And if so, what engine do you have and what plug are you using?

 

I've been using Bosch Platinum plugs in my 87 Vette conv't now for over 14 years without any problems whatsoever. My engine is a partial Lingenfelter 350 with over 195,000 kms, and I have many mods on the engine and it runs like new. I inspect the plugs before I put it away for the Winter, and I change these plugs every 25,000 kms whether they need replacements, or not. A lot of people don't like the Bosch platinums, but they've been excellent for my Vette.

mypetu39

 

I use the Delco Iridium plugs on my 86.

 

I have the Bosch 4208 Platinums in my Cast Iron L98 - so far, so good.

 

I am using 4205's (Aluminum heads) and they seem to be great. Left them gapped as-is out of the package, although I cannot remember what that is/was now.

 

Ooh...not good. The gap 'out of the package' is about .045 - .050 - which is way out of spec. You should have gapped them to .035 mate.

 

According to my GM service manual(s) ($120 via the Internet - thank you) the gap for a VIN P (LT1 motor) should be .050. The AC/Delco's that came out were gapped at .045 ~ .047. The only reason I replaced them with all new ones was because I broke an insulator trying to check the suckers.

The VIN J is specified as .035.

CG

 

Silly me - I was assuming you had the L98.