which plugs

[hockeydad1189]

hi i have a 68 340 engine slighty modified i was wondering which sparkplugs work better right know the car has rn14 yc in it i know the original plugs where n9yc any thoughts on those two or any better plugs out there also the car has a high energy ignition .

 

[fishy68]

The 14's are a lot hotter than 9's. Compression ratio has a big effect on what plugs you need to run and yours is an older high compression engine that Chrysler found 9's to be the correct heat range for. Since it's modified from stock the only way to positively identify what plugs you should be running is to read them. The ground strap should show a heat line right about in the middle. If it were mine I'd put 9's back in it (because that's what it started life with), take it out for a hard run, come back and pull the plugs and read them.

Here's a link to an article on reading plugs

http://www.dragstuff.com/techarticles/how-to-read-plugs.html