mach1magnum

i have what i believe is a gen 4 7.4 small port heads it has a mechanical fuel pump carb motor i know it is a replacement motor not sure what brand i am getting conflicting info on plugs does anyone have the ac delco number i need also i do have a number on the block for what it is worth it is 99593 thats it please help

mach1magnum

just wanted to add the plugs i took out are br6es ngks and the part store gave me ac delco mr43lts there is a huge difference in the length of these 2 plugs

Hematite

I can only give a general reply. In my experience, NGK plugs are far better than AC Delco plugs, but that is my experience. Others may disagree.

mach1magnum

i really don't care what plug i use as long as its the right one but the ac plug is 1/2 inch longer than the ngk that was in the motor and its not running very well at idle now i did find a bad plug wire so i am sure that has a lot to do with the way its idling

mcollinstn

An NGK BR6ES and MR43LTS should both be 3/4" reach plugs.

But

You only need short reach pugs - not long reach ones.

What you need is a BR6FS or MR43TS.

Are you sure you had "ES" plugs? They are too long.

MC

mach1magnum

i see it now i have the mr43lts but i need mr43ts so the L must be for long ?
thanks makes sense now this motor was installed by the last owners guy and i have found lots of things done wrong so it makes me double check everything he did so this engine does get the short reach plugs