still too high of rpms..

[weider1717]

1984 19ft I/O dixie ski boat with a 1.50 mercruiser and a 5.7 liter GM 350 rated at 260hp.

It had a 19p prop on it and did 51mph and 5,000 rpm's changed to a 21p mercury vengence and with 2 men and a full tank of gas ran 55mph however, my rpm's still hit 5,000 at WOT???

should I have gone with a 23p mirage or something instead? my engine I think it rated up to 4600 rpm so I can't run it WOT too long still even with a 21p prop.

the 19p prop was a redone ss prop but it had power tech stamped into it plus a number ending with 19p..surely that meant it was a 19p prop..maybe someone formed it to a 21p prop? no clue.

 

[Adirondack]

Re: still too high of rpms..

1984 19ft I/O dixie ski boat with a 1.50 mercruiser and a 5.7 liter GM 350 rated at 260hp.

It had a 19p prop on it and did 51mph and 5,000 rpm's changed to a 21p mercury vengence and with 2 men and a full tank of gas ran 55mph however, my rpm's still hit 5,000 at WOT???

should I have gone with a 23p mirage or something instead? my engine I think it rated up to 4600 rpm so I can't run it WOT too long still even with a 21p prop.

the 19p prop was a redone ss prop but it had power tech stamped into it plus a number ending with 19p..surely that meant it was a 19p prop..maybe someone formed it to a 21p prop? no clue.

Sounds like you could easily go to a 23p prop, but you mention it's a ski boat. If used as such you have to be careful that you don't lose too much of your "hole shot" for deep water starts when skiing. (probably not a big problem with a 5.7) A lot of prop sizing has to due with service application, and not just WOT operation. Of course you should never operate an engine above the specified rpm so backing out of the throttle a bit is a must.

 

[weider1717]

Re: still too high of rpms..

if i plunge for ANOTHER new prop should I see some MPH on top end? 55 is the best I've seen it with the 21p so far.

havent had my gps with me everytime tho but I def saw it on 55 with 2 men.

should i expect maybe 60mph with the 23p?

 

[Adirondack]

Re: still too high of rpms..

In theory you should see an increase in top end. Probably not 60 mph. You only gained 4 mph going from a 19p to a 21p. I would expect a bit less gain because remember your aim is to actually drop WOT rpms along with raising top end. A way to look at it would be that along with gaining mph you will be gaining efficiency. Me personaly, I can't tell the difference between 55 and 60. That's moving right along in a pleasure boat no matter how you cut it, and way fast for any sane watersport.