how do I choose cc's?
bigger better?
which one do I need for 750-800 hp on top of 540 cu in?noncharged

thnx

Have you decided what RPM your are comfortable with? 4800, 5300, 5600, 6000?
How much compression are you running? Premium fuel? Race fuel? Is the fuel going to be available where you go boating?
Carb or EFI? Do you need a choke on the carb for easier starting?
How big is the boat?
Do you need extreme amounts of torque or just high horsepower?
How about adjusting the valves and replacing worn valve springs on a regular basis. Are you willing to do this after only 50 hours of running time?
Do you have to idle a long way in a no wake zone?
Is the engine going to see constant high speeds or is it very seldom going to need full power?
How quiet does the engine have to be? Are you going to need mufflers?
Salt water corrosion problems? Aluminum or cast iron heads?
Closed cooling or standard cooling?
These questions (and others) need to be answerd before you make a cylinder head selection.

Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

dear Dennis;

Have you decided what RPM your are comfortable with? 4800, 5300, 5600, 6000?
5600

How much compression are you running? Premium fuel? Race fuel? Is the fuel going to be available where you go boating?
94 octane pump gas

Carb or EFI? Do you need a choke on the carb for easier starting?
carb -no choke

How big is the boat?
40-v bottom -hi-tec light boat

Do you need extreme amounts of torque or just high horsepower?
horsepower

How about adjusting the valves and replacing worn valve springs on a regular basis. Are you willing to do this after only 50 hours of running time?
no

Do you have to idle a long way in a no wake zone?
yes

Is the engine going to see constant high speeds or is it very seldom going to need full power?
full throttle as much as possible (3000 rpm's cruising)

How quiet does the engine have to be? Are you going to need mufflers?
no

Salt water corrosion problems? Aluminum or cast iron heads?
salt water but no corrosion problem because we rebuilt it every season

Closed cooling or standard cooling?
standart

Do you think I can receive around 750 hp under this combination?
thnx for your help;

Dear Timucin,
When you get up into the 750 horsepower range you will have constant valve train problems. This amount of power requires a camshaft with an almost square lobe. You really have to open the valve fast, open the valve high, hold it open for a long period of time (duration) and close it fast in order to let enough air/fuel mixture into the engine to make that kind of horsepower.

The camshaft lobe literally smacks the lifter and puts huge side pressure on the lifter body. The lifter base (roller) has extreme downward pressure on it from strong valve springs. This requires, at the very least, solid roller lifters. If you couple solid lifters with the extreme expansion and contraction of aluminum heads the valve lash will move around constantly requiring constant valve lash adjustments (especially with long periods of engine idle and extreme engine temperature fluctuations).

The stiff valve springs will fatigue very quickly while the engine is running and when the engine is not running some of the valves will be open and some will be closed. The open valvesprings will take a set and lose tension. Valve spring replacement will become necessary every 50 hours or so.

Valve seats will have to be inspected and touched up often.

Mercruiser High Performance suggests that the complete valvetrain be rebuilt every 50 hours on the 900 SC.

Your horsepower is going to be limited by the amount of maintanence that you are willing to perform on the valve train.

Comp Cams has some new hydraulic roller lifter camshaft profiles made just for marine engines. Because they are hydraulic you won't have to be constantly adjusting the valve lash. These marine camshafts also have slightly lower valve lift than a typical high performance (automotive racing) camshaft. The lower lift is compatible with lighter spring pressures (less spring replacement). The problem is that you are not going to make 750 horsepower with these more sensible camshafts.

Using the Comp Cams Xtreme Marine XM296 HR camshaft, the World Products 345 cc CAST IRON Merlin Marine head, flat top pistons with a tight quench, the World products MARINE single plane intake manifold and Holley MARINE Dominator carb, a CMI header exhaust and a good induction style ignition you might have around 600 horsepower at 5,600 rpm with good pump premium gas. The engine would be fairly reliable with oil changes required every twenty hours and valve train maintanence every 100 - 150 hours (pulling the heads).

You should also use a full thermostat cooling system for stable engine temps and an oil thermostat so the oil temp will stabilize and reach at least 200 degrees soon after starting the engine.

Hope this helps someone!
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Good points on the solid roller stuff, but my experiences have been very good. The cam I am running now has 272/280 duration @ .050" lift with .714" lift on a 112 + 4 installation. I have 22 hrs. logged on this motor. I check the lash every 7 hrs or so and haven't had to re set the lash yet. I run Dart 325 pro 1 aluminum heads, with Jesel shaft rockers, and I hardly ever idle for more than a minute or so. If you like to turn wrenches solid cams MAY be for you. If you would rather just go boating, stick with the hydraulic variety. I like wrenchin, so solid it is. Hey Dennis how much HP is my little 496 makin. The heads are fully ported with 2.3 intake 1.88 exh. The cam mentioned above with 13.2:1 compression. It breathes through a Merlin intake and a Nickerson 1050 Dominator with CMI E-tops. It likes to run 5900 to 6300 RPM and pushes my Baja 210 into the upper 90's on GPS when the air is cool. I ran out of money for the dyno!!
Craig

Wette Vette
Sounds like a great combo! I really like 496 engines (non siamese bore), you must be at LEAST 560- 590 horsepower @ 6,000 rpm don't you think? I know that 530 horsepower at 5,800 rpm with a much milder cam is relatively easy with a 509 (850, dual plane, Merlin Ovals, 9.5:1, 234/242 duration). Big money for the Jesel shaft rockers but I bet it is one of the reasons that the lash stays on specs. What amount of full advance and octane gas do you run with the big compression ratio? (the torque must be awesome!)
Sincerely
Dennis Moore

thnX Dennis!

I agree with you Dennis never liked the siamiseded blocks for endurance applications they suck

The 13.2:1 compression 496 burns the official fuel of NASCAR. 110 octane leaded Union 76 race fuel. The motor seems to like 36 to 38 degrees and I run the timing locked in. My boat went 65 MPH with a stock 7.4 L, 330 HP so I would guess the HP to be at least 650 to push it 97.8 MPH, but who knows. The torque is awesome!!!

650 .....+100 Now we're getting close!