91 Octane

[1olddude]

Where I live, the highest octane I can find is 91. Do any of you experts know if that is high enough or do I need to add some booster to each tank? The car seems to run fine but I don't know if higher octane gas would make a difference in the performance. Will octane booster hurt anything in the long run? Any thoughts would be appreciated.

[BYprodriver]

In CA 91 is the best available & works ok. I don't think pour in octane boosters would be worth the hassle & cost. Try to find 91 octane with the least alcohol content.

[blue2000s]

93 octane fuel tests at (and is rated at) 91 octane at high altitude. I assume you're well over sea level in your part of Utah. You don't need any octane booster.

[BYprodriver]

Originally Posted by blue2000s

93 octane fuel tests at (and is rated at) 91 octane at high altitude. I assume you're well over sea level in your part of Utah. You don't need any octane booster.

How does the altitude alter the fuel octane rating?

[blue2000s]

Originally Posted by BYprodriver

How does the altitude alter the fuel octane rating?

It's a matter of air density. Because there are fewer molecules of air and fuel to rub against each other in a combustion chamber at altitude, the tendency to auto-ignite is lower. Thus the lower octane number because it's correct for the altitude where it is sold, and the lower octane requirement.

[t2-bxtrs]

To put in an observation here in Toronto we have a 91 octane and a 94 octane available, and every now and then i alternate using either one..
Not much difference observed, i figured as long as your Box is tuned properly, and mechanically sound would be very minimal difference...
thx

[j.fro]

FWIW, Grassroots Motorsports magazine has a test of different octane and ethanol content fuels in this month's issue. They dynoed for HP and torque. Pretty interesting read.

[BYprodriver]

Originally Posted by blue2000s

It's a matter of air density. Because there are fewer molecules of air and fuel to rub against each other in a combustion chamber at altitude, the tendency to auto-ignite is lower. Thus the lower octane number because it's correct for the altitude where it is sold, and the lower octane requirement.

The 91 fuel at the pump in Colorado IS the same fuel as the 93 octane at seal level.

If fuel rated at 93 octane at sea level is used at high elevation (2,500 ft & higher) it may increase the octane rating, but it definitely will not lower the octane rating.

[blue2000s]

Retracted statement

[shadrach74]

Originally Posted by BYprodriver

If fuel rated at 93 octane at sea level is used at high elevation (2,500 ft & higher) it may increase the octane rating, but it definitely will not lower the octane rating.

It really should not do anything to octane rating. The only reason some engines are fine to run lower octane at higher altitude is due to reduced manifold pressure. A turbo charged engine that needs 93 octane at sea level would do well to have it in Denver as well. You could likely get away with running lower octane in a turbo car at altitude, but not without some performance degradation due to the timing being retarded.

[ekam]

Local PCA guys along with FCA guys use Shell 91 octane, zero ethanol exclusively... so that's what I use.

BUT if you have a FI car you must use 94 octane or else it'll ping...

[thstone]

In Cali, 91 octane is the best that we can get (at a regular service station). Everyone uses it and it works fine. I wouldn't worry about it.

[1olddude]

Great info. Thanks for the help.