Do I Need A Bigger Prop?

[livetofish28]

So I have a 1999 Stratos 273 vindicator. I just repowered this July with a new Yamaha HPDI 150. I added a jackplate and started with a 23 pitch trophy 4 blade and then moved up to a 25 pitch 3 blade my jackplate set at 3 3/4 below pad. I ran 67.1 mph on gps at 5800 rpm my water pressure is still at 26psi and I want to keep going up should I go to a 26 pitch or even bigger? thanks in advance 

 

 

   tight lines 

 

     Andrew

[tomustang]

26 is too much for a 150.

You should be most concerned with where your revs are. Max on the motor and where each prop gets you to

[Way2slow]

NO, you don't want to go to a bigger prop yet.   I would start trying to raise the motor about 1/2" at the time.  Watch the water pressure in turns and make sure it does not drop below 16 psi.  Pay attention to the tach and gps and it the tach rpm increases and the gps speed does not, then drop it back down a 1/4".  Also pay attention to the bow lift, if it won't hold the bow up or you are having to trim it up a lot more to get the bow up, drop it back down some.   31/2" is a good starting point, depending how the boat is balanced out, it may need to go a little deeper or it may be able to come up another inch or so.  It's all determined the by bow lift and if it will hold it up, the speed and the rpm, and making sure your water pressure does not drop below 16 psi in turns.

[livetofish28]

NO, you don't want to go to a bigger prop yet.   I would start trying to raise the motor about 1/2" at the time.  Watch the water pressure in turns and make sure it does not drop below 16 psi.  Pay attention to the tach and gps and it the tach rpm increases and the gps speed does not, then drop it back down a 1/4".  Also pay attention to the bow lift, if it won't hold the bow up or you are having to trim it up a lot more to get the bow up, drop it back down some.   31/2" is a good starting point, depending how the boat is balanced out, it may need to go a little deeper or it may be able to come up another inch or so.  It's all determined the by bow lift and if it will hold it up, the speed and the rpm, and making sure your water pressure does not drop below 16 psi in turns.

I don't want to turn any higher rpms than what I am currently if I set it at 3 1/2 I will turn right around 6000 which is too much. Water pressure is not an issue right now as its rather high. I know if I go up in prop my rpms will drop I know that which will counteract my raising of the motor. therefore keeping my rpms at a safe level. in theory.

 

    tight lines 

 

     Andrew

[Rick Howard]

I must be a wet blanket.... I would be trying to slow down. 67mph is about 27mph beyond my comfort zone lol

[Way2slow]

Don't worry about it turning 5,800, it will probably perform much better all the way around there than if you drop it back to 5,500-5,600 and you are not hurting the motor. Also, is that with just you and a light load, or is that with two people, gas, and full live well. If just you, it's not going to turn that with a load in it.

That's why I say start working on your setup. Get your setup dialed in and it might gain a few more rpm, if you get it to 6,000 rpm then look at going to the next size prop. There are tons of people turning those motors at 5,800-6,000. If I remember right, the rev limiter in it comes in at 6,200 rpm, but I wouldn't bet the farm on it.

Rick Howard, I guess you had better never go fishing with me, his max speed is just a little more than my cruising speed. Mine gets another 15 mph faster than his.

[livetofish28]

Don't worry about it turning 5,800, it will probably perform much better all the way around there than if you drop it back to 5,500-5,600 and you are not hurting the motor. Also, is that with just you and a light load, or is that with two people, gas, and full live well. If just you, it's not going to turn that with a load in it.

That's why I say start working on your setup. Get your setup dialed in and it might gain a few more rpm, if you get it to 6,000 rpm then look at going to the next size prop. There are tons of people turning those motors at 5,800-6,000. If I remember right, the rev limiter in it comes in at 6,200 rpm, but I wouldn't bet the farm on it.

I turned 5800 with 2 people and water in the wells. I have to have water in it for it to balance out.

[Way2slow]

I guess I should have had my glasses on when I read you first post.  My old brain registered it as you having a 150 Fast Strike, so I need to back up and regroup since I see you are running a HPDI.

 

Being a Yama 150 HPDI, and turning 5,800 with a load, you might want to look at trying a 26" Prop.  That is a lot of prop for a 150 anything on that size boat, but I would say you are pretty close to the max you want to over rev it.  Come winter time when the water and air gets colder, it may also gain a couple hundred more rpm.  I'm not familiar enough with the Yamaha's to know how much over rev the fuel injectors will handle before they lean out a cylinder, and that ain't good.  RPM wise, it's not bothering the rotating system, but some direct fuel injected motors don't have large enough injectors to compensate for a lot of extra rpms. 

 

Just sane through the replies here on these forums, some of the unknowing will always preach you should never turn a motor over the manufactures recommended max, but that usually does not apply except for certain DFI motors, for instance, the old fichts can melt piston at 6,000 rpm because of the injectors, and that's the factories recommended max.  After lessons learned from those, the newer e-tecs can turn 10,000 rpm on factory injectors, and that's using factory crank, rods and bearings in them, just changing the porting and flywheel.  So, over rev'ng one is not hurting the rotating assembly on most motors, it's just the porting is not designed for it and it's not going to be making much power once you get very far over the peak hp rpm.

 

I always say it's better to over rev a two stroke 200 rpm than load it down 200 rpm below the max recommend rpm.