I was wondering what i should be running for a spark plug gap and how to determine it?

Run it stock unless you have upgraded the ignition.

Close it down if you run nitrous.

.005" increments to evaluate changes.

Nothing about my car is even close to stock now lol So how would I go about figuring it out?

Start by looking at the information about your heads, calling the manufacturer if necessary. That's were 90% of the variability lies.

I just got off the phone with AFR and MSD and AFR told me to call MSD and MSD said .050 to .060 would be fine with a sbc with 10.5:1 cr N/A. Does this sound about right it seems to be a bit big but maybe not. Thanks

Sounds about right.

Back in the early days of HEI, the factory was using .060" gap. MSD should be able to zap that without any trouble.

I'm surprised AFR didn't have more to say.

Yea I thought AFR would have more to say as well. I think I'll probably set it at around .050 unless anyone thinks differently? Thanks again

Mine are at .035 but I'm also dumping a lot of alcohol into the cylinders. Same goes for NOS. You need a smaller gap so the spark doesn't get blown out but need a hot ignition to keep it lit. I use a HCV-2 coil. 2 full amps of spark energy.

I've never played with plug gaps very much. I increased them to .045" once and didn't notice much of a difference.

What about all you sbc guys that are N/A with an MSD ignition? what are you's running? Thanks for the help

I've been running mine .030 - .035.

Is that also because you have nitrous or no? Anyone else tell me their gap size because now im confused why the guy at MSD told me .050-.060" Thanks guys

Even with my smaller sbc's and the MSD ignition i never took them past .040. I've been using Autolite racing plugs for the past 4 years...they have an AR in front of the part #, cut back electrode and i think once i put a feeler guage in there to see where they were out of the box and it was right around .038 so that's where mine have always been gapped...out of box whatever Autolite sets them to....and for the record...good luck trying to open that gap with these race plugs, nothing like a junk factory type plugs.

I've never noticed any performance difference with any of the plug brands nor gapping when i used to piddle around with that stuff back in the day, but like i said, i've been very happy with these new race plugs, they've never crapped out on me, i just change them once maybe mid season for piece of mind, but they always look great and have never put me into a spot where i had to swap them out.

Trying different gaps doesn't make a big change in power. Indexing the plugs probably has a better result. Index the plugs so that the ground strap is up. This allows the spark to go directly at the top of the piston instead of around the ground strap. The main reason I index my plugs is because I have huge dome pistons and if the plugs are not indexed, the piston will hit the ground strap.

Read this page

http://www.centuryperformance.com/sp...ch-spg-26.html

We have to index the plugs in the S10, talk about a major PITA!!!! if i ever had an engine like that, then i know for sure they would get installed new at the start of the season and that would be it...indexing sucks azz!!!

Indexing with the heads off is so much easier. When indexing, buy 2-3 sets of plugs. They're not really that expensive. I think my NGK race plugs are less than $3 each. Keep trying different plugs in each hole until you get them indexed without needing washers.

Of course if you want to try a different heat range, you need to index another complete set and have them marked for specific cylinders when you change them. I was going to find some way to have an 8 plug holder that could fit in a drawer just for that purpose. I found a nice 6 compartment holder that would work but couldn't find an 8 compartment one. Look in the fishing section of a sports store. Lots of cool little tackle holders just the right size to hold plugs.

I'm running AFR's with a digital 6 and .035. Seems to work fine. Even with the MSD unhooked it still fires fine.

I am using AC Delco 41-629 plugs.

That and it seems to not break up at the top end like it used to with a larger gap. Mosts of my runs are off the nitrous but I'll be using it more now that the car is legal to run quicker than 11.49.

I have had different results with different plugs. Mainly I run autolite ar3910, gapped at .035 (untill i went up on nitrous) that plug is a projected tip, I have tried an AR3932, which is one step colder and non-projected, that plug just doesnt work at all for me, no matter what gap or weather i index them, it will not run good under load. I was going to try some NGK plugs but some unknown debris in oil pan stopped that, turned out that the valve springs were deburring the head lol

lol oops... NGK plugs are all I've ever run in this motor.