224/230-Duration, .581/.592-Inch Lift, 114 LSA -- FAST LSXR 102mm Intake Manifold
You didn't think we could test all of these camshafts without wondering what a new intake manifold would do, did you? In true go big or go home fashion, we decided to ditch the stock LS6 intake manifold and 75mm throttle body for a new FAST LSXR 102mm manifold (PN 146302) with a matching 102mm throttle body (PN 54102), fuel rails (PN 146033), and Precision-Flow 33 lb/hr injectors (PN 30332-8). On a stock cubic-inch LS1, the 102mm intake manifold may sound large, and many people have argued over its merits on such an application, which made it perfect for our test. As you would expect, the FAST intake bolts directly in place of the old LS6 and everything hooked back up perfectly. After bringing the engine up to temp and checking for leaks, Bob made a couple of test runs with the new manifold, recording a peak 475.5 hp and 437.5 lb-ft of torque, a gain of 12.3 hp and 4.9 lb-ft over our previous 224/230 testing. Interestingly, the FAST LSXR 102 did give up some low end torque below 4,000 rpm, to the tune of 7 lb-ft, but by 4,100 rpm, the FAST was already pulling ahead, carrying torque all the way to 6,900 rpm, where it was still up 11.3 lb-ft. Horsepower, obviously, followed suit, up 14.8 hp at 6,900 and holding over 470 hp from 6,000 rpm all the way until 6,800, as opposed to the LS6, which never even made 470hp peak. Peak power was moved up by 200 rpm, coming in at 6,500 compared to the LS6 peaking at 6,300. Going forward, all testing will be done with the FAST LSXR 102, for consistency and power.
231/239-Duration, .617/.624-Inch Lift, 113 LSA
Knowing what our 224/230 camshaft did, the next logical step was to add more duration and lift to see what effect they would have on the overall power and the general curve. Comp Cams sent us a nice 231/239-duration, .617/.624-inch lift camshaft on a 113 LSA (PN 54-459-11), which serves as a great camshaft for someone looking for a little more power without giving up huge chunks of mid-range torque. Along with the camshaft, we also installed a set of double valvesprings (PN 26926TI-KIT), which are rated to .675-inch of lift, to help keep us safe. Compared to the stock camshaft, we saw nice gains of 67.9 hp and 17.0 lb-ft of torque, bringing our final numbers to 485.9 hp and 439.0 lb-ft of torque. Where the stock camshaft peaked at 6,000 rpm, the 231/239 was already over that power by 5,100 and then it came on strong, making over 480 hp from 6,200-6,900, and finally falling off around 7,200 rpm. No doubt, the 231/239 can be spun much harder than the stock camshaft without giving up any power. Torque was also up 17 lb-ft and, amazingly, made over 400 lb-ft from 3,500 to 6,300 rpm, which tells us this camshaft would pull great on the street with a little bit of gear or a mild stall converter. Of course, to make all that steam up top, the 231/239 did give up some torque down low, but came in stride by 4,100 rpm.