Clone spark plug??

OVALTECH1

Site Supporter
Both pretty cold plugs. That’s a 6 of one half dozen of the other thing. Is this a plate motor or unrestricted?
 

OVALTECH1

Site Supporter
they are both the same style and reach the only difference is the heat range with the 10x being a bit hotter plug. This time of year when the air is cooler and air/fuel tends to lean out a bit either would be ok. I’d probably just stick with the 10x on gasoline.
 

Bumpy

Member
From the Autolite Site
"Autolite Heat Ranges - The larger the last digit in the part number, the hotter the plug is. Example a AR3935 (good street/strip plug) is hotter than a AR3932 plug which is very cold used for lots of nitrous."

AR3910X is about the coldest plug on the planet. I bolded and underlined 'very cold.'
The 3910X is 2 steps colder than the above listed 3932.
I think the only reason the 3910X became popular is for the extremely minor amount of compression increase due to the
electrode design.
 

OVALTECH1

Site Supporter
I’ll
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Bumpy

Member
My bad.
OvalTech is correct.
It seems AutoLite changes #s for heat range between families, in this case the X series is coded differently than a non X series.
The 3910X is still a cold plug and sort of unnecessary in a low compression Clone.
 

OVALTECH1

Site Supporter
Yeah both of them in my eyes are a bit colder than I’d ever care to run in my stuff. Not to mention I hate the plug design. I’ll still with my NGK dash series plugs.
 

1fasttiller

Member
Can anyone shed some light on a hotter plug that works with the clones? Especially a restricted engine with a very rich carb?
 

meracer9

Site Supporter
90% of clones I see are running the 3910X plug. Rather it be restricted or unrestricted the 3910X seems to be the plug of choice.
 

OVALTECH1

Site Supporter
We run the NGK 5671- series. I run them in the big car so I use them in the karts too. They run from -10 cold to -7 hot. We use the 8 in unrestricted motors and the 7 in our plates. There is another NGK that’s a laser iridium it’s a BPR5EIX I believe real hot plug for purple back to red.
 

flattop1

Dawg 89
Indexing isn't that kind of a hold over from the flathead .
it may provide a minuscule benefit .
Certainly not hard or big enough to offset a dns or dnf .
Once the fires lit the jobs done .
No fire no work .
 

Bumpy

Member
I switched to extended nose plugs after several blubbering restarts where
the 3910X was fouled almost to the point of not working during the multiple
slow laps. WOT it does OK and as FT1 says 'after the fire is lit the job is done.'
There are some interesting developments in extended nose plugs.
I have a plug that will change idle RPM by +~300RPM just by switching. :cool:
 
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