I have a 94 sylvan 209 Barrritz with a 5.0LX merc i/o. I am planning to change engines this offseason. I have a new 383 that my father built and never used. It has 4 bolt mains and a SCAT comp cast crank. I am planning to use either Edelbrock aluminum ETEC 170 or cast iron vortec heads to get the compression ratio down to 9.3:1. Also using an Edelbrock performer dual plane intake with 600cfm Holley 4 bbl marine carb. Comp Cams Xtreme Marine flat tappet hydraulic cam with 1.5 roller rockers. I will have to modify the vortec heads, if used, for the increased lift. I plan to re-used the Thunderbolt IV ignition, and stock exhaust manifolds for now. Currently the exhaust is thru prop only, but as part of this swap I plan to remove the Y pipe completely and go dedicated thru hull. Future plans include CMI E-top small block headers and MSD ignition as budget allows. This combination should yield 335 hp / 390 ft.lb. torque through the stock exhaust.

Questions:

Is the 600 holley enough carb with marine exhaust? Or do I need to go with a 750? Or should I keep my quadrajet?

Is it worth spending the extra $700 on the aluminum ETEC heads to cut 35 lbs of stern weight?

Ist it worth the $700 upgrade to go hydraulic roller cam and lifters? The roller cam has faster ramps which increase flow without making reversion an issue.

Has anyone ever installed thru hull exhaust on a boat like this one? The swim platform forces the outlets very low (at water level when stationary). Side exit isn't possible either due to hull shape and contours. I can get it done with 3" manifold riser spacers then (2) angled elbows per side to spread the outlets and match the transom angle for exiting. I'm doing this mostly to get the heat out of the outdrive.

I would like to put the gen 1 alpha 1.32 upper gears in if they fit???? to help reduce torque multiplication and drive stress from the increased engine torque. What else should be done to the outdrive to help it survive? The drive is original and I do plan to blueprint it this winter to replace any suspect gears / bearings.

Can the alpha water pump keep this engine cool? Can I ditch the circulating pump and install a crossover cooling system with thermostat to eliminate another 20 lbs from the back of the boat? Or are these more of a racing setup only?

Is the Thunderbolt IV ignition good enough for this combination or will I have problems?

Will the stock mechanical fuel pump be adequate?

Thank you in advance for any helpful advice that you can send my way.

Do not waste your money on CMI E-top exhaust. You will see no appreciable performance increase.

A 600 cfm Holley would likely be adequate.

I would not buy the ETEC aluminum heads for weight savings. The Vortecs would be fine.

I would invest in a hyd roller cam.

For the exhaust just make sure there is enough drop from the elbow to exhaust exit (I can't remember the number but there is a recommended drop as per CG regs).

You are overthinking the gearing on the drive. You will needlessly limit your prop selection by using those gears.

I would not ditch the recirc pump. Again I think your are over reaching in the weight reduction department.

Fuel pump and drive should be able to work adequately for your app.

A few things to remember, an Alpha won't take a hard holeshot and it won't last if you launch totally out of the water. Also, if your engine hatch it close to your flame arrestor, you may have to re engineer the cover due to carb clearances caused by a higher intake. Use a valve spring kit from Alex's parts for the swap, they make it simple with no machining. You can use stock rockers to save some cash too.

Search Vortec Head on this site, there's a ton of info and it seems like you're on the right track!! Good luck!

The reason I am trying to dump weight, (especially stern weight), is for it's size this boat is very heavy. 3300# empty. It has excessive bow rise out of the hole. I could probably address this with trim tabs or a stabilizer fin? Or a 4 blade stern lift prop? But overall removing over 100# from the stern would be significant. Speaking just on functionality though, what is the reason to not get rid of the circulating pump?

Also is their any gain from an aftermarket manifold at the horsepower level I'm going for? I was looking at the headers from weight as much as performance, but realize if I added the headers the HP would increase well above the initial target I mentioned.

Imo, I wouldn't try to make it to complicated. Find a set of aluminum exhaust manifold and the aluminum intake and you saved some weight. The small block set up from mercruiser is proven that it works. I would stick with a 350 mag Rochester. It will give you more fuel then the 305 one. The thunderbolt ignition ran well on 454 mags so it should be fine on your mild small block. The outdrive I wouldn't worry to much about the gearing. I would make sure you have the remote oil reservoir. And possibly a shower if you plan on running over 4,000 for long periods. The big question is what do you want to turn rpm wise. Also how do you plan on driving it. You may be putting a lot of money into a boat that's not worth it. You may also want to do the tabs not just to get on plane but also for stability later.

The outdrive does have the remote reservoir. I was planning on a drive shower regardless as we do a fair share of high speed cruising. The boat is used for a good mix of pulling tube and cruising on medium sized lakes. I would like to build around a 5200 to 5400 rpm top of power curve. This way I'm up in the power band tubing but still have plenty left to open it up and cruise. My 305 will only be around 4300 rpm wide open with a full boat and with 2 people I'm out of prop at 5000 rpm. Totally understand the value thing, but I am very hands on and enjoy the challenge of making something great out of nothing rather than buying it done.

Okay, buy a good drive shower. Your getting close to the top rpm of the alpha. Anything over 4000 rpm they get pretty hot. I would look into a roller cam if possible in your block. It frees some h.p. and you don't need the zinc in the oil then. You seem to have a pretty good plan on what your looking to do.
The torque of even a 350 mag would give you a much better ride with out so much change in rpm with the load. Like I stated earlier I would try to get a Rochester because everything from merc bolts to it. Also you get better fuel economy in the 2 barrel and when the 4 barrel opens it really picked up. The 350 mag Rochester should be fine for your application. Good luck with it and let us know how it runs

Okay, buy a good drive shower. Your getting close to the top rpm of the alpha. Anything over 4000 rpm they get pretty hot. I would look into a roller cam if possible in your block. It frees some h.p. and you don't need the zinc in the oil then. You seem to have a pretty good plan on what your looking to do.
The torque of even a 350 mag would give you a much better ride with out so much change in rpm with the load. Like I stated earlier I would try to get a Rochester because everything from merc bolts to it. Also you get better fuel economy in the 2 barrel and when the 4 barrel opens it really picked up. The 350 mag Rochester should be fine for your application. Good luck with it and let us know how it runs

Eddie Marine manifold system for SBC's is 88lbs lighter than the Merc cast iron exhaust. I weighed them.

Depending on your cam specs, you might have to change out the TB IV module to a different ignition curve to work with your setup.