Well, I had got these plugs from the Chevy Dealer when I went in and asked for a set of plugs for my heads. They gave me AC Delco FR5LS. After reading a thread here on the board, it stated to use A/C MR43LTS

What plugs do you all recommend that I use with those heads (aluminum 113 heads) 10.5:1 ratio, TPIS big mouth intake, etc. Can I use any of the Bosch Platinum +4 plugs? Is that even recommended?

Thanks,

Pat

 

My work sells the bosch +4's THEY ARE CRAP, waste of time and money, just get ac delcos, bosch plugs just have more tips to burn off, i would nt sell em to anyone

 

Ok, thanks for your reply, that's good to know. By chance, does anyone know which AC Delco plug to use with these heads?

Thanks,

Pat

 

Does anyone know if the ACDelcos that are in the ZZ4's when they are shipped are 'good enough'? I'm going to start my newly installed ZZ4 in the next few days and was going to use them.

I could post the part number tomorrow when I get a chance to check it in the garage.

Edit:- The plugs supplied with the engine from GM in mine are AC. MR43LTS.

 

Well I spoke to one of the parts guys at my local Chevy Dealer, (one of the most knowledgeable), and he looked this up and said that there are 2 options for the plugs.

The fr5ls and the mr43lts and then added that the m43's are for marine and aluminum heads.

So it looks like those are the correct ones for the Aluminum 113 castings. Now my question is exactly the same as Dr G's. Are those good plugs to use or is there something better to use with this setup? It's a ZZ4 build.

Thanks,

Pat

 

Those are the plugs the factory put in those heads. They're fine.

 

I got the AC Delco 41-906 Iridium. With the MSD 6A and the Blaster coil and MSD 8.5mm wires I gapped them at .085 and this thing gets up and flys! MSD recomends a gap from .045-.065, but that's with regular plugs. With the Iridiums, they can be gapped larger due to less resistance. Plus the wires only have 40-50 ohms per foot.

 

plus no home mechanic is able to gap iridium plugs that is why gap is included in the part number as changing the gap ruins the plug... besides iridiums are for RICERS R' US