I have a 2009 Volvo Penta / Mercruiser SBC with Multi port Fuel injection. It has Vortec heads and Marine L31 Intake manifold.

Stock it suppose to make 300hp, but when i try and pull a skier it bogs in the low rpm. I dont know what the cam is, but i do have hydrualic roller lifters.

I am thinkin of installing Compcam 08-417-8 with 218/224 and roughly .500 lift. I will also use self aligning rockers, ls9 valve springs with the correct ti retainers.

Now given the fact everyone will say anything to sell everything, am i on the right path for more low to mid range power?

I am also thinkin of installin the wet timing belt from compcams pn 5100. This way its less load on the bearings...

What are your thoughts plz, this is a marine engine so load is a bit higher than for street cars...

 

Its just a mild small block, itll make a good cruiser motor. dont expect neck snapping power or high rpms. like i said it will be a good cruiser motor

 

Also consider tuning the efi system for the cam even the stock calibration has room for more power. If its a mefi controller which most GM marine stuff is if you wanna DIY tune MEFIburn is the cheapest at $700 http://www.mefiburn.com/ or you pay someone to do it. See what pcm runs it all before you go swapping the cam and go dohhh i forgot abt that.

 

I normally work on Ls series engines. How hard is it to swap the cam and rockers on the SBC? Do i have to remove the intake manifold or is there a nice trick i can do to save me on gaskets and making a bigger mess in my boat...

I have hydraulic roller lifters,

 

your problem is because it's a boat and has no transmission, or it's one gear ratio and that does not change.
the motor may make 300 hp, but that's maximum at 4500-5000 rpm.
what matters is the torque output at low rpm, and the pitch of your prop and number of blades of prop and what rpm the prop really starts to bite at.

so if you were to put a large 4 or 5 blade prop on, the more blades the better the prop will bite. that's bad because with a skier being dead weight drag on takeoff, you're motor is going to see that load right at 1000-1500 rpm and the motor makes very little torque in that rpm range. the result is the motor will really bog and you'll never get the boat on plane or skier out of the water especially a slalom. a fix for this is using a 3 blade with less pitch that will give more prop slip, so when you stab the throttle the motor will rev up to 2000+ rpm before the prop really starts to bite, at which point the rpm's are high enough where the motor can make enough torque to get skier out of water and on plane, and as you get going faster the engine rpm's get higher and things are fine.

i don't know what cam is in your volvo now but it's most likely a 19x/20x cam. the shorter duration allows for more torque output in the low rpm range where you require it. if you go to a 21x/22x cam the result will be more torque in the high rpm range but less in the low rpm range. the torque curve shifts from flat across the rpm range to sloped with lower torque at low rpms but with higher torque at higher rpms. ok for cars with transmissions and high stall torque converters, very bad for boats. you do that and you'll be worse off, unless you somehow fit a 4L60e between your motor and outdrive.

your best bet is to undo the fuel injection, put on a dual plane intake with a 4-barrel 650cfm carb and tune the carb. i would say tune the mpi injection but there's probably no aftermarket tuning for that, and it would probably be cheaper to get a new intake, carb, and fuel pressure regulator for the carb.

and if you change out the oem cam, now the computer programming for the fuel injection by volvo will be wrong and you would need to modify the computer.
i don't understand the wet timing belt, sounds like a waste. millions of sbc running timing chains for last 40 years no problem, unless you have a lubrication problem the bearings are fine. your best bet i think for more torque and power is to go with a new intake and carb that you can tune. a new cam with higher duration really won't help, they rarely give more torque output in the lower rpm range. the other thing is having the heads reworked or putt on aftermarket heads to give you more compression, along with a higher rocker ratio. different valve springs or rockers won't do a thing for you, they only help with high rpm (over 5000 rpm) which is irrelevant in your case.

 

I bought a used stock cam and also found out my rockers are already 1.6:1.

I also googled my heads and found that they flow the best around 500 lift. Once i know what my stock duration and final valve lift is, i can then properly judge my upgrades.

You are right the wet belt system is a waste of money, Compcams couldnt tell me the change intervals in hrs, just every race season.

My best guess for my current cam is 195/207 450/450 lift with the 1.6 rockers. If i were to change just the rockers and valves like you said i will see more peak numbers, but also down low my torque will increase as the valve is lifting higher with the roller than the stamped version...However, if i do decide to change the cam, i will also change the rocker ratio from 1.6 to 1.52. Keeping the lift around 500. Less stress on the valves, cam and hydraulic rollers.

I am on the look out for dynojet piggyback components, they plug in between the ecu and injectors and i am able to control the fuel. I will first try the following steps

Check the ignition timing
check the drive angle

then i will continue to alter the fuel and then cam if needed.

 

Wow that's a lot of work and expense to dig into the engine. Torque/speed/fuel economy characteristics can be changed on a marine engine in 1 minute with a prop change.

Keep the high speed/fuel economy prop on for normal use, then just put the torque prop on when you go skiing. It's good to have a spare prop anyway just in case you make a navigation error.

 

I have the stock prop and a pitch higher already...

I am just going to go with the Dynojet CMDM with auto tune, Ls6 spring upgrade, and Lt4 1.6 self-aligning rockers. This way i dont have to take off the intake manifold, and i will gain some mid and top end power...

During a test on Hightechchevy they tried stock rockers vs roller rockers and there was a 15-20% gain in power, additionally if i control the fuel properly, 13.9 idle, 13.0 light cruise and 12.0 WOT i will also see a benefit. My tune stock is 13 idle, 12.5 cruise and 11.5 wot.