L92 vs LS1 and LS2 Heads - Sick Flow, Less Dough- Tech
If you've been reading GMHTP lately, you know that the new L92 heads are superior to stock LS1 and LS2 heads. But what happens when you put them to task against one of the best 15-degree heads on the market? This is exactly what SLP Performance Parts wanted to know shortly after putting together its new L92 cylinder head package. The previous Air Flow Research/SLP 225cc cylinder head package is one tough customer, and the L92 package costs considerably less. So would the L92 setup be able to match up on one of SLP's ZL402 strokers? We tagged along while Director of Engineering Hank Daniecki conducted the test to find out.
SLP L92 Heads and L76 Intake Package vs. AFR/SLP 225cc Heads and LSX 78mm IntakeOur test car belongs to Steve Moffa of Cherry Hill, New Jersey, and when it arrived back at SLP's newly reopened installation facilities, it was equipped with SLP's high compression ZL402, aggressive 236/236 duration cam (PN 51014), Air Flow Research/SLP 225cc heads, FAST LSX intake manifold, and 78mm throttle body, in addition to every bolt-on in SLP's catalog, including Tuned Length Long Tube headers and Loud Mouth exhaust. Steve was nice enough to take his seldom-driven convertible CE Trans Am on the salty roads last February to test out SLP's new L92 head/L76 intake package. Little besides the heads and intake would be changed, leaving the .590/.590-inch lift, 112LSA hydraulic roller, and lifters in the block. SLP previously conducted a similar swap on its engine dyno using another iron block ZL402 equipped with the AFR/SLP heads, but that had an LS6 intake and a soon-to-be-released 224/228 duration, .591/.600-inch lift cam. Results were an impressive 18hp jump from 484 to 502 at 5,500 rpm, and torque climbed from 477 to 495 lb-ft at 5,300 rpm. SLP was hoping to replicate these results on its Super Flow chassis dyno with the larger duration cam, but only time will tell.
Before we get started with the test, let's compare Steve Moffa's previous setup with SLP's new L92 package. In the chart to the right is a complete breakdown of how the SLP L92 heads stack up against the high-flowing AFR/SLP 225cc heads. The most notable difference you'll see is the runner shapes and the much larger intake valve on the L92 heads. It is easy to assume that the L92 heads' strength lies in the LS7-style rectangular intake ports and 2.16 intake valves, which should prove superior to the AFRs. On the exhaust side of the equation, the more rounded ports and slightly larger valve on the AFRs may very well have the upper hand. If these assumptions are correct, the test should show a higher peak horsepower figure with the L92 heads, and better low-rpm torque numbers with the AFRs; however, there is one other important variable: the intake and throttle body. The L92's specially designed intake ports require use of the L76 manifold, which comes complete with 39 lbs/hr injectors, fuel rails, and a 90mm throttle body. Daniecki Sr. should easily be able to adjust the tune for the new injectors, but the change in geometry of the L76 manifold and the substantial increase in throttle-body size should yield different results than the previous LSX intake and 78mm throttle body.
Prior research would seem to indicate that the 402ci mill would benefit greatly from the larger 90mm throttle body; however, it is impossible to tell if the L76 manifold can keep up with the highly touted LSX, since they are not interchangeable. In a nutshell, it's anyone's game. The one certainty is that the L92 package is ridiculously cheaper than Moffa's old setup. SLP sells the complete L92 package for $2,295.95, including the intake, throttle body, injectors, fuel rails, and all necessary conversion parts. An extra $149.95 will even get you new head gaskets, head bolts, valve cover gaskets, and necessary seals. F-body (and other cable throttle applications) will also have to fork out an additional $530 for a cable throttle, like the FAST unit used in this test. Meanwhile, retail price for an LSX intake, 78mm throttle body, 36 lbs/hr injectors, and the AFR/SLP 225cc heads comes to about $4,170.34. That's a difference of more than $1,300! Those not requiring a cable throttle body are looking at over $1,800 in savings.
SLP L92HEADSAFR/SLP225CC HEADSValves 2.16/1.59 2.08/1.60CombustionChamber64cc65ccIntake/ExhaustRunners 260/90cc 225/85cc Intake/ExhaustRunner Shape Rectangular/D-shapedCathedral/RoundAdvertised Flowat .600-inch lift330/202cfm320/250cfm
FLOW COMPARISONLIFTSLP L92 DECKED HEAD SLP AFR HEAD.10074.2/57 cfm 68/59.1 cfm.200154.1/113.9 cfm 146.5/116.4 cfm.300208.2/150.7 cfm 210.2/168.6 cfm.400244.4/171.5 cfm 254.4/202.6 cfm.500270.7/185.9 cfm 283.8/216.6 cfm.600 287.9/191.5 cfm 265.8/223.4 cfm
REAR-WHEEL HORSEPOWER
AND TORQUE COMPARISON*RPML92 Heads/L76 IntakeAFR Heads/LSX Intake3,000248.1 hp, 423.7 lb-ft 243.9 hp, 415.4 lb-ft3,250272.6 hp, 438.3 lb-ft 267.0 hp, 434.4 lb-ft3,500304.1 hp, 444.7 lb-ft 311.5 hp, 455.4 lb-ft3,750316.2 hp, 446.0 lb-ft 326.8 hp, 458.9 lb-ft4,000358.4 hp, 462.9 lb-ft 358.2 hp, 465.4 lb-ft4,250383.8 hp, 471.6 lb-ft 385.8 hp, 474.0 lb-ft4,500410.8 hp, 473.9 lb-ft 416.2 hp, 478.0 lb-ft4,750432.1 hp, 476.5 lb-ft 427.9 hp, 476.0 lb-ft5,000451.9 hp, 477.2 lb-ft 449.3 hp, 471.1 lb-ft5,250473.5 hp, 473.8 lb-ft 462.8 hp, 465.7 lb-ft5,500483.7 hp, 460.7 lb-ft 471.6 hp, 451.4 lb-ft5,750493.5 hp, 449.5 lb-ft 481.3 hp, 440.5 lb-ft6,000496.8 hp, 434.4 lb-ft 488.3 hp, 428.7 lb-ft6,250488.3 hp, 409.3 lb-ft 484.7 hp, 406.2 lb-ft

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