I’m sure there are several posts on this subject; however, I couldn’t get the forum search function to work today.

I’m currently running the AC Delco Platinum plugs #41-943 on my high-compression 396 stroker. And, I've had some fouling problems with minimum use.

So, what is everyone’s opinion on the best spark plug to run in a high-compression LT engine and why?

WD

 

Well, fouling means it's either too rich or the plug is too cold. You are in the best position to judge which it is.

Rich

 

Platinum does not belong in a performance engine, if you look I bet you are lossing some of the platinum pucks.

Not sure if the AFRs take the same plug as stock heads but I found NGK TR55 to not work was well with the high compression as they had when the motor was closer too stock and switched too Autolite 104s which are as easy to find as a Walmart. If you like NGK TR6 is a little cooler than the TR55.

 

I was running the delco's then went to a 104 autolite....all the platinum tips were gone after a few weeks at the track and no street miles..also had a hi rpm miss.....I think it was blowing the spark out@.045

 

The new delco platinums don't have the problem of the platinum pucks falling off like the older ones. I was running autolite 104's and replaced them with the 104XP's which are said to have a 20% bigger flame than standard plugs. I had NGK's in and they fouled within a few days not a fan of NGK plugs. My compression ratio is a bit over 11:1 btw.

 

Please point us to a reference on this design change. When did it happen?

 

Sorry its the new iridium ones that I am refering to. Thats what comes original in the GM's now and I have yet to see one with the puck missing on the ground electrode.
http://www.acdelco.com/parts/sparkplugs/iridium.jsp

 

Try the Autolite 103.

 

i don't see how you can be running cold on a platinum plug. i always use tr6's on my 11:1 setup. they work fine. bret bauer suggested i use these or a similar plug to be safe. I've yet to foul one out after 4k miles

 

I use the Autolite 3910 (heat range 9, I believe) on the AFR heads...Works great. Takes just a little longer, maybe 10 seconds (at most) in the morning before cleaning up (over my old heat range 4 plugs).....These are the same plugs I used when I had a 248/248 on a 109 LSA Duration cam in there, with 8 1/2 inches of Idle vacuum. It's all in the tune...I have atleast 50 flashes (including cyl balancing) just for idle area...

 

Ngk Br7ef