I would like to try some of the NGK UR series for my peanut head SL6. I have a mild build-up (see below), but I don't want to buy two sets of spark plugs to find out which ones I need. The Champion RV12YC's work fine, just want to see if there is a difference.

So is the recommendation UR4 or UR5?

bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

The difference between them is heat range. The 4 is hotter, and the 5 is cooler. Me, I would probably pick the UR5 or maybe even try a slightly colder UR6 to start with for extra ping-resistance, unless the engine tends to foul spark plugs, in which case I'd go UR5 or UR4.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I have used GR4, GR45, and GR5 on my 64 motor (10.5:1 comp, yadda yadda). Works fine. I think I saw a slight drop in accel with GR5s, but no diff with GR45s. These are drool-tube plugs, but assumedly heat range is same.

Lou

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