Venus XT Setup

A few questions. Setup is 1987 Venus xt w/83 2.4 200 w/following mods: wiseco pistons boost ports enlarged bottom of pistons opened up and scalloped balanced w/lightened and balanced rods. Nickel composite lined blocked by us chrome, big bore carbs, boysen reeds, lightweight fly wheel, exhaust opened up and radiused on back side 260hp tuner, canister removed. Bob's low water pickup 6 inch manual set back. Motor set@ 1 1/2" below pad, 24 old style mazzco prop w/ lots of cup. max rpm 6000 running mid 70's 150 hp heads compression 140. Looking at max jack from bob's 10" hyd. set back. Going to try other props. Doesn’t seem to be getting max bow lift w/o going to positive trim. Is mid 80's possible? Going to blueprint hull over the winter. Any other suggestions?

Doug Grimes

 

Doug,

With all the mods. your motor has, you will need to spin it at least 7000 rpm to make any form of power.  At 6000 rpm, I doubt it is making 200 hp.  The question is, how do we get you to pick up 1500 rpm and not lose any speed.  I would run the prop with minimum cup.  Lots of cup just eats rpm at the expense of top speed.  If you need lift, there are easier ways to get it than with heavy cup.  You could change to 2/1 ratio in the gearcase.  This would give you some added rpm.  The power curve of this motor is such that you will not have much power til 6800 - 6900.  Then it will come on the pipe.  The part number:  41941 exhaust tuner, is much better than the 260 pipe.  The 260 pipe is so large that it makes the motor think it has no tuner at all.  The open exhaust chest is also making the motor very high rpm oriented.  Don't be surprised if it takes 8000 rpm to get decent power.  If the boat/prop setup will not allow you to get to the rpm, you will not have power and your speed will be lower than expected. This is why we need to get you some rpm before the speed will come. Your 10-15mph off the pace but with the power available at that rpm it all comes together and makes sense. Get more rpm! 

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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