Viper Setback & Props

Randy, I am restoring a 1981 viper .The motor will be a 2000 115 Johnson Fast Track with low water pick up. I need to know what size jackplate to use for maximum speed. In the past you recommended a 2 and a half inch jack plate. Is this true for all 1981 vipers? I donít know how to get one less than 4 inches. My lake has a horsepower restriction of 115. I must get the most speed with what I have to work with. Any tips for maximum speed will be appreciated.

 Darren

 

Darren,   

    Check with Bob's Machine Shop in Florida, as he had a 4 inch jack and a 6 inch that was reversible to 2 1/2. The main reason for the short setback, is as we move the motor back on a viper or vector, the boat picks up a nasty porpoise in the mid-range. Try to stick with a 2 1/2 to 4 inch jack if you can. Set the prop shaft about 2 inches below the bottom to start. See if you can find a 14x24 Yamaha drag prop and have it rehubbed. A 26 would be better for top end and would work equally as well. Other than these props, there is not a lot of V4 performance propellers out there. A 24 raker prop would be an ok choice also, but it might be a little light on pitch. Try these to start with and see how close to 70 mph you get. This will determine the next moves. 

Randy

 

 

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.

Thanks,
Mark C.

 

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