I am curious as to what spark plugs I should be using for the best performance? My car has the original 1975 350 block .030" over,10.5:1 flat-top hypereutectic pistons, vortec heads, 650holley DP, performer intake,2700 stall, MSD 6A ignition,Accel HEI supercoil,and 8mm Taylor wires. I changed the thermostat and she runs at 170-180 deg consistantly. Is there any other info that you would need to know? I know very little of mechanics therefore the question. I currently run AC R44TX PLUGS. The plug color is good. I am looking for the best plugs! Thanks for any input!!
Gerry

Gerry,
I've been running NGK plugs with good results.
When the LS-1 was introduced , there was a strike at AC & Chevrolet was about to equip the first LS-1's with NGK plugs , if that is any indication of what GM thinks of them.......good luck

If the plug color looks good, stick with what you have. From the way you've built the engine, you might consider one heat range colder, but that's really if you push the motor. Casual driving, not a problem.

I believe proper heat range is more important than brand, overall, but most everyone has different experiences. In my '67 Dodge Charger, I tried Splitfire plugs. It didn't take long before several of them cracked their ceramics. I changed back to OE (Mopar/Champions) with no problems at all. In my '78 L82 and '69 L71, I have AC plugs. From my experience, the fancy and expensive plugs simply aren't worth the extra expense.

A buddy who used to drag race an old Chevy II told me his preference was Champions for a small block Chevy and AC for a big block. He based it on his experiences, so who am I to disagree?

Thanks for your input! I think that I will stick with what is working! Thanks Again!
Gerry

It's also time for new plugs ...I've heard good thing about AC Delco's Raipd Fire, they cost abot $3.50 each... But if I go stock it's between AC & NGK.

I always use A.C. keep your G.M. all G.M.

I am also running vortec heads on my 350 with about the same compression. The vortec heads take a different spark plug than the L82 or L48 heads that came on our corvettes. The threads are longer. I have been using the AC Delco R44LTS6 and re-gapping them to .045". They come out of the box with a .060" gap. This is a little wide for an HEI.

I tried Split-Fires as well without any real improvement. When my engine was performance re-built they used Champions. I've since switched to AC. Both seemed to be good. Another thought, MSD suggests running a bigger gap than stock to get a wider spark. (One of their engineers told me it was because their spark was more intense that it could support a bigger gap and thus provide better combustion.) My compression is 9.5:1 and MSD said start at .050. Their opinion was that the plug brand was somewhat secondary compared to the rest of the ignition system components.

That in theory does sound good, the wider gap because of the higher output of spark from the MSD! Does anyone else out there knowledgeable in this area have any input on the sparkplug gap! I know that I could check out the performance difference with the various gaps, but just how far should I go?? Any suggestions?? And what to consider about the different head sizes, stock L48 versus the vortec? And thanks SST & 73 PO, interesting input/suggestions!!

In the January 2004 issue of Super Chevy, there is an article called "Cloning Experiment". They built a 422 HP, 452 ft.lb torque small block 350. They used the Vortec heads on this motor. They reference Autolite AR103 spark plugs. They do not tell the gap though. These plugs are pricey. Their web site is www.autolite.com. They should be able to provide recommended spark plug gapping for your application, but I would go to MSD for their recommendations. One thing to keep in mind, on higher compression motors you typically want a colder plug. A colder plug provides more/longer spark for a complete burn. If you gap your plug too wide, you will have a larger quick flash, but not a continuous spark for a complete burn in the combustion chamber. The guys at MSD can explain and help you with your application.