What Octane is best Gas to Use?

Interceptor97 · 09-20-2004, 01:58 AM

I live in Idaho where regular gasoline is 85 octane. I have my choice of course of 85,87 or 91 octane. Does anyone know what the suggested octane level is for a 1997 CV PI 4.6L ?

Thanks, Gary

ModMech · 09-20-2004, 09:56 AM

The answer is very easy. Since these cars do NOT have knock sensors, and therefore they are tuned to run on about 85 octane, that's what you should use.

Basically, use the LOWEST octane you can without getting "heavy" pinging. You should get *some*, like when going uphill at a steady speed, but it should not be heavy.

bjdm151 · 09-20-2004, 10:22 AM

NO,
you should be using the minimum octane without any pinging/knock,
if your getting knock even under moderate load that can still kill an engine-- burn holes in pistons, burn valves, detonation at any load is bad

Interceptor97 · 09-20-2004, 10:51 AM

Thanks folks for your speedy responce. I would have thought the opposite being a v8. But then again I know very little about cars. You guys are a great help. Thank You again.

Gary T

ModMech · 09-20-2004, 12:30 PM

bjdm..,

Nope. I am VERY well versed in Ford EEC systems, and the engieering theories behind them, both from performance, efficiency, and durability.

If you NEVER ping, you are costing yourself in both efficiency and emissions. The spark tables are good if you ping slightly under moderate loads at steady cruise (like pulling a hill), but not at other times (like under acceleration).

Basically, you should run the lowest octane fuel you can w/o excesive ping. Some is ok.

Ford's testing is quite through, and even moderate knock will not hurt anything for short periods. It is true that heavy knock WILL break the ring lands, or the plug electrodes if it happens long enough or is VERY severe, but that is well outside the scope of this question.

Interceptor97 · 09-20-2004, 01:09 PM

Thanks, Right now the engine is so quiet, you almost have to put your ear on the hood to hear it running. I had already filled the gas tank only once with 87 octane. From now on I will go with 85 octane, and if nothing changes I will stick with it. Thanks for the feedback "ModMech"

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