I've got vortec SBC and I was told that the delco MR43LTS is the best plug for these heads. I am also curious about the R44LTS. I do know the M in the part number is for marine application. Any thoughts?

Im also using a TBIV ignition. What gap should I use on the plugs with vortec heads?

The 44 is a 'warmer' plug than the 43's. With ACDelco, the heat range #'s go up as the plug get's a 'hotter' designation and vice versa.

Typically 'coldest' is 41 and 'warmest' 45 or 46.

The 43's should be perfect.

.035"-.040" gap will also be perfect.

also keep in mind that thoce heads dont like alot of timing,,32* max

i have the same heads and msd and box ignition and run ngk tr6 and my total timing is 32 to 34 i think

you are not supposed to "i think" your total advance. be sure. i think a couple of degrees too advanced and bad things happen to piston tops. a couple of degrees too retarded and you are wasting fuel being passed by sundancers.

also vortec heads use a long reach plug, not the same as a std small block...

MR43LTS is a long reach plug