After reading another thread on how someone gained a substantial amount of HP from changing plugs, I figured it was time anyway.

2 questions (and yes, I did search and read thru 20min worth of threads :))

1. after 17k miles on my old iridiums, plug color was fine, gap went from 0.028" to 0.035". What effect does the increase in gap have on our FI'd motors in terms of performance?

2. all my plugs were only finger tight on removal. This time I torqued them to 25lbs instead of by hand. How does loose plugs affect performance...loss of compression? loss of boost?

Lastly, FYI, Advanced Auto Parts special ordered these next day for only $6.99 each. Cheaper than anywhere I've seen online.

You don't want the gap too big or else you'll get misfires...from what I understand. You want to keep the gap between .024 - .028 from all the research I've done. I had misfires all the time when my gap was at .028. Once I lowered the gap to .025, I haven't had one since!

Okay as far as loose spark plugs, you are correct loss of compression if they are not sealed properly. On spark plug gap, it's my understanding when running a FI car you are increasing cylinder pressure. With increased cylinder pressure the more voltage it takes for your ignition to jump the gap on the plug. On higher boost applications for example it requires less for your coils to jump the gap at 6psi.boost vs. 13psi. boost. In order to properly fire the plugs the gap is decreased.. That's why to much gap on a FI car can have a misfire. Running a cooler plug helps to prevent pre-detonation.

Thanks for the replies.

Took the car for a drive, and did not notice any dramatic power increase...confirmed by lining up with a friends E46M and ran him pretty much same as before. I guess the plugs were not loose enough on my low boost application to hinder performance.

However idle seemed smoother, and part throttle acceleration seemed better, but this can just be a placebo effect. Was hoping for another 20hp :)

long time ago i had one plug back out and my car sounded like a diesel truck. but yeah them being hand tight is no good. and the extra gap is probably due to wear on the electrode and ground. good time to change out.

>>after 17k miles on my old iridiums, plug color was fine, gap went from 0.028" to 0.035"<<

I dont have alot of personal experience with Iridium plugs, as I just changed to my Densos 5k miles ago.. But, I thought one of their characteristics was longevity! Not as long as Platinums, but considerably longer than Copper.. This wear rate sounds pretty similar to what I used to experience with the copper r5671A-7, and is the main reason I changed to Iridiums from them in the first place! Can other iridium users confirm this rapid wear rate also? Since they are so fragile, while some people do gap them, Id probably just replace. But, at their elevated prices, if theyre going to wear as fast as the copper r5671a-7, why not just use the coppers in the first place?! First, theyre MUCH easier to gap, and Second, they cost much less to begin with.. If their longevity is just a myth, Ill probably go back to the coppers then.

interesting , i just bought the same plugs myself, so ill be going from cooper to irridium. ill have to see what type of differences there are, i always thought though that plugs were suppose to be tightened to 18-20lbs even though there arent many if any torque wrenches that go that low.

18lbs w/antisieze, 25lbs w/o. Last time I did the "feel" method...obviously they need to be torqued properly. Luckily my torque wrench goes to 20lbs.

If next year after 15k miles the gap increases same I'll try copper.

i see your using the same charger as me, you said that you had old iridium plugs in before, which ones? the same as you just put in? (BKR7EIX) or a different set? i dont know if you remember but did or do you remember a difference going from possibly copper or platinum?

IIRC, Ir is only on element off from plat? So IR has almost as many electrons to lose, that's where your wear resistance come from.
But the resistance of Ir is 1/2 that of Plat so you get a hotter spark.


www.sparkplugs.com/faqmain.asp (http://www.sparkplugs.com/faqmain.asp)

www.sparkplugs.com/glossary.asp?kw=Should+I+gap+my+Iridium+Plugs?&manID=0 (http://www.sparkplugs.com/glossary.asp?kw=Should+I+gap+my+Iridium+Plugs?&manID=0)

www.sparkplugs.com/glossary.asp?kw=Iridium (http://www.sparkplugs.com/glossary.asp?kw=Iridium)

i see your using the same charger as me, you said that you had old iridium plugs in before, which ones? the same as you just put in? (BKR7EIX) or a different set? i dont know if you remember but did or do you remember a difference going from possibly copper or platinum?

sorry, missed this question. I bought the car and the PO put in BKR7EIX, same plugs. Therefore, I can't say if there was a difference. Please post your result here after going from copper to iridium since we have the same setup. If there's no noticable difference, next year I'll save the money with copper.

will do