What plugs are you running/recommend?

[MrHernandez]

Getting ready to change my plugs and thought I'd ask. I have the stock 305 block/bottom end with 520 vortec heads (comp internals) and edelbrock intake/carb . I was thinking of using NGKs since they outperformed the Champions I had in my 71 Triumph bike. Currently running ACs but figured I'd get a little input before making my final decision. Not looking to buy any gimmick plugs either. Thanks

 

[Fox80]

NGK hands down they are the only plug I use in anything, the Japs can build a plug I will give them that, literally the only plug that works in a race motor from my experience

 

[olds307 and 403]

X2

 

[MrHernandez]

NGK it is. Now whether to get the UR4 or 5. Stock calls for the 4 while the heads I have called for the 5. What's the difference?

 

[Fox80]

The number is the heat range, NGK's are *ss backwards, the higher the number the colder the plug. So your "4" is hotter than your "5". Depending on what mods you did to the motor I would just stick with the "4", a plug that is to cold will foul and that is a pain, most street motors can be a couple number to hot and never notice it because they have very little load on them. But to cold and it can foul a plug on choke closed cold start, or even idle for a long period. Aluminum heads cool a plug more efficiently so that can call for a hotter plug, headers evacuate a cylinder better leading to a colder combustion chamber, hense also needing a slightly hotter plug, cams with aggressive overlap change the cooling of a combustion chamber, by contaminating the fuel mix at low engine speeds, removing the EGR or PCV could warrant a colder plug because now you took contamination out of the combustion chamber, made the motor more efficient= more cylinder heat. Even if you don't wet foul a to cold plug you will in time carbon foul it, leading to more plug changes. Think of this NGK says the plug needs to reach 900 degrees for it to clean itself, if you don't reach that for various reasons you will carbon foul or wet foul them. You need to get to I think 2,000 degrees to damage a plug, not even possible in a street car, it will ping (pre ignite) before that so you will hear it. Go to NGKUSA.com they have an amazing tech section

 

[MrHernandez]

This is the answer I got from NGK, just doesn't seem right to me...12.2:1!!

 

[Fox80]

Are you sure you specs are correct? If I enter 8cc in for a four valve relief flat top piston and the rest of what you entered it's close to the same number, do you know how far the piston sits in the hole? And what head gasket do you have that is so thin? NGK has a pretty spot on tech advice department so the plug recommended by them is probably correct, it's if all your info is correct

 

[MrHernandez]

Are you sure you specs are correct? If I enter 8cc in for a four valve relief top piston and the rest of what you entered it's close to the same number, do you know how far the piston sits in the hole? And what head gasket do you have that is so thin? NGK has a pretty spot on tech advice department so the plug recommended by them is probably correct, it's if all your info is correct

Don't get me to lying, the engine is stock '78 305 freshened up, top end is '96 305 w/520 "vortec" heads. I dont know how far downthe piston sits and the head gaskets are felpro 1094 .015" thick steel.

 

[Fox80]

By freshened up do you mean you put in an aftermarket piston? I'm not saying your a liar but people get numbers mixed up if this stuff is new to them, .020 here or 20cc there makes a big difference. That head gasket is .020 thinner than most, plus a small chamber head. If you don't know the deck to piston drop you could just use .035 as a number most all blocks are at least that bad, if you did use a aftermarket piston use the negative number for the dish in the equation and calculate the comp ratio with one of the many calculators on the net

 

[Fox80]

Here is what I come up with in my comp ratio calc, by now entering the .035 we assume because the block is not decked it knocks you down to 10.6-1 a much more real world number