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Words And Photos: Richard Holdener
If you had to pick the best factory intake manifold for your cathedral-port LS, which one would you choose? Now that you have secured the best factory intake, how does it compare to something from the aftermarket? Good questions, as the factory offerings include a pair of car and a pair of truck intakes.
We were unable to secure an LS2 intake for this testing, but we know from previous testing where the LS2 stacks up against the other factory offerings (better than the LS1 but less than the LS6, despite the larger 90-mm throttle opening).
Checking in for this test were no less than four different factory manifolds, including those topping the early and late trucks (Trail Blazer SS) and the 5.7L twins, the LS1 and LS6. Keeping the factory performance in check was the darling of the after market, the 102-mm FAST LSXR. Running the five different intakes allowed us to demonstrate not only how much power was available on a budget with the stock manifolds, but also whether it might be worth spending a few extra bucks on the LSXR.
Rather than run the test on a stock 5.3L, we decided to build a suitable test motor. Staring with a fresh 6.0L block from Gandrud Chevrolet, the test mule was stuffed with a stock crank swinging Carrillo rods, CP flat-top pistons and Total Seal rings. Also present in the 6.0L build up was a COMP 54-469-11 LSr cam, matching lifters and hardened pushrods.
Topping the modified short block was a set of CNC-ported, AFR LSX 230 V2 heads. The AFR heads offered plenty of flow to tax even the 102-mm LSX intake, to say nothing of the factory pieces. The heads were secured using Fel Pro MLS head gaskets and ARP head studs, while the stock truck oil pan was filled with 4.5 quarts of Lucas 5W-30 oil.
Each intake was tested with the appropriate-sized throttle body to match the throttle opening in the intake and run with a Holley HP EFI system controlling the injectors. To ensure accurate data, the air/fuel and timing values were optimized (duplicated) for each intake.
Results
To establish a baseline, we first ran the early truck intake. Due to its availability and use on the 4.8L/5.3L twins, the early truck intake has a well-deserved reputation of offering plenty of power and torque for most LS applications. Run on the modified 6.0L, the early truck intake produced 549 hp and 481 lb-ft of torque. There are a number of applications where the truck manifold just won’t fit, but judging by the results, there is a sacrifice to be paid for fitment.
Equipped with the LS1, the 6.0L produced the lowest power of the test, managing only 535 hp and 468 lb-ft of torque.
Things improved greatly with the LS6 intake, as the improved version of the original LS1 offered 557 hp and 483 lb-ft of torque, bettering not just the LS1 but the early truck as well (at least above 5700 rpm).
The late-model truck intake offered the best power curve of the bunch, offering both more power and torque than any of the other factory manifolds, with peaks of 563 hp and 597 lb-ft of torque. Naturally we saved the best for last, as the 102-mm FAST LSXR stepped up the power output to 591 hp and 505 lb-ft of torque. Now all you have to do is decide whether to go factory or spend a few extra bucks for the extra 42 hp offered by FAST.
Low man on the intake totem pole was the factory LS1, which was down by 14 hp and 13 lb-ft to the early truck intake. The LS6 bettered the early truck intake, but only above 5,500 rpm. The late-model truck intake offered the most power and torque of the factory manifolds, and even out-torqued the FAST LSXR up to 4,600 rpm. The big winner was (of course) the FAST LSXR, which produced 591 hp and 505 lb-ft of torque. Compared to the early truck intake, the FAST LSXR offered an additional 52 hp and 24 lb-ft of torque. It topped the wimpy LS1 by 66 hp!
Sources
ARP
arp-bolts.com
COMP Cams
compcams.com
CP Pistons/Carrillo Rods
cp-carrillo.com
FAST
fuelairspark.com
Holley/Hooker/Weiand
holley.com
Lucas Oil
lucasoil.com
