Read into each response with some realization that elevation and temp plays a big roll in how much is too much. My friend got away with 16 psi from 8000 to 9000 feet and 17 above 9000 feet with the 0.063 thousands shim on 50:50 pump race mix, totaling roughly 100 octane. If you run an 0.080 thousands shim you can get away with a little more at 17 below and 18 psi above at 100 octane (straight av). Keeping things simple, if you drop to sea level, you need to take roughly 4 to 5 psi out of it from what you run at 9000 feet, depending on baro. Baro, which is absolute pressure, at 10,000 feet is roughly 10 psi and baro at sea level is roughly 14.7 psi. Keep in mind, the boost values are in weather where the temperature differential is greatest, meaning the temperature on any given day was no higher than the mid 20s fahrenheit. If in spring snow where the air temp is in the 30s or 40s, take a pound or two out of it to avoid detonation since the intercooler looses efficiency as the delta between air temp and boost temp drops. If you have race gas at 110 or higher, then you are safe up to 20 psi on a boondocker kit with the head shim. I have seen a little more on occasion at high elevations with race gas, but then you are at risk of the motor blowing up if the engine isn't built with stronger rods and pistons. In the end, if you have a built motor, then race is great. If your on stock internals, you are not able to really get the benefit much past 100 octane since most motors won't take the beating for long durations.
As noted, 17 is a great threshold for keeping things together. The other thing to watch is making sure you are using the RPM the apex wants. Make sure at full throttle the clutch trims out at 10,500 RPM to 10,600 RPM, and over revs stay below the limiter somewhere around 10,750 from memory. Past that, you may hear the motor pop and possibly damage the motor on high boost as the computer hits the rev limiter. If you lug the motor, you are more likely to detonate or bend a rod at higher boost. And, the sled won't feel like it is running hard at the higher boost numbers. Lastly, the same principles apply if you are running pump gas or no head shim (stock compression). But you would need to get the top numbers from someone who has ran it that way or call boondocker to see if they have a recommendation. Good luck.
