My friend has run nothing but avgas in his '63 Pontiac Catalina for the last five years. Factory engine (389), had 100K miles on it when he got it, and it just chunked a cam bearing about a month ago at 145K miles (and he drove it hard all the time). Tore the engine down, clean as a whistle all except for the cam bearing that was shot. Maybe you know something I don't, but I'm just talking from experience.

 

Motorhead, if I read your post correctly, I understand your motor "pings" on regular gas, but the "ping" goes away when you use high-test.

I don't believe your statement contradicts my premise, "A properly-tuned engine, operating WITHOUT engine knock/pre-ignition/detonation on
regular gasoline, will not produce more power by burning higher octane fuel." (emphasis added)

Since your engine "pings" (pre-ignites, detonates or knocks) on regular fuel, it's not surprising it runs better on premium.

I think your experience confirms the other side of the premise; if an engine DOES ping/pre-ignite/detonate/knock on regular fuel, it MAY develop more power with higher octane fuel.

Tree Farmer

 

I thought I read somewhere that a stock 4 stroke will run cooler with higher octane..any truth,or myth?
Would it be easier on the engine in the middle of summer with temps 85-95 degrees,going slow,or working hard in mud?
THANKS...BILL

 

Clueless

Octane level is, by definition, the fuels ability to control spark knock. The higher the octane level, the less volatile the fuel. So, if you have high octane fuel, which is less volatile to begin with, sitting around for a while, then you have even deader fuel in your tank when you go to run the machine! The volatilty of the fuel drops as it ages.

Cowboy,

You indicated your truck had better gas mileage with higher octane fuel. In the same paragraph you stated that it was mildly built. There is the answer. As stated in the original post, if the engine is modified it may make a difference when you run higher octane fuels.

A stock, low compression engine, designed for '87 octane fuel, won't run any better on a higher octane fuel. It is all perceived differences. Smoke and mirrors.

A side note. 87 Octane here in Canada is not generally the same as 87 octane in the US. There must be different methods of determining octane in the 2 countries. My travelling car runs on 87 octane in Canada without pinging. The 87 octane I buy from Michigan to California, does cause the car to ping. Any thoughts on the different methods of determining octane level?

DJ

 

I have run regular, then switched to premium+108 Octane Boost+ SplitFire plug. Now I am back to regualar fuel and the original plug. I could not empirically determine any benefit. I still got stuck.

 

Yes there are 2 ways of rateing Octane, I cannot rember what they are, something like RM+2 method or something. One thing, all EFI trucks and cars can sence the octane and will adjust there timing to get the most power off the fuel used, so if you do fill up with 92 octane, there will be a slight performance increace due to the computer senceing less knock and it will advance timming. Joe

 

I think you misread or misunderstood what I was saying. The engine pings slightly on regular grade gasoline (87 octane), and when I switch to Premium (92 octane), the ping completely disappears. According to your statement, since the engine no longer pings on Premium, then any fuel with higher octane than Premium will not produce any more power. To the contrary, however, when I run Avgas (100 octane) it produces more power, which disproves your statement because the engine didn't ping on 92 octane, yet still produced more power with 100 octane. I hope I was more clear in my explanation this time.

 

Okay guys, let's use a little logic here. The Octane rating of a fuel is determined using a standardized piston engine with variable compression ratio, and the higher compression they can achieve before pinging, the higher the octane rating. This may not be 100% accurate, but it's generally true from what I've read. This means that undoubtably higher octane fuel will cause less spark knock (pinging) in high-compression engines. However, this DOESN'T mean that is the ONLY effect higher octane fuel has, it's just ONE effect that is easily measured and standardized.

You also can not assume that because high-octane and low-octane fuel have equal specific heats that they will produce the same amount of power. On paper, in ideal conditions, they will, but in an internal combustion engine it's a completely different story, there are literally thousands of variables that effect how the fuel is burned.

Ultimately, the problem is you are making too many assumptions, not taking enough variables into consideration, and relying only on what you've read on the subject. As I said in my previous post, you need to go out and TRY IT. And just because the seat of your pants can't feel the difference doesn't mean that it's not there. If you can't feel the difference, then by all means buy the cheap gas, but don't assume that there was no difference just because you couldn't feel it. The human body is far from a precision instrument. Ultimately any engine will perform better with higher octane gas, BUT high-performance engines will see a bigger improvement than low-performance engines.

 

108+, and pretty much any other off-the-shelf octane boosters, are a joke.

 

Motorhead, is it possible the vehicle you cite is equipped with Electronic Fuel Injection (EFI), possibly including an "octane" or pre-ignition/knock sensor that automatically adjusts the spark advance optimally for the fuel used?

You made a good point in a later post about variables; I tried to limit them in my premise and discussion in the initial post:

"Now for the possible advantages of higher octane fuel. More power is possible from "high-test" if
one or more of the following adjustments/modifications are made to the engine:

1) Spark timing is advanced."

If the improved performance relative to higher octane fuel in the vehicle you cite involves adjusting the spark advance, even if the adjustment is an automatic one transparent to the operator, it's still an adjustment taking advantage of the properties of the higher octane fuel.

Again, if your vehicle pings on regular, I'm not surprised it runs better on premium. And, if its EFI system automatically advances the spark for even higher octane fuel, I'm not surprised you obtain even higher performance with more octane boost.

The initial premise was intended for the ATV world (I'm told ATV's are occasionally discussed on this Forum (smiley faces)). I'm unaware of any ATV with a mechanism automatically adjusting spark advance optimally for the octane of the fuel burned. Some hotty, hotty, go-drive-fast motorcycles have EFI and may have that feature, but I'm unaware of any ATV's so equipped, yet.

You get may better performance in your EFI-equipped vehicle with higher octane fuel; Cowboy may get better mileage in his, because of the automatic spark advance adjusment feature. However, I wouldn't expect any given carbureted ATV engine, properly tuned and running without ping/knock/pre-ignition/detonation on regular fuel, to gain from the use of high-test, without engine adjustment or modification. Limiting variables, I don't include shelf-life, volatility, smell, etc., etc., in this consideration.

Now, perhaps you HAVE disproved the premise, as you claim. If so, I stand corrected!

Tree Farmer