and the mag 454 MPI for 1998 different than the 1998 454 MPI and both are GEN VI

MerCruiser 454 Mag MPI Bravo (Gen. VI) GM 454 V-8 1998 Distributor & Ignition Components Parts

I know some if not all gen VI big blocks using oval port heads use a long reach plug vs the old short MR43's

So in reality no one knows for sure what year engine, model etc he is referring to. I get the avitar show 98 crowine but...
His question was the difference btwn the two plugs stated and his manual stated mr43t. Is it a generic manual or is it possible he doesn't have original engine? Just saying! �� We do know it's a 454 carbed engine just not a 100% certain on year. I've had a boat with 3 different gens and size engines so it would be like going to Napa looking for plugs for a 76 escort although you have a modified 302 crammed in it. You'd likely leave with 4 incorrect plugs.

just putting this out there Merc did not make any carb engines for big blocks in 1998 nor in 1997 - their last carb big block was 1996 - 454 and no 502 carb engines for 1996. info is for black production side.


1997 454 was TBI and MPI
1998 454 was MPI and I believe last of the TBI s

the L 29 / 454 used the long reach plugs

It's good info bup. The simple days are gone. Honestly I like all the pre early ninety merc stuff. Probably cause it's what I worked on the most and could do most anything with a blindfold if I had to. Maybe a quick peek for timing. Lol... I get it though things change for better or worse.

keep in mind you have to account for replacement long block engines, where mine got screwed up, no plug #'s came with engine, so what we had been using is what we used, wrong for about 4 years, until pulled one engine down saw the plugs were way short...but seemed to run fine, but never saw over 4000 either

4 years.... at least they don't owe you anything.

I just went this route today, but wasn't sure about the gap size(went with NGK's BR6FS plugs). I went onto NGK's website, but their gap recommendation is set at .032, but set them at 35. I keep reading 40, but for the MR43TS.
How much of a big deal will it make, .040 vs .035?

MR43TS are available here, but as someone posted a link, they also cross reference to NGK BR6FS(which is why I went with NGK. Can anyone cite references on the correct gap?

Thanks

Your engine serial number is ??? Thats the way all parts and procedures goes by for the marine end. regardless what year the hull is.

I have the latest NGK app guides as well for all powersports. NGK has not had a new guide out in about 3 or 4 years. The new guide came out past couple of months.