Need advice on replacing 454 Mag EFI. Looks like leak down test showing air getting past on several cylinders per mechanic. Looking to repower. Options and recommendations? 1995 Formula 252 Bow Rider with Bravo 3 Drive. I have 24 and 26 pitch props already. Don't want to go spending big money on older boat. Prefer to keep it fuel injected sine I boat at 6500ft and sea level but open to carbed motors if it makes sense. Had a 502 before and loved it but open to others. Prefer reliable power that can run on 87-89 Octane. Let me know thoughts and resources for motors.

If you are happy with the way the boat/engine combo performed, have you considered having the existing engine rebuilt at a reputable shop?

Air getting past where?? Valves or pistons???

Lowest cost will probably be to rebuild it.
Fastest would be to buy a complete replacement longblock. Then sell your longblock as needing rebuilt to recoup some $$$
https://www.michiganmotorz.com/produ...marine-engines

This is what I got from mechanic. Boat seems to run fine at all rpms on hose. Runs fine on water too but then somehow water is getting into cylinders after a long run with some WOT and then won't restart until dried out. I would like a 502 or similar for the torque. Boat is 4800lbs so not a light weight and we usually boat with 5+ people and tubes at altitude. Thoughts?Leak down test by cylinder. I have raw water cooled Gen VI 454

1- 10%

2- 60% with air heard at valve cover and air intake

3- 20%

4- 30% with air heard at valve cover and air intake

5- 70% with air heard at valve cover and air intake

6- 70% with air heard at valve cover and air intake

7- 35%

8- 20%

Those numbers are terrible. They do indicate blown head gaskets between cylinders and probably worse.

Hi jack

I have new 454 magnum paid $6500 make offer motor in Florida PM me!

Is it worth doing head gasket and intake gasket. Compression was consistent and it runs. Does 48-50 gps around 4200rpm. Once you go higher it bogs a bit. Once you turn off engine it wont start again until cylinders are dried.

Hard to believe that compression numbers were consistent with those leak down numbers. What range were compression numbers???

If you were only getting 4200 rpms at WOT, you need at least 2" less pitch on your prop. That is lugging the engine hard.

You may be able to do just a valve job, head gaskets and top end refresh and be fine, but you won't know for sure till the heads are off.

+1 for Griff's post - For the cost of labour, you can have the heads pulled for inspection which would also show if/where the head gaskets were failing....if it is limited to heads or intake, the service can still be done in-boat vs. pulling the engine completely. If evident the blow-by is past piston and rings, it's easier for the tech to pull the long block b/c that is the next step anyways so it's not "lost" $$$.

At this point you are having them pull the heads in the boat or in the shop..

For a stock motor that you are happy with power, replacement long block or rebuild at a reputable engine builder that will stand behind their work

I've done a top end refresh in the boat ONCE and never will again.
I would much rather pull the engine and do it on an engine stand.