Thread: Spark Plugs/Gap/Timing recommendations for my 2.7" setup?

I am getting my car ready for a dyno event coming up on Oct 25th. Well currently I am running Autolite 104 spark plugs with a 0.54 gap with the setup that is in my signature. This is currently on a 2.7" pulley, stage III IC, 11.8 AFR, and 18-19 WOT timing that I haven't increased since dropping it a few degrees when I went from a 3.0" to a 2.7". My plan was to bump my timing back up close to what it was with the 3.0 pulley which was 19- 21* because I haven't seen any KR what so ever since the pulley 2.7 pulley swap and 18-19* of timing. I also have a 2.55 pulley I would have liked to try out but without an 8-rib or belt wrap system I think I am going to run into slipping issue's.

My spark plugs have close to 16K on them and I wanted to swap them out for newer replacements before going onto the dyno.

The funny thing is now last night I did a WOT pull and I felt my car misfiring at certain RPM's. I didn't have my HP tuner in the car but according to my Aeroforces I didn't notice anything out of the ordinary or KR. So I think this is also an indication that my old 104 spark plugs are starting to wear out? My stock AC delco wires have around 24K on them. I really hope its a misfire and not my transmission slipping. That only had 17K on it!

Anyway, a few days ago I picked up another set of Autolite 104 spark plugs. However I have always been told that with my setup I should be running Autolite 103 spark plugs? However if I saw no KR or misfires with 104's gapped at 0.54 should I just keep it the same setup? Or should I step down to 103's and push for even more timing?

A few members have suggested that I go with Autolite 103 spark plugs and gap to 0.45-0.50.
I also was given this guide from another member and this is what they suggest:
Guide to Spark Plugs - 3800Pro.com Forum

Intercooled
3.25-3.0” pulley: Autolite 104 @ .050-.052”
2.9-2.7” pulley: Autolite 103 @ .046-.048”
2.6-smaller: Autolite AR94 @ .044-.046”

What should I do guys?

Originally Posted by bluegtp91

Yeah for that small of a pulley setup I'd get 103's...gapped at .050...I ran my 103's at about .052, even at one point I was running them out to .055...so it all depends what you can get away with...or you can get a MSD Ignition setup like Reptile...and I think his plugs are gapped something crazy like .065 or .070 if I remember right...

.075.....so you're close.

Here's how to tell if you need to run a cooler plug....look at the porcelain end, and if it looks bleached white, then you have too hot a plug, and you need to step down to the 103's....if they look sooty, then you don't want to go with a colder plug.

This site here will give you a decent general idea of how to read spark plugs....although you can google "reading spark plugs" and it will pull up a great deal of info.

Spark Plugs

NGK Spark Plugs USA
The point of all of this is to make sure that your plug isn't on the verge of fouling out, hence the importance of the heat range. KR will play an important factor in the heat range as well, but if you're not seeing any now, then you should be good. Gap them as far as you can until you're getting misfires, then close the gap back down a couple thousands. Once you get that set, then start bumping up your timing. Of course, the draw back of dropping pulley sizes is that you end up having to lower your timing like you have. I think you're on the right track though.