Hey everyone new to the forum. Hoping to get schooled from more experienced boaters here. I have 2004 owned since 07, 242 Baja Islander 6.2ltre 320hp,Bravo one 3x19pitch. Re powering 4th time always same thing loss of compression. Anyway I have two questions. 1 does anyone know if this 6.2 engine a known problem child of mercruiser or not?
2 My mechanic is selling me 454MagMPI engine out of another boat. We are having it sent to the machine shop and to be freshened up. I am getting itch for more HP and speed out of the boat. So my mechanic suggested we put a HP500 cam in the block and run a carb, He said the EFI cant be messed with to develop more power etc. I want to know is this a good set up? Has anyone done this before and what might i see for power out of this set up? Also how much power is to much power for my 242? Any advice be great thanks again

Why did the 6.2's lose compression? Was it the same thing all 4 times? One or multiple cylinders? 4 identical failures to me would point to a rigging, maintenance, or operating problem.

Insumption??

Which was explained to me is when the engine sucks water in from exhaust.
All the engines were rebuilt or replaced bone stock. On engine 3 I put marine stainless exhaust as requested by the previous mechanic to help reduce this from happening again.
Mechanic #1 said bad risers caused engine 3 to fail so install ss exhaust.
Engine 1 and 2, were covered under warranty so I never much cared for the reasoning. But happened same way. Fail to start , Mechanic inspects and no compression in multiple cylinders.

I am on to mechanic #2 and refuse to go back to the 6.2!! He initially suggested ordering new one from Merc but I refuse to run that engine again! So I purchased used 454 MAG MPI from him I would rather experiment then keep bashing my head against the wall with this 6.2

Judging by his remarks about the efi, and "reversion" I'd start looking for mechanic #3

I like that...insumption!

Reversion I think you mean.

Do a search here on REVERSION .

Reversion!!!!! YES THATS WHAT HE SAID Sorry all not super familiar

Calling the first two " mechanics " would be a stretch .

So does anyone have experience with 454MAG MPI engine? Is it better to put a HP500 cam and go carb or leave it stock EFI? The engine is rated at 385 HP but it is heavier then my old 6.2? I would like to get the boat over 65mph if I can

The 6.2 is not the problem. Bad risers? Bad as in how? If the motor also reverted water with the Stainless Marine manifolds and risers then the problem lies elsewhere. I assume the motor has external exhaust? If so, what kind of exhaust tips do you have? Are the flappers internal or external? Are they present and in good working order? Do you have Captain's Call? How is the angle from the exit of the risers to where the exhaust tips exit thru the transom?