Our engine liked 37 degrees total advance, and changing that by one degree up or down didn't make much difference. A total of 40 degrees of ignition timing saw a small power decrease, indicating our engine was suffering a little spot-detonation. We also tried different timing curves (which dictate how quickly the timing comes in) using the springs and bushings provided with our MSD distributor. Our 427 small-block responded well to the blue distributor bushing, which gave the second lowest amount of advance, along with the tightest springs so the timing curve would advance slowly. By using this setup, we netted our peak torque number without sacrificing top-end horsepower. Remember that when jetting, start big and work your way down. With timing, start small and work your way up to stay safe. Each engine is different, which is why an engine dyno is such a critical tool for safe and effective engine tuning.
Once the mixture and ignition timing of the engine are satisfactory, and a baseline is established, the engine can be tested to find the effect of carburetor spacers. Carb spacers are manufactured by many different companies, in all types of configurations. And while we can say that generally a carb spacer of some type will improve power, the type of spacer needed greatly depends on the engine itself. Since a dyno corrects for outside factors, this is a great place to test multiple spacers and see the results.
We knew the long stroke of our small-block would like more plenum volume, and experience tells us that large-displacement engines like carb (or throttle body) spacers. With the 1,000-cfm carb, we first installed a 1-inch open spacer, gaining nearly 10 hp from our baseline pull with a marginal increase in torque. Installing a 2-inch open spacer netted even better results, improving power by 14.4 for a best pull of 609.6 hp with the 1,000-cfm carb. After testing the open spacers, we installed first a 1.5-inch, then a 2-inch tapered spacer. While each of the tapered spacers made 3-5 more horses than our baseline, our combination clearly preferred the open versions. In fact, we thought about stacking the open spacers to learn our point of diminishing returns, but ultimately discounted the idea, since hood clearance would become an issue in the real world.
We love being able to make precise adjustments and see a result on the dyno, and camshaft timing is another area where this is possible. And while we can't add variable cam timing to our engine like some modern engines have, our Jesel beltdrive timing system means that resetting the cam timing only takes several minutes. Better still, it can be accomplished without invading the crankcase of the engine.
Though confident we'd chosen a good cam with the help of the engineers at Comp, we wanted the option of moving the power and torque curves up or down the rpm range by adjusting timing. This meant calculating piston-to-valve clearance for multiple cam settings, and cutting the valve reliefs to provide adequate clearance. This would allow us to really fine-tune the combination, and find the best average torque and power numbers.
We began by running our engine with the camshaft installed at our baseline of 108 degrees intake centerline, and calculated the average torque and hp between 4,000 and 7,000 rpm. Then, without changing the tuning (other than correcting ignition timing for the camshaft movement), we advanced and retarded the cam timing two degrees in each direction—to 106 degrees and 110 degrees, respectively—and recalculated our averages.
We discovered that although the engine made slightly more peak power with the cam at 108 degrees, the average hp and torque were some 1-2 percent higher at 106 degrees, meaning the engine would make more power throughout the rpm range at that setting. Additionally, by advancing cam timing to 106 degrees, the peak torque and hp occurred at a lower rpm, which is better for street driving and all-around durability.