Merc 2.4 Mods

I have a hydrostream Ventura, I am in the process of building an 83 2.4 200. Some of the mods I am planning are to modify the exhaust chest, leave the liner out maybe dry stack the tuner. I was planning on using the short 2.4 tuner. There are some piston mods I was planning, as I saw on the scream and fly forum. This engine also has the wh-20 carbs. As far as air box mods go, I was planning on cutting the front half, like poormans velocity stack. What do think of these modifications? What prop would you recommend? What speed can you expect from this hull design? Thanks!



Didn't know how I'd answer this one but I decided to lay it all out there. None of the following is directed at you but I feel I need to explain that most of the stuff that was on that forum was "window dressing" and had no real benefit for what you are planning. 

The first thing we'll discuss is the infatuation they have with "cryo" treatment of the internal parts. If that really worked wouldn't a person think Ferrari, Williams BMW, McClaren Mercedes, and all the other F1 teams that spent over 1 BILLION dollars last year alone on their engine programs would be using it. If you treat the metal part in an extreme cold and then repeatedly heat it up it kind of takes the effect out the whole process. 

Next the exhaust chest. It effectively raises the tuned RPM band 500 to 1000 rpm and with the rpm produces a little more power. With the increased rpm also comes all the problems of durability so more expensive and stronger parts are needed or failure will result. Keep in mind that you can machine the exhaust chest many different ways and not all of them work. My shop doesn't do the machine work as I have learned it is best to employ the very best so we use the most proven and experienced people in this regard. Like the widening of the rod slot area, the work shown on that thread we have tried and believe me he won't see much of anything on his V-king. There is a much more effective crankcase mod that directs the fuel charge to the boost ports. It wasn't my idea but it is SO MUCH more effective that it is the only way to go. Dry stacking is fine for a real race boat but the heat that comes with it will cause your pipe to fail prematurely and your center section to change its appearance. Restricting the water flow but allowing a small amount to drizzle on the pipe will have an almost equal effect without all the problems. Removing the liner goes with that. The piston mods such as D-porting the boost holes is ok but you can do more just running slightly hotter heads. All the mods in that thread are 1or 2 hp mods that when added give you no more than if you just ran good basic heads with a well built motor. 

On your rig I would use the PRO MARINE 2.4 pistons for they have a much better silicon content and are stronger that the Merc pistons. Use the 41941 tuner off the 2.4 bridgeport but your 83 should have that already. The WH-20 carbs are good for your setup as the only bigger ones were the WH-15 and the WH-22 carbs. These had a lean midrange though. I would crossport the intake and use the carb airhorn that the SST-120 and SST-140 motors ran. Then I would use the Boyesen 265SP reeds as these are rubber coated and last much longer. Get rid of the advance module and set the timing to a max of 25 degrees. A good head to use is the stock 150XR2 head. Run this with the .052 thick head gasket and you can run 92 octane gas with a great deal of performance increase over stock. Jetting will probably end up at .088 or .086 but start with .092 or .094's and work your way down. I would think a cleaver in the 28 pitch range will be good as the boat has a ton of lift. Keep the set back to a minimum and the diameter closer to 14 inches on the prop. I ran a Ventura some years ago like this and speeds would be close to the century mark if you can keep it down. It gets mighty flighty over 85. 

Why the big speech? I can't stress enough that if you follow the basics and build a robust strong package the results you will have exceeded your expectations. To often the "net" leads people on the wild packages that only work if you twist the motor to the moon. Your rig and the V-king in the thread can expect the rpm to be in the 7000 range. This is where the meat of the horsepower band is, 6000 to just under 7000rpm.  Heck, he was going to go through all that stuff and still use the small "fishing motor" rods. These work great at the rpms you'll run but at the RPM they claim in the thread it's a game of Russian Roulette. 

Hope this gives you some info you can use. I believe your rig can surprise a lot of people and it just needs the key ingredients. Feels free to write back with comments or questions if you want. 

Good luck with your project,



Please submit whatever questions you have to  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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