My 305 is a 350


Goat Herder
Supporting Member
Dec 1, 2014
Upstate NY
Hey, those two plugs aren't interchangeable, or I should say you need to use the plug of correct 'reach'.
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
Galaxy far far away
For intake manifold gaskets I like to use embossed shim gaskets rather than fiber ones as they resist being sucked in better.
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American Muscle 79

Thread starter
Jan 29, 2018
San Diego, CA
Hey, those two plugs aren't interchangeable, or I should say you need to use the plug of correct 'reach'.
Right you are, my friend. The plugs I had were for the straight plug 305 heads. I thought I could just throw them on these angle plug heads without thinking that the angle would affect the reach of the plug. When I had issues firing it up, I checked the manufacturer's recommendations and these longer plugs were what was suggested.


G-Body Guru
Feb 20, 2018
AC/Delco plugs have been my go to's for a long while so got to know them fairly well. The base plug for your 350 was probably an RTS 44. That is a plug with a recessed electrode. One range hotter would the the RTS 45. What I elected to run was the RTX 45 which is the extended electrode. The diff is that, sitting side by side for comparison, the electrode on the X-45 extends out farther. This exposes it to the air/fuel mixture more completely so the combustion burn initiates faster. The S-44 was pretty much what I'd call a smog plug due to it being less exposed in terms of how far it placed its electrode into the combustion chamber.

For most of the street engines I have ever had I chose to fit them with the RTX-45 simply because it was a hotter plug and both tended not to load up as badly when having to deal with stop and go commuter b*s* plus fired better in cold weather. That made the time between plug changes longer and reduced the amount of invective generated due to having to deal with 7, and 8, particularly when there was an A/C box in the road.

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