2002 2.5 modified

[mt0264]

I Have a 2002 mercury 200 I bought to build. the 200 2.5 block was trashed but everything eses was in great shape. I took a 150 optimax block (2.5) and modified it alot as you can see from the pic intake and exhaust. the mid section baffle has been removed as well, block punched out .010 over running the stock 200 carbs timming set at 18deg. My boat a 1985 Heavy 20.5 ft wellcraft center console came with a 1998 OMC 175 ocean runner fuel injected motor and would push the boat 32 MPH top speed. The questions I have is #1 the new modified motor pushes the same boat 50.5 what kind of HP do yall think I am making? yes I am using the same pitch prop on both motors 19P. #2 what else can i do without hurting anything to make more power. I have the motor torn down now I lost a conecting rod bearing at idel and did crank and cyl damage .020 will clean the cyl up. #3 is it ok to just step one cyl up to .020 this is not a racing boat only turnes around 5700 rpm.

Thanks Guys for your input

[mt0264]

Another question for yall as I have noted the timming is set at 18, what can i run it at and will that make more power? or cause damage?

thanks mike

[patchesII]

Yes its ok for one cylinder to be a different size. You can move your timing to 23

[motorheadbishop]

LIKE ERIK SAID MOVE OUR TIMING UP TO 23*....
ALSO CUT YOUR HEADS LIGHTLY (EVERY 0.020 IS WORTH 5PSI IN COMPRESSION)
gET YOUR COMPRESSION AROUND 140-145...
IF YOUR RUNNING A 5 PEDDLE MOTOR, CHANGE OUT THE 5 PEDDLE CAGES FOR THE RUBBER COATED 4 PEDDLE CAGES,
RUN A GOOD SET OF FIBERGLASS REEDS,
RUN GOOD GAS IN HER
AND LET'R EAT!!!!

[mt0264]

what can i expect at 23 deg timing over the 18 I am at now will that be harder on the motor?
Thanks guys

[perfmarine1]

What rpm did the 175 turn? Like 3800!

[MercNuts]

I think something is BAD wrong in your numbers. It would take a MASSIVE horsepower increase to put almost 20 MPH on your boat. I would not have any trouble believing that the 2.5/150 with some mods could put out more power than your 175 OMC but not enough difference for 20 MPH which would probably take over 100 extra. It seems like the OMC must have been really sick.

[mt0264]

the OMC turned the same RPM 5700 give or take 50RPM same pitch prop 19, I could not belive it either both motors were tested with the boat topped off with gas no fishing gear and just me and the mech in the boat. so weight was the same as well. the mech was shocked that with the boat on the trailer straped down the motor was strong enough to turn 5700 RPM he said that most have a drop, I know the OMC motor did on the trailer. both motors were and are runing 87 gas to. when he cut the 150 2.5 block he said he cut the exhaust ports the same as a 250HP and that was the only diference between 150,200 and 250 HP 2.5's other than gas supply, I am using the 200 carbs jetted a little heaver than what came on it

[MercNuts]

the OMC turned the same RPM 5700 give or take 50RPM same pitch prop 19, I could not belive it either both motors were tested with the boat topped off with gas no fishing gear and just me and the mech in the boat. so weight was the same as well. the mech was shocked that with the boat on the trailer straped down the motor was strong enough to turn 5700 RPM he said that most have a drop, I know the OMC motor did on the trailer. both motors were and are runing 87 gas to. when he cut the 150 2.5 block he said he cut the exhaust ports the same as a 250HP and that was the only diference between 150,200 and 250 HP 2.5's other than gas supply, I am using the 200 carbs jetted a little heaver than what came on it

Okay, here is a simple physics lesson. If the motor turned the same RPM give or take 50RPM as you stated, with the same prop and the gear ratio is the same, and the engine height is the same, then the boat runs the same speed with either engine. If your mechanic told you that he cut the ports the same as a 250 "and that was the only diference between 150,200 and 250 HP 2.5's other than gas supply" you need a new mechanic because this one does not know anything about Mercs. Mercury never made a 250 HP 2.5. There are many differences between a 150, 200, 245, 260, and 280 2.5 Merc other than the ports and gas supply.

[mt0264]

I dont know about the gearing in the lower unit didnt think about that. and yes their is many differences between all the motors from size to year I understand all that. I didnt go into detail. and I am not sure even if the 250 is a 2.5 block but i did see the diference in the ports on the diferent motors. the size of the ports all got larger as the HP got bigger on the 2.5 that is what i wanted to do with this experimental 150 block go bigger than the biggest still using everything else from the 2002 200 motor. with doing just that, porting bigger and jetting the carb the bottom line is my boat now will run 50.5 where it would only run 32 wide open. I am not sure about the height of the motor on the boat, both were 25 in lower units and I am not sure how much effect that had on the MPH. in the end MPH dont lie and in the bay I can run past most fishing boats and thats what counts and it sounds great and turns heads as i go by or fire it up at the dock.. Bask to the origial Question (How much HP do yall think it is making) the mech seems to think it is up around 240 or so I dont know but it is fast and strong at 18 degrees I dont know if I move it to 23 what kind of dif it will make? that was the other question I had

[perfmarine1]

the OMC turned the same RPM 5700 give or take 50RPM same pitch prop 19, I could not belive it either both motors were tested with the boat topped off with gas no fishing gear and just me and the mech in the boat. so weight was the same as well. the mech was shocked that with the boat on the trailer straped down the motor was strong enough to turn 5700 RPM he said that most have a drop, I know the OMC motor did on the trailer. both motors were and are runing 87 gas to. when he cut the 150 2.5 block he said he cut the exhaust ports the same as a 250HP and that was the only diference between 150,200 and 250 HP 2.5's other than gas supply, I am using the 200 carbs jetted a little heaver than what came on it

:leaving:

[mt0264]

I do have the 4 peddle cage with stock reeds. will moving the timming up from 18 to 23 make a big difference and will changing the reeds make a difference???