevrolet Avalanche Installing Tailpipe

Photo 27/27   |   2003 Chevrolet Avalanche 408 Lsx Supercharged Engine Dyno Stats
25 On 93-octane pump gas the Avalanche recorded 700-rwhp and 608 lb-ft of torque on the Dynojet chassis dyno. With more tuning to go and methanol injection, Greg feels pretty confident he can squeeze more power out of it. Tuning the Avalanche at this power level (roughly 850hp at the crank) proved tricky as it maxed out the mass airflow sensor and the VE tables. In the mean time he is happy to report that it lights up the tires at 1/8 throttle and will soon resume full-time duties.


Kooks Custom Headers
Statesville, NC 28677
Seffner, FL 33584
Holley Performance Products
Bowling Green, KY 42101
Ventura, CA 93003
Corsa Performance Exhaust
Berea, OH 44017



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