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[quote=Anonymous][quote=Anonymous]I drive a luxury car and was always under the impression that the different grades were a bit of a scam. If you can get someone to think it's better, they will pay more but really it's all the same. A bit like most organic vegetables. [/quote]

Which is why you’re not an auto technician or engineer.

Octane grades exist for a reason. The higher the octane rating, the more resistance to spontaneous ignition of the fuel (“knocking”).

Higher performance engines or engines with boosted intake pressure (turbocharged or supercharged engines) or high compression engines produce more power for their relative size, because the higher volume of air being squeezed into each cylinder during the intake stroke and then compressed prior to spark ignition contains more oxygen. So more work is produced by a cylinder with higher compression, and those engines are more powerful (or smaller, while producing the same power as a normally aspirated/lower compression engine.

The problem though is that the fuel air mixture with 87 octane fuel can detonate early in higher compression engines. When this happens, the most noticeable effect is a slight loss of the car’s felt “power” in the seat of the pants.

But the other issue- the one you can’t see happening- is inside the engine, inside the cylinder where the pre-detonation is occurring. When the fuel air mixture detonates early, part of the flame produced during this explosion “squirts” (for lack of a better word) back up into the intake valve openings, which are in the process of closing right at that instant. Part of this high pressure flame imparts high velocity, high temperature gas forces onto the seats of the valves, which aren’t meant to be exposed to this, since normally the valve would be closed by the time the flame front got to them. But since the mixture detonated early, they aren’t. The other thing that’s occurring is that combustion deposits (think “soot”) are being deposited on the back sides of the valves, forming a crust which disrupts smooth flow of the incoming fuel air mixture. These deposits rob performance by causing turbulence and slight restriction of the incoming fuel air mix. Between wearing the valve seats and causing deposits to accumulate, predetonation of fuel will absolutely, positively cause engine damage over time.

I’m sure you’re good at whatever it is you do. But you know nothing about cars or engines.

Stay in your lane and stop giving people harmful advice. [/quote]

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