mcollinstn

175 heads OR Mod-VP style heads... Smaller combustion chamber for higher compression.

Older 2-piece heads actually do a better job of cooling than the later 1-piece heads.

Don't raise compression too much or you'll have to run race gas. If you raise the exhaust port height, you can shave the heads to bring the compression back up cause you'll lose a little with the port mod.

Stock, you have 200 hp. Fiber reeds, remove exhaust liner, shave the heads to 150 psi, and remove the ignition advance module (they can fail and smoke the motor), and time for 30 degrees advance - this will get you around 215-220 hp.

I think you are better off with near-stock motors...

I can dang sure talk you up to 275 horses or so, but you get them kind of finicky and loud. Just a matter of what you really want...

Air Dog

mrv8outboard,

What is a porta bracket?

Do you have any pictures of one?

Air Dog

Those sound like good ways to tweak some more HP.

I have heard that if you tweak too much, then you will undoubtedly blow up your powerhead.

Is this true or is the risk worth it?

mcollinstn

Too much tweaking, eh?

Here's the scoop.
Modifying the ports removes the chrome plating on that portion of the cylinders. The best way to ensure long cylinder and ring life after a port job is to replate.
Also, with port mods, care must be taken to create a smooth transition from cylinder contact to open port to cylinder ocntact again for the rings. This requires smooth radii and a "crown" across the top edge of the port to allow the ring to smoothly re-engage contact from the sides inward on the compression stroke - otherwise you will hang a ring and flake chrome or pull a burr into the cylinder which will break the ring and gall the piston over a short time. Port finishing should be left to somebody with a good assortment of "arkansas stones" and a lot of time in front of the telly polishing port edges by hand.

RPM is also a life-shortener, but a good compromise on a 2.4/2.5 V6 is around 6500-6800 rpm.

If you're carb'ed then you should lose the air silencer and bell-radius the intake side of the front carb plate for better flow.

As far as blowing up a merc, if you run ring end gaps towards the "open" side of the tolerance, run Merc pistons, don't screw with the chrome on your bores, keep compression under 160 psi, keep timing under 30 degrees, and keep rpm under 6800, run Hiperf oil, and keep the jetting safe (piston crown color between milk chocolate and light chocolate - not gray) then you should be in high cotton.

If I were you, I would NOT play with my cylinder porting unless you have a good source for rechroming (the lure is there, cause raising the exhaust .060" is good for 200 rpm by itself). If you are disassembling the motor, I WOULD square off the finger-port holes in the stock pistons to allow more charge thru - if not planning to tear her down, I'd not worry about it. I WOULD add aftermarket fiber reeds and (if you have a ten-petal front half I would cross-drill the intake - I'd leave it be if it is a 14-petal front half). I WOULD ditch the carb silencer and radius the front carb plate. I WOULD add louver strips to both sides of the top of the motor cover. I WOULD pull the powerhead and yank the exhaust bucket (liner) from the midsection and drill (5) 1/2" diam holes above each side of the anti-cav plate. I WOULD pull the rear exhaust plate off the rear of the block and relieve the exhaust area with a die grinder (or if you're pulling the motor apart, I'd drop it on a mill and hog it out good). I WOULD lose the stock piss pipe and run a length of fullsize water hose out the back of the cowling for the water dump. I WOULD run the stock thermostats (most will tell you to lose them). I WOULD run a water pressure gauge and a temp gauge tapped into the line at the BOTTOM of the head, not the TOP like usual. I WOULD cut the heads until compression is around 150-160 psi. Before you reinstall the heads, get some .050" thick hardened washers to put under the heads of the head bolts. When reinstalling heads, use CopperKote spray on both sides of the gaskets and dip the bolts in motor oil before putting them in. Torque to 20 ft lbs then take it to 35 in 5 pound steps (from the center out every time).

Lose the ignition advance, time for 30 degrees, put in larger main jets, and go make an easy pass - get a little flashlight that has a tiny bulb on a flexible stem that you can stick into the sparkplug holes... look at the color of the piston crown. If medium brown, then you can make a harder run and recheck. After you are WOT, if your color is safe, prop for 6400-6500 and recheck your jetting. You can now lean to a light brown.

Should run fine. Should pick up 20 hp or so (much more to be found via porting, but remember - greed spills parts).

Tweaking won't blow er up - excessive rpm, lean combustion, snagging a ring, too much timing and or compression for the fuel used - those are the blower-uppers...

JUST REMEMBER THIS - if you like your motor to run quietly, leave it STOCK. Open carbs and relieved midsection makes for a wailer..

mcollinstn

Just re-read my post:
Water pressure tap in normal location.
Water temp tap in low position.
(post made it sound like you should run BOTH low, which is not the case).

mcollinstn

OH, and for rough-water hard running, you WILL need to find an aluminum flywheel.

7000 rpm over rough water will fatigue the end of the crankshaft with that heavy stocker on there.

tripps

Hey air,this is a pretty popular post isnt it!! I have a 8 inch setback for you for a hundred,a alumn flywheel for 350,dont forget my friend that has bolton nosecones,and a chopper prop is a good choice,start with a 22 pitch and see how it runs,if it reves to high,put some cup in it ,seya tripps

ps still tryin how to post pics

Air Dog

I think I will take a second mortgage on my house and just drop my boat off at Mcollinstn's.

Mcollinstn, I will eventually like to accomplish all of your recommendations, thank you. However, just got some new Banana Boat project info.

My nemisis with the 22 Baja. He has a Parts motor which is a perfect match year and HP to my Merc 200. The powerhead is broken, but everything else is their and seems okay.

The guy he bought it off of was from Hyannis, Ma. It was on the back of a center console boat. He was on his way back from fishing when the engine started to knock loudly. He said he decided to just keep going and by the time he got all the way back the motor was dead. He just pulled it off and bought another one.

I am thinking about buying it and having the power head re-built, instead of tweaking my motor.

What do you guy's think?

mcollinstn

Ya mean like converting to a twin? Or replacing your existing motor? Which?

There are several houses offering warrantied rebuilt Merc powerheads on exchange. You may want to check in with them.

I am guessing that you will be quite pleased with your boat's performance with twins.

Air Dog

No, I want to keep my motor, it has low hours and runs great.

I was thinking about fixing the blown powerhead and doubling my pleasure.