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Discussion Starter #1 (Edited)
If you've read the owner's manual by now, you'd know your BRZ requires a minimum of 91 octane to run safely without damage, and that Subaru recommends 93. Anything below 91 will most likely result in lots of detonation, and even motor death. I want to stress here that running 87 or 89 is NOT safe and if you do that and blow your engine up under load, you only have yourself to blame.

What is detonation? We'll, it's basically when the air/fuel mix explodes in the combustion chamber when the spark plug fires creating pressure spikes usually due to low octane fuel or bad tuning. This causes damage to piston rings, among other things. It usually sounds like a loud tapping or knocking noise. Knock happens most easily when a lean Air:Fuel ratio exists, and when ambient temps are high. If you've ever heard this sound, you know how terrible it is to hear particularly if your car is on the dyno running at full load. I've seen engines nearly explode on dyno days mostly due to bad tuning or just stupidity of not having enough fuel capacity for their setups.

"It's just a four banger! Why would you need to run premium? It's not like it has a turbo!" This engine has a very high compression ratio of 12.5:1. This is high in the realm of street cars, which is why you need fuel with better knock resistance.

"So why do they recommend 93 vs 91?" They have to design the car to run on 91, because some areas of the country only offer 91 at the pumps. However, they can design the ECU to recognize 93 or 91. This car uses a dynamic advance to compensate for the lower octane (thanks visconti!). No one should have any problems running 91. Get 93 or higher of course if you can get it in your area, you'll get slightly better performance.
 

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You're right, done.
Go to technical discussion? In part, it already is a sticky. See : Everything you wanted to see... " thread and then go to "MANUAL", page 420.

My suggestion, although making it more time consuming than just initiating a thread with a question or statement, would be to do some personal research first and THEN bring up the subject.
If it is technical, make a reference to established information.


For many members, including myself, it is sometimes difficult to determine whose statements or opinions are accurate.
 

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Discussion Starter #5 (Edited)
Go to technical discussion? In part, it already is a sticky. See : Everything you wanted to see... " thread and then go to "MANUAL", page 420.

My suggestion, although making it more time consuming than just initiating a thread with a question or statement, would be to do some personal research first and THEN bring up the subject.
If it is technical, make a reference to established information.


For many members, including myself, it is sometimes difficult to determine whose statements or opinions are accurate.
What part of what I posted wasn't common knowledge? It was moved because it pertains to the engine, not because it's technical.
 

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Accidentally ran 87 for a bit, and there was very small, faint knocking luckily. Currently there's a small whistle/cricket sound after flushing it with 93 octane, and the humidity rose greatly along the same time so I'm unsure what exactly might be causing it... only happens at lower revs.
 

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prob the mixtures after 1 or 2 tanks the 93 should be good or boost it up to 94 octane and just run that for a few tanks then 93 or 91
 

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91 at the lowest. Now for a more interesting debate.. 91 no ethanol vs 94 with 10% ethanol. What is better for high compression DI engines?
 

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Discussion Starter #9
91 at the lowest. Now for a more interesting debate.. 91 no ethanol vs 94 with 10% ethanol. What is better for high compression DI engines?
Looks like no one wanted to start this discussion, so I will. 10% ethanol in gasoline is actually beneficial to performance. Ethanol increases knock resistance and has a cooling effect on the intake charge. The only downside is reduced fuel economy.
 

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Unless your car's engine was designed from the outset to run on ethanol-E85(flex-fuel vehicles, anyone? than any ethanol will reduce power, fuel economy and gum up fuel filters and gas lines. Granted today's cars CAN handle some ethanol, that doesn't mean you should subject your sports car to it. Ethanol simply put does NOT have the same power density as gasoline, PERIOD! its called chemistry, anyone that wants to argue with that, simply needs to google it. Yes race cars that were designed for it can handle it and make more power. Same with Drag racers that run methanol, or Nitro-street engines are not designed to run those mixes. Ethanol was only added to make it more environmentally friendly, THAT's ALL! End of story! hope anyone with any knowledge can prove me wrong, otherwise stop spreading BS.
 

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What is detonation? We'll, it's basically when fuel ignites before the spark plug tells it to (before the piston reaches TDC). This causes damage to piston rings, among other things. It usually sounds like a loud tapping or knocking noise. Knock happens most easily when a lean Air:Fuel ratio exists, and when ambient temps are high. If you've ever heard this sound, you know how terrible it is to hear particularly if your car is on the dyno running at full load. I've seen engines nearly explode on dyno days mostly due to bad tuning or just stupidity of not having enough fuel capacity for their setups.


^=sorta correct,
what you are referring to, is called pre-ignition and yes it is bad, typically it's the result of a hot spot (unburned fuel-usually not running properly or someones tuning mistake) in your cylinder chamber that results in the fuel pre-igniting.

Detonation is the WORST, and is the result of using bad gas or a lower than required octane fuel that results in a immediate explosion when the spark plug does fire, rather than a even flame prognation, of the fuel and air mixture creating 1000's of PSI pressure spikes that blow rings, ring lands, bend Con-rods, and or blow holes threw your pistons, and maybe even blow the crank out the bottom-in extreme cases. I don't want to get into all the science specifics about it, as people can google on their own. but basically those are the two basic forms of bad ignition.

Hope this help to clarify some things.
 

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Discussion Starter #13
What is detonation? We'll, it's basically when fuel ignites before the spark plug tells it to (before the piston reaches TDC). This causes damage to piston rings, among other things. It usually sounds like a loud tapping or knocking noise. Knock happens most easily when a lean Air:Fuel ratio exists, and when ambient temps are high. If you've ever heard this sound, you know how terrible it is to hear particularly if your car is on the dyno running at full load. I've seen engines nearly explode on dyno days mostly due to bad tuning or just stupidity of not having enough fuel capacity for their setups.


^=sorta correct,
what you are referring to, is called pre-ignition and yes it is bad, typically it's the result of a hot spot (unburned fuel-usually not running properly or someones tuning mistake) in your cylinder chamber that results in the fuel pre-igniting.

Detonation is the WORST, and is the result of using bad gas or a lower than required octane fuel that results in a immediate explosion when the spark plug does fire, rather than a even flame prognation, of the fuel and air mixture creating 1000's of PSI pressure spikes that blow rings, ring lands, bend Con-rods, and or blow holes threw your pistons, and maybe even blow the crank out the bottom-in extreme cases. I don't want to get into all the science specifics about it, as people can google on their own. but basically those are the two basic forms of bad ignition.

Hope this help to clarify some things.
You're right, I should've differentiated the two. I'll try to amend the first post in a little while.
 

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Discussion Starter #14 (Edited)
Unless your car's engine was designed from the outset to run on ethanol-E85(flex-fuel vehicles, anyone? than any ethanol will reduce power, fuel economy and gum up fuel filters and gas lines. Granted today's cars CAN handle some ethanol, that doesn't mean you should subject your sports car to it. Ethanol simply put does NOT have the same power density as gasoline, PERIOD! its called chemistry, anyone that wants to argue with that, simply needs to google it. Yes race cars that were designed for it can handle it and make more power. Same with Drag racers that run methanol, or Nitro-street engines are not designed to run those mixes. Ethanol was only added to make it more environmentally friendly, THAT's ALL! End of story! hope anyone with any knowledge can prove me wrong, otherwise stop spreading BS.
All cars made for the US market have been designed to run on E10 for years now.

From the BRZ owner's manual:

"SUBARU recommends the use of cleaner burning gasoline
Cleaner burning gasoline, including reformulated gasoline that contains oxygenates
such as ethanol or MTBE (Methyl Tertiary Butyl Ether) is available in
many areas.
SUBARU recommends the use of cleaner burning gasoline and appropriately
blended reformulated gasoline. These types of gasoline provide excellent
vehicle performance, reduce vehicle emissions and improve air quality."

The use of E10 will not reduce power. Ethanol is a high octane additive, an oxygenate. You're right, it doesn't have the same power density as 100% gasoline resulting in reduced fuel economy. So to counteract that loss in power density, the car uses more fuel because the ethanol mixed with gasoline burns faster than pure gasoline does. Ethanol burns at a 9:1 AFR while pure gasoline burns at a 14.7:1 AFR. Cars of today still run 14.7:1 in closed loop, it just uses more fuel it's as simple as that. The mix also creates a clean burn, reducing emissions and it actually keeps the fuel system clean.

Of course you can't run E85 in non-flex fuel vehicles, I don't remember saying you could. I'll say though that with significant fuel system modifications (huge injectors, higher capacity fuel rail and pump), and lots of tuning, E85 can be used as a race fuel on high hp cars (performs similar to 110 octane race fuel).

Ethanol was added not only to make it more environmentally friendly, but because the use of MTBE (another oxygenate) has been banned (cancer causing substance).

I'm not saying ethanol doesn't have its problems, it has many. Older cars were never designed to run it and results in as much as a 30% fuel economy deficit. The government subsidizes the crap out of it. Farmers are making out while we burn more gas. Some say they use more gasoline to make ethanol than it saves by mixing it in. The fact is we're pretty much stuck with it for now. Over 90% of US gas stations use E10 fuels.
 

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I have one more argument, than I promise to drop the subject all together. If adding ethanol is suppose to aid in cleaner emissions, better burn, etc. how is burning more fuel(ethanol mixed) per mile, better for the environment if all it does is make you fill up more often?...So in saying that, is it not better for the environment and our engines to simply burn pure gasoline? I think the original argument was to chose either 91 without ethanol or 91/93/94 with ethanol....food for thought! personally I'm choosing 91 without ethanol which is provided by shell, at least in Canada. Otherwise your wasting money buying something that has ethanol in it. Btw gasoline in itself is known to be carcogenic. That cancer stuff is a load of shit.
 

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Also, just as a comment for those who have just taken delivery of a new vehicle, These days many dealers are delivering them with a full tank, but I'm convinced mine was delivered with a full tank of regular. Hope know what the helper in the shop puts in all the new cars he takes down to the corner gas station. As soon as I topped it off from half with premium, perfomance notably improved and again more so at the next half tank. If I bought this car over again, and it came with a full "unknown" tank, I'd probably drive straight to the auto parts store for some octane enhancer.
 

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The most common detonation problem in modern engines is premature ignition of fuel/air end gas. Hot spots are not usual and pre ignition from the spark plug is exceptionally rare, especially in DI engines.

The high compression ratio and relatively fixed speed of the flame front, together with high rpm and large bores conspire to over pressure the outer limits of the combustion chamber. The pressure wave resulting from the ignition event precedes the spread of the flame front compressing the end gas to the point of compression ignition. This is why DI with its precise injection timing, ability to promote turbulence and a modified stratified mixture allows such high compression to be used in the first place. When combined with full 3D mixture and ignition timing as well as significant charge cooling not available with port injection you get higher combustion chamber pressures, a superior expansion ratio and significant knock resistance.

Don't mess with the wrong fuel, you'll regret it.
 

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While Ethanol may have its downsides, when a car is tuned to run on it the results are impressive. Yes, I spray 30% MORE E85 than I do 93 octane but I also put down way more power across the board. It burns WAY cleaner than pump gas and leaves no carbon build up behind. E85 has an octane equivalent of 105 allowing for far more aggressive timing (by aggressive I mean advanced) and more resistance to knock. FI applications are where E85 gets really fun!

Don't, and I repeat DO NOT, put E85 in your BRZ without having the car properly set up first. A solid ecutek tune and a flex fuel kit with an ECA is the way to go.
 

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that sound happens to all brz's, at least that I know of. There was a service bulletin about that so if you take it to a dealership they will get it fixed. It is something about the fuel distributor or something like that, I forgot
 
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