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These look like Nology knock offs. Nology's are good wire's and make a cleaner burn but no way are you gonna see any real HP gains.
I ran them 20 years ago on my 69 Shovel and they really didn't make any difference although the engine wasn't high performance either. I think the motor would really need to be at least somewhat high performance to realize any seat of the pants gains.
Look at the picture on the Arlen Ness website(above link). Looks like the filter is mounted one way if you don't use a cover but then reversed if you do.
And I agree with everyone about BS on 12 HP gain from just plug wires. Hell, with that kind of increase, a V-8 car would gain 48 HP.
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