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Kirkham Motorsports

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Old 05-10-2016, 08:55 AM
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Default Spark Plugs in Shelby Aluminum FE block

Does anyone know what the best spark plug combination is for the Shelby aluminum block? Mine is opened up to 510 CI.

Thank you.
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Old 05-10-2016, 09:17 AM
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I use Autolite 3924 in my Pond 487. Not racing, not platinum, just copper.
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Old 05-10-2016, 09:19 AM
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Thank you, I haven't driven it much lately since the clutch slave went out. Lots of starts to test. I'm sure they are fouled.
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Old 05-10-2016, 09:33 AM
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My drivetrain installer recommended NGK R5671A-7 or -8. I'm using -7 and have been fine. My engine is 468 ci.
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Old 05-10-2016, 09:56 AM
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Displacement doesn't matter, but compression ratio does.

For a lot of combos, an AR3924 will work. If you have a compression ratio over 11:1, I would start going down.

The AR plugs are much easier to read the strap, you just have to keep an eye on them if you spend a lot of time putt-putting around.
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Old 05-10-2016, 10:51 AM
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Slightly off topic: I have a SB 408W that I use the 3924 plus in. Since most of my driving is local light-to-light, I have been considering a hotter plug. But I can't find any mention of 3925 or 3926 plugs anywhere. Other recommendations?
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Old 05-10-2016, 11:08 AM
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You can get both, but I wouldn't switch unless absolutely necessary. As hot as it gets down there, I wouldn't want to introduce any preignition.
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Old 05-10-2016, 11:24 AM
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Im using AR 3924 in an aluminum block with aluminum heads. Comp is 10.85:1 and running 100 octane. Seems to work.
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Old 05-10-2016, 11:29 AM
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Great feedback. Thank you, guys.
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