‘Week To Wicked’ C10 lives up to name with new FAST intake manifold

Words/Photos: Brandon Flannery

The evolution of a better intake manifold has been at the forefront of performance since the days of hopped-up flivvers. Year after year, technology inspires another wave of “ground-breaking” intakes, and just when you think it’s all been done, the folks at FAST come ashore with the LSXrt Race Plenum system.

The LSXr manifold broke new ground as a composite two-piece unit for LS3-style engines with adjustable runner configurations. The removable top exposes a set of removable runners that come in three lengths to tune for ideal RPM ranges.

Once the FAST engineers had created their three runner designs, the shortest set proved to make the most power, though it did move the peak up the tachometer and come at the expense of low-end torque. This “Race runner” set enabled a 30-percent gain in power and is perfect for racers who stay in the higher RPMs.

The ability to remove the top offered an opportunity for engineers to create the LSXrt, or “raised top” as it’s unofficially known. This was created as an option for truck owners, since the truck serpentine belt system sits higher than that of the car, and right in the way of the throttle body. The solution? Raise the roof! The entire plenum was designed taller, moving the throttle body up in the process.

With the air stream raised and more volume in the plenum, dyno-testing engineers were surprised to see an instant horsepower gain by simply switching tops. Further testing of the interchangeable runner system showed the medium-length “High HP” runners made the most robust gains in power, though in the upper RPM range and without sacrificing low-end torque. The package was named the “Race Plenum.”

While in-house testing is always helpful, nothing beats real-world results, and one of the earliest new Race Plenum manifolds was shipped to MAST Motorsports. MAST was in the middle of building an LS7 with LS3 heads for the Classic Trucks Magazine “Week to Wicked” project C10.

FAST sent Matt Maxwell out to assist with tuning the Sportsman EFI system and real-time testing that included making pulls with the regular car top and then the raised top. The result? A gain of 20 horsepower, without touching anything else. We asked Matt for the specifics:

“MAST has a state-of-the-art facility, and the guys were very easy to get along with. They typically use their own in-house EFI system on most of the engines they build. They were a little concerned about breaking the engine in with our FAST Sportsman XFI fuel management and EZ-LS ignition system, since they had never used one.

We started with a base tune, and luckily, the guys at MAST had a good idea of where similar engines like to be on air/fuel ratio and ignition timing. We had the engine ready to do the break-in procedure within about 10 minutes. After about 20 minutes of break-in, we were ready to start making some dyno pulls. From there. we dialed in the fuel map to find the best horsepower, then finished up with finding the ignition timing that also provided the best power.

The engine made 681.5 hp at 6,600 rpm and 601.9 lb-ft torque at 5,100 rpm with the car top on the LSXR intake. Then, we swapped it out for the LSXrt top, and power jumped to 703.3 hp at 6,800 rpm and 603.5 lb-ft at 5,400 rpm.

The guys at MAST, and myself, were very impressed by the gains in horsepower the LSXrt top provided, but more importantly, no torque was lost.”

With a solid 700hp on the dyno slip, the engine went out to California to be installed in the Chevy C10. The Classic Trucks “Week to Wicked” project turns a stock or restored vehicle into an updated version of itself in a week to make a SEMA appearance. For the 2016 event, they started with a C20 longbed and, with the help of a “shortening kit” from sponsor CPP, they turned it into a corner-carving short fleetside.

We had a chance to drive it around, and even though the actual power probably lost a few ponies with the exhaust manifolds instead of the dyno headers, power was strong. MAST hand-builds great engines, and this one had no problem propelling the Chevy into ticket speeds at will. Pedal-to-the-floor offline torque and pull was strong, and just about the time you started nodding your head “yes” it really woke up and pulled seamlessly to the redline without being peaky. It’s a smooth transition that just steadily ate more road until you let off.

The CPP suspension features a full coilover conversion with Viking adjustable dampeners and fat sway bars. Handling and tracking are now a far cry from the farm truck ethics of the past, and more in line with an autocrossing ‘69 Camaro. The Scat bucket seats and factory Blazer console keep you firmly in place, and the CPP disc brakes bring everything to a halt with a quickness without any fuss. We were able to spend a full day with the truck and really settle into its essence. It was a blast from stoplights, it powered through the curvy two-lanes like a cat, and the “60-to-90 passing game” was ridiculous when the engine downshifted the 4L80E and grabbed some rpm.

If you have the room, and are the kind of person who likes getting pushed back in the seat among the growl of high RPM, the LSXrt is an easy way to add even more power to your LS. Dyno results, real world driving — it talks the talk and walks the walk.

Sources: FAST, fuelairspark.com