Venus/225 ProMax

Randy -

I'm Chris Thomas of Venus fame on Marks site. I have a 2000 promax 225SML and it is in for warranty work as the cases have a leak and they must reseal them - it will be out of warranty after that.

They did a compression test and 125 across the board, this seemed low to me.  I was wondering if I could shave the heads some (and how much 10-15 thou?) and still run 92 octane safely or change heads to what? and still run the same fuel, how much gain in horsepower will I achieve. I am also going to align the block and midsection exhaust ports as I can see carbon indicating some die grinder alignment needed.

The exhaust liner question is next as the power head is currently off it would be easy to pull out now. Do you know how much horsepower gain I will get by removing it and how much louder and any other effects? Lighter flywheel might be a thought too but want to retain the 40 amps and again gain verse cost/ reliability question.

The boat ran 94.2 mph gps 30" et last fall at 6600 or so rpm and I only did two short runs with my newly acquired et so I think a little more is possible with seat time, paralift jackplate just a hair (thick) above the pad, I'm happy with that speed but if I can get more... why not.

Your input is be appreciated as information other than my own experiences and experimentation around here is practically non existent. Plus I don't want to blow the thing up! I would like to see 95+ on any given day that would be great for that motor on my rig. A 280 and I know 100+ but I like the reliability of the promax.

Thanks in advance.





 The best heads we have found to work on pump gas are a version of the F1 Champ head. Yours can be modified to that spec. Call Jim Ruck at 920-233-3833 and tell him you want your heads to the 34cc spec he does for me. You can remove your liner for a very modest, if any, gain. If you drill the relief holes your motor will be louder but that's about it. Absolutely no gain there. I'd install part # 41941 exhaust tuner for the most bang for the buck. If you pull the liner buy don't drill the holes the motor will be throatier but not much louder. Keep the stock flywheel. With a lighter one you will be hard pressed to notice a difference. A 280 would not be much faster than your motor with the 2.4 bridgeport pipe and head mods. The nice thing is your ProMax will last longer.

Hope this helps,


 P.S.   Got your phone message on the 25th but you left no phone # for me to call back.



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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