I hope this isn’t a stupid Question, but I’m going to jump out the window, what is the best spark blush for a 406 6.6 (Oldsmobile). Please explain which ones are the best and why.

 

There is really no right or wrong answer here, its personal preference and performance application if you mod'd the engine.

 

Stock motor? Stock ignition? What is it in, year make, model?

 

# on the engine
To be honest idk, this is all new to me, this is why I come to this forum to learn. i couldn't find the year of the engine, the last forum they told me to look under the first spark plug, I didn't see it, all i know its a 403 6.6L with a X on it. my car is a 1955 Oldsmobile

 

thanks for that, idk if the engine was Modified

 

The 403 engine was produced for three years from 1977 to 1979, and they were all essentially the same. Can you post a photo of the distributor to show if it's a points style or HEI? I don't think that really changes the spark plug choice, it just lets us know what you have.

Any plug for an Olds engine would work (except the .060 and .080 gapped ones as those gaps are way too wide); knowing your application just helps get the heat range right.

 

Disturber Cap

 

Any of the plugs listed in this link will work, I'd gap them at .045 instead of .060:
https://www.rockauto.com/en/catalog/...park+plug,7212

 

I’m so used to seeing the 403 in the trans am. What Olds cars got these engines?

 

Distributor looks to be a stock GM HEI, that's good. They are reliable and easy to get parts for.

What plugs are in it now and how do they look? The current plugs may be the answer for the heat range, convert that plug to an AC Delco plug and gap at.045 as suggested.

Good luck!!!

 

NGK XR45 gapped to .045" on a stock 403, XR5 is the next coldest plug. I have had 0 issues on my 9 to 1 350. I have found them smoother running over AC Delco or Autolite Chinese plugs.

 

why would you gap them at .045 instead of .060?

 

The larger the gap the more stress on the coil. .045 is more than sufficient to fire a plug hot enough to ignite the fuel load.

 

The .060" and .080" gaps were used on smog era engines with EGR (maybe AIR also?) and, from what has been posted here, that wide gap was needed to get the very lean mixture to ignite. There's no reason to use that wide of a gap on your setup.