between 19p and 21p, Which one is best for me?

[firehawkws6]

Think i'm going with the Stielleto II advantage with 14 1/4'' by either 19 or 21. the prop i have now is 14 1/2 x 19p stainless, not the best shape, nicks and scraches and may be bent a little, but rpms are at the highest recommended rpm at 4600 at 37mph, engine is an OMC 4.3L. If i go to the 21p it will put my engine around 4200-4300 rpm at its lowest recommended rpm range. What would be the better choice and is it hard on my engine to bog it down? Would i even gain anything going to the 21p. Looking for top speed more than holeshot. If anybody could help me that would be great, thanks

 

[Silvertip]

Re: between 19p and 21p, Which one is best for me?

Holeshot and top speed are at opposite ends of the performance spectrum and few if any props can provide both optimally. If you think about your car, low gear has lots of grunt (hole shot) but very little top speed. High gear has good top end speed but you can't pull a sitting hen off her nest. The prop is the transmission for your boat and it has only one gear. Hope you get the connection. Now then -- you always want to select a prop that puts the wide open throttle rpm at or very near the top of the manufacturers rpm band with what you consider an average load. Top speed will be whatever that prop provides. If you prop for top speed with an average load you may end up with good top end, but add a couple people to the boat and the thing will likely struggle getting out of the hole. With the proper prop you can achieve great hole shot and reasonable top end. This also gives you the opportunity to throttle back for comfortable cruise rpm. If you have too much pitch which puts the engine at the lower end of the band, you will generally be forced to run with more throttle opening than necessary because you are loading the engine more (call it lugging if you wish) and that equates to higher fuel consumption. Seems to me you are pretty close on the setup with what you have.

 

[steelespike]

Re: between 19p and 21p, Which one is best for me?

It would help to know what boat.Size,dry weight load at given speed. if possible.

 

[firehawkws6]

Re: between 19p and 21p, Which one is best for me?

1990 sunbird, 4.3 OMC, open bow, 19ft, 20-25 gallons of gas, usually only 2 people in boat, don't know the dry weight of the boat itself.

 

[steelespike]

Re: between 19p and 21p, Which one is best for me?

The motor will be better off being able to rev freely within its rpm range.At this point the 19"
appears to be the right prop. However guessing the motor is 175 hp and the boat about 2400
lbs I think you should be over 40 mph.If you get the 19 repaired it might get you there.
Make sure the motor is in excellent tune,(good compression)the throttle opens all the way,
bottom clean and smooth.

 

[firehawkws6]

Re: between 19p and 21p, Which one is best for me?

Forgot to mention that, engine has good compresion, and had to repair hole on bottom so all crap and residue is cleaned out.

 

[Dhadley]

Re: between 19p and 21p, Which one is best for me?

Whenever we're faced with this delima we are inclined to go with the smaller of the 2 pitches. 1- you cannot change the X dimension easily in an I/O so we're stuck with the engine height. With an outboard we might try adjusting the set up so we could run the 21.

2- We take into consideration of the make of the existing ss prop. In most cases we'll find a Stiletto probably bites a little harder than some other makes. Not all 19" pitch props are created equal.

3- You can always have the prop "adjusted" a little in either direction. However, it's much more desireable to add efficiency to the 19 rather than take away efficiency from a 21.