A couple of questions about upgrading to Vortec heads

Hello, let me start by saying that I have searched and read all of the relative threads I can find on this upgrade.

I have a 1993 Crownline 225 bowrider with a 350 mag alpha. The motor runs well but being that the boat is big and beamy, it is a bit of a dog when pulling skiers or trying to get out of the hole. I am running a stainless 3 blade prop running right at 4400 RPM's WOT. I feel the setup is optimized for the power the motor is making. My engine serial number is 0D849146.

That being said, I have a couple of sets of Vortec 5.7 heads. I would like to swap a set on the boat as well as getting an updated Vortec style intake manifold to match. I plan on sticking with the marine style stainless headgaskets even though this boat is used in freshwater only. Here are my questions:

1) Are the automotive valves up to the task or should I upgrade the valves to inconel or sodium filled valves?

2) I know that the 350MAG MPI motors have a WOT rating to 5000 RPM's. With the freer breathing heads will my desired WOT move up to this area? And if so, is the bottom end strong enough to sustain 5000 RPM's?

3) Will my camshaft (which I believe is roller after doing several parts lookups with my engine number) be compatible to get me close to the 300hp mark I am hoping for? If not, will the Vortec automotive camshaft be a better choice? And if so, I am assuming my distributor drive gear will be compatible.

4) Aside from changing to screw in rocker studs, will the Vortec heads need any other modification? I believe the valve springs will be compatible with the relatively mild camshaft I will be running.

5) I have the stock Weber 4V carb. Will I need to do any rejetting to the carb to avoid a lean condition?

6) Any other potential pitfalls I am missing here? I am an ASE master tech so I feel this swap can go pretty smoothly for me, but being that I have not done any major marine motor work I want to make sure I have my I's dotted and T's crossed. The boat is in really nice condition and the stock motor only has 350 hours on it, so I would much rather put a little time and money into this boat rather than find another boat that would pull a bit stronger.

Thanks in advance for any advice you guys can share.

Matt Burns

Re: A couple of questions about upgrading to Vortec heads

If you haven't already done so, try asking your question on this forum
http://www.offshoreonly.com/forums/index.php
Its more of a marine high performance place.
When I rebuilt my 260 Mercruiser 350 SBC, I was also thinking of vortex heads since my heads were cracked. That meant getting a new manifold--which meant getting a different choke set up for the carb. What cam to use, what would be the compression ratio when using a certain cc sized vortex head when used with flat top or domed pistons. Many other question similar to yours.
I decided to go stock, use the KISS method.
I'm sure you will get your answers-
How about a 383 build--The added torque is what you want in a marine engine!!
Chris

Re: A couple of questions about upgrading to Vortec heads

mitsu matt said:

Hello, let me start by saying that I have searched and read all of the relative threads I can find on this upgrade.

I have a 1993 Crownline 225 bowrider with a 350 mag alpha. The motor runs well but being that the boat is big and beamy, it is a bit of a dog when pulling skiers or trying to get out of the hole. I am running a stainless 3 blade prop running right at 4400 RPM's WOT. I feel the setup is optimized for the power the motor is making. My engine serial number is 0D849146.

That being said, I have a couple of sets of Vortec 5.7 heads. I would like to swap a set on the boat as well as getting an updated Vortec style intake manifold to match. I plan on sticking with the marine style stainless headgaskets even though this boat is used in freshwater only. Here are my questions:

1) Are the automotive valves up to the task or should I upgrade the valves to inconel or sodium filled valves?

Click to expand...

I have been running stock valves for two years.

2) I know that the 350MAG MPI motors have a WOT rating to 5000 RPM's. With the freer breathing heads will my desired WOT move up to this area? And if so, is the bottom end strong enough to sustain 5000 RPM's?

Click to expand...

All else being equal, the MPI will make more HP than carbed. The MPI is 300HP at prop. The TBI (similiar to carb) was 280HP. Bottom ends are the same, but if yours is tired, the extra hp will accellerate its dimise.

3) Will my camshaft (which I believe is roller after doing several parts lookups with my engine number) be compatible to get me close to the 300hp mark I am hoping for? If not, will the Vortec automotive camshaft be a better choice? And if so, I am assuming my distributor drive gear will be compatible.

Click to expand...

A stock marine cam is better than stock car cam and slightly better than truck cam. A performance cam to get you over 300HP will likly require head changes for clearance. The melonized drive gear is fine with roller cam.

4) Aside from changing to screw in rocker studs, will the Vortec heads need any other modification? I believe the valve springs will be compatible with the relatively mild camshaft I will be running.

Click to expand...

A perf cam may require new springs and depending on lift, other mods.

5) I have the stock Weber 4V carb. Will I need to do any rejetting to the carb to avoid a lean condition?

Click to expand...

Probably will need tuning for optimal performance. If it is elec choke weber with Thunderbolt V ignition, it probably has the 2 step rods and jets. Finding tuning parts may be a Merc dealer only thing. If a mech choke or T4 ignition, it has the standard 1 step, which there is an abundant amount of parts for. The mech choke will need to be converted to elec or get by without one. The weber on your 350 mag is 750 cfm, more than enough.

6) Any other potential pitfalls I am missing here? I am an ASE master tech so I feel this swap can go pretty smoothly for me, but being that I have not done any major marine motor work I want to make sure I have my I's dotted and T's crossed. The boat is in really nice condition and the stock motor only has 350 hours on it, so I would much rather put a little time and money into this boat rather than find another boat that would pull a bit stronger.

Click to expand...

Minor stuff. I converted mine and I am only back-yard certified
Vortec intake, for fresh water, Edelbrock Performer or RPM.
Vortec Intake Gasket.
Misc mounting stuff, stuff that use to be mounted to intake.
I did a latter model ('96) which had serpentine belt and acessories. Don't think the seperate belts cause issues, though. Check where accesories bolt into heads and make sure the equivent hole is in the vortecs.

Thanks in advance for any advice you guys can share.

Matt Burns

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