Does 93 octane at sea level = 91 octane at 4000 ft?
Thread Starter
Staging Lane
Joined: Aug 2011
Posts: 96
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From: rapid city, sd
Does 93 octane at sea level = 91 octane at 4000 ft? My car is tuned for 93 octane at sea level with no o2s, ill be trailering it to my new house this week which is at 4000ft elevation. They only have 91 octane im guessing to compensate for the thinner air. My question is, does the octane difference compensate enough for the elevation diff or do I need a retune? Will I run stupid rich or have spark knock issues?
You will be fine...
Depending on the shape of the high end of your spark table, you may run more advance and be at more risk for slight spark knock.
This is not due to the fuel octane, it is due to the fact that at higher elevations the car will never see the manifold pressure kpa that it does at sea level, and will thus use a different section of the spark table. If the numbers are much higher at say 80kpa instead of 100, then it will command more WOT spark. Thus making you more prone to spark retard.
The altitude will compensate slightly, but only so much.
The REAL answer to this is to scan the car at the new location, on the new fuel and make sure theres no knock retard. If there is, make sure your tuner understands what part of the spark table he needs to tune, or the desired result will not be achieved.
A lot of tuners say the altitude doesnt matter and the "car will compensate" while that's true in most cases for fueling, it is NOT always true for the spark, due to what I just explained.
But in general, you will be fine. No you wont run "stupid rich" if the car still has a MAF.
Depending on the shape of the high end of your spark table, you may run more advance and be at more risk for slight spark knock.
This is not due to the fuel octane, it is due to the fact that at higher elevations the car will never see the manifold pressure kpa that it does at sea level, and will thus use a different section of the spark table. If the numbers are much higher at say 80kpa instead of 100, then it will command more WOT spark. Thus making you more prone to spark retard.
The altitude will compensate slightly, but only so much.
The REAL answer to this is to scan the car at the new location, on the new fuel and make sure theres no knock retard. If there is, make sure your tuner understands what part of the spark table he needs to tune, or the desired result will not be achieved.
A lot of tuners say the altitude doesnt matter and the "car will compensate" while that's true in most cases for fueling, it is NOT always true for the spark, due to what I just explained.
But in general, you will be fine. No you wont run "stupid rich" if the car still has a MAF.
