Test Motor #3-Wild LM7 5.3-Liter
Pistons: Stock 4.8-liter (flat-top)
Cam: COMP XR281HR .571/.573 lift, 228/230 duration split, 112 LSA
Heads: TFS GenX 205
Intake: FAST LSXR
TB: FAST 102 mm
Headers: QTP 1¾-inch long-yube
Peak Power: 501 hp at 6,500 rpm
Peak Torque: 452 lb-ft at 5,400 rpm
Torque Curve: Exceeded 425 lb-ft of torque from 4,200-6,100 rpm
11. The GenX 205 heads featured full CNC porting to maximize flow to our test motor.
12. We also swapped out the stock truck intake in favor of a FAST LSXR intake and matching
13. Run with the COMP cam, GenX heads and FAST LSXR intake, the wild 5.3-liter produced 50
This wild combination was designed to cater to the needs of the adventurous few who are looking to maximize the power output of their 5.3-liter. The stock 5.3L short-block was retained, but with one small change. The stock dished pistons were replaced with flat-top versions from the 4.8-liter. It is also possible to utilize an L33 HO version of the 5.3L factory equipped with flat-top pistons. The flat-tops were combined with a set of TFS GenX 205 heads designed specifically for the small-bore 4.8L/5.3L motors. The GenX heads offered tremendous flow while retaining the small combustion chamber to optimize the static compression ratio. The heads worked in conjunction with a COMP XR281HR cam and FAST LSXR intake. Run with lightweight Lucas synthetic oil, we managed to fine-tune this 5.3-liter up to 501 hp and 452 lb-ft of torque. Make no mistake, this motor was happiest higher in the rev range, but we were surprised by the torque production. Though we expected the combination of added head flow, cam timing, and runner volume in the LSXR intake to at least trade off low-speed torque, this combination offered more power and torque from 3,000 rpm to 7,000 rpm.