In Pull 1, we learned that the 598 was lean and in need of larger jetting. We started with 0.90 jets in the primaries and secondaries. Based on air/fuel ratio and brake specific fuel consumption (BSFC) numbers, McAfee concluded we needed to step up to 0.92 jets in the primaries. Benton Jackson, MCE Engines fuel system specialist, took care of this in short order. Ignition timing is conservative at 32 degrees BTDC to eliminate any chance of detonation and engine damage. McAfee's regimen includes step pulls in order for the engine to stabilize before rpm increases.
On the second pull, we were still too lean. McAfee increased jet size one step at a time again as a measure of fine-tuning. "Quantum leaps in jet sizes only add to the confusion of tuning," McAfee tells us, "at one jet size at a time, you know back to back from one pull to the next whether you're rich or lean without having to backtrack." The 0.92 primary jets did add 14.4 hp and 21.0 lb-ft of torque. McAfee elected to go up a jet size in the secondaries to 0.93 to see what happens next.
In the wake of our third and final pull due to time constraints, our 598 T-Rex produced 915.7 hp and 827.1 lb-ft of torque. We are thrilled these numbers surpass McAfee's expectations. However, we're convinced that with more dyno time, this engine would be courting the 1,000hp mark. And if you run out of dyno time, you can always continue your testing once the engine is in the car and at the track. Keeping good records will go a long way in documenting the changes and performance or your engine.