Thanks to the stroker upgrade in part three, Modern Mouse was thumping out some serious power and torque. Our series began by subjecting the 5.3L to cylinder heads, cams, and an LSXR intake manifold. From there, we followed up with even wilder cams and a small dose of nitrous oxide.
Not content to leave well enough alone, we decided it was time for some additional displacement in the form of a 383 stroker assembly from Procomp Electronics and Probe Racing. In addition to a sizable increase in average power production, the forged crank, rods, and pistons also provided sufficient internal strength to allow us to safely subject the little rodent to boost. If you are looking to transform a good motor into a great performer, simply add boost! Whether it comes from a turbo or blower, boost acts as a multiplier for the existing normally aspirated combination. The better the normally aspirated power, the lower the boost required to achieve a desired power output. Adding boost to our (already healthy) 383 stroker pushed the power output up into the serious zone.
Given the popularity of the current small-block, it should come as no surprise that a number of options exist for LS enthusiasts looking to add boost. Each system offers its own benefits and limitations, but for our needs we chose a 2.9L, twin-screw supercharger from Whipple Industries. Not only does it help our Mouse make serious horsepower, but if you are running cathedral-port heads (like we are), you choices in a positive displacement supercharger are limited. This one fills the bill nicely.
As with our previous adventures with Modern Mouse, the object was not to maximize power production but rather to illustrate what is possible at reasonable (street) boost levels. Further illustrating this point was the fact that we never ran more than 9.2 psi of boost. The Whipple certainly had more to offer, and the motor would safely take more pressure (and power), but maximum output is not always the answer.
Super Chevy readers will remember that the stroker combination from part 3 consisted of a forged crank, rods, and pistons from Procomp Electronics and Probe Racing. Trick Flow Specialties supplied a set of CNC-ported Gen X 215 heads and a Track Max cam. The mild hydraulic roller offered 0.575 lift (both intake and exhaust), a 220/224-degree duration split (@ 0.050), and a 114-degree lobe separation angle. Run with a FAST LSXR intake, 102mm throttle body, and a set of 1-3/4-inch long-tube headers, the 383 produced 510 hp and 507 lb-ft of torque. While we appreciated the combination of power, torque, and idle quality, we couldn’t help but marvel at the power numbers produced by Modern Mouse’s wilder sibling, Mayhem Mouse (see part 3 of our series). We didn’t want the elevated compression or wilder cam timing of that combination, but we decided to split the difference by subjecting Modern Mouse to yet another cam change. Out came the mild TrackMax grind and in went a slightly wilder profile from Comp Cams. The LSR cathedral-port grind increased the lift split to 0.617/0.624, the duration figures to 231/239 and the LSA to 113 degrees. Once again the factory hydraulic roller lifters were reused.
Naturally we had to reestablish a baseline in normally aspirated trim prior to the installation of the 2.9L Whipple twin-screw supercharger. It is important to remember that any gains offered in normally aspirated trim can be multiplied by the boost. The higher the normally aspirated power output, the lower the boost required to achieve a desired power output. The lower the boost, the lower the inlet air temperature, which further minimizes the chance of harmful detonation. The upshot of all this is that it is possible to run elevated power levels safely on pump gas.
Run once again with the new Comp LSR cam, FAST LSXR intake and TFS GenX 215 heads, Modern Mouse produced 541 hp at 6,100 rpm and 518 lb-ft at 4,700 rpm (peak gains of 31 hp and 10 lb-ft). Equipped with the new cam, the power was up from 3,000 rpm to redline from our previous test, always a good sign. The idle vacuum had dropped by just over 1 inch but was still more than acceptable for a daily driver. The 383 offered a broad, usable torque curve, with torque production exceeding 475 lb-ft from 3,800 rpm to 6,000 rpm. With our normally aspirated power output up by over 30 hp, it was time for some boost.