I use AC Delco R45TSX in both of my 350s. .060 gap for the HEI. R45TS is the smaller points gap at around .030-.035
I've used AC Delco, Autolite, now I'm using NGK. Nothing fancy, no precious metals like platinum, iridium. They spark, and mixture goes BOOM
NGK always fires up. Just match up to whatever engine year you have and go with that plug. I think UR 5 is what I have used. I use one now that is for the nitrous so it is not an extended type plug. Seems to work fine on just the motor but I am at 10+ compression. When I ran the HEI I used the R45 TS, then you can go with a 35 gap I thought the TSX plug with its 60 thou gap was too much for the coil to I went with the TS plug. I would check the mechanical advance of the HEI if it came from a mid 70's Buick I think some of them may be advancing too far. Check that total timing can do it with real light springs on the advance and I would limit it to 34* total. If that initial is at "0" now then it advances too far since we know that the initial needs to be at 10. At 10 initial then the total is at 44, that is way too much.
The brand is of secondary importance to your ability to tune and read plugs. When I think I've found a plug the engine is happy in it's particular application (or if I think the book is way off and am looking for a starting point),,,,, I'll change out one bank with three different types/brands and give it a brief full throttle run. Enough to heat mark the plug. Despite the crossover charts, they do not exactly have the same heat range across brands. On a couple of 36 ft motor homes, I was able to triple the mileage from factory and by testing plugs, know that the owner could take it anywhere and avoid detonation issues. If I were posing the question to a forum, I'd describe my build and application and inquire more about the physical characteristics of the plug, such as projected tip? , what aspects led to what changes...such as the post right above this one.
TSX are the factory plug for the HEI cars. I'm using a TA HEI. TA recommends initial at 12, has 22 advance in it. I have mine set at 10 initial. So 32 by 3400 is where I'm at. Engine has 500 miles on the rebuild, plugs are a nice beige color, no detonation/ping. Likes 91. SP 350 with .042 gaskets, so around 9.5:1 (give or take .25). I should bring the advance down to around 3000, but I'm lazy.
Beige? cool, More importantly...where is the heat mark on the strap? What about the fuel ring on the insulator or the base ring and near the threads?
I like NGK V-Power plugs. I have been using them for 10 years plus. The V-Power plug is of projected nose design, it positions the spark deeper into the chamber. In Theory, projected nose plugs have a wider heat range. When I had iron heads, I used the UR-5 plug. It comes gapped at .039. You can open or close the gap .008. The NGK numbers increase as the plug gets cooler. The 5 approximates an AC Delco R43TS. The UR-4 is closer to the R45TS. If you like bigger plug gaps, the UR-55 is a UR-5 with a longer ground electrode so you can gap them bigger. The UR-55 comes gapped at .059. Again, NGK says you can increase or decrease the gap by .008. My aluminum heads take a flat seat plug with a metal gasket. I use the FR-5, same plug as the UR-5. In addition, NGK plugs come with plated threads. No need for any anti seize compound because of this.
Same results here and using the UR5. I am currently using YR5 for the nitrous and this plug is not extended at all.
Not sure about the 300 heads Jim. How does the reach requirements compare to iron 350-455 heads? The FR-5 is the same as the UR-5, just flat seat instead of tapered seat. The reach is .460 for the tapered seat plugs and .750 for the flat seat.
And that would be a flat seat plug. The FR-5 has a 3/4" reach, so some threads would extend into the combustion chamber, not a good thing.
