Spark plug heat ranges!

Just a caution for anyone buying from big online parts sellers.. I just went to purchase good plugs to replace the "throwaways" that were in my engine during the first start, and I noticed the ones that are in it are TWO HEAT RANGES too hot for my application. They are bosch plugs equivalent to #4 NGKs! NGK part finder suggests a #5 for a stock engine, and their tech support suggests moving to a #5.5 or 6 for something that has higher compression and/or will be worked hard. Just because they say something fits your application doesn't mean it's right. Yes I know I should have double checked the applications guide first but I didn't.

If this thing had been tuned in closer than it is, I could have hurt something.

i'm not very fond of using bosch anything, let alone plugs. GM DIS wastespark systems seem to eat through them unusually fast.

AC Delco, any for that engine, the special metal ones just last longer, I like the cheap regular cause I can't go 100k miles on plugs...

Robert, I'm not a fan of bosch plugs either but they were overstocked and 67 cents each, I knew I'd most likely foul them or otherwise screw them up anyways so I figured it was better to throw away 7 bucks and change instead of $50+... or whatever good plugs are running.

Not sure yet Mark, I've always had good luck with NGKs and have heard good things about them in the BBCs, but I've always had good luck with Delcos in my SBCs. I like the "half" heat ranges of the NGKs also, not sure how Delco compares.

Interesting. I've achieved 100k plus several times on Bosch Platinums. I used reboxed Denso Iridiums in the Cavalier. Buy Delco plugs for the series II supercharged 3800 and see what you get. The plugs in the Toyota are Iridium, too. Not because I paid, but because they were free when a customer of a speed shop I worked for insisted they be changed. The fleet vehicles generally use single platinum Autolites for 100k tune up intervals.

I have yet to find a satisfactory spark plug for my 1981 300SD.

I am running NGK's in all 3 of my jeeps, heck, I even have one in my lawn mower...lol
No complaints from me, they seem to work really well.

FWIW, the plugs out of my LX9 3500 say "ac delco" on the ceramic, and then "NGK" on the ground.