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Aperantly premium hurts the performance on a stock 7. Heavy mods requiere more octane to help reduce detonation. Higher octane less chances of blowing your motor when turbocharged.
Oooh really? I've used premium since I bought it. The manual says to use high octaine (such a high amount that they don't use anymore) so I always have. Tonight was the first time I've put regular in it. Whoops
Premium and regular have the same energy content! Only real difference IS, one pre-ignites or sends out detonation waves at a lower compression pressure+temp then the other! A non-boost rotary running 9.4:1 will never have a problem with running regular unleaded. If its got high compression like the renesis, then it needs higher then regular unleaded octane.
Regular mixed with either 1/3 a bottle of MMO or some 2 stroke oil. Anything but reg is overkill and not needed, waste of money. No need to prevent detonation in a naturally aspirated engine with a low compression ratio.
In the eighties, mazda raced with 83 octane fuel. The lowest I can get is 87, so that's what I use.
Octane's only purpose (as many people here have mentioned) is to resist detonation (or premature explosion of the air/fuel mixture because of compression).
Two things can make an air/gas mix explode:
1. A spark
2. That mixture being compressed into too small a space
If your engine's compression ratio is high enough, there's a danger that #2 will cause your air/fuel mix to explode BEFORE you want it to, which pushes against the spin of the engine, causing running problems, loss of power and in many cases damage to the engine. To prevent this, using a higher octane fuel will make the mixture harder to detonate by compression and makes it so that only a properly timed spark will ignite it.
Higher octane = more pressure you can put the air/fuel mix under
When is this useful? High compression engines or forced induction (turbo, supercharger) engines.
The N/A rotary has a compression ratio of 9.4:1 (for the stock FB engines, both 12a and 13b).
This is not enough to cause a problem with premature detonation due to pressure. So the mixture will *always* fire only upon spark from the spark plug. Buying more expensive, higher octane gas makes absolutely no difference. The amount of power available to be extracted from 94 octane is almost EXACTLY the same as 87 octane *.
If you run turbo or super, don't use regular. Detonation = death.
So shake the common misconception that octane = power, and just buy the cheap **** for your car. It'll save you money, and your car won't notice the difference.
*ed note: (Some could argue that 94 octane has marginally lower amount of energy to release because adding anything is a dilution of the original gasoline. If that additive doesn't have more stored energy itself, the total stored energy of the diluted mixture would be less than the original gasoline. Of course this is so amazingly marginal that it really doesn't make any measurable difference either way)
It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. Using a fuel with a higher octane lets an engine be run at a higher compression ratio without having problems with knock. Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Some high-performance engines are designed to operate with a compression ratio associated with high octane numbers, and thus demand high-octane gasoline. It should be noted that the power output of an engine also depends on the energy content of its fuel, which bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is mostly falseóengines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octant rating is minimal.