SLP was essentially born back in the days when it looked like smog controls would make it impossible to tweak and tune modern muscle cars without running afoul of the law. Smog-legal headers, exhaust systems, intake manifolds and more were all part of the mix, and the company eventually developed a relationship with General Motors that yielded the Firehawk and other special vehicles.
Today, SLP Performance Parts continues to offer special parts to enhance the output of late-model performance cars, including those from Ford and Chrysler, in addition to GM. Among the current offerings are a number of crate engine packages for the GM LS-type engines, including the recent addition of the ZL427 series. These are brand-new engines, built using new GM LS7 blocks that are then fitted with a Callies 4340 forged steel crankshaft, SLP/Manley 4340 forged H-beam connecting rods and SLP/Manley forged pistons yielding 11.35 compression when paired with the GM L92 castings, as assembled by SLP. There’s also an SLP camshaft with .591/.600-inch lift and 224/228 duration with a 113-degree lobe separation angle.
The ZL427 crate package also comes with a GM L76 intake manifold, a set of GM LS7 65-lb./hr. injectors and LS7 fuel rails, plus an SLP double-row timing set and heavy-duty oil pump, ARP head bolts and MLS head gaskets. SLP offers the ZL427 in several configurations, to accommodate cable-throttle or drive-by-wire applications, and also offers either 58-tooth or 24-tooth reluctor-wheel variations.