I recenly picked up a Ventura II and 1977 omc v4 140 crossflow and I'd like to do some engine work. My question is what rpm should I try to zone in at? The motor had 1 5/16" carbs. I will be moving to 1 3/8". Reeds are also in the plans. Would raising the exhaust and lowering the intake by 1.5mm be overkill? I will be running this on the lake on weekends so I don't want to boost the compression up too much with head work - still want to run pump gas!

In 77, hp was measured at the crank so I'd like to get 140+ at the prop.
Thanks for your help!


Raising the exhaust and lowering the intakes would be a very bad idea. The motor is peaky already. The only possible way to get more than 130hp at the prop would be on $5.00 per gallon race fuel. The motor will not see much of anything with the carbs. Big carbs = slow velocity. Smaller carbs higher air velocity. The intake of that engine only needs so much. Work on setup and props that put you in the 6000 RPM range. The results will pay off.




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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