Maybe someone can explain Octane ratings and how that applies in my situation.

We live in Colorado Springs which is around 6000 ft elevation. ALL the gasoline sold in this area is 2 points (?) lower than the gasoline in lower altitude. Regular unleaded in 85, Mid grade is 87, High grade is 91.

The owners manual say use 87, and not to use anything lower than 86 at high altitude. Ok, so I buy mid grade. Many owners manuals I've seen also call for 87, but they sell alot of regular unleaded at 85 here.

Here's the questions, How does octane rating relate to altitude? What are my options if I go with the Super Chip which requires 93?

Thanks,

 

RTF,

I can't be definitve on altitude/octane requirements but a SuperChip does not require 93 octane. I believe it requires minimal 90/91 octane so you should not have a problem with this issue. Here in New Jersey the octane issue is normally 87, 89 and 93 so I don't have a choice but to buy 93. If 91 were readily available I would use it.

I am sure Mike Troyer from Performance Products can be more specific but 93 octane is not the minimum requirement with a SuperChip.

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Dunbarton "The Middle Aged Kid" '99 XLT SC SB 4x2 4.6 auto 3.55 ls The occasional Z-71 Eater! Wedgewood & Denim, SuperChipped, Airaid FIPK. Man, I got it all!

 

The same thing happens in norther Arizona; Chevron in Tucson is 92 and in Pite Top/Lake side about 7000 foot altitude it is 91. Did they lose a point trucking it up the hill?

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97 F-150, 2WD, Reg Cab,Flareside,Dk Toreador Red, 4.6, 3.55 LS, EGR Bug Deflector, ******* Bed Cover, Bed Liner, XL Full Length Running Boards, Air Aid Kit, Gibson Single Out Cat Back, Superchips, TransGo Shift Kit, Hellwig Rear Sway Bar, Hellwig 2500# Overload Springs

 

This is an excerpt from http://www.cs.ruu.nl/wais/html/na-di...line-faq/.html . It basically says that the octane requirement is reduced by 0.2-0.5 for every 1000ft of elevation above sea-level.
That would explain the lower octane ratings of the fuel in your area.

<begin quote>
7.11 What is the effect of altitude?
The effect of increasing altitude may be nonlinear, with one study reporting
a decrease of the octane requirement of 1.4 RON/300m from sea level to 1800m
and 2.5 RON/300m from 1800m to 3600m [27]. Other studies report the octane
number requirement decreased by 1.0 - 1.9 RON/300m without specifying
altitude [38]. Modern engine management systems can accommodate this
adjustment, and in some recent studies, the octane number requirement was
reduced by 0.2 - 0.5 (R+M)/2 per 300m increase in altitude.
The larger reduction on older engines was due to:-
- reduced air density provides lower combustion temperature and pressure.
- fuel is metered according to air volume, consequently as density decreases
the stoichiometry moves to rich, with a lower octane number requirement.
- manifold vacuum controlled spark advance, and reduced manifold vacuum
results in less spark advance.
<end quote>

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MarkS
1999 F-150 XLT, 4x4, ORP, SC, SB, 5.4 Liter, 3.73ls, Husky Truck Box, Westin Chrome Nerf Bars, TOFF Spray-in Bedliner, FORD Blue-Oval Hitch Cover, & Superchip.

 

Thanks everyone,

great info, Funny thing is I never really noticed a performance difference or mpg difference running the 85 or 87 grades. Really makes me wonder if there is a true difference between the two.

Later,

 

Don't know about everyone else, but I have a 93 F150 SCSB with a 5.7L. Mods are KN, Cat back and superchip. I run 87 Octane when not hauling, 92 when pulling my trailer. No problems with pinging. Runs GREAT!

 

Hmmm, I wouldn't recommend using anything less than 91 octane if you're using the Superchip, whether you're towing or not. Your vehicle's knock sensor system (if so equipped) may have enough adjustment range in it to prevent detonation using 87 with the Superchip, (the vast majority do not, by the way) by reducing spark advance, but I sure wouldn't recommend doing that.

There's an old saying that goes something like, Whatever works, works. But anyone using the Superchip should be running 91 octane or better, that's what it's designed for.

Not all detonation is audible, and that's just one reason why I wouldn't recommend using anything less than 91 with the Superchip.

Good luck to all,

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Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com

 

It's been a long time since I looked at this but it goes something like this.

Next time you're filling up look at the little yellow sticker that says what octane gas you are getting. It should say R+M/2 method. The R+M/2 method was required by law for fuel companies to grade their product. Some of you may remember octane ratings in excess of 100 not so many years ago and this is why we get R+M/2. The R component is found by taking pure gasoline with no impurities and running it in an unloaded engine until the knock RPM is found (the RPM where th engine knocks on pure gasoline) this gives the baseline. Now run the fuel in question until it knocks. Cut the pure gasoline with (this is part of what I can't remember) a chemical whose name will be ommitted until it knocks at the same RPM as the gas in question. Using how much of that chemical you add and some fancy math gives you the R value. Now go thru the whole procedure again but this time put the engine under a government mandated amount of load and fimd the M value. Divide the sum by two and you get your standardized octane rating.

The way companies were getting >100 octane ratings was by not using the engine under load method and putting in lots of additives to make the gas appear better than pure gasoline. Then uncle sam stepped in and made everything better.

Please correct any mistakes I have made here, like I said it's been a long time since I learned this and I hope I got most of it right.