Spark Plugs


New Member
May 12, 2018
What would be a good spark plug for my 84 Hot Air car? I did a search and all of the plugs suggested do not come up on searches at auto parts stores. The posts that came up in the search were from several years ago.

The engine appears to have been rebuilt but I don't know if it is stock or not. Mystery motor but it seems to run OK except for when I get into the throttle it will ping/knock and it feels like the ECM is reacting and it starts to buck and pop through the intake.

ac r44 plugs should be fine but your issue sounds like too much boost for your fuel supply and you're leaning out .. could be maf , could be fuel supply (pump- filter or chip is wrong for mods ), could be too much boost .. you need to watch the boost with a real boost gauge , o2 mv and kr
You might want to run a bit cooler plug like an ACR43TS but changing out plugs won't solve the issues you describe. You need to do some troubleshooting and look into the items Paul mentioned.

I agree with neal. IMOP I wouldn't run anything warmer the the AC CR42TS.

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You like the UR4 for the 86-87? 25psi w/alky?
I like them for a hotair. For an IC car it's either UR4s or UR5s. The alky really means it takes specific trials depending on how much cooling the alky brings to the actual combustion chamber.

(NGK's get colder as they go higher numerically)
Just swapped plugs in my T, Previous owner had AC CR44ts’s in it, plugs were not that old, but seemed like it had a miss at idle, changed them out, by a matter of consensus, went with NGK UR5’s, doesn’t even seem like the same car, idles smooth, and very responsive.