Hopping up a Merc 150 XR2

Hello Randy,

     I own a 1987 Stratos 179V bass boat with a Mercury 150 H.P. XR2 BlackMax (2.0L) motor.  I am running a Quicksilver 25 pitch stainless prop.  To my knowledge, the whole rig is bone stock.  I have only replaced the water impeller, carb kits, thermostats, and tuner plate gasket.  I am currently getting about 63 MPH (GPS) top speed, and I have a real problem with my motor loading up when I idle around hunting for fishing spots.  I have to shift to neutral, rev up the motor, and then it will plane off and run.  My hole shot is very slow compared to all the other guys I fish with. 

     I want to soup up my boat with maybe new Boyesen reed valves, but that just doesn't seem like enough.  I would like to see significant horsepower gains, and top speed increase (70+ MPH), with hopefully easy modifications.  Can you please make some suggestions as to what I can do?  Maybe change prop size, carb. jet size, etc.  I have been told that I can change to 200 H.P. jets, and Boyesen reed valves, and be at 200 H.P.   Is this true??  Please help me.  Any charts and breakdowns would be very much appreciated.

Thanks for all your time and great knowledge,

Bryan Blick


Bryan, Selina and Colten, 

 Unfortunately the things you've been told don't happen that easy. If you just add horsepower, it takes about 10 horse to gain 1 to1 1/2 mph. You'd need 80hp to get what you want. Not going to happen. Luckily, you are probably running the old 25 laser II prop that was hot back then. The 179V's that I've done like 5 or 6" of set back to pick up all the fishing stuff in the boat. Then believe it or not we ran a 23 or 25 OMC renegade prop. Don't know why it liked it so much but the combo was 5-6mph faster than any other we had. This would put you (with the plate and the propshaft about 2" below the pad) very close to your goal. The 23 worked good because the 25 laser you have now just slips a lot and doesn't lift the boat. You can run a less pitched prop and go faster than the poor prop at the same rpm. The low speed problem could be a recirculating system problem or a float not seated. Have this checked out. Because of the half over hub/half thru hub of the renegade your hole shot will be awesome. Adding Boyesen reeds will do nothing but give you a few HP's but not anything you'll feel. It would take several thousand to PROPERLY mod the 2 litre to make any gains that your boat would feel. Set up is everything, and way cheaper. 

Good luck, 




Please submit whatever questions you have to IHRTechTalk@yahoo.com.  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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