I am running 9.XX:1 compression on my 1980 truck and want to replace my Champions. Which NGK UR-4 or UR-5?


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

Both will fit, UR-5 will be cooler than the UR-4, so i you have any fouling issues the '4' would be a better choice... you can always start with the 5's and see if the plugs are a good color, if they are a bit black then you can move up to the 4...

-D.Idiot

The UR4 is a little hotter-running plug, the UR5 a little cooler. You may want to try the UR5 first, since a cooler-running plug will buy you some room for more timing advance before you get ping. But pull and check a couple of them after you've run them for awhile; if they're not running clean you'd want to bump up to the UR4.

(d'oh...sorry for the incorrect initial post. DI is correct; in the NGK plug numbering system a higher number means a cooler spark plug.)

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

For reference:

I am running the NGK UR4 in my 9.5 to 1 rebuild and they are coated with a very light cinnamon color at 30,000 miles. I am running 16 degrees initial advance with 16 mechanical and a .040 gap with no ping, on Cenex gas.

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Aggressive Ted

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG