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Old 02-22-2010, 02:02 PM   #20
fdryer
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Join Date: Jan 2006
Location: NYC
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2003 L-Series 3.0L Sedan
Default Re: Fact or Fiction?: Premium Gasoline Delivers Premium Benefits to Your Car

Quote:
Originally Posted by Djb200882 View Post
The higher compression ratio the engine has the more octaine it needs. My old chevy is 9.5 to 1 and it pings with 87 octaine
Yes but does this Chevy have a distributor ignition system or distributorless ignition, with or without knock sensing? Old school mechanical distributors with rotors, caps, and contact points never had anything but spring loaded centrifugal weights and a vacuum diaphragm for some semblance of advancing/retarding timing. Nothing was done for pinging/detonation prevention except maintaining timing though mechanical means. Those engines couldn't have ideal timing and still prevent pinging so it was more important about which octane was needed. Although those systems were state of the art back then, they still had a lot to be desired. EFI systems with totally electronic controls makes timing more fuel efficient as well as allow better engine performance to take advantage of maximim advance timing right up to detonation where knock sensors are listening for and tell the pcm to retard timing just enough to stop it. Electronics at its best for the highest reaction time to continously changing engine performance as governed by our right foot application - lead footed all out acceleration or granny driving. Knock sensors and the programs to deal with it automatically adjust to every octane number we put in our tanks to maximize engine performance but only up to a point. A car rated for 87 octane will not gain 10, 20, whatever hp (some think) will be gained by using higher octane fuel, only that the engine will run somewhat smoother because of the higher knock resistance accompanying higher octane fuel allowing maximum advanced timing.

Driving a car hard does not mean higher octane is needed. If that were absolutely true then every vehicle manufacturer is lying about octane requirements. I can stand on my gas pedal all day and run with the recommended 87 octane and still never make my engine detonate/ping/knock. I have knock sensing to prevent it and still make maximum power all because of electronic fuel injection and all that it implies. My engine has either a 10:1 or 10.5:1 compression ratio.

Last edited by fdryer; 02-22-2010 at 02:11 PM..

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