Two steps colder spark plug part numbers?

[Alexia]

I am having difficultly identifying which are the correct spark plugs for two steps colder.

NGK ZFR7F-11 - Seems to be correct, but having trouble finding it. Available to purchase, but out of stock in most places.
Champion RC9LYC - Can not even find it to purchase.

Any luck?

[SilverXJ]

Have you tried looking by the stock number instead?

A ZFR7F-11 is stock # 6855

A ZFR7F is stock # 5913.

The '-11' means it has a 1.1mm (.044") gap. Without any '-' number means 0.8mm - 0.9mm gap.

http://www.ngksparkplugs.com/pdf/StocktoPart11x17.pdf
http://www.ngksparkplugs.com/docs/tech/ ... _plugs.pdf

[Alexia]

Found out I was wrong on the Champion part number and it is actually RC9YC.

I did try the stock numbers for the NGK plugs and was not able to find any in stock that I could quickly get.(Not even next day shipping!)

I picked up a set of the RC9YC which are apparently roughly between a NGK 6 and 7. RC7YC and RC8YC appear to exist, but suffer the same problem of availability.
http://www.ngk.com/learning-center/arti ... sion-chart

[CandyCaneXj]

I have had the RC9YC plugs in possesion but I didnt use them because they were ALOT shorter than the RC12LYC. Wouldn't a shorter plug technically lower the compression(less combustion chamber space bein taken up?) and also a less efficient burn with the spark being less centered? I guess champion does not make any other ones that would work? The RC12LYC seem to work good in stock engines but i'm suprised how white they get for being made for these 4.0s. I think i still have the RC9YCs. If I do i'll post a pic of the two plugs side by side.

[IH 392]

Be aware that NGK plugs are numbered backwards, a colder plug will have a higher number.

[jeepman]

Some good Info Here...
http://www.sparkplugs.com/learning-cent ... otter-plug

[CandyCaneXj]

I cannot find the rc9yc plugs to measure them. Must have got rid of them.

[Rockhound]

I have been trying to figure out this spark plug thing too. I sent ngk an email and they told me that they have no cooler plug that will work in my application. Something about longer thread size. I ran the stock champions in the old stroker, but this rebuil is going to be higher compression and much more...
Champion sent no reply.

Oh, hello by the way

Jay

[SilverXJ]

You must have gotten a lazy representative then. NGK answered my question of spark plugs for the stroker with these two recommendations: Iridium plug: ZFR6FIX-11, stock # 6441 & V-Power copper plug: ZFR6F-11, stock #4291 . Those are one heat range colder than the stock plugs.

[Rockhound]

That's quite possible! Thanks, I will try the copper plug. Little higher compression so I may need one cooler.