What grade of gas?

[Soundguy]

octane is the RESISTANCE to fuel burning ( in non precise terms ).

the higher the octane the harder it is to fire off the fuel.

as another said.. no gain by using a higher than spec'd octane for your engine.

keep in mind that ethanol is also an octane modifier.

higher octane is needed in high rpm / high compression engines. using too low an octane in those engines can cause spark knock / ping... ever wonder why fuel wwas 'leaded' with tetra ethyl lead? they didn't put it in as a valve lube.. it was an octane modifier.

this info is easilly verifieable..

soundguy

 

[schoolsout]

and I always thought the higher octane rating meant it was more readily combustible

Thanks for the info!

 

[Soundguy]

nope.. lower. that's why hi-pro race cars need the 100+ stuff...

soundguy

 

[lostcause]

higher octane does have benefits and pitfalls:

as was said, higher octane has a higher flash point, meaning it requires a higher temperature to ignite. this has been known to cause problems with hard starting and plug fouling in cold climates for some fuel injected and carbureted engines.

the benefit that goes with the higher flash point is a faster burn cycle. lower octane starts burning sooner, but the burn lasts longer. the quicker burn cycle of the higher octane means the combustion is completed faster, and there is less heat built up in the engine. simple version: slightly lower engine temperature.

with that lower engine temperature can come another issue: water cooled engines are generally designed to run at a certain temperature - often in the ballpark of the boiling point of water. by burning a higher octane fuel you are fighting the engine's fuel system.

personally, i will only use a higher octane for a couple instances: when the manufacturer recommends it such as performance / older vehicles, and in small air cooled engines. chain saws often take a lot of abuse in very hot temperatures, not to mention a very small engine turning 12k-14k rpm.

i have first hand experience with a carbureted snowmobile that fouled plugs on high test. i would have had to alter the plug heat range or re-jet to compensate. i have been around a fuel injected snowmobile that did not run well on high test because it could not get the engine temperature where it wanted to be. i have drag raced a snowmobile where running high octane aviation fuel allowed an insane reduction in jet sizes that did not melt the engine down because it kept it from getting too hot. i have also seen many vehicles with fouled plugs on cold mornings from trying to start on high test. i have heard stories of factory fueled high test vehicles not starting in the winter on dealer lots, but i can't back up that story.

 

[Soundguy]

tures, not to mention a very small engine turning 12k-14k rpm.

.

yep.. high rpm and or high compression engines generally benefit from higher octane.

soundguy

 

[Bird]

In 1956 my dad bought a Texaco service station. In those days Texaco had Fire Chief (regular) and Sky Chief (ethyl) gas. I still remember the state inspector telling us he'd never use Texaco Sky Chief. As he said, it was advertised as "more power" and he said, yep, same thing as adding a little kerosene to the gasoline; said it produced more power but would sure foul spark plugs in a hurry. Of course I didn't know then, nor do I actually know now, whether he was right.

In 1968, I bought a new Plymouth Roadrunner and about the only thing I didn't like about that car was having to change the spark plugs about every 3,000 miles. That's how quickly they got fouled with my wife driving it mostly very slowly on short trips to the grocery store and such.

In 1971, I bought a new 3/4 ton Chevy (350 4 bbl. engine) with a 10.5' slide-in camper. In the Spring of 1972, I traded the camper for a 25' travel trailer. The truck was less than a year old, still in warranty, the first weekend we went to a state park, pulling the travel trailer. We started home Sunday and everything was fine until I stopped for a red light. When the light changed and I stepped on the gas, it backfired and went to running very rough (missing). I didn't think it was going to get us home, but we didn't far to go and we made it. The next morning, I took it to a dealer and when I picked it up that evening, the guy said there was nothing wrong except fouled plugs. And he asked what kind of gas I'd been using. Yep, I'd been using ethyl and he said to not use anything but regular, which I did from then on.

I've been using regular ever since except in my small engines.:laughing:

 

[oldyellr]

Sounds like the only downside to using premium is the cost Considering we only use about 5 gals a week it adds upto $1 a week. I can handle that.:thumbsup:

But what would be the UPside if your engine does not require premium? Since premium gas is only used in high performance engines, it probably sits in the tank at the gas station much longer and could have condensation in it. There is absolutely no reason for using premium gas if your engine does not specifically require it.

 

[Soundguy]

yep, as it is harder to ignite, and could lead to hard starts and fouling in engines really not designed for it.

soundguy

 

[Diamondpilot]

Sounds like the only downside to using premium is the cost Considering we only use about 5 gals a week it adds upto $1 a week. I can handle that.:thumbsup:

That $1 per week is the best money you can spend. I just spent $83 on a customers carb in just parts. Total repair was nearly $150 on a gas power washer. I have also had to do carb work on his kids go cart. Cheap insurance.

Chris

 

[YesDeere]

Diamond, you really use aviation in small engines? Never heard of it, sounds strange but I'd like to know more. Is it just cleaner burning, more power, or like a detergent for the whole system? And where do you get it other than an airfield. I used to know a place that sold cam2 only pumped into a can, not car.

I've always just used reg with stabil when it gets close to being put up for the season. In my weedeaters and saws I always use the Stihl mix. Not sure if it's true but I was told it had a stabilizer in it already. Never had any major problems. But with ethanol in the gas that may be a YET.

One more thing, in my boat I run 93 and add the BG gas dryer. Has seemed to work great for the last two years. The water attracting ethanol does worry me