While Ken and I worked with...
While Ken and I worked with the basic tool, Brian whipped up this tool using an old rocker, a 3/8-inch socket, and some 1/4-inch flat-stock steel. His "made-in-a-pinch" tool really came in handy changing the springs on the rear cylinders. Notice the long 3/8-inch extension connected to the special tool. On the No. 5 cylinder, we have the new rockers, springs, and retainers already installed.
On the left is the SLP 1.85-ratio...
On the left is the SLP 1.85-ratio rocker that adds 10 percent to the max valve lift (lift increases to 0.544-inch). The SLP rocker also speeds up the valve action (i.e., opens and closes the valve faster), which increases the air velocity through the motor while adding power and throttle response. SLP's springs are manufactured by Manley and have increased pressure, 110 pounds at 1.80 inches installed height closed, 350 pounds at 1.22 open. When new, the stock spring (far right) was rated 76 pounds at 1.80 inches closed and 220 pounds at 1.32 open. (It would be a good idea to move up to a fresh set of springs on an '01-'02 LS1 as well to have better springs with less chance of valve float at the high rpm.)
Even though the SLP springs...
Even though the SLP springs are engineered for easy installation, we wanted to be sure the installed spring height (1.80-inch) was right. The new titanium retainer and keepers are inside the measuring tool. Fortunately for us, the spring height checked dead-on, and we didn't need to use any shims (we had them ready if we did).
At first, we dyno-tested the...
At first, we dyno-tested the 1.85:1 rockers and 85mm MAF combo and gained 12 rwhp. Here we see how easy it is to use the DiabloSport II programmer. It features exclusive SLP custom power tuning to trim the air/fuel ratio and spark advance. Once again, we put the T/A to the rollers and witnessed another 9 rwhp. The total 375HP Pac added 21 rwhp as well as more throttle response and fun to that go pedal!
Shown here is the fan-control...
Shown here is the fan-control switch package. It helps '93-'02 F-bodies keep cool whether stuck in traffic or between runs at the track. We can flip the three-position switch to activate the cooling fans at any time, even if the car is off or running. The factory setting for the fans to start is 229 degrees for Stage 1 (low-speed) and 237 degrees for the Stage 2 fans (high-speed). That's too hot!
SLP's 160-degree thermostat...
SLP's 160-degree thermostat will let the coolant start flowing through the LS series motor and radiator at 35-degrees cooler than the stock 195-degree thermostat. Using the SLP fan switch and thermostat as a team can help reduce engine-operating temperature for more power.
Note: the '98-'00 LS1s need to have the valvesprings changed due to the 0.500-inch-lift cam ('01-'02 LS1s have a 0.464/0.478-inch-lift cam). The 0.500-inch max valve lift becomes 0.544 lift with the 1.85:1 rockers and could cause coil bind with the stock springs. The SLP spring package is made by Manley and includes titanium retainers to reduce weight at the valve tip and lessen the odds of valve float at high rpm (5,000 and up). Rocker and spring installation took us nearly four hours to perform (the motor was hot when we started). Some of the time was spent fixing and replacing a few cracked emissions hoses. SLP recommends only competent and experienced people attempt the rocker and spring change.
We changed from the stock 75mm MAF to SLP's 85mm unit, which flows 895 cfm compared to the stocker that flows only 805 cfm.
On The Dyno
Back to the dyno with the aforementioned parts installed, we noticed that the temperature rose to a sweltering 98 degrees. Still, Brian put the hammer down, and we were up to 301 rwhp and 308 lb-ft of torque at 5,200 and 4,200 rpm, respectively. But wait, we weren't done yet. We needed to plug in the DiabloSport II Programmer to complete the 375HP Pac installation.
The hand-held power programmer installs SLP's custom high-performance tune. Optionally, it allows you to trim the air/fuel ratio and spark advance for mods beyond SLP's package. It also functions as a scan tool to read engine diagnostic codes. This electronic tool can improve performance, drivability, and efficiency.
Once the power tuning was set, we spun the rollers and observed 310 rwhp and 318 lb-ft of torque! Overall, the 375HP Pac proved to be worth 21 hp at the rear tires. Flywheel horsepower would equate to 372 using 20-percent driveline loss as a guideline. That's a significant gain when you consider we didn't go digging into the motor as you would for a cam or head swap.
On The Strip
When we strip-tested the 350HP Pac, it was with cool springtime air. Knowing we would be following up with a strip-test in the summer heat, we decided it would be wise to install SLP's 160-degree thermostat and the three-position fan control switch. Once done, Brian custom-tuned the PCM (powertrain control module) to enable the fans to activate at a lower temp (SLP proprietary) to work with the new 160-degree thermostat. He also increased the transmission shift firmness.