5.7 mercruiser upgrades???

[spoolinawdtsi]

I have a 89 23 ft cabin cruiser weighs 4500lb that I would like to add little more power to. Boat has 260 hp 5.7 mercruiser with cobra outdrive. Boat runs bout 32 ish but I would like to see 40 + if possible. Motor is stock but what are good investments for creating more power on the water. I'm mechanically skilled as I've drag raced for yrs. I assume Cam, heads, carb, and exh are good places to start? Any recommendations???

[502 JET]

Welcome to ***boat!
Your on the rite track. Don't get too crazy with the cam or you wont get the idle down low enough to shift it without hurting the alpha. You will need to upgrade the exhaust system to center rise manifolds if you still have the stock type rear rise manifolds.
I have a 79 AMF Crestliner 22' deep v cuddy cabin. A trailer shop told my boat weighs close to 5500 lbs loaded. It started life as a mercruiser 260 alpha. It now is a .030 over so 355 cid with flat top pistons. I have 194 fulie heads on it and a maine/rv off the shelf hyd. cam (dont remember specs). Still running the stock cast iron intake and q-jet carb. I run OSCO center rise cast iron exhaust manifolds. The motor is balanced.
Running wide open and trimmed up I can GPS 55 mph. I usually cruise 35 -37 mph when the ocean is flat. Its just my fishing boat I don't like to beat on it so I don't open it up often, just when the ocean is flat and the fish ain't biting.:D
You didn't mention where you boat but if salt is not a concern running aluminum-heads, intake, and exhaust manifolds would save a bunch of weight and help you go faster.

[cfm]

What kind of boat ?
What are your current wide open rpms ?
What style of prop?
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32mph sounds to me like your propping is way off. I added an intake manifold to a 22 cuddy cabin boat that went 46 baseline to 48mph with intake swap. 5.7 merc.
WFO for these motors should be approx 4600-4800rpms.

[spoolinawdtsi]

I live in ky mostly green river or Cumberland lake. seems like the exh manifolds already center dump.
The boat Is a 89 Sunbird Berletta 22'9 with 260 hp mercruiser with cobra outdrive. I'm sure stock prop still but seems like rpms are around 3500-4000 at 30 ish. but i've floored it an seems like rpms come up little but there is little progress in in speed 32 maybe.

[502 JET]

Mercruiser with a Cobra drive?:confused:
Isn't the Cobra drive OMC?:confused:
For some reason I thought I read Alpha last night, I must have been falling asleep.:D
Check your throttle linkage is adjusted properly and you are achieving WOT.
What is the condition of your prop? One in poor shape will not perform very well.

[spoolinawdtsi]

yes 89 yr has the omc cobra outdrive. Prop looks to be stock but is in perfect condition! Motor just seems like not enough torque to get the boat moveing like I like....lol
What would be a good cam grind for a marine eng? under 500 lift or over, mechanical or hyd?

[cfm]

3500-4000rpms at WOT ? Not good! Need to be 4600-4800.
Do you not have a tach? If not, get one and get an accurate one !!!!
Doing engine mods when your current set-up has totally wrong prop is just a waste of money BTW !
Compared to being overpropped as you are, A prop that puts you in correct WOT range will typically give you faster planing and accelration too.
Your boat feels like a pig because your propping is making it a pig.
Let's get a tach and change props first - you will probably be very pleasantly suprised !!!
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You do drag racing stuff so I'll make an analogy.
Say a person has a 3800lb Chevelle with 350, stock torque converter, and 2.73 rear gears. He wants to halfway cheaply go faster down the track. Do we throw a cam, intake, and heads on it or do we get better gears ? If you could only do one or the other.

[steelcomp]

CFM and 502Jet both have good suggestions. Linkage adjustment is the first thing I'd check, then a simple timing adjustment check. If all's well and everything seems to be in order and the engine running at it's optimum, you're definately pushing the wrong prop. After all that, if you're happy with your set up and just want more power, send me a PM with your contact info. I can put together a complete top end package designed specifically for your app, or any variation of upgrade you might be interested in.
Scott

[spoolinawdtsi]

Yeah gearing is everything....
Well I was wondering what the idea rpm range is on this motor! I have run the rpms up to 4600 but seems to have no change in speed from there to 3500. I'm assume the pitch on my prop is to high? I'm not sure on what the manufactored prop is for this app

[SB]

I have run the rpms up to 4600 but seems to have no change in speed from there to 3500.
Well that would be a problem. Check your speed on GPS while your checking your rpm.
What carb do you have?
You're moving a big
I dunno the max hp that drive will take, but let's say you want 300-350 hp. That probably means you need better heads, and maybe more carb. More cam might not be needed.
So when steelcomp says, "I can put together a complete top end package designed specifically for your app, or any variation of upgrade you might be interested in." He is on the right track, talk to him.

[tbanzer]

If your numbers are correct you are going to need about 100hp to gain 8mph. Probably about $2000 in parts to gain 8mph, thats providing your labor is free. Heads, Camshaft, thru hull exhuast and prop swap.

[spoolinawdtsi]

still runnin cast intake with quad 4 b.
Thanks guys 4 all the info!!!!!