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.
Since our 383 was no longer a simple 5.3L truck motor and lacked any of the accessories, including the manual water pump, Whipple decided to supply its 2.9L "Tuner" kit (lacking components like the flash tool, air filter, and misc. hardware). The highlight of the kit was obviously the 2.9L W175ax (front-feed) supercharger, but every bit as important was the integrated air-to-water intercooler core. Heat is a natural byproduct of compression, which is another way of saying that all forms of forced induction heat the inlet air supplied to the motor. The higher the boost, the higher the associated inlet air temperature. One of the tried and true methods of decreasing the heated inlet air temperature is to pass it through an intercooler. Whether air-to-air or air-to-water, intercoolers are designed to eliminate a portion of the unwanted heat. The Whipple system employed an air-to-water intercooler core positioned directly below the discharge of the supercharger in the lower intake manifold. Twin-screw superchargers are highly efficient, meaning they minimize the unwanted increase in air temperature, but that doesn’t mean they won’t benefit from intercooling. The only thing better than boost is intercooled boost.
As with all superchargers, the boost supplied by the Whipple was a function of two things, the normally aspirated power output and blower speed relative to engine speed. The blower speed was controlled by the drive ratio between the crank and blower pulleys. As the drive pulley, an increase in diameter of the crank pulley will increase boost pressure while the opposite was true of the blower (or driven) pulley.
Wanting some adjustability, we requested a variety of different blower pulleys to work with the supplied ATI crank pulley. Though it was likely overkill at this boost and power level, Whipple supplied a 10-rib pulley system to eliminate any chance of belt slippage. We may put them to the test at a later date with Modern Mouse, but for now it was nice to have a repeatable boost curve run after run. Whipple offers kits for a variety of different LS applications, ranging from trucks and SUVs to the LS3 Camaro. Our kit featured (or required) the water pump and pulley offset from a 2011 Camaro. A cool alternative would be the 2010 Camaro electric water pump offered by Meziere (see photo).
Initially the Whipple supercharger was set up with a 3.875-inch blower pulley. According to the company website, this pulley combination was designed to provide 10 psi of boost (at 6,500 rpm) to a stock 6.2L LS3 Camaro engine. On our modified 383 (6.27L) stroker, the pulley combination netted a peak boost pressure of 7.4 psi. Run with a pump-gas tune (18 degrees of timing and 11.5:1 air/fuel), the supercharged combination produced 671 hp and 598 lb-ft of torque. A splash of 100-octane allowed us to safely crank up the timing to 22 degrees, where the same pulley combination produced 718 hp and 626 lb-ft of torque.
The supercharged motor responded very well to additional ignition timing, but care must be taken not to get too greedy. The power output of a supercharged motor often continues to increase with ignition timing right up to the point where all the magic smoke comes out. Detonation is quick and decisive and can ruin a perfectly good combination regardless of the presence of forged internals. Running just 7.4 psi, the Whipple increased the power output of the normally aspirated 383 from 541 hp and 518 lb-ft of torque to 718 hp and 626 lb-ft.
The question now was who wouldn’t be happy with a motor making over 700 hp? The answer was (obviously) a guy looking for 800 hp! Knowing there was more power to be had from this supercharged combination, we decided to do what all blower owners do—crank up the boost. In just a few short minutes, off came the 3.875-inch blower pulley and on went the smaller 3.625-inch pulley. The smaller blower pulley increased the peak boost pressure supplied by the Whipple to 9.6 psi and the power output right along with it. The supercharged 383 now produced 778 hp and 672 lb-ft of torque. Being so close to the 800hp mark, we decided to go for it. Rather than increase the boost, we decided to simply install a set of larger 1-7/8-inch headers from American Racing. Thinking that a motor exceeding 775 hp would benefit from additional exhaust flow, we installed the larger headers. We also added 1 degree of timing to the top of the curve. Our efforts were well rewarded as Modern Mouse thumped out 804 hp and 682 lb-ft of torque at a peak boost reading of just 9.2 psi. The increase in exhaust flow was responsible for the drop in boost pressure. There was obviously more boost and power available from the Whipple supercharger, but even at its present power level, any Ford going up against Modern Mouse will be totally screwed!