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Mast Motorsports LS7 Crate Motor - Going Overbored

An Inside Look At Mast Motorsports' 669HP LS7 Crate Motor

Stephen Kim Dec 7, 2010
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Quick Notes
What We Did
Follow the build process of a 650hp LS7 crate motor at Mast Motorsports

Bottom Line
Way more power than a stock LS7 for not much more money

Cost (Approx)

As legend has it, the 638hp supercharged LS9 is the baddest production small-block ever built. While that's certainly true from a strictly empirical standpoint, for traditionalists raised on massive cubic inches and pressure-differential induced airflow, the LS9's reliance on an external breathing apparatus somewhat diminishes its mystique. Despite the fact that the 505hp LS7 comes up more than 100 hp short of its huffed-and-puffed stablemate, it's an even more impressive specimen of race-bred engineering. Highlights include an enormous 4.125-inch bore, a 4.000-inch steel crank, titanium rods, 11:1 compression, billet steel main caps, dry-sump oiling system, 211/230-at-0.050 cam with nearly 0.600 inches of lift, and CNC-ported 12-degree cylinder heads that flow 370 cfm. Available from GMPP for about $14,000, it's hardly surprising that tons of hot rodders have plunked crate LS7s into their project cars. Considering all the tricks the LS7 has up its press-fit iron sleeves, when Mast Motorsports informed us that it had substantially improved upon GM's original design at a similar price point, we felt compelled to take a closer look at its 650hp LS7 SS crate engine package.

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Wise engine builders know that change just for the sake of change isn't always prudent, so shop owner Horace Mast takes an engineer's approach of building upon the stock LS7's strengths rather than haphazardly redesigning the most powerful naturally aspirated GM small-block ever built from the ground up. To that end, Mast sticks with the factory LS7 block and 4.125x4.000-inch bore/stroke dimensions, but upgrades the rotating assembly with a Callies/Compstar 4340 steel crank and rods, and forged 11.7:1 Mahle pistons. The factory LS7 head castings are improved as well, with a proprietary CNC port job that increases airflow to close to 400 cfm. Likewise, the LS7 SS's 246/260-at-0.050 hydraulic cam is quite a bit larger than stock, but not outrageous considering the 427 cubic inches of displacement, and slight bump in compression. With a factory LS7 intake manifold, the Mast 427 produces 650 hp and 560 lb-ft of torque. Upgrade to an optional FAST intake and the hp and torque figures jump to 669 and 583, respectively. Since factory LS7 engines are rated using the latest SAE testing standards, their 505 hp actually translates to roughly 540 hp under the STP correction factor used by most engine shops. Even so, Mast's combo still kicks out over 100 hp more than a stock LS7 for $16,995, and includes an 18-month/unlimited-mile warranty. That's not exactly pocket change in this day and age, but quickly adding up the costs of the individual components ($3,000 block, $3,000 heads, $2,500 rotating assembly) used in Mast's LS7 SS puts its value into perspective.

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While the performance figures speak for themselves, what really sets Mast's LS7 SS apart is the comprehensiveness of the overall package. In addition to the motor, the combo includes a calibrated Mast standalone ECM, a complete wiring harness, a drive-by-wire throttle body, an accelerator pedal, a GM starter, a balancer, a water pump, an air filter, coil packs, spark plugs, and plug wires. Upon dropping a Mast crate motor between the framerails, all you have to do is add fuel and hook up three wires before firing it up. For muscle car enthusiasts thinking about jumping on the LS-swap bandwagon, it doesn't get much easier than this.

Design Philosophy
Not long after walking through the doors at Mast Motorsports, it's refreshingly obvious that the place isn't run like your typical engine shop. While the company's massive facility-complete with four dyno cells, a machine shop, and engine assembly room-is very impressive, it's not what makes the place stand out. What's most unique is Mast's meticulous approach to not just assembling motors, but designing them as well. A mechanical engineer by trade, shop owner Horace Mast takes his engineering seriously. "Our goal is to apply a true engineering methodology to our crate engine packages," Horace explains. "Making lots of power isn't good enough. Our engines must also provide OEM-caliber durability."

To accomplish this, every Mast engine combo is subjected to a grueling seven-step design process. The first step involves using cutting-edge computer software to optimize engine parameters such as bore and stroke dimensions, port volume, compression ratio, valve size, and cylinder head flow. Next, a prototype motor is built using top-notch components. After designing four to five custom camshaft profiles using engine simulation software, they are all dyno tested to see which one works best. Afterwards, the air/fuel ratio is fine-tuned on the dyno to maximize volumetric efficiency, then the spark maps are established for optimized torque and power. Only after installing the motor in a test vehicle for real-world testing and final tuning changes is it approved for production. Like we said, Mast's crate engine packages are thoroughly engineered, in every sense of the word. Currently, the company has a plethora of naturally aspirated and supercharged Gen IV engines including L92s, LS3s, LS7s, L99s, LY6s, and aftermarket-block-based combos. Additionally, Mast offers engine packages for marine and airboat applications, as well as turnkey short-blocks.

Although the standard Mast LS7 SS is rated at 650 hp and 560 lb-ft, the optional FAST intake manifold on our test engine increased those numbers to 669 and 583, respectively. At just 2,500 rpm the motor is already producing over 400 lb-ft, yet the big LS7 keeps on pulling past 7,000 rpm. How's that for a flexible power curve? To keep the test data as accurate as possible, Mast prefers step testing its engines on the dyno instead of the more common sweep testing procedure.


Mast Motorsports
Nagodoches, TX 75964



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