mls head gasket on a 650 hp engine,why?

Also, this gets into better flowing heads = less restriction = less boost conundrum, which is great for me!

Why not? Bob suggests an MLS gasket, and My builder also runs cometic mls head gaskets.

Oh and not to split hairs here, but according to your dyno sheet could be 690hp lol

Something thats been going thru my mind lately. Maybe one of you guys can help straighten me out.

We all by now, know the importance of velocity, and how without it, we get poor cylinder filling, esp at low speeds, esp on an engine relying on atmospheric pressure. Now, in my boat, at cruise, lets say 3000RPM. My intake manifold, is right around 0" of vacuum. If my boat was N/A, obviously I wouldn't have 0'' manifold vacuum, unless of course I was WOT.

Roots style blowers do not compress air, they simple move air. Kind of like a fan. It takes air from one place, and moves it to another, but at a greater speed. Forcing this air into the manifold, produces a positive pressure, or "boost". So, even though technically my engine at 3000RPM, is not seeing "boost", its still seeing a higher pressure, than if it were naturally aspirated. This is not a car running down the highway at 2000RPM in high vacuum. So in reality, even though your roots/screw blown marine engine is not technically registering boost on the gauge, its also not just running "on motor" so to speak. The blower is still helping. Whether or not its making more power at the flywheel at that point, I guess depends on the parasitic drag from the blower being more or less than its actually helping.

I guess my question is, while we can flow a port at 28" of mercury, and see numbers, what do we see when we are in real world? I suppose if the small high velocity port, never becomes a point of restriction, then there would be no power loss anywhere in the rpm band, and probably nothing to be gained. But, if it does become a restriction, say maybe at 5500RPM, where a larger head may start making more power, than obviously, its a loss above and beyond that point.

On the dyno, at 3000RPM with a roots blower doing a pull with the throttle blades wide open, and say 6psi of positive pressure, that is not what things are shaped like at 3000RPM, with 0" of pressure, nor 6'' of vacuum when cruising down the lake at 3000RPM. Just thoughts that run thru my head, and may not make any sense whatsover lol

Yes the blower does compress air... maybe not very efficient, but it does. And I get what you are thinking in your last paragraph. Different loads, throttle positions, barometric pressure, etc...will change what you see on the boost gauge. Thats why if you take a blown carb'd engine it will have different numbers from dyno, to boat, or say a single engine 19' to a single 30' boat; or put that same motor in a car.

totally makes sense,we also must remember that boost is as you said simply positive pressure in the manifold created by the supercharger.lets say you are at 5000 rpm and seeing 6 lbs of boost,now you pull back on the sticks and the boost instantly goes to 0.why did the boost go to 0,because closing the butterflies in the carb caused a restriction and the air could not get passed through.if this same engine was in a stick shift car and you are turning 5000 rpm and you lift your foot off the gas,the engine is still turning almost 5000 rpm but you have no boost,why?same reason,when the throttle blades closed they caused a restriction so the air could not pass. don,t know if this answers any questions but it is something to think of.

a standard roots blower does not compress air in the supercharger unless it has a delta opening,most high helix roots blowers have a delta opening,most standard helix roots blowers do not.a psi or whipple screw blower does compress air in the blower.a standard roots blower simply moves air from one place to another.

Mike, thats like saying a piston does not compress................ Is it not?

the correction factor on the dyno i use does not get calibrated by the operator,the computer is hooked up to a devise that feeds the info and the computer makes the correction factor.i assure you the dyno i use is accurate and repeatable.if your dyno operator changes the calibration to produce the numbers you want to see,RUN FORREST RUN.if i may ask,how much dyno experiance do you have?