99Hammer

I am replacing the plugs on my 99 7.4l mpi. They are NGK's, what is the correct gap? the only mod I have done is replaced the stock flame arrestor with a K&N.

Raypanic

I went with what was on the engine. 2000 454Mag MPI .035" Gap. Check your engine or manual to be sure

pstorti

i also have a 99 7.4mpi it says on my engine that the gap is .045 and the plugs should be mr43lts. The manual doesn't have any info.

hauling ass-a

Most should be gapped at .35 max should be.45 you can always split the differance a .40

99Hammer

Thanx, fella's. I gapped them at .045. What would the diff. be if I gapped them at .035? The old ones I pulled out did not even look like they were gapped(most were .020). I let the marina do it last time. I f have started to do all my own maint.

RickA

The Mercury shop service manual indicates .035 to .040 is the stock gap for NGK or MR43LTS.

I just replaced my plugs with AC Delco Rapid Fire #1's. These are great plugs. Outstanding idle and startup. Gap for these plugs is .045

Rick

pstorti

I just bought a set of the rapid fire #1's I'll let everyone know if there's a difference in performance. I'm running the original plugs now that are 2 years old. Haven't had any problems figure its just time to change them.