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

I threw a set of (automotive stock) vortec heads on an 1987 (260hp) 5.7l & it made an nice improvement for pulling skiers. From what I remember just the heads are worth 30+ hp w/ no other modes.

Think I had the pushrod holes opened up to allow for the bigger pushrods & roller rockers.

I know this doesn't answer all your questions but its worth the effort. The only other advise I would recommend is to upgrade your cam while your in there.

Matt,
The valves should be up to the task, but you really need to figure out what your compression ratio will be with the Vortec heads to see if the available fuel will work ok. The Veortecs are a lot smaller chamber than your heads And will bump the compression up to around 9.5 to one if I am correct. In my opinion, this is pushing the limit for 93 octane unleaded in a marine application.

You will most likely have to rejet the carb only because of the additional power you will be making.

Hope this helps,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

I doubt you have a roller cam,look into a comp cam xm design camshaft.you boat is probably a heavy one at that,keep the duration at a minimum.i have bolted these heads on with no problems with fuel,93 should be enough..just make sure you use the correct rocker arms for those heads,you should know this already tho being a gm tech..or look into the GM 330 hp crate cam specs(327/350 hp cam),i have installed that engine into my buddys 233 celebrity cuddy,before instlation the boat did 47 mph..now with the 330 crate engine it tops out at 55mph.

good luck

GM went to roller cams in 87 on the SBC's. All 87+should be a roller motor. 87 model year are not all roller though. Depends on when it was built.

Valves are fine. Bottom end is fine. I used to spin an all stock GM shortblock 5600rpms all day long for 360 hrs. I would upgrade valvesprings and screw in studs. Add a set of 1.5 roller rockers, Performer Air Gap intake, Upgrade the cam to a Comp XM264HR. This is a good grind for your application. With the Vortec heads it will provide a nice increase in lowend and midrange power and pull to 5000rpm nicely. It will also work nicely with stock exhaust and idle very similar to stock with no bad idle manners in no wake zones. It can also be used with your stock dist gear. Using a stock cam is going to be leaving alot of power on the table with better heads. I would also upgrade the carb if possible to at least a 650 Holley or similar. Jetting will be required either way you go.

WOT now @ 4400 rpms is really low for a 350 MAG. You need to spin at least 4800 to make peak power stock. You might just need to do some prop testing and get your rpms to 4800-5000 with your current motor. If you like the way the boat runs with your current prop then have it taken down a pitch or two to get more rpms. This will in turn give you a better holeshot and power to pull skiers.

with it being a carburated 350 mag i doubt it!! If it were a 350 mag efi then it would probably a roller cam..
see for yourself...

http://www.marinepartsexpress.com/Me...5982_0F600999/

Donzi matt i forgot to add,a four blade propeller would help to..

what style donzi do you have?

Ryan,
GM only went to rollers in the cars in 87, truck engines, which most of the marine engines are based on, did not switch until 1996. I am not sure exactly when Mercruiser started but I would be real surprised to see a 1987 engine with a roller cam in it. I can find out for sure on Monday at the shop.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

My engine is a 93, and looking it up by serial number what I have found looking at parts lists indicates that it is a roller cam motor, but I have no way of knowing till I pop the intake off.

The compression ratio difference does concern me a bit. According to the #17 Mercruiser manual my motor is rated at 9.3:1 CR. I can't find anything that lets me know what size chamber are on the current cylinder heads. If they are 76CC heads, then the compression ratio will be way too high for pump gas available around here. Does anybody know what my heads currently are? Are their different thickness marine headgaskets available? I don't know if I could effectively drop the compression enough without changing pistons.

I am planning on doing this in the boat, so I am not going to swap cams. I am not trying to break any speed records, just bolt on a little more power for towing the kids around. Thanks so far for all the replies.

Oh, I had a Donzi 22 classic, but sold it a couple of years ago since it wasn't too practical with 3 kids.

Matt

as stated!! you work for gm,look up the 330hp crate motor,it would be the same set up your looking to do but minus the cam upgrade..it has flat top pistons like yours and its rated for 93..cant you pull the distributor and look into the vally with the new snapon bore scope to see if its a roller cam?


I have a x18,i bet you mis the get up and go of the 22

Here is where I am not sure on things. My 93 motor is rated at 9.3:1 CR. I do not know what the pistons are (assuming they are flat top though) and I don't know what my head CC is currently. If they are 76CC heads then I am going to throw the compression up higher than I want. If they are already 64CC then I am fine for what I want to do. The 330 crate motor lists at 9:1 CR with 64CC Vortec heads, but again I don't know if the pistons are in fact the same. These are the things I really want to know before I do this. I cannot sacrifice any reliability as this boat gets used like a rented mule in the summer by my wife and kids.

I am sure I could easily pop the distributor and look for the lifter retainer, but I am not sure why I need to if I am not going to swap cams anyhow. I don't want to pop the motor out of the boat, and I don't think I can pop the timing cover without dropping the oil pan and not run the risk of an oil leak down the road.