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Map 2 on Colorado 91 Octane
- Thread starter Abauer
- Start date
Volfy
1000 Posts Club!
Gas stations there in Denver sell 85 regular and 91 Supreme because at higher elevations air is considerably thinner. This means less air molecules are squeezed into the combustion chamber for each stroke. The engine make less HP as a result. This also means that peak cylinder pressure will be lower. So... the same map 2 that normal calls for 93 octane at sea level might do just fine with 91 in mile-high Denver.
Some would argue that turbo charged engines compensate for the reduced atmospheric pressure. That's true to some extend, in that if Map 2 is tuned to produce 20psi max boost, it will do that whether the car is driven at sea level, or a mile higher in Denver. Except... those two indicated 20psi boost pressures are not exactly the same. This is because boost pressure is almost always measured by the ECU as gauge pressure. That is, the pressure relative to atmospheric pressure. Well, atm pressure at mile-high Denver is about 12 psi, vs. 14.7 psi at sea level. So, in reality, that same 20 psi boost pressure is actually 2.7 psi less dense than here in Houston. Less dense means less air molecules to mix with less fuel, making less HP, creating less peak cylinder pressure, cause less likelihood for pinging, which in turn reduces likelihood for timing retard/corrections.
That said, every car and every engine is different. It is still up to you to test your car and make sure 91 octane is kosher with Map2 with the way you run, where you run your car.
Some would argue that turbo charged engines compensate for the reduced atmospheric pressure. That's true to some extend, in that if Map 2 is tuned to produce 20psi max boost, it will do that whether the car is driven at sea level, or a mile higher in Denver. Except... those two indicated 20psi boost pressures are not exactly the same. This is because boost pressure is almost always measured by the ECU as gauge pressure. That is, the pressure relative to atmospheric pressure. Well, atm pressure at mile-high Denver is about 12 psi, vs. 14.7 psi at sea level. So, in reality, that same 20 psi boost pressure is actually 2.7 psi less dense than here in Houston. Less dense means less air molecules to mix with less fuel, making less HP, creating less peak cylinder pressure, cause less likelihood for pinging, which in turn reduces likelihood for timing retard/corrections.
That said, every car and every engine is different. It is still up to you to test your car and make sure 91 octane is kosher with Map2 with the way you run, where you run your car.
Thank you for your detailed response, I knew the effects that elevation has on gasoline but that information brought me even more insight. I just logged at map 2 and map 1 on 91 octane (was on map2 as first in the log then switched to map1). Could somebody please look at this and tell me what they think?
Scorpion24
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Your logs aren’t log enough to tell. Most recommend full throttle through 3 and 4th gear.
And I haven’t been able to run map 2 on 91 only. My timings go too high. I usually add a 1-2 gallons of e85.
