https://www.offshoreonly.com/forums/ en Wed, 20 May 2026 11:27:04 GMT vBulletin 120 https://www.offshoreonly.com/forums/images/misc/rss.jpg https://www.offshoreonly.com/forums/ https://www.offshoreonly.com/forums/do-yourself-boating-budget/388067-mercruiser-454mag-1991-updating-help.html Tue, 19 May 2026 15:04:42 GMT Two years ago I rebuilt a 1991 MerCruiser 454 Magnum engine. It had a Quadrajet carburetor, where I changed to slightly richer #69 primary jets/metering rods and AX secondary rods.
The intake manifold was the original "perf" 6269318, with “188” rectangle-port heads and original 3999295 forged pistons with the small dome.
I replaced the original flat tappet camshaft with a Comp Cams Marine 218/224 hydraulic roller cam and retrofit roller lifters.
The boat was a Chris-Craft 245 Limited, and with this setup it ran very well: WOT was 4800 rpm and 49 knots. The drive was a Bravo One with a 1.50 ratio and a 22” Bravo One propeller.
Now I’ve sold that boat and bought another similar Limited with the same engine, but this one has a King Cobra cone-clutch drive 😁
I’m rebuilding this engine as well, and now I’d like some advice on what I should do differently to get more power. I’ll still be using the original water-jacketed exhaust manifolds, so for example: would a Comp Cams Marine 230/236 hydraulic roller cam be a better choice than the 218/224 I used before? I do not want reversion problems.
All tips and advice are welcome.
]]> Do It Yourself, Boating on a Budget marko84 https://www.offshoreonly.com/forums/do-yourself-boating-budget/388067-mercruiser-454mag-1991-updating-help.html https://www.offshoreonly.com/forums/do-yourself-boating-budget/387909-build-your-own-crane-stern-drive.html Wed, 29 Apr 2026 16:02:34 GMT Why can you load a photo? Why can you load a photo? ]]> Do It Yourself, Boating on a Budget SweCaptain https://www.offshoreonly.com/forums/do-yourself-boating-budget/387909-build-your-own-crane-stern-drive.html https://www.offshoreonly.com/forums/do-yourself-boating-budget/387904-sci-575-head-replacement.html Tue, 28 Apr 2026 18:03:27 GMT I pulled my low hr sci 575 for cam head upgrade, 112 hrs on engine, it was running perfectly, no leaks, no issues. Not happy with the deck condition, it's flat i checked that but there is some pitting. I have a set of cometic gaskets l always use copper coat but I'm concerned about leaking with these pits, I've assembled plenty of car engines that looked like this with no issues but this is alot of work to take back out if I have problems. If I had more time I'd deck it. Reason for post is I'm considering just using a felpro marine gasket, 17048. I've never had any problems with those gaskets. Engine is getting afr heads with head studs.

Option 1 cometic with copper coat and a skim coat of rtv around water ports, very thin skim.
Option 2 just use a felpro marine 17048 gasket.
engine will be around 750 hp 5-6 lbs boost with the tbs 250 blower.

it looks worse in pic, you car barely feel them and the block is flat. I also have a merlin block 555 short block ready to assemble i was going to put in boat in couple years but this engine only has 112 hrs on it and has a bunch of life life
compression was 140 accross board with very low leak on leak test. No oil consumption no smoke. ]]> Do It Yourself, Boating on a Budget hpmaniac https://www.offshoreonly.com/forums/do-yourself-boating-budget/387904-sci-575-head-replacement.html https://www.offshoreonly.com/forums/do-yourself-boating-budget/387863-489-build-sheet.html Sat, 25 Apr 2026 01:19:39 GMT Looking for anyone that’s built a 489. Have a 454 that’s 0.030” over with 4.25” scat crank and rods. Need to figure out pistons/heads/cam. Looking for any help to point me in right direction. I have: Holley 850 rect port dart single plane intake Looking for anyone that’s built a 489. Have a 454 that’s 0.030” over with 4.25” scat crank and rods. Need to figure out pistons/heads/cam. Looking for any help to point me in right direction.

I have:
Holley 850
rect port dart single plane intake ]]> Do It Yourself, Boating on a Budget THUNDERBOLT19 https://www.offshoreonly.com/forums/do-yourself-boating-budget/387863-489-build-sheet.html https://www.offshoreonly.com/forums/do-yourself-boating-budget/387837-liberty-cyl-heads.html Tue, 21 Apr 2026 00:17:10 GMT Anybody use themwhat did u do before use j know check ex guide clearance Anybody use themwhat did u do before use j know check ex guide clearance ]]> Do It Yourself, Boating on a Budget tripps https://www.offshoreonly.com/forums/do-yourself-boating-budget/387837-liberty-cyl-heads.html