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Discussion Starter #1
When I bought my 2002 GT the dealer told me that the car was spec'd for 87 octane. I would normally discount anything I was told by a dealer, but I have read the same thing earlier on a site I can't recall (Autoweb or one of those that lists specifications).

I tried my first two tanks with 93, then two with 89, then two with 87. I recorded mileage and feel, and couldn't tell a difference. And, of course, these cars are so quiet, especially compared to my '93 5.0, that I can't hear knocking even if it was occurring.

So, does anyone know what this car wants? Will any harm come of using 87?
 

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Higher octane takes more energy to combust. Normal compression cars can use 87 fine. Higher compression cars will detonate (bad) with low octane because it preignites, thus you then needto use higher octane. Ideal is the lowest octane you can run with no detonation, which sounds like ball bearings rattling around in the engine. Contrary to popular belief, more is not necessarily better with octane, unless it's required.
 

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I can only run 87 in my stock 02 if it is cold and rainy ( not often in california). Can run 89 without detonation. California has that MTBE crap gas. Tried to run 92 on a 40 degree night at the track and the car slowed down .2 and 1.5 mph so too much octane is no good either. Ray
 

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raise your octane with mods

If you start mod'ing your car then I suggest you bump up your octane also. For example you definately want high octane with a power adder or if you decide to advance your timing. Otherwise the difference is negligable. Stick with 87 for stock.
 

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Discussion Starter #7
It feels weird to run 87 because my stock-engined '93 GT won't accept anything below 93 (even the 91 you can get in some states!) else it knocks like crazy. It certainly saves money, though.
 

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Cherub said:
It feels weird to run 87 because my stock-engined '93 GT won't accept anything below 93 (even the 91 you can get in some states!) else it knocks like crazy. It certainly saves money, though.
If it's not because you've advanced the timing (which will push you to use higher octane) , then it could very well be caused by carbon buildup. The best cleaner I've used is a fuel additive from Chevron called "Techron". You can get it at most auto parts stores. They used to have one formulation for cleanup (probably stronger or more concentrated) and another for maintenance. It may tank a few tankfuls of it, but it should clean the engine up to a point where you can run the lower octane again.
 
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