Ive done a bunch of drag racing and what I found out quick was have a plan, a cam with heads that cant take advantage of it is a waste of money and so are all the parts you can think of. pick a speed that you want to hit and build the boat toward it from the prop-outdrive-engine to the hull. ask a ton of questions and dont make a move until you understand what needs to be done

Like CR said its the combination that does it. I have been doing this for about 36+ years and there are no short cuts. It is all cubic dollars. There are only two ways to make horse power "More bangs or bigger bangs". I have heard it so many times before, "I just hopped up my engine (car, bike or boat) and it doesn't go any faster" (read that slower),whats wrong?". In aboat the firstthing I would do is start changing props, There are more props than the Marage plus and BravoI.

blue thunder
A friend of mine had an early 90s panther, 540s, bravos on boxes. Ran low 90s. Trust me, that was beyond the designed max speed.
Gary

I saw an infomercial about an air swirler (called tornado) that fits in the air filter. Want to bet someone will be marketing that for boats soon. It should be worth another 50hp.
Gary

Ok guys ! The "design Maximum Speed" is an engineer/designers relative term for the speed range at which a boat is designed to operate. It is not a precise figure +/- 1 mph. Formula just told me that increasing the horsepower can drive the boat beyond its designed operational limits-ie: handling quirks- extreme chine walk, etc. They cannot tell you what or at what precise speed bad things will happen. ...
Just that they WILL !!

I too sat through that dang infomercial on the Tornado. I don't know if the theory makes sense to me or not, so I've held off buying one. Has anyone out there taken the plunge and tried one of these gizmos? If so, are they worth it or just a bunch of hooey? If ya got taken, don't worry...We won't laugh at ya!!!

My theory is simple. If these thing worked, whether it be magical oil additives or the Tornado, you would see them on every Formula one car, race boat, etc etc...before they ever made it to the consumer market. Think about the usual trends in high performance products. Track first, then the street. Us motorcycle guys are salivating over the thought of the new 4 stroke GP technology trickling down to the showroom floor over the next few years.

I think the best way of looking at how to increase performance is to realize that an engine is nothing more than an air pump, and the fuel that you burn is directly related to how much air you can move.

Thats why just like Tomcat said originally, you must have the whole package, exhaust manifolds will do nothing for you if the motor cannot move enough air to take advantage of the manifolds.

Putting a K&N air filter on a motor is also a waste of money, if the motor cannot move enough air to take advantage of it.

As far as horsepower gains are concerned in advertisements, such as 50hp by installing new manifolds, air filters, etc. The manufacturers of these products may have tests to prove it, but in their tests the manifolds or air filters are the final piece of the puzzle.

For instance, lets say you take a 5O2 that produces 550 hp with exhaust manifolds on it.
Replace the manfolds with stock exhaust, now the motor only produces 500hp because it can no longer move as much air with the restrictive exhaust. (This would be the baseline figure the exhaust manifold manufacturer uses in the advertisement)

Now we put the manifolds back on the motor, do another dyno pull and we are making 550hp for a gain of 50hp just by putting on aftermarket Exhaust Manifolds.(You now have a 50hp gain for the advertisement)