Inliners International Forums General Discussion Hi Performance need help picking a cam for my chevy 250

I am currently building a motor for my boat and I am at the point where I have to choose a cam and compression. I have built many small blocks and ls motors this is my first in line 6 though. I want to keep the motor happily running on 87 fuel. Any advice you can give to help me I would be more than grateful for. The goal for the motor is 200-225 hp at 5000 rpm and as most torque as possible. I all ready have a clifford performance 4 barrel intake and a holly 450

thank you ahead of time
Chris

The Clifford manifold is not a good low RPM intake manifold.
Low port velocity, huge runners. It is like running a single plane intake manifold on a SBC compared to a dual plane.

An Offy intake would be a better choice especially for a boat.

MBHD

Thank you those are the types of things I need to know but don't know. what do suggest for heating the intake. I know there are a few setups.

Since you have a boat, you only have exhaust as an option to heat it.

If you plan on running lake water thru the block, you are forced to use a marine exh/ intake manifold. They are a combo unit. Some of them used 2 bbl carb ,even seem some with 4 bbl. I have a few taken from motors sitting in storage that could be sold.

For a cam. If running in lake water, you do not want a cam with a bunch of exh reversion. Water can come up the exh and into a cylinder at times when the engine is idling or after you take it down from a wake.
Recommendations-
Langdons Marine cam
My own Small Turbo cam.

why would I be stuck with the stock manifold it is already through hulled so there is nothing special except the flange and the coating on the current exhaust.

What is the term "through hulled"? Does the cooling water come from the lake and go through the exhaust manifold before hitting block?

You can't run lake water straight to the block. It is too cool and will damage the engine.

The exhaust will come strait from the headers and then goes to a pipe that goes to a anti siphon tube and thorough the hull with a flapper on the end. I will be running a coolant heat exchanger so all the problems that go with lake water are eliminated. but I would want to still minimize re verb in order to keep noise down.

Most boat exhaust goes through the outdrive and out the center of the prop. Thru hulll has the pipe or pipes comming out the back of the boat. The exhaust and the water just dump out the back of the boat. A really neat option is Captins Call that lets you switch between both exhaust systems. Jay 6155

intergrated j 78 is right the way I am designing the exhaust it has 18 inches of rise and a anti back flow valve so the over lap is not the problem. what I want is maximum torque as soon as possible and still keep is as flat as i can to a peak of 5000 rpm. so I sold the intake for 280 and bought a offy I also bought a set of lumps for the head to help flow. Also to improve low speed velocity in the port. I also installed a heat exchanger on the boat so I don't have to worry about heating the lake water. I was told to look at rv cams but allot of them tend to fall off to early around 4000 rpm and that wont give me the Hp i need to hit my goal of 60 mph head speed.