rsvert89

I have a 1997 Larson 206 Sei with a 1997 Mercruiser 350 that started out as a 2bbl. 210hp. I swapped to a 4 bbl intake and a Edelbrock 1409 carb when I bought the boat, which helped some on top end speed. The engine does have a roller cam in it already, and has the non vortec 14096217, 64cc heads on it. I bought a freshened set of 12558062 Vortec heads, that are also 64cc. Have been doing some reading here, and a couple other forums, and want to get some ideas what intake and cam to add to the engine.
According to the mercruiser manual I am looking at, it shows my cam is part #431-811658 at .394/.404 lift.
The cam I am looking at is the GM# 14097395, which is .431/.451 lift, and has .109 lobe separation.
I have read Vortec head valve springs can't handle much over .460 without some spring/seat/keeper mods
Does this cam look decent?
Also, with that lift, etc, would I need to get the rocker studs machined for screw in style?
Would the cam swap net me much more HP? Or would I be better to stay with the factory roller cam


Intake manifolds I am looking at are the Edelbrock RPM air gap Vortec, and the Performer Vortec. Any idea which one would work better with the cam. Boat is used in fresh water, no salt, and does not have closed cooling.

I would like to stay with the Edelbrock 1409 600cfm carb if possible

I am hoping to get close to the 300-310hp range. Does this setup seem like it could get me close?
Boat has thru prop exhaust, and I like not making a bunch of noise, so I would like to stay thru prop.
On a GPS, I can run 55 right now on a nice calm water day, trimmed up, running 4500-4600 rpm with a 1.62 ratio Alpha One Gen 2 and a Turning Point 21P Stainless prop
I would love to see 60mph if that seems possible

Thanks for any input you can give.

79formula

I ran a merc 260 in my 79 formula til she blew. 53mph. I rebuilt using flat top pistons, comp xtreme marine 262h cam, air gap intake, vortec heads, and thru hull exhaust. I ran it with both an edelbrock and a holley 750dp. Ran way better with the Holley. I ran 32* of timing and the holley to get 65mph. That combo made peak power at 5200rpm. I would bet it pushed 375-400hp. You would go 65 with that setup.

rsvert89

Thank you for the reply. Did you change your rocker studs to Screw in, rather then pressed in like the factory ones? Did you do many mods to get the heads to clear for that much camshaft lift?

Jonesyfxr

iTrader: (1)

I'm building a Vortec headed 355 right now. I have flat tops going in it with an Extrem Marine HR cam, Crosswind intake and 750 vac sec Holley. I'm running Alex's Parts valve springs to handle the cam lift. I'll be right around 9.25-1 compression. I feel this set up will come in at a conservative 300 horse.

79formula

I used stock springs and press in studs. I ran the motor with for a while with no issues. Sold the boat and the new owner is running it still. I get my hp number from several magazine articles that dynoed about 400hp and also my speed gain is in line with my hp gain.

79formula

This is the engine I copied. My cam was within a degree or 2, but mine was flat not a roller. http://www.superchevy.com/how-to/678...cam-355-build/

rsvert89

Thanks for the info. Not sure I want to do a cam in it this year. With how the engine is placed in my boat, I would almost have to remove the engine to get all the bolts loose. Maybe just the heads and intake for this year, with the cam swap this winter.

79formula

The heads and intake would pick up some hp

rsvert89

Have any of you in this group ever had a 350MPI or any Mercruiser with Vortec heads torn down to see the tops of the Pistons? I am wondering Mercury runs in their engines. I have heard a D shaped dish works really well, and also have had people tell me Flat Top with the typical 4 valve reliefs. Right now the engine in my boat has a small circular dish to the piston, as does the Vortec truck engine I got the heads from. Is the D shaped dish piston worth adding if I rebuild the bottom end I have? Thanks in advance.

Mr Maine

The d dish would lower compession I assume? They all have the slight dish 4 relief and are 9.4:1ish with 64cc heads.
lt4 hot cam (218 228 .525 lift with 1.6:1 roller rockers) works well among others. Need to cut the heads or use beehive springs for clearance.
performer rpm air gap with a 650 double pumper and decent exhaust (glm aluminum, stainless marine etc.)

I picked up a little over 100 horse or so and 8mph. Could run more pitch and cruise faster. Boat was totally different, formula 206.