I have Autolite 104's that I am using on my 97 LT1, and am wanting to know what Gap I should set them at? Naturally Aspirated stock motor, few bolt on mods. LT headers with Y pipe, cat back exhaust, 52 mm Holley TB, K&N CAI, LT4 Damper with underdrive crank pulley, computer tune.

Dave

 

Im running autolite XP105's in mine and have them set to stock gap at .050". The 104's im not sure, I believe they are a colder pulg(I might be wrong about this). If they are colder and depending on your tune, would prob want to open them up a lil, maybe .055". But like i said i might be wrong on this one. Im used to the champion plug heat range.

Someone please correct me if I am indeed wrong.

 

Thanks for the reply! Yes it is a colder range plug. Hello Injuneer...chime in please when ya can.

 

I never heard of gapping a colder plug wider than a warmer plug. Interesting.

Anyway, i actaully recommend closing up the gap from the spec of 0.050". I run one heat range cooler NGK in mine and closed the gap down to 0.035".i got a smoother idle and no untoward side effects.


All that said, why are you going with a colder plug....you're stated mods don't warrant a change in heat range.

 

I run the 104's at 0.040 in my 381 on straight motor (when I know there will be no nitrous use). Why do you feel you need a colder than stock plug? I can see using them in a 500HP setup, but not sure about a bolt-on motor. The shop that built my engine selected them, and claimed they were 1 step colder than stock, but there is a spark plug selection guide on the "N2O Tech" forum that lists them as only 1/2 step colder.

 

Fred I could have sworn I read somewhere that 104's were recommended. What would you recommend then in as far as plug and gap???

Dave

 

You want a smaller gap if you are using conventional (non-platinum) plugs. The platinum (or iridium) resists erosion from the spark, allowing them to last for 50,000 - 100,000 miles without the gap opening up. The conventional plugs may only last 20,000 miles as the gap erodes. Unless you are running a power adder, I would stick with a stock iridium plug, with the stock gap (0.050).

I'm running the 104 on a 500HP setup, and we used a 103 with a 125-shot on top of that. With the 300-shot, it needs even colder plugs, and they will foul in minutes with the car idling excessively. Unfortunately, it's so long since I've even had the car running that I' not sure it will even start.

 

OK Fred appreciate your insight!

Dave