I agree while dad runs 91 in his we have a friend that runs his on 89 as well
reading spark plug
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From: Sitting in his Nowhere land Hanover Pa
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Melting Slicks
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From: Dadeville AL
Regarding the plug - I've read that reading a plug for rich/lean performance needs to be done at the end of a wide open throttle run (e.g., drag strip) with the engine shut down immediately. Otherwise you're reading other running conditions (i.e., idle to low RPM). So my question for the OP is, what condition are you wanting to evaluate by reading the plugs?
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It’s much harder to read plugs today with the lack of lead, cleaner fuels, and detergent additives than back in the good old days when you could practically see the dinosaur tooth marks on the plugs.
That said, your plug looks good, perhaps a bit lean. And that said, too much octane not only wastes money it can delay flame propagation eroding power. Also, this strange obsession to avoid any ethanol is puzzling. Fuels with 10% ethanol have been proven safe and non-corrosive in older engines in every test performed. More than 10% however, can cause problems with older seals and materials. I run 93 octane with 10% ethanol in my L72 with no issues as I have in every high performance engine I have owned over the decades since it has become a standard additive with zero issues. And finally, 11:1 compression in an oem engine is questionable at best with 93 octane today measured equivalent to 98 octane back in the day means you have no issues even at 91 octane.
That said, your plug looks good, perhaps a bit lean. And that said, too much octane not only wastes money it can delay flame propagation eroding power. Also, this strange obsession to avoid any ethanol is puzzling. Fuels with 10% ethanol have been proven safe and non-corrosive in older engines in every test performed. More than 10% however, can cause problems with older seals and materials. I run 93 octane with 10% ethanol in my L72 with no issues as I have in every high performance engine I have owned over the decades since it has become a standard additive with zero issues. And finally, 11:1 compression in an oem engine is questionable at best with 93 octane today measured equivalent to 98 octane back in the day means you have no issues even at 91 octane.
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Melting Slicks
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From: Dadeville AL
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From: Sitting in his Nowhere land Hanover Pa
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From: Sitting in his Nowhere land Hanover Pa
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I’ll be honest I have one of them too 5 mins away that offer 110 and 99 low lead gas. And I only used it once in 12 years I have been driving my car.
Safety Car
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From: Corpus Christi, TX
Your plug looks perfect. If you don't have any surging or "trailer hitching" at light part throttle cruising, like a steady 60 to 70 on the highway, you're not running too lean.
That and unless the gas has lead, the octane won't change the plug appearance at alll.
That and unless the gas has lead, the octane won't change the plug appearance at alll.
Last edited by Avispa; Apr 24, 2022 at 01:30 PM.
Le Mans Master
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From: Folsom CA
Keep in mind that the Chevrolet L79 was advertised at 11:1 compression but in fact most measure in the 10.3 to 10.5:1 ratio. With a proper tune yours should work well on premium gasoline and save you some money.
11:1 sounded good but was optimistic and overstated by GM. Maybe on your rebuild they shaved your heads and you have higher than normal compression but probably not.
Mark
11:1 sounded good but was optimistic and overstated by GM. Maybe on your rebuild they shaved your heads and you have higher than normal compression but probably not.
Mark