What's the benefit of running high octane?
- Thread starter ScottSchwarzer
- Start date
It really comes down to mods. more compression needs higher octane to eliminate detonation or knock. blasty's like premium stock but there really is no need to use any race fuels without really high compression. the point of high octane fuel is to achieve more complete combustion. high octane is actually less flammable than lower octane fuel. believe it or not.
Gasoline is made up of about 80 major hydrocarbons. The proportion of those chemicals is the "makeup" of the fuel. anything from 25% by volume down to .00001% by volume will change the chemical composition and combustion properties. Octane is a measure of how strongly a fuel resists predetonation (firing before it's supposed to because of compression or "hotspots") and "race gas" or "aviation fuel" is usually used to refer to fuel with a MON (motor octane number) rating of over 100 octane meaning that it's more resistant to "knock" (and a few other properties like a higher vapor pressure to resist vapor lock and boiling at low atmospheric pressure).
The advantage is that you can build an engine to use higher octane fuel, you can raise the compression and make the squish area or the head smaller to raise the thermodynamic efficiency of the engine ( MO POWA!). There is an advantage to building an engine around the use of higher octane fuel... there are also a few disadvantages.
While "knocking" engines produce FAR more heat than they are designed to under any circumstances, any increase in the amount of fuel burned will increase the natural heat load on an engine. This decreases the safety margin between operating temperature and oil film breakdown temperature. A highly tuned engine cannot survive a small air leak due to the increased heat and decreased safety margin.
Also, avgas or race gas is more expensive to run and generally engines tuned to run it require more of it....
If your engine isn't built to run race gas or avgas, there is virtually no advantage in putting avgas or race gas in it as the thermodynamic efficiency isn't higher (like a built engine) and the higher octane fuels actually contain less energy by volume.
The advantage is that you can build an engine to use higher octane fuel, you can raise the compression and make the squish area or the head smaller to raise the thermodynamic efficiency of the engine ( MO POWA!). There is an advantage to building an engine around the use of higher octane fuel... there are also a few disadvantages.
While "knocking" engines produce FAR more heat than they are designed to under any circumstances, any increase in the amount of fuel burned will increase the natural heat load on an engine. This decreases the safety margin between operating temperature and oil film breakdown temperature. A highly tuned engine cannot survive a small air leak due to the increased heat and decreased safety margin.
Also, avgas or race gas is more expensive to run and generally engines tuned to run it require more of it....
If your engine isn't built to run race gas or avgas, there is virtually no advantage in putting avgas or race gas in it as the thermodynamic efficiency isn't higher (like a built engine) and the higher octane fuels actually contain less energy by volume.
So, would modifications such as a better exhaust, cut airbox or better filter apply to this since they are allowing more air into the engine? Also, could a colder heat range spark plug, that has a lesser gap, fix a misfire instead of having to use higher octane fuel to deal with the higher compression?
Better exhaust, open airbox lid and better filter increase the AMOUNT of air (and thus fuel) that get into the engine. The changes that require higher octane fuel are internal and have to do with a rechambered head.
There is very little that will "substitute" for the proper way to deal with an engine that is setup in a certain way. Running a one step colder spark plug is generally recommended even with a relatively mild trail build to reduce the temperature (and thus stress) on the center of the piston crown (where the piston has the least amount of strength).
By allowing in more air, you compensate wit a bigger jet to supply the extra fuel.
No need to use any other plug than the stock B8ES.
93, 95 octane is fine for simple mods such as pipe, filter, air box lid.
It is only when you get into the realm of porting, high compression, advanced ignition, that you need to consider using high octane fuel and different heat range plugs
No need to use any other plug than the stock B8ES.
93, 95 octane is fine for simple mods such as pipe, filter, air box lid.
It is only when you get into the realm of porting, high compression, advanced ignition, that you need to consider using high octane fuel and different heat range plugs
Okay that clears a lot of things up for me. Thank you guys. And that 9 dollars a gallon is pretty intense! New York has it bad haha. Down here in Eastern NC it's only around 4 dollars.
thats the price of 110 octane, i shoulda mentioned that lol. regular is about 4.07/gal
the short answer.. there are none. high octane gas actually burns less furiously than lower octane. it burns cleaner though. the only reason you need higher octane (and i mean only reason) is if your advance your timing or increase compression. the higher octane rating keeps the fuel from detonating early (i.e. predetonation) it is harder to ignite this keeps the engines combustion cycle in order. to high of an octane rating and you are robbing power. to low and you may be doin damage because the gas is igniting before the piston is at tdc. having an exhaust or even getting port work doesnt warrant higher octane. milling the head to increase compression or getting a stroker crank or advancing the timing all increase the compression and thus require the higher octane.
This kinda explains why my lawn mower runs like sh*t...I dump the cheap stuff in. Starts hard, the idle speed is ripping (with no adjustment screw) so it sucks fuel thru it like no tomorrow....1/4 acre and I get 1.5 mows out of a tank. Blah!
Just put some premium race gas in her slap a few number stickers and go to the mower races and haull ass or mow some grass WHHHHHOOOOOOOO!!!!!!!!!!!!!!!!!!
So should you just run regular in a blaster or be safe with the premium (next octane grade up right?) What do you guys run?
92-93 Octane, stay away from 89. 89 should only be used in liquid cooled machines or autos. I don't even run that stuff in my road bike, only my car and truck.
