High Octane at High Altitude
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Freshman User
Joined: Apr 2005
Posts: 35
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From: Cody, WY
High Octane at High Altitude
I own a 99 F150 5.4 with automatic trans. I live and drive at 5000 ft here in Wyoming. I have been told that high octane 91 is not worth the extra $ at this altitude because of the lighter air. True-false. Will it make a difference if I purchase a chip like the predator or should I be looking for performance elsewhere ?
New User
Joined: Aug 2004
Posts: 22
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Flat lander here, but since you have less air...why not open up you intake K&N,AFE what ever but get rid of the air box. Install a Flowmaster in the stock exhaust. I do not see any advantage to hi-test at altitude without a programer. The Hypertech unit gives you both reg. or hi-test options.
Senior User
Joined: Dec 2004
Posts: 376
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From: Ballard, WA
I just moved from 5400 ft. My efi 5.8 never had a problem, even on 85.5 gas, and didnt get an improvement from anything else. However, my roommates was a little pickier, and would give a little ping if he didnt use 87.
Higher octane is designed to be used with higher compression motors. You should be able to use whatever gas your book recommends at any reasonable altitude.
Sometimes Ill put in the mid range, just because I cant validate paying 2.35 a gallon for 85.5 gas, even if it does nothing for my old truck.
Higher octane is designed to be used with higher compression motors. You should be able to use whatever gas your book recommends at any reasonable altitude.
Sometimes Ill put in the mid range, just because I cant validate paying 2.35 a gallon for 85.5 gas, even if it does nothing for my old truck.
Posting Legend
Joined: Sep 2001
Posts: 30,255
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The gas sold as reg, plus, or premium varies octane with altitude. The higher the altitude the lower the octane sold in the area for each grade. When driving in the mountains on a carb I used to keep two grades in the tanks and switch back and forth depending on altitude.
Postmaster
Joined: Jan 2004
Posts: 4,758
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From: colorado
the higher you go the less octane you need.on a computer controlled EFI engine you should use the octane rating that the mfg. reccomends.
heres some good info on octane:http://www.leeric.lsu.edu/bgbb/7/ecep/trans/b/b.htm
heres some good info on octane:http://www.leeric.lsu.edu/bgbb/7/ecep/trans/b/b.htm
Last edited by wlihntr; Apr 16, 2005 at 12:44 PM.
Post Fiend
Joined: Jan 1997
Posts: 23,165
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From: Enjoying the real world.
With the Predator you'll be able to adjust the timing optimally for the given octane. Advance the timing 1% at a time and drive it for a day or so. If you don't get ping, advance it another 1%. Once you get spark knock (ping), back it off 1% and its optimal. 
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