a few places iv looked online for superchargers or any motor performance part they list either 93-97 or 99-02 454 mpi mercruiser....what happened to 98? my motor is a 98 did i get the odd ball year? is there a difference in a 97 98 99?

Did you verify it is a 98 by your motor's serial number? That might of been a transitional yr. I think one diff. with the 99 and up was the serp belt setup.

good point, what number in the serial number would tell me the year?

96-97 I think was the transition year. They ditched the VST tank and lift pump, and went to the cool fuel system. I think that is also when the serp belt was used.
Here is a manual for the 98. http://www.mercruiserparts.com/selec....asp?type_id=8

1997 was the transition year for the cool fuel system and I believe 1998 was the transition year for the serpentine belt system. I have a 1997 with the cool fuel system and v-belts.

My 97 had the cool fuel system but no serp belt.

Here's the '98 right here...
http://www.mercruiserparts.com/selec...M+454+V-8+1998

Check to see if your serial is in that range.

Oh, and don't assume that if your hull is a '98 that your motor is too.

98 is an odd ball year. It is the rear they transitioned from V-belt to serpentine and from a Mefi 1 to Mefi 3. Some engines had a V belt and Mefi 1, some had Mefi 3. The same with the serpentine, some had a 1 and some a 3. The only way to tell is by serial #.
If you are looking to supercharge it and you have a Mefi 1, than plan on replacing it with a Mefi 4 ecm and harness. If you have a 3, then you are good to go. The Mefi 1 has no way to tune in boost. All of the tuning is basically done with fuel pressure and injector pulse width.
Eddie

Does the Mefi 1 use a 1-bar MAP sensor? What happens if you go out of range with a Mefi 1? Let's say you put a blower on an engine with Mefi 1...once the MAP goes out of range, what does it do, anything?

Mine was a 97 with VST and V-belts.
As Eddie stated, If you have the MEFI3 that would be your best option for upgrading.

It will only read up to 100 Kpa. It does not recognize anything over that. It will still think it's 100 Kpa. The Mefi 1 doesn't have any boost tables, so there is no way to tune in boost or run a 2 bar map sensor. That is why Merc used the Mefi 3 on the 575 SCI. Of course, we use a Mefi 4 now. It's a much better piece than the 3.
Eddie