Skyking in right re: non-pressurized ac.
I've got a 337A normally aspirated, and it takes a LONG time to get to 15,000, and . . . of course, requires supplemental oxygen. However, sometimes, the winds are good enough up there on a long trip that patience and supp o2 is rewarded.
If you buy that or any other non-pressurized bird, my unsolicited opinion is that it's worth your money to buy supp o2 regardless because it just makes life easier, safer, and more flexible. Plus, anytime I go over 7000' on a long trip I use it towards the end of my flight just to knock the edge off and eliminate any "hangover" effect.
It's worth the $.
Keven
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Suzuki Dr650 History