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 Post subject: Spark plugs
PostPosted: Sun Oct 24, 2021 7:32 am 
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Joined: Tue Nov 06, 2012 10:23 am
Posts: 1496
Location: Texas
So currently I run Autolite AR3924 plugs. 359C with Trick Flow 225cc heads 60cc chambers and flat top pistons. Compression is 11:1 As far as I know they seem to work well but the power valve in my carb (6.5) I believe was to high - to rich (engine vacuum was around 8" in gear at 1000 rpm - engine at temp) . I just changed to a (4.5) and it seems to be much cleaner at idle. So I need to put new plugs but I was wondering if I should change to a different brand. A couple buddies keep telling me "go with NGK - go with NGK" Im like ok well what NGK will be in the same heat range as my Autolite AR3924 plugs? All I get are " I don't know" answers. So based off your guys experiences what plugs do you like? Also does anyone know what would be the same heat range of NGK as my current plugs? Oh and I only race with 110 VP fuel.
Thank you, Matt


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 Post subject: Re: Spark plugs
PostPosted: Sun Oct 24, 2021 8:04 am 
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Joined: Mon Oct 29, 2012 2:49 pm
Posts: 1339
Location: Orange County, NC
My experience, there is no difference in power between NGk or Autolite plugs. I run NGK because they are cheaper, and because they arent a side gap plug like the Autolite racing series, they last longer.
A quick search shows that is equivalent to a NGK 5 series plug; that's hotter than I would run with 11-1 compresison, but I also dont use aluminum heads.


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 Post subject: Re: Spark plugs
PostPosted: Tue Oct 26, 2021 6:49 pm 
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Joined: Tue Nov 06, 2012 10:23 am
Posts: 1496
Location: Texas
kv racing
Thank you for your reply. I will have to check out the NGK 5 plugs


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 Post subject: Re: Spark plugs
PostPosted: Thu Oct 28, 2021 8:28 am 
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Joined: Tue Nov 06, 2012 12:02 pm
Posts: 494
We ran the ar series autolites, before that we ran champions and also ngks. They were all swapped midway through the season, so no longevity issues were noticed. Our engine builder recommended the ar autolites because he saw more power with them on the dyno. Being on a circle track, stuff wasn't consistent enough to tell a difference out there between the plugs.


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 Post subject: Re: Spark plugs
PostPosted: Thu Oct 28, 2021 9:05 am 
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Joined: Mon Oct 29, 2012 2:39 pm
Posts: 1726
I use NGK in the AFD heads but they are 7 series. That was with 11.5:1. I'm thinking same plug even at the someday new 12.5:1. Or Autolite equiv. I bought several NGK and Autolite in different heat ranges , but that was a year ago so I've already forgotten what's in that pile of stuff.

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Chris - Merkel, TX
http://raceabilene.com/kelly/hotrod
"Owner built, owner abused."


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 Post subject: Re: Spark plugs
PostPosted: Thu Oct 28, 2021 9:17 am 
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Joined: Mon Oct 29, 2012 2:49 pm
Posts: 1339
Location: Orange County, NC
I had a buddy who swore up and down the AR's made more power on the dyno and were faster at the track. So I started using them. Right out of the gate, the first thing I noticed was, they were not faster in my car than NGKs. The second thing I noticed, it didnt take long for the corners to start getting rounded off from the spark eroding it. And I mean the corners on the ground strap "over" the electrode as well as the bottom electrode. If I went too long without changing them, I started to have some issues where the car wouldnt start very good. Maybe it's because it was on alchy and there was too much fuel in the cylinder for it to ignite once the gap started to get too wide, I dont know. I know once I went back to running NGK plugs, I could run them all year without issue.


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