Anyone have the correct part number for the stock spark plugs for a late 90's era 454 Mag MPI? Do the heads on these engines have the heart shaped fast burn chambers like the Vortec heads have, or are they the standard 119 cc chamber such as was used on the carbed 454 and 502 Mag?

Thanks!

The are rectangular port heads with 118-119cc chambers.

Stock plugs are AC MR43T or NGK BR6FS

That's what I thought, Griff. Someone told my buddy that his 454 Mag MPI had the vortec-style fast burn heads on it. Not sure if the plugs for those engines are different.

I suggest Champion RV15YC4 spark plugs for an upgrade to the 454 Mag.
They are an extended tip plug and will increase performance and fuel economy. They are designed to be gapped at .045 inches and will increase spark plug voltage output.
Available at any auto parts counter for $1.99 each (or less).

The 7.4L (1996 and newer) will use a different plug than the 454 Mag.

So I assume the RV15YC4 plugs would be the ticket for a 1999 454 mag MPI?

I see/read a LOT of recommendations for NKG BR6FS or even the AC Delco Rapid Fire Platinum #1 for both the 454 and 502 mpi's. I use the AC Delco Rapid Fire Platinum #1 plugs.

I am running AC Rapid Fire #1's and I am happy with them. They dont seem to foul out as easy at idle. They are a little more expensive but I only change them once or maybe twice a year. I used to run AC R43TS's and they worked good too. Good luck.

Once or twice a year! Holy Hell man. I change plugs every 2 or 3 seasons with superchargers!
I run Autolite somethingorothers. They are $0.99 each, solid copper core.

Yikes!!! I just changed mine for the first time after about 7 years...and they still looked and performed great. Only reason that I changed them was that I was replacing the plug wires.

Check out E-Bay 160366655037 for more info on spark plugs for your 454 Mercruiser.
Dennis