nay thoughts on shaving the head

[thompy]

started pulling apart my spare powerhead to do some porting on a 140hp wondering if it safe to bring up the comp and if so how much can be machined off the head, i need some more power to get the hull out of the water, the trim seems to have little effect

 

[jerryjerry05]

Re: nay thoughts on shaving the head

Your not gonna raise the comp that much by shaving the head.
Boring out the pistons and re=jetting will help some.
You neglected to say anything about the boat.Size,weight,passengers, fuel capacity etc.What condition is the boat motor in?? Done a comp/spark test.
Is the foam waterlogged?Any info will help.
Unless the boat is huge and so under-powered.You should have no trouble getting up on plane.J

 

[thompy]

Re: nay thoughts on shaving the head

thanks Jerry the boat is a 20-4 avantage banshee tunnel hull, with steps in the hull, no foam, the motor runs pretty sweet but have to check comp, the last time my brother check it was 140-145 a few years ago, but it has only been used a hand full of times since then for fishing, i believe its just under 2000 lbs, i will run this motor untill i go through the spare, Frank gave me some porting tips, just trying to find out what else i can do, not looking for a racing set up, but some mods, will clean all cast flashing while porting

 

[Frank Acampora]

Re: nay thoughts on shaving the head

FIRST: DO NOT port the exhaust side. Since all cylinders dump into a common exhaust chest, and since #2 and #3 fire consecutively, porting exhaust WILL result in increased backflow of exhaust into the cylinders and LESS power than stock!

It is safe to mill the head about .060 inch--try attaching the head without the head gasket (which is around 1/16 inch thick) and turn over the engine by hand--you will see that the pistons will NOT hit the head. But then you may need to use premium fuel and retard timing a bit since compression will likely go over 155 PSI.

Use a 2 to 1 ratio lower unit and the engine will perk up. If you don't mind the noise, vent the lower unit for less backpressure -- see the attached photo just above the cavitation plate. That 140 pushes that 21 foot cuddy hull at 36-39 MPH and will pull a slalom skier out with no problem.

You can try some aftermarket reeds some people swear by them. Me? I like the stock ones.