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  Conquest 21, Honda 225: Engine Mounting Height

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Author Topic:   Conquest 21, Honda 225: Engine Mounting Height
Dave Fahy posted 09-16-2014 12:25 PM ET (US)   Profile for Dave Fahy   Send Email to Dave Fahy  
I have a 1999 Conquest 21 with a 2004 Honda 225. Have other Conquest owners raised their engines to gain performance? On my boat the engine is mounted [unclear, probably means one-hole up from lowest position]. It has been recommended I raise it two more [holes]. Has anyone with a Conquest done this? What were the results? Thanks--Dave
jimh posted 09-17-2014 02:08 AM ET (US)     Profile for jimh  Send Email to jimh     
Engine mounting height is measured in units of holes (0.75-inch) and measured in the upward direction from the lowest position.

Please describe the present mounting height of your engine with that method.

How well an engine will work in an elevated engine mounting height is really dependent on the propeller being used. Some propellers can tolerate being run with very high engine mounting height, and other propellers cannot.

jimh posted 09-17-2014 10:19 AM ET (US)     Profile for jimh  Send Email to jimh     
A good way to assess the engine mounting height is by observation of the anti-ventilation plate position relative to the water stream when the boat is running on plane and the engine has been trimmed properly. See a prior discussion with many illustrations at

for some examples of engine anti-ventilation plate position relative to the water stream.

Setting the engine mounting height so that the anti-ventilation plate is running dry on plane may result in the propeller having a tendency to blow out under some conditions, for example, during high speed turns or in rough seas. One has to consider if obtaining the maximum top speed in calm water by raising the engine--I think this is what you mean by "to gain performance"--is the most important goal, even if it comes at the cost of having a risk of propeller blow out in other circumstances. This will, again, depend on the propeller. Some propellers will hang on tenaciously even at high engine mounting heights.

Whether or not other owners of a 1999 CONQUEST 21 with a 2004 Honda 225--a rare combination of boat and engine--have raised their engine mounting height won't be binding on the performance you might get. A great deal will depend on the propeller.

Teak Oil posted 09-17-2014 10:46 AM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
What is your current prop and performance in mph and WOT rpm
Dave Fahy posted 09-17-2014 11:08 AM ET (US)     Profile for Dave Fahy  Send Email to Dave Fahy     
[The Honda 225] is currently one-hole-up from the lowest setting. RPM at WOT is 6,000 with top speed of 41-MPH. I need to check the propeller type; it was new this spring as a replacement for a propeller deemed too large by the mechanic. I am not trying to get people with the exact engine and boat, but just other Conquest owners to report what they have done. I do realize [performance] will not be exactly the same. I want to see if Conquest owners on the ocean were running with their engines higher up.

Thanks again,


Teak Oil posted 09-21-2014 04:52 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
It can probably go up at least one hole, maybe two. I would not go all the way up since you are on the ocean and rarely will be going WOT, and you may run into ventilation problems if you go too high.

I would raise it two holes and give it a try. It is very easy to raise it using the trailer jack, I would use a good clear silicone like GE brand it is much easier to work with than caulk.

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