Compared to the stock LS3 cylinder heads (left), the Mast castings have a much thicker 0.7
The thicker decks of the Mast heads require longer 8.150-inch pushrods. Mast offers its ow
Stock L92/LS3 rocker arms can be used on Mast’s cylinder heads, but they must be bolted to
Call the specs girlie if you must, but it’s tough to find fault with a 64hp gain we witnessed on the dyno, bringing the grand total to 533. That’s right, folks, 533 hp from an otherwise-stock LS3 with nothing more than a cam swap. Examining the dyno sheet reveals that the Mast cam effectively moved peak torque up to 480 lb-ft at 5,400 rpm compared to the stocker’s 465 lb-ft at 4,700 rpm. While the Mast cam only yielded an additional 15 lb-ft, moving the torque peak higher up on the powerband boosted peak power big time. The cam did give up some grunt below 3,000 rpm, but after that it produced 400 lb-ft of torque or more all the way up to 6,200 rpm. Mast attributes this remarkably broad powerband, in part, to the cam’s wide 115-degree LSA. “The stock LS3 heads flow so much air that you don’t need a ton of duration to make lots of power,” Horace Mast, of Mast Motorsports, explains. “This cam was designed for a stock displacement engine, and our goal is to increase power while retaining smooth idle quality and OE driveability. We also offer a slightly larger 230/237-at-0.050 cam that makes an extra 8-10 hp.”
Without question, the biggest aces up the LS3’s cylinder sleeves are its outstanding factory heads. These 260cc castings borrow their basic architecture from the LS7 heads, utilizing raised rectangular intake ports and monster 2.165/1.590-inch valves. With 320-330 cfm of flow right out of the box, they can easily support 600 hp. As great as the stock LS3 heads may be, Mast says that their brand-new castings blow them away by 40-50 cfm on the flowbench. To see if those bold claims actually held true on the dyno, we had to test them out.
Mast’s all-new CNC-ported castings sell for $3,600 fully assembled, and feature 256/89cc ports, 2.165/1.600-inch valves, and 69cc combustion chambers. Those critical dimensions are similar to stock, but Mast says that flattening out the valve angle from 15 to 12 degrees and revising the port geometry gives its heads a substantial increase in flow. Despite repositioning the valves, the heads are fully compatible with stock pistons. On a 4.070-inch bore fixture, Mast advertises 351 cfm at 0.600-inch lift, and 370 cfm at 0.700-inch lift on the flow bench. Once bolted to the crate LS3, the Mast heads lived up to the hype. Output jumped to 568 hp and 507 lb-ft for gains of 35 and 27 numbers, respectively, over the stock hardware. Last we checked, 507 lb-ft of torque from a 376ci motor—which works out to 1.34 lb-ft per cubic inch—is stout by any measure, a testament to how efficiently the Mast-modified LS3 fills its cylinders with air.
Mast Medium-Bore LS3 Heads
More Inches, Please
Although a 99hp gain with a cylinder head and cam swap is mighty impressive, unless you’re willing to turn 7,500-plus rpm, a 376ci short-block is far too small to take advantage of 370 cfm of airflow. To demonstrate the potential of the Mast heads, given more cubes and cam, we bolted them up to a 416ci stroker short-block and matched it up with a 242/260-at-0.050 cam ground with 0.615/0.642-inch lift and a 114-degree LSA. Essentially a stroked LS3, it’s comprised of a 6.2L block bored 0.005-inch over, a Callies 4.000-inch forged crank and rods, and 11.2:1 Mahle pistons. The enlarged short-block did bump up compression a half-point over the stock LS3, but it’s safe to assume that the majority of the gains were attributable to the extra cubes and more aggressive cam. The final dyno tally registered 630 hp and 555 lb-ft of torque for an increase of 62 and 48 numbers, respectively. Just imagine what this puppy would do with another 20 degrees of cam duration.
|GMPP LS3 crate engine
|Mast cam and valvesprings
|Mast cylinder heads
Just for fun, we bolted up a Performance Inductions single-plane intake manifold onto the
As no surprise, matching the Mast heads up with a bigger 416ci short-block and 242/260-at-
In addition to its line of handbuilt stroker motors, Mast also carries the full line of GM