www.iFourWinns.com
https://www.smwebhead.com/phpBB3/

New Prop
https://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=3010		 Page 1 of 2
Author:  impulse [ Mon Mar 16, 2009 6:29 pm ]
Post subject:  New Prop
I don't have a spare prop for the boat yet and I'll be getting one fairly soon. I figure while I'm at it why not try to improve performance a little too? My goal would be to increase top speed without sacrificing take off too much. (can you do one without affecting the other?) My plan is on my first outing of the season to run her at WOT and make note of what RPM's I'm running, that way I'll know if I can go to a lower? pitch prop to get more speed (is that right)? Without running to close to my max RPM's. Is my line of thinking correct? What about "cupping" I think it's called, the fins will this help with top speed?
Author:  millhaven_nice_guy [ Mon Mar 16, 2009 7:16 pm ]
Post subject:  Re: New Prop
Up in pitch for speed

Down in pitch for hole shot

I think you will find the factory pitch is going to give you the best all around performance. According to Four Winns you should currently have a 14 3/4 x 19 prop. You can verify this by removing it and looking inside the hub area.
Author:  Walt [ Mon Mar 16, 2009 7:35 pm ]
Post subject:  Re: New Prop
Once you get good WOT data, plug it into here....
http://www.go-fast.com/Prop_Slip_Calculator.htm

That should tell you where to go, and what to expect.
Author:  cougarcruiser [ Mon Mar 16, 2009 9:59 pm ]
Post subject:  Re: New Prop
toss a stainless 21 on it and you will dig it!
Author:  impulse [ Tue Mar 17, 2009 8:37 am ]
Post subject:  Re: New Prop
Walt wrote:
Once you get good WOT data, plug it into here....
http://www.go-fast.com/Prop_Slip_Calculator.htm

That should tell you where to go, and what to expect.


Where can I find my gear ratio?
Author:  07H200SS [ Tue Mar 17, 2009 8:39 am ]
Post subject:  Re: New Prop
impulse wrote:
Walt wrote:
Once you get good WOT data, plug it into here....
http://www.go-fast.com/Prop_Slip_Calculator.htm

That should tell you where to go, and what to expect.


Where can I find my gear ratio?

Mine is listed on the tag on the outdrive.
Author:  jsimon [ Tue Mar 17, 2009 8:40 am ]
Post subject:  Re: New Prop
impulse wrote:
Walt wrote:
Once you get good WOT data, plug it into here....
http://www.go-fast.com/Prop_Slip_Calculator.htm

That should tell you where to go, and what to expect.


Where can I find my gear ratio?



It will be on the data plate on the side of the outdrive
Author:  impulse [ Tue Mar 17, 2009 8:51 am ]
Post subject:  Re: New Prop
Ok, cool. As I'm sure everyone is, I am dying to get the boat out on the water. Once I get my WOT RPM's and gear ratio figured out I'll report back.
Author:  impulse [ Tue Mar 17, 2009 11:19 am ]
Post subject:  Re: New Prop
Walt wrote:
Once you get good WOT data, plug it into here....
http://www.go-fast.com/Prop_Slip_Calculator.htm

That should tell you where to go, and what to expect.


So, I'm trying to use this calculator to play around with some numbers and it's not working for me. I put in 1.95:1 for the gear ratio and 19 for the pitch and hit calculate above the RPM's and that should give me the RPM's right? Well I get a value of NaN, so I'm assuming one of my numbers is wrong or something. Do you have an example I can follow?
Author:  mco804 [ Tue Mar 17, 2009 11:54 am ]
Post subject:  Re: New Prop
I got a 5.0 carb on a 20' horizon and bought a 19 pitch enertia prop. My rpm run about 4900 trimed up. I'm sure your motor will push a 21 pitch just fine. Hope this help.
Author:  Walt [ Tue Mar 17, 2009 4:16 pm ]
Post subject:  Re: New Prop
impulse wrote:
So, I'm trying to use this calculator to play around with some numbers and it's not working for me. I put in 1.95:1 for the gear ratio and 19 for the pitch and hit calculate above the RPM's and that should give me the RPM's right? Well I get a value of NaN, so I'm assuming one of my numbers is wrong or something. Do you have an example I can follow?


Plug in your current prop pitch (add about .5 if using stainless), gear ratio (I assume you just found it), your WOT throttle RPM on the same prop, and plug in your actual speed at stated WOT RPM (by GPS) in the very last column. Use the "Calculate" buttons to find your theoretical speed, and % slip. Keep this % slip number handy, because it should be fairly constant for your boat. You can use it before trying other props for good results. This should be around 15%.

That should work for you.
Author:  powellcrazy [ Wed Mar 18, 2009 8:20 pm ]
Post subject:  Re: New Prop
With my last boat, 7.4L single prop King Cobra, I was fortunate to have a really good parts guy at my dealer. He let me take a few props of different pitches and 'test' them out to see what I liked. This is the ultimate way, no prop slip calculator is going to tell you real world performance of any prop on your boat to your liking.
See if you can find a prop shop that will let you test a couple.

Our last boat was mainly used for towing, (skiing, tubing, knee board, wake board) so hole shot was very important to me, I didn't care so much about top speed.
current boat has no speed :lol: but very nice to camp on, and have jet skis for 'speed'
Author:  Beer-garita [ Wed Mar 18, 2009 10:56 pm ]
Post subject:  Re: New Prop
When the props on our old V278 (T-OMC/Volvo 5.0 EFI single props) needed reconditioning, I decided it was time to upgrade. I went to 4-blade SS by Michigan Wheel (in Grand Rapids) from the stock 3-blade setup. I picked up about 5 mph, better hole shot and still hit the rpm target WOT. What a difference! The old 3-blades became spares. Something you might consider.
Author:  impulse [ Sun Mar 22, 2009 9:07 am ]
Post subject:  Re: New Prop
Beer-garita wrote:
When the props on our old V278 (T-OMC/Volvo 5.0 EFI single props) needed reconditioning, I decided it was time to upgrade. I went to 4-blade SS by Michigan Wheel (in Grand Rapids) from the stock 3-blade setup. I picked up about 5 mph, better hole shot and still hit the rpm target WOT. What a difference! The old 3-blades became spares. Something you might consider.


That is a perfect scenero for me. I'll definately consider it. The boat is at the dealer getting one more warrenty item taken care of and I hope to get it in the water in the next week or 2.
Author:  ht32bsx115 [ Sun Mar 22, 2009 11:30 am ]
Post subject:  Re: New Prop
Howdy,

Before you buy yourself a new prop, you'll need to know how fast you're going.

You can only do that with GPS. The paddle-wheel or pitot speedometers are not very accurate.

Also, tachometers are sometimes not very good either.

You need to know if you're turning max RPM without being held back by the rev-limiter, which is usually set for about 100-200 rpm above the max range. the rev limiter for example on my 1997 454 is set at 4700. Mercruisers recommended WOT RPM range is 4200-4600 rpm. So a tach that is off by only a couple hundred RPM could screw up your calculation.


Once you have good speed and rpm numbers, you can use the prop-slip calculator to give you ballpark numbers before you get another prop.

If you're already turning about 5000 rpm or so at WOT then you're pretty close to where you want to be. (Most marine small block chev's want to turn 4800-5100 at WOT) Propping yourself to turn the lowest RPM in the (recommended WOT)range may not give you more speed.

Propping for any RPM lower than the upper recommended WOT RPM will just about always cause poorer holeshot.


Regards,


Rick
Page 1 of 2 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/