I didnt know detergent levels were different.. I know some of the octane rating is produced by the addition of alcohol/mtbe which may make it burn better in the right engine and in turn cleaner. In a lower compression engine 93 octane is a waste of money and can actually hinder performance.

For 10.3:1 though I dont think 89 will cut it I would say 93. I guess it would depend on the cam and timing somewhat but in general 93.

For 350 hp I doubt you would need to go past 9.5:1 it would give you less problems especially if you run steel heads and I would guess the HP gain at that level is less than 5% for 1 point of compression.

 

They are higher, and some of the better brands use as much as five times the amount of detergent in their premium gas as what's required by law. The higher octane is ussualy obtained from Ethanol, ussually derived from corn in this country, although other grains can work, and Brazil, which uses E85 for something like 60% of it's vehicles gets it from sugar cane, in something that resembles uber-rum. 93 Octane can use as much as 10% Ethanol and still be called gasoline. The real issue here is that gasoline ignites at a lower temp than ethanol, and burns more rapidly, which leads it to be more prone to detonation. The Ethanol promotes a slower burn, and more even fuel consumption.

I've never heard of 93 Octane hindering performance, how exactly does that work?

 

I can spell, it's just hitting the same key in tandem.

 

The benifit of ethanol really doesnt come in until you raise the compression ratio it has less caloric value than gas for the same given amount (in turn less energy) this is evidensed by the fact e85 will produce less (10 to 15%) milage in a conventional low compression engine. Ethanol will make more power than gasoline in the correct high compression engine; it is oxygenated burns slower and you can run more of it through the engine. It is my opinion that in a low compression 8:1 engine that because of the caloric value of the fuel additive and no need to stop detonation the fuel will produce less power.... but this is only my opinion I could be wrong..

 

On an EFI engine, there is an anti-knock sensor. It adjusts the timing. It has a preset maximium amount of timing adjustments. With 87 octane you have maybe 2 degrees of play either way, if that. If you put in a higher octane, you can advance the timing to allow for a more complete burn. Since the computer can allow only so much advance, you can't burn all the fuel. You could change to hotter spark plugs, but then you'd have to run premium all the time and it's not recomended.

On the contrary, if you put too low of an octane in, it will start to knock because the computer won't allow it to retard any more. If you have a car that says Premium ONLY, you could get away with 89 Octane. That is within the computer's control parameters.

As far as E-85. Look at the 2001 Explorer. The regular gas one gets a rated 18MPG and then the FlexFuel gets 13MPG.

 

I'm thinking that MAY be incorrect. I mean, seriously, have you ever watched a thin older woman next to a large body builder at a driving range? The guy is strong, but never played golf before, so he hits hard and fast, and is quite satisfied with his 200 yards. Then, theres an old lady of about 55 or so, who's been golfing for years. She calmly draws back, hits smoothly and confidently right in the ball's sweet spot. 310 yards. The big guy is 87 Octane, hits hard and fast, but not as smoothly as he could, and he may have more power in him, but he can't focus it the way it needs to. The woman is 93, she's not as strong, and she may have less mileage in her, but she damn sure knows where to put the power she DOES have.

Just a thought.

 

TIGER- im loving that saying, funny stuff

 

Come on....seriously a golf analogy to explain cylinder combustion thats a new one... ok here is my anology the bodybuilder steps into the T quickly makes his swing hits the ball a short 200 yds, the less powerfull lady steps into the t takes her good old time goes to swing and her time runs out she wasnt able to fully complete her job of hitting the ball.

Because the high octane fuel needs higher heat/compression to fully burn the fuel the fuel is not burned completly in the low compression engine and is discharged through the exhaust this combined with the fact that there is less thermal value in most of the high octane fuels leads me to believe my assumption is correct .... in a low compression engine high octane fuel is a waste of money and may actually hinder performance...

 

Not to mention, all that unburnt fuel from 92 octane can clog the catalytic converters and mess with the O2 sensors.

 

I think that there are a whole lot of confused people here about " octane ". I've explained this before but I'm going to do it for the benefit of all those in doubt. I have extensive knowledge because of a personal relationship with Steve Burns who is the founder and CEO of VP Racing Fuels. Steve began VP in the back of Our Race shop in San Antonio, Texas in the mid 1970's. He was my wifes back neighbor as they grew up. As He has pounded into My head many times, Octane is a word used to give the average person an idea ohow automotive fuel works. Octane used by the big companies and is posted on gas pumps is derived at via a formula that is very complicated and does not relate to race fuel at all. First of all, octane is not raised or lowered by the use of any form of alcohol. The amount of hydrocarbons ( percentage ) is what controls burn rate ( octane ). A high burn rate ( less octane ) has a lower percentage of hydrocarbons. An engine that has high compression ( above 10-1 ) needs a slower burning fuel ( higher Hydrocarbons to make the burn last longer ) to allow the engine to use the fuel at a different rate so it does not use up the fuel before the burn cycle ( firing stroke ) before the cycle is complete. When You hear an engine pinging or detonating, it's because the fuel has been burnt too quickly and it needs a slower burning fuel, or less ignition timing. The reason the timing is important, is because the more advanced the timing is, the sooner the burn starts. By retarding the timing, You reduce the burn time requiring less octane. A Race engine with upwards of 17-1 compression requires a very slow burning fuel making the need for a speciality fuel such as VP's C16 which has 20% hydrocarbon content a requirement. Engines with 12-1 can run fine on C12 which has a 12 % hydrocarbon content. Expanding on this, An engine using NOS does very well when using C16 as the fuel injected with the NOS from a seperate fuel cell. It helps slow the burn rate and helps prevent burning up all of the fuel with the NOS. So, what the major fuel companies do, is to add hydrocarbons to increase " octane " and slow the burn rate. The use of any form of alcohol or ethanol is for different purposes. An engine will only have unused fuel if it's running rich ( just too much fuel volume for the engine to burn ). Modern fuel injected cars will computer compensate for this by sending less fuel through the injectors, It will also use the knock sensor to retard the timing to eliminate detonation. I know this is a bit long winded but I feel that everyone that has a performance car should understand this process so they can know the reason for the fuel requirements of their car.