Words and Photos By Richard Holdener

If we believe the age-old adage that our beloved internal combustion engine is nothing more than a glorified air pump, we must also believe in the simple philosophy that more air must be better. From the most basic standpoint, increasing the power output of any motor requires nothing more than improving the airflow though the system. It is important to understand the distinction between airflow through the system (meaning the motor) and simply increasing the airflow of one individual component. More intake, head, or even (in our case) throttle body flow may or may not increase power. The question is can the motor utilize the additional airflow supplied by the component or is there another restriction elsewhere in the system?

Extreme examples make this easier to understand. A throttle body (or any other component) capable of supplying airflow to feed 900 hp will be of limited use on a 450-hp (stock) motor and may not show any power gains at all. The problem is not in the flow rate (or quality) of the component tested, but rather in the engine combination itself.

The Mast top-end components were applied to our 427 LSX short block. The combo included an LSX block from Gandrud Chevrolet stuffed with a Lunati crank, Carrillo rods, and CP pistons. Also present was a Total Seal ring package, Moroso oiling system, and BTR Stage IV LS7 cam. Note the ARP head studs and Fel Pro MLS head gaskets ready to accept the Mast LS3 heads.

For this test, Mast supplied a set of their Black Label LS3 280 heads. Designed for engines running a 4.125-inch bore, these six-bolt LS3 heads flowed 390 cfm at .700 lift.

 Thanks to full CNC porting, the exhaust flow offered by the Black Label heads was equally impressive at 249 cfm.

 These 280cc heads featured 12-degree valve angles, a 2.20/1.60 stainless steel valve combo, and 70cc combustion chambers. The finish quality of the CNC work was first rate — we (almost) hated installing them.

Of course, there are also times when simple airflow devices show impressive power gains. This test run with throttle bodies on our 427 LSX was a perfect example where more airflow offered more power. The test was run on our familiar 427 LSX short-block, but we made changes to the induction system. The 427 itself featured the 4.125-inch bore GM LSX iron block supplied by Gandrud Chevrolet. The freshly machined block was stuffed with forged internals from Lunati, Carrillo, and CP, not to mention components from Total Seal, Moroso, and a cam from Brian Tooley Racing. The additional components included an ATI Super Damper, COMP Cams front cover, and Meziere electric water pump.

Having already run both cathedral-port and LS7 induction system, we decided it was time the LS3 boys got some love. To that end, we installed a set of Black Label LS3 heads from Mast Motorsports, topped with one of their impressive CNC-ported single-plane intakes. Having run their systems in the past, we were excited about testing them on our 427.

The Mast heads were available with a variety of different spring packages, but we opted for a set of Platinum springs from Brian Tooley Racing. Due to the difference in valve guide diameter, installation of the BTR spring kit required a set of COMP 4682-18 spring seats. Note also the dedicated rocker stands supplied with the Mast heads.

 Though the heads featured LS3 port locations, these Mast heads were designed to accept the factory 1.8-ratio LS7 rockers.

 Thanks to our boys at Holley, we were finally able to replace that ugly DOD valley cover with this finned aluminum version. We liked that the paint job matched the LSX block!

In addition to the trick Black Label LS3 heads, Mast also supplied this two-piece, CNC-ported intake. Configured for the cathedral-port LS3 and LS7 applications, the manifold was also available with either 4150 or 4500 carb/throttle body flanges. We chose the 4150 flange for our EFI LS3 application.

Based on the specs, the Mast Black Label LS3 heads looked impressive. In fact, the 427 might not have been enough motor to take full advantage of the airflow offered by the heads (or intake), but we knew we at least had enough to make some real power. The Mast LS3 heads featured 280cc intake ports that offered 390 cfm, or enough to support 800 hp (or more) on the right application. The amazing flow potential can be attributed to a combination of the 2.20/1.6 valve package and full CNC porting. The finish quality was excellent, and the Mast heads have always proven powerful in previous testing. The heads also featured exhaust ports that flowed 249 cfm, 70cc combustion chambers, and .750-thick deck surfaces — making them a great choice for forced induction applications. The heads were supplied with valves only, which we finished up with a valve spring package from Brian Tooley Racing. The Mast heads relied on larger-diameter valve guides, requiring a set of 4682-16 spring seats to work with the BTR spring package. The Mast heads were secured using ARP head studs and Fel Pro MLS head gaskets.

Fuel was supplied though the fuel rails to a set of 83-pound Holley injectors.

Before running the 83-pound injectors on the 427 LSX, we made sure to test the flow rates on this ASNU injector machine. They checked out perfectly, even after sitting unused for a few months.

All testing was run through these 1-7/8-inch Hooker long-tube LS swap headers feeding short collector extensions.

 We relied on this FAST XFI/XIM management system to dial in the air/fuel and timing on our 427 LSX.

 Topping the Mast LS3 heads was one of their single-plane intake manifolds. The two-piece designed allowed full CNC porting and, like the heads, was a serious piece of engine porn. Mast offered intakes for the all three LS engine families (cathedral-port, LS3, and LS7), as well as with 4150 and 4500 carb flanges. Adding to the mix was the availability to run EFI (with injector bungs) or simply as a carbureted intake. We ran one of their LS7 version previously on a 495-inch motor to the tune of 810 hp, so we know these intakes are capable of serious power. We chose a 4150-flanged EFI version for our 427. The injected combination was run with a set of 83-pound Holley injectors using a FAST XFI/XIM management system. Also present was a set of Hooker 1 7/8-inch headers feeding collector extensions (but no mufflers), 1.8-ratio LS7 rockers, and a remote K&N oil filter.

Since the Mast intake was flanged to accept a 4150 throttle body (or carb), we installed this FAST 4150 throttle body.

Run on the dyno with the 4150 throttle body, the Mast-headed 427 produced 669 hp at 6,600 rpm and 574 lb-ft of torque at 5,300 rpm.

 Next up was the 4500-series throttle body from Accufab.

 Installation of the larger 4500-series throttle body onto the 4150-flanged intake required a 4150-4500 adapter from Speedmaster.

First up was the 4150 throttle body from FAST. With the throttle body in place, we ran the 427 in anger to the tune of 669 hp at 6,600 rpm and 574 lb-ft at 5,300 rpm. We expected more power output from the Mast-headed combination, so we went looking for the culprit. Thinking the 4150 throttle body might be limiting airflow, we decided to step up our game with a larger 4500-series throttle body. All we needed was the 4150-4500 adapter to mate the larger throttle body to the 4150 flanged intake. Speedmaster came to our rescue with just such an adapter.

Run with the larger throttle body, the Mast-headed LS3 produced 681 hp at 6,600 rpm and 578 lb-ft of torque at 5,200 rpm. Obviously, the Mast intake required more flow to feed the needs of the LS3-headed 427.

Throttle Body Test-4150 vs 4500 (Mast 427 LS3) As is evident by the power curves, the Mast-headed 427 LS3 was in dire need of additional flow. Despite being flanged (and sized) to accept a 4150 carburetor or throttle body, the Mast single-plane intake wanted more airflow than the 4150 throttle body could supply. Equipped with the 4150 throttle body, the power leveled off at 669 hp at 6,600 rpm. After installation of the 4150-4500 carb adapter and 4500-series Accufab throttle body, the power output jumped to 681 hp at 6,600 rpm. Note the majority of the gains occurred higher in the rev range; this is typical of improvements in airflow.

After installation of the 4500-series Accufab throttle body, the power output of the Mast-headed 427 rose to 681 hp at 6,600 rpm and 578 lb-ft of torque. As expected of a flow restriction, the gains offered by the larger throttle body were most prevalent at the top of the rev range (where airflow is most critical). The simple throttle body upgrade netted an additional 12 hp. That the power came with no change in intake shows the 4150-flanged Mast intake still had more to offer. Now, all we need is more test motor!