CONVINCOR 251

I'm look for some Idea's I'v got a 454 mag 365hp and thinking of putting on some upgrades ,like a BIGGER solid flat tapit cam ,merlin rectangle port heads ,dart oval port intake and 830 or 850 holley carb ,STOCK BOTTOM END. would like some ideas or recommdations. THANKS

f252tbird

I did just the type of thing your looking for over the last winter.
I went with Edelbrocks new aluminum rect-port heads, Cranes hydraulic roller cam w/ 228 intake, 234 exhaust @ 50 duration w/
587 and 610 on the exhaust side. I also used cranes gold race rockers, full msd ignition, holley 830 cfm mechanical secondary race carb on a edelbrock performer RPM intake and gil exhaust.
I had my engine run on the dyno and it posted peak numbers of 467hp at 5300 rpm and 523 ft/lb at 4100.

paradigm shift

Do some more research.I would run large oval ports as you will get more torque. If you will not be turning over 5500 then you don't need rectangle ports.

Check out this thread LOTS of GREAT info here on this board. Read listen and learn. There is a lot of good expierance here and most are willing to share there hard earned knowledge. You do have to sort thru some of the #$%^s sometimes. Good luck.

http://www.offshoreonly.com/forum/sh...threadid=31011

Tinkerer

Have Jim V. put wedges in your stock heads and set you up with the right combo and it will really fly. His shop is in Grand Rapids MI

cdscarab

Best advice, get Dennis Moores book on building marine big blocks. Read it thoroughly and then build a plan on what you want to build for a motor. Knowledge is power and isn't that what your looking for? The info in the book will help keep you from making a lot of commonly made mistakes, like solid cams. A hydraulic roller will make better power with less maint. Aluminum heads and salt water don't mix, not necassary if your running less than 10.5:1 comp., and alot more money. Oval port vs. rect. port heads; rect. port heads were designed for drag racing motors and make best power in rpm ranges too high for average boat motor. yes they come on motors from merc., because they come on motors from gm, because gm standardize on the rect. port heads when the large ovals were no longer being made, not because the rect. port heads were better for boats. Example, engine builder friend who has dyno in shop builds two equally radical motors, #1 is a 509, #2 is a 540. #1 uses ported 290cc merlin oval ports, #2 used ported rect. ports. The 540 only made about 20hp more power than 509. 540 also made more torque, but then it should have, 31 more cubes. Engine builders opinion, oval port heads are greatly under appreciated and utilized.
Get the book, save money , make better power.
Holland, as in Europe?

Crazyhorse

Dyno and SuperV are running Merlin oval-port heads with mild hydraulic flat-tappet cams. SuperV's dyno'd at 505 hp. Both boats have been very reliable. Contact Dyno for further info.

formula31

Yea same here. I run the early GM large oval ports and they work well with large valves. If I had the money, it would be oval port merlins. My personal opinion is the 850 carb is too big for a 454. I use 780's and they started and idled better, with better fuel usage than the 850. Top end was the same.

Cord

Put a 250 on it. Keep the boost to 4 or 5 lbs. Keep the stock cam, pistons, and bottom end but use a big 4150 carb-NOT a dominator. Retard the timing to about 24* and you should be over 500hp. About the cheapest/easiest way to get alot of power out of that engine.

Tinkerer

The problem with the oval port heads is the tight radius into the valve opening and into the cylinder. With oval port heads the port is at the bottom of the head. What Jim Valakeo does is put wedges in the bottom of the rect. port heads. This raises the floor of the port about 1/2 inch and greatly increases the radius of the port to cylinder turn. He also put 2.3 intake valves in my heads (509 cubes). These engines ARE NOT SLOW and have more torque down low than I need to get on plane.

DOCTOR DAVE

you are still dealing with a 454, and dealing with limited torque. to make more speed you need torque, that only comes with cubic inches and stroke to make torque, or supercharging. all the cylinder head work by who everever will not gain you very much speed, unless you increase those things.