Octane and Altitude

How many times will this horse have to die?

camperpaul wrote:
You cannot buy a container of "octane" because it is NOT a substance.

So 8 carbon atoms and 18 hydorgen atoms together is not a substance?

Wikipedia wrote:
Octane is a hydrocarbon and an alkane with the chemical formula C8H18

I think you're confusing "octane" which can be slang for "octane rating" with the substance "octane" that the rating was derived from.

facory wrote:
What is in 'octane booster'?

google octane booster msds, and read to your heart's content.
One of them I looked at is 95% Kerosene, and a chemical that is so long that I'm not going to make any attempt to type it.
If you want to narrow it down, just type in your favorite octane booster followed by MSDS, and google will take you to the company's Material Safety Data Sheet. Some of them will say that the active ingredient is a trade secret that will only be provided to medical professionals.
I can just about guarantee that you till not find "octane" listed as one of the ingredients in any octane booster!

What is in 'octane booster'?

Modern engines can run 87 octane gas and have higher compression ratios because they have knock sensors and computers that will retard the timing if detonation is detected. Most modern engines are operating at the absolute limit of detonation on 87 octane with compression ratios well above 9:1. Without the sensors and computer, we'd have to run compression ratio's at 8:1 or less to run 87 octane.

When you're running 87 octane and your engine retards the timing, it's reducing the power output and possibly the fuel mileage. Most modern engines will simply run better on mid-grade 89 octane gas as it will provide a cushion against detonation and allow the engine ignition to run at optimal timing. Mid-grade gas is not much more expensive (as a percentage) and might cost you an extra $2.00 per fillup. I think it's worthwhile.

You cannot buy a container of "octane" because it is NOT a substance.

camperpaul wrote:
Octane and cetane can not be added.

However there are boosters that can be added

Ethanol and tetra-ethyl lead are both octane boosters.

Let me put it this way. :S

If I put 87 octane fuel in my car and then put an octane booster in the tank and it raises the octane up to 90 ..................I have added 3 points of ____________________________. You fill in the blank.

Before I moved from So. Cal I bought a new SIlverado 1/2 ton with the 5.3 and always used the 87 octane. I moved to Utah and saw trucks much larger than mine (3/4 and 1 ton)filling up with 85 octane. So I started to use 85 octane and if there is a difference the truck and I can't tell.
All these trucks tow travel trailers and 5th wheels and most are 4WD where my Silverado is not.

Back to the OP, I normally fill up with 87 octane in my gasser engines the last tank prior to descending to lower elevations for any significant period of driving time. It really isn't that important with modern engines though as they will detune themselves in order to prevent engine damage. You'll just loose a little power. On Engines with simpler electronics though, such as my Polaris RZR, it will sometimes knock when I push it hard with to low an octane fuel so I'm much more careful with it when I am heading down hill so to speak.

Regarding the side discussion this post has drifted too, it's been a lot of years since I went through school on aircraft power plants, but the simplified basics as best I recall were that detonation at with any given octane rating of fuel occurred at an absolute pressure point, with some variations you had to account for in the temperature area. As a result, the engine having a fixed amount of compression, if the air charge based on air density at sea level brought you to a point just under detonation with a given octane of fuel, the Lower density air at elevation would result in lower absolute pressure values at full compression, and thus your being even farther below the detonation pressure. As a result, you don't need as high an octane rating of fuel to keep the engine from knocking. Of course this only applies to naturally aspirated engines so the eco boost folks need not pay any attention. The turbos on those engines inject a fixed air charge into the engine by adjusting the amount of boost to compensated for altitude air density changes amongst other things.

Bottom line is - don't waste your money on higher octane fuel thinking that it will give you more power and performance. It won't, unless your engine is designed for it.