Technical > Matt Shaff's Engine Shop

Plug Gap

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wideopen231:
Gap on blown motor is still based on ignition type. A 3 amp mag and a 44 amp mag are going to have different requirements. Yes that is extreme but making point. Its not blowing the sparkout its more of the spark working to burn more fuel in tighter compression situatuion.More air more fuel in same space needs stronger spark.

Back to op's question. All combos are different and require fine tuning.Plug gap is just another tuning tool. Start in middle. Work in one direction until car slows or you feel its a waist,then try other direction and see whatr works best .As stated ther is very littler gain in most combos after .035 and we normally ran .025 to .030 in alky motors.

ricardo1967:

--- Quote from: wideopen231 on January 04, 2015, 05:18:57 AM ---"... Its not blowing the sparkout its more of the spark working to burn more fuel in tighter compression situatuion.More air more fuel in same space needs stronger spark.
..."

--- End quote ---

^^ This

masracingtd1167:
I also agree ! .025 to .030 should be just fine . I have never really seen any magic in larger gaps ! 

dreracecar:
I set my plugs @ .020 (Mag III, NGK B9ES) and valve lash @ .020 that way I only have 1 feeler gauge in the tray

Frontenginedragsters:
 SpitzerScott:
A plug gap of .035" should work fine.
My 2 cents is the same as Duster Dave: No power increases on our dyno.
My other 2 cents is to look close at the Autolite spark plugs.
We used them for years but quality has gone down.
NGK number R5671A-8 / 4554 work really well for us.
Big difference between Japan and China. 8)

Matt

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