Hey all, I am curious as to the advantages of going with all 9's as opposed to the factory set up of 2 7's and 2 9's. I had all 9's in my FD which has all of the PFS mods including the purple computer. Car ran great except for the requisite backfiring and obnoxious popping, however I had to go back to the 2 9's and 2 7's in order to pass emmisions on my last try. Is going with all 9's a reliabilty mod or a performance mod? My mazda mechanic (who has much experience with FD's) says anyone whom says their gaining any performance is fooling themselves. I know my car does not "bark" like it used to with all 9's, it sounds tamer. Who out there has knowledge of or experience with this issue?

 

9's are a colder plug and helps to resist detonation/pre ignition. The benefit is you can use more boost and will help keep you from having problems in that area. The down side is they foul out much easier so you have to be tuned right. If your running stock boost or just a little more than stock dont worry about the plugs. If your running a bar or more you need to go with 9's or maybe even a colder race plug. Hope this helps.

 

try running NGK B9EGV's see if you can pass emissions with them

if running 14PSI or more go for NGK B10EGV plugs

 

9s make the idle a little worse on cold starts in my experience. 7s and 9s are probably fine for most cars until you have intake, IC, and full exhaust.

I had 7s in my car for emissions testing recently and got some activity on the J&S knock sensor that went away when I put the 9s back in. My car has a street port, and I understand that porting is one of the main reasons to need a plug change.

I recommend the stock plugs for light to moderate mods.

-Max

 

Thanks guys, I do often run 12- 15 pounds of boost which is the setting for the mid and high settings for the PFS computer low is 9 Lbs or stock. I am usually in mid which is 12 lbs. I think I will go back to the 9's for piece of mind, I would agree with maxcooper's assessment about cold starting and idle. Thanks for the input.