Back in part 7 of Modern Mouse, not only did we add boost to our LM7 test mule (now displacing 383 ci), but we threw in a single turbo test on a stock 5.3L LS as well. We also promised (and delivered) testing on an LS3-based stroker combination from Texas Speed and Performance entitled Monster Mouse (October 2012 issue).
Though we’ve started our dalliance with Monster Mouse, Modern Mouse is still alive and well. Loyal readers will remember that Modern Mouse started out life as a simple 5.3L LM7 pulled from a wrecking yard. The iron-block 5.3L was subjected to all manner of upgrades before tearing it down to bump the displacement to 383 ci. The hike in displacement came from a forged rotating assembly that included a 4.00-inch stroke forged crank and matching rods from Procomp Electronics, combined with forged pistons from Probe Racing. Though a variety of different heads have been run on Modern Mouse, it was sporting a new set of CNC-ported heads from Procomp Electronics for this test. Given the ported heads, healthy Comp cam and CNC-ported heads, the 383 was primed and ready for the new LS Perimeter Plate nitrous system from Zex.
Designed specifically for LS applications, the Perimeter Plate Blackout system featured a unique intermediate plate designed to sandwich between the throttle body and intake manifold. It was designed as a direct fit for all 90mm (factory) and larger aftermarket manifolds, including the FAST LSXR and LSXRT. A machined O-ringed insert was used to step down the 102mm opening to fit the smaller 90mm throttle bodies and intakes.
According to Zex, the Perimeter Plate system offeres a number of other design features including perimeter injection, Cryo-Sync, and airflow enhancement technology. The Perimeter Injection employed 12 injection points that combined nitrous and fuel to optimize atomization and distribution in the manifold. Flowing super cool nitrous (-127 degrees) through the plate effectively turned it into a Cryo-Sync (or heat isolator) to help cool the intake and throttle body. Flow of the nitrous and fuel through the spacer plate and into the manifold also created a low-pressure zone to further enhance airflow into the motor. On paper, the Perimeter Plate sounded pretty effective, so we installed one on Modern Mouse.
Using jetting to control the nitrous and fuel flow, the Zex system was adjustable from 100 hp to 250. For Modern Mouse, we chose to run the system at 100 hp, then again at 150 hp, both reasonable for street use when adhering to the recommended timing retard for each power shot. According to Zex, the timing should be retarded by four degrees for the 100hp shot and six degrees for the 150hp shot. While our LM7 was now sporting a manual throttle body (102mm from FAST), the Zex Perimeter Plate system was also designed to run on drive-by-wire applications. Using a sophisticated controller, the system will self-learn, and only activate at wide-open throttle. This was an important safety feature, as you never want to activate a nitrous system at low engine speeds or part throttle. Hooking up the system according to the instructions was straightforward, and Zex was kind enough to supply a bottle heater to ensure optimum bottle pressure (over 900 psi).
Before running the new nitrous system, we had to establish a baseline. The 383 stroker was equipped with a Comp 281LRHR14 cam offering a 0.617/0.624 lift split, a 231/239 duration split and 113-degree LSA. The forged short block featured Fel Pro head gaskets and ARP head studs to secure the CNC-ported LS1 heads from Procomp Electronics. Stock rockers were used with 7.300-inch length hardened pushrods from Comp Cams. The induction system consisted of a FAST LSXRT intake, 75-pound injectors, and XFI management system.