what would be the advantages and disadvantages of using 93 octane gas in my car?

Typically, there would be no advantage and it would cost more. However, with a higher mileage car, if you are experiencing detonation or "knocking and pinging" it can help. Carbon build up can cause pre-ignition and/or detonation which can be controlled by a higher octane fuel. But you would need to take steps, by utilizing fuel additives and high quality fuels, to reduce the buildup.

The thinking that a higher octane fuel creates more power is mostly false. It can, under the right engine conditions, make more power but generally speaking, octane is just the fuel's ability to control detonation "knocking and pinging".

I have 200,000+ miles on my truck and it can live a long and healthy life with 87 octane (regular) as recommended by the manufacturer, under normal conditions. However, with it's high mileage, the hot Texas summers and pulling my boat, I need to use 89 octane (mid-grade) in the summer, in order to control the detonation.
 
Being a mechanic I never tried going cheaper on lower octane gas. A friend of mine has the same 3.8 supercharged motor in his car and has been using 87 octane gas for over 5 years with no pinging or damage. That being the case I switched from the recommended 93 to 87 octane and even though I have a stage 1 ECU, headers and a 3.0 pulley on my supercharger, I have had no problems as well.
87 octane burns better then 93 octane because of fewer additives to stop pre-ignition or "pinging" under accelleration, so if you don't hear the pinging under hard accelleration go with the cheaper 87 octane.
 
This gets asked daily, and there's thousands of websites that explain octane.

Higher octane is meant for higher compression engines. It lowers the chance of detonation.

If you have a lower compression engine, which you do, going to a higher octane will do absolutely nothing.

The octane you're using now, already provides all the protection for detonation that it needs. It doesn't need any more.

You'll waste your money, and that's about it. Higher numbers, don't mean higher performance.

Here, I'll save you the trouble : http://www.straightdope.com/columns/read/2565/whats-the-difference-between-premium-and-regular-gas
 
Being a mechanic I never tried going cheaper on lower octane gas. A friend of mine has the same 3.8 supercharged motor in his car and has been using 87 octane gas for over 5 years with no pinging or damage. That being the case I switched from the recommended 93 to 87 octane and even though I have a stage 1 ECU, headers and a 3.0 pulley on my supercharger, I have had no problems as well.
87 octane burns better then 93 octane because of fewer additives to stop pre-ignition or "pinging" under accelleration, so if you don't hear the pinging under hard accelleration go with the cheaper 87 octane.
 
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