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.
The flow numbers appear quite a bit different than normal, since they were tested bare with no adapter on the intake or exhaust. But with SLP's modifications to each of the heads, the results were just about even. At low-lift between .100 and .200 inches, and again at .600 inches, the L92s had the clear advantage on the intake side. Meanwhile, the AFRs outperformed the L92s at mid-lift, before surprisingly peaking at .500-inch lift and not .600, like the L92s. The L92 had the best peak flow at 287.9 cfm, but the AFRs weren't far behind at 283.8 cfm. I'd call that too close to call. On the exhaust side, the AFRs are clearly dominant, though, so it's still anyone's guess what the dyno would read. One thing to consider is that with valvetrain deflection, the valve will not actually open quite as high as the cam commands. But then again, flow isn't everything. | 
Daniecki Jr. adjusted the tune to compensate for the larger injectors and throttle body, while leaving other parameters alone, such as the spark table, for consistency in the test. As evidenced by the air/fuel graph, the two were near dead-nuts even. After a few pulls, it was apparent that though the L92s and L76 intake gave up a little down low, they were clearly dominant from 5,000 rpm on up. SLP's Super Flow chassis dyno revealed 496.8 SAE rear-wheel horsepower at just under 6,000 rpm, which is a gain of 6.8 hp over the AFRs at their 6,100 rpm peak. At a touch under 4,500 rpm, the AFRs reached 478.8 SAE pound-feet of torque at the wheels,... |
...but the L92s started turning up the heat at just over 5,000 rpm, where they reached their 477.5 lb-ft peak. Though not a true apples-to-apples comparison, as we had 78mm and 90mm setups with a 90mm throttle body and the 90mm LSX intake, the AFRs would have had a better shot at keeping up with the L92s (adding another $110 to the $4,100-plus price tag). Though the performance results were somewhat mixed, the price difference gives the far-and-away advantage to SLP's new L92 Cylinder Head Package. We'd love to even the score a bit and see what these babies could do with a good CNC program. Now that's a fair fight. | |