Here is where the fun began. The Edelbrock timing module uses plug-in chips that represent different timing curves. We used the No. 2 module, which offers up 36 degrees of total timing. Frankly, all the modules eventually employ the same total timing of 36 degrees, with the differences mainly in how quickly the low-speed curves build to max timing. Unlike the MSD 6010 timing module, the Edelbrock module does not allow changes to the curves using a laptop computer, so we couldn't alter the timing. It's possible we could have made slightly more peak power had we been able to lower the total timing. As far as jetting was concerned, we leaned the total air/fuel ratio about a half ratio, but the power remained the same.
After the first two pulls on our new combination, our LS1 made its best power with a 499hp peak, and torque came in at 455 lb-ft at 5,400 rpm. The longer-duration cam obviously pushed the peak torque up 1,400 rpm, but the peak horsepower rpm remained at 6,400, which means the midrange torque jumped dramatically. If you look closely at the numbers, you can see 60-plus lb-ft of torque gains in the midrange. That is something you can feel in the seat of your pants every time you hit the throttle. Sure, the headline 85hp gain at the top with 499 hp is cool, but it's that major torque improvement in the middle that will move your car much quicker down the 1,320.
We tried really hard to push the little LS1 into the 500hp zone with the dual-plane intake, but it just couldn't cross over. We bolted on an Edelbrock LS1, Victor Jr. single-plane expecting a rather sizeable improvement in peak power. While the LS1 did pop up to 506 hp, it was clear from the torque loss due to the shorter intake runner length that this particular combination would be far happier, quicker, and more fun to drive with the dual-plane.
We had to slightly modify this dimple on the driver-side valve cover to clear the rocker.
We reused the stock LS timing set because this engine has very few miles. If yours is a bi
The dual-plane with the Holley 750 carburetor ended up being the best overall combination
Dyno Test Results
Test 1 was the baseline test using the stock LS1 '04 GTO engine configuration enhanced with a set of 1 3/4-inch chassis headers, an Edelbrock cathedral-port carbureted dual-plane Performer RPM intake manifold, and a Holley 750-cfm HP-style mechanical-secondary carburetor.
Test 2 is the big test with the addition of the TFS Fast As Cast 220cc heads, a bigger hydraulic camshaft, stronger pushrods, and the matching Harland Sharp net-lash rocker arms. Note that peak torque and horsepower rpm points didn't change very much while adding a sizable amount of power in the usable rpm range.
Test 3 is where we thought we could push this package above 500 hp by using a single-plane intake manifold. While we did accomplish that goal, the peak horsepower gain wasn't worth the major torque loss between 3,000 and 4,800.