J
I'm not a turbo expert and what I'm about to write is more "cocktail napkin" math than something to 100% hang your hat on. That said, when going on a trip (new elevation) here is what I do to figure out how much boost I can get away with.
Atmospheric pressure at sea level is 14.7psi. Obviously, our sleds were designed to run on 91 octane at this level without issue. In my experience, you cannot push more than 16.5-17ish total air pressure on pump gas without running into DET problems. So at near sea level riding this would mean you could run about 3 (maybe) psi with good fuel and not have any problems. (I'm assuming you are riding 1,000-2,000 feet in this scenario and *starting* at sea level).
Now, lets apply this math to elevation. At 7000 feet atmospheric pressure is 11.3psi; at 8000 feet atmospheric pressure is 10.9psi. At 5psi I'm somewhere between 15.9 and 16.3 psi. Obviously, the higher I go up the less net pressure there is. (boost + atmosphere). The sled has been 100% fine on pump gas at these pressures (haven't hit det yet).
At 11,000 feet atmospheric pressure is somewhere around 9.7. So running 7 puts you around 16.7psi - which is within possible but its not a risk I'd want to take.
Personally, I wouldn't do it. There are other factors at work here too. Temperature, charge air temps (which will go up as you run more boost) etc.
End of story, if you are looking to run pump gas, run the 5psi spring and be on the safe side. Keep the 7, some av gas and the clutch setup that comes with the sled if you want to add an extra 20ish horse.
PM me for clutch setup at 5.
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