To boost octane or not to boost octane..that is the question.

[jjtarnow]

Okay, seems like everyone has the same question regarding the need to boost octane above 94 pump gas. Outside 11:1 compression it seems like there is a real need to assure even burn but what about the vast majority of us that are inside 11:1? Does it really cause the engine to run cooler, steadier, and just all around better? I'm running 10.5:1 and tried 104+ and noticed no difference at all (as a matter of fact the car had a harder time starting with the o-boost). What do you guys think? Personally, I'm not looking for a text book answer here..more real life experiences (but then again who am I to limit discussion!).


Josh

[Ron61]

Josh,

If you have aluminum heads then in your state where you can still get GAS you most likely won't notice much difference in the 104 and your pump gas. In the Republic of Calif. they use our pump gas to put out fires. Two of my cars have 11:1 and I run 110 racing gas in them and I can tell a huge difference if I have to drop back and use some of our premium 91 watered down pump gas. I am not sure why you had a harder time starting the car with the higher octane. I have never had a problem at all with that. Some of the people in your area can tell you more as they have access to your pump gas.

Ron

[Back in Black]

You can subtract one compression ratio due to better cooling effect. This means that my 514 which has nominal 9.8 to 1 compression, in reality acts like it has 8.8 to 1.

I ran premium and it was a waste of money and the motor did not like it. I use regular pump gas only now.

[ByronRACE]

Higher octane fuels burn more slowly. The only reason to run a higher octane fuel is if your engine detonates with more than about 20deg BTDC top-end timing advance on whatever fuel you're trying to run in it. If you run less than about 20 to avoid detonation (I don't like to see less than 26 personally), you're generating a bunch of heat out of the exhaust from all the retard, and possibly putting your exhaust valves through hell. If that is the case, then running a higher octane fuel and advancing the timing is for you.

One thing to keep in mind...if a typical Ford V8 is found to detonate at 34deg total, and run optimally at 32 total on 94 octane, increasing the octane to 104 and NOT advancing the timing will LOSE power every time. The 104 burns slower and acts like timing retard. Rule of thumb; advance .5deg for every octane point. (104-94 = 10) (10*.5)=5; advance timing 5deg from whatever the "optimal" point was on 94 octane.

And, if you're building an engine on california 91 octane mule piss, it's interesting to note that we're making the same power on 8.5:1 engines and this crappy gas with about 32-36deg total as we do with 10.5:1 engines running 20-24deg total. And, the low compression engines run cooler/happier. And...in both cases, our numbers compare to other builders/tuners across the US. Yet more information that says "octane alone does not make power".

Byron Reynolds
RACE Systems
San Jose, CA

[jjtarnow]

Byron,

Thanks for the information. It is incredibly helpful and partially explains some of the effects I experienced when I put in the boost.

Josh

[Mr.Fixit]

Octane rating and burn rate are separate.

[Bob Parmenter]

You used the word boost, and the trade name 104+, an "octane booster", so I'll assume you meant that product and not a gasoline blended to 104 octane rating. I took some of that product with me on a 1600 mile road trip in a SBC powered street rod I had a few years ago as "insurance". The engine wasn't particularly finicky, but would ping on occasion at higher operating temps and higher loads. So I took the booster along in case I needed it. At one point on the trip I got some pinging, so put in a recommended dosage. After a few miles the car began to run more poorly. As the miles progressed it got worse. At our next overnight stop I pulled the plugs after cool down. They were covered with a beige colored deposit that nearly bridged the electrode gap. After purging the fuel system the "problem" went away. I've never used the stuff again!! Perhaps it was that my plugs were too cold for the content of the booster, but whatever, I didn't like the results. You may want to check your plugs as the source of your complaint.

Just to concur with Race, in the absence of pinging, higher octane alone won't change results. There has to be a change in timing to realize "improvement". An EFI system with a knock sensor might make a difference since the computer will "adjust" the timing (as well as other functions) according to sensor inputs.

Octane requirement is largely dependant on operating temperature. So the faster heat disipation of aluminum explains why higher compression ratios are enabled. But so too will air density, air temp, load, air/fuel ratio, timing, etc. Any function that affects temperature in the combustion chamber.

[Excaliber]

Lower octane fuels are more likely to 'cause engine "run on" after the key it turned off IF your engine is prone to such a condition. Some are, some arent. Idle speed, type of carb, etc also play into this.

I'm not sure I would charaterize higher octane as "slower burn" rate, it's a more "stable" burn and NOT as easily subject to self detonation.

Concur, if your engine does not require higher octane your throwing your money away and NOT increasing power in the least!

Octane boosters as found in the "store" are a joke. They say the will raise your octane 2 or 3 poiints? So thats 94 octane to 94.2 or 94.3 octane. Do the math on the cost, it's a rip off.

[jjtarnow]

Just to restate...I had a heck of a time getting my Cobra started when I used the requisite amount for my set up. Same operating environment but with no 104+ Octane boost and she kicked over right away and ran better. I fully realize some of you will discount what I am saying and attribute it to some other variable but...

Josh

[Excaliber]

Well JJ, it does sound rather odd. But I hear what your saying! Kind of fits with what Bob P. was saying.

In other words, this octane booster stuff is unpredictable in it's results.

,,,,I'm gonna try some toulene myself.....

[Ron61]

I got some stuff called Fast Forward that cost a fortune and it seems to work ok, but adding a gallon of my racing gas is much better. The Fast Forward is supposed to work with either gas or alcohol and I carry a can of it for an emergency, but I have never found an over the shelf additive that really made a lot of difference. Only good thing about the Fast Forward is I don't have to measure the amount. But I still don't think it is anything to get excited about.

Ron