Mongoose Muscle—Testing Airflow Research’s Mongoose LS3 cylinder head

Air Flow Research is one of the go-to companies for aftermarket cylinder heads and for good reason, as AFR products have always produced impressive results. When we had the opportunity to test AFR’s LS3 Mongoose cylinder heads, we jumped at the chance.

Available in both 4-bolt and 6-bolt options, AFR’s LS3 Mongoose cylinder heads are designed for engines with 4.000-inch or larger bore applications up to 454 cubic inches, and with an operating range of up to 7000 rpm. They are also certified as emissions-legal replacements for 2007-2016 6.2-liter LS engines under CARB #D-250-5.

The AFR Mongoose LS3 12-degree cylinder head is a rectangle port design that is 100-percent machined on the company’s 5-axis CNC equipment. They are cast in A356 aluminum and feature the highest quality components, such as titanium retainers and PAC valve springs, with further upgrades available. The heads are CARB-certified and emissions legal for 2007-2016 6.2-liter LS3 engines, too, so if you feel your Camaro is ready for a bump in power output, these are ready for you and will still pass inspection.

On the engine side of the heads you’ll find 2.165 intake/1.600-inch exhaust valves nestled nicely in a 69cc combustion chamber. For boosted applications, AFR recommends its Inconel exhaust valve and heavy duty intake valve options for added reliability.

Equipped with a 260cc intake runner volume and 95 cc exhaust runner volume, the LS3 Mongoose cylinder heads require a minimum bore size of 4.000-inch to clear the 2.165 intake/1.600-inch exhaust valves, and they are intended to be used on engine applications up to 454 ci and with a rev range of 7,000 rpm. Combustion chamber size comes in at 69cc and the heads are available in 4- and 6-bolt per cylinder fitments.

In addition to the competition 5-angle valve job, AFR also performs CNC porting on the intake and exhaust runners. The LS3-style rectangle intake port measures 2.610-inch x 1.300-inch and port volume comes in at 260cc.

While our test engine is on the smaller side of this cylinder head’s capabilities, you’ll see it still offered a noticeable improvement over stock heads, and they are ready for the next step in this engine’s evolution.

The included valve springs are from PAC Racing and are a 1.270-inch OD hydraulic roller spring set with 155 lbs on the seat. Max valve lift is .650-inch and maximum RPM is 7,000-7,200.

Our subject test engine is a 408ci stroker based on a Gen III 6.0-liter iron truck block. It features a 4.030-inch bore size and a 4-inch stroke and was machined by United Speed World of Tampa, Florida, and assembled by Greg Lovell of Antivenom in Seffner, Florida. The rotating assembly consists of 6.125-inch Eagle H-beam connecting rods, an Eagle crankshaft, and Wiseco pistons with +6 cc dome.

With us using a carburetor to supply the air and fuel to this engine, we needed an ignition system suitable for the application. To that end, we employed this trusty Daytona Sensors Smart Spark coil-on-plug system, which is fully programmable.

Our baseline cylinder heads are stock LS3 castings with a Brian Tooley Racing upgraded valve spring package good for .660-inch of valve lift, and the compression ratio checked in at 10.5:1. To facilitate dyno testing, the dyno runs were performed using a carbureted induction package that consisted of a Quick Fuel Technologies 750cfm carburetor, a Mast Motorsports 2-piece intake manifold, and a Daytona Sensors Smart Spark for the ignition.

The test engine was machined by the staff at United Speed World in Tampa, Florida, and Phillip Joiner Jr, (at left) handled the dyno testing duties and assisted the engine builder, Greg Lovell (at right) of Antivenom with the cylinder head swap.

United Speed World in Tampa, Florida, has been a fixture in the Tampa Bay area automotive community for decades and it continues on today as a speed shop as well as offering full machining, assembly, and dyno services.

After bolting the engine to United Speed World’s Superflow dynamometer, a set of 1 ¾-inch primary long-tube headers were fastened up, and the LS powerplant was fed a mix of 100-octane race fuel and pump gas. We ran the engine in this configuration to establish our baseline numbers, and then bolted the Air Flow Research Mongoose 260 heads on. After that comparison, we also tried out a larger 850cfm carburetor and carb spacer that United Speed World keeps in the dyno room. The combo has proven to be a reliable performer on numerous other engine builds, and it didn’t disappoint here, either. Check out the photos and captions to see the results.

The stock LS3 cylinder heads used for the baseline tests were fortified with a spring package from Brian Tooley Racing to keep up with the Texas Speed camshaft used in this build. The hydraulic roller camshaft offers 251/259 degrees of duration at .050, and .660/.663-inch of valve lift—the lobe separation angle checked in at 111 degrees.

As there was no plan to bolt on a power adder, we went with the 4-bolt Mongoose heads and Lovell and Joiner got to work swapping out factory head castings for the AFR pieces.

The OEM LS3 rocker arm rail mounts will not work with the AFR 260cc LS3 heads, so AFR includes new rocker rail stands. Looking at the photo, you can see that the mounting hole is moved just slightly to accommodate the design in the cylinder head.

For rocker arms, AFR recommends OEM LS3 rockers with upgraded trunnion bushings, and prefers aftermarket roller rockers with 2.155 intake/exhaust rocker bolt centers. For this build, stock 1.7:1-ratio LS3 rockers were employed and fitted with Comp Cams’ trunnion kit.

Baseline testing of this 408ci engine combination offered a stout 584 horsepower at 6,400 rpm and 521 lb-ft of torque at 5,000. Doing nothing more than bolting on the AFR Mongoose heads turned the numbers up to 598 horsepower at 6,900 and torque checking in a 518 lb-ft at 5,000. We later tested an 850cfm Quick Fuel piece that United Speed World keeps on hand as it’s dyno mule carburetor, and employed the company’s favorite 2-inch carb spacer for an additional test. With this change, horsepower pumped up to 616 at 6,600 rpm and torque improved to 538 lb-ft at 5,000 rpm once again. This engine is definitely ready for more—more cam and more cubic inches for sure, and the AFR Mongoose cylinder heads will be there to support them.


Air Flow Research
(661) 257-8124

(813) 690-0175

Brian Tooley Racing
(888) 959-8865

Competition Cams
(800) 999-0853

Eagle Specialty Products Inc.
(662) 796-7373

Daytona Sensors
(386) 322-7390

Mast Motorsports
(936) 560-2218

Quick Fuel Technology
(866) 464-6553

United Speed World
(813) 264-5505

(800) 321-1364