Prop for 65 16footer

[raritan]

Help!!
65 skisporter, 280 non trim volvo, 350 chev balanced. Stock x dimension Holly 650 double pumper.
1. What prop do I need to get max top end?
2. What props will fit on this drive?
3. I believe that the prop on the drive is a 15x23 and the puppy wont run past 4000 rpm
Please give me some advice

[Forrest]

Something is not right. You should have 1.61:1 gears in that Volvo drive. A healthy 350 should easily turn that 23" pitch prop on that 16. One of the three following things may be apparent: 1) Your prop pitch is higher than 23" for one reason or another. 2)Your gear ratio is higher than the standard V8 ratio of 1.61:1. 3)The 350 Chevrolet is not putting out full power.

Reason #1 is out if the prop is stamped "23" and doesn't look bent.

Reason #2 is out because I don think you can get a Volvo-Penta 280 outdrive with a higher ratio than 1.61:1.

Reason #3 is a possibility. Make sure that your total ignition timing is where it should be - at least 32-degrees BTDC. Then make sure that your carburetor is opening up all the way.


------------------
Forrest

[This message has been edited by Forrest (edited 07-11-2001).]

[raritan]

Forrest,
How about if the prop is cupped? I am not sure about the prop since it has Michigan numbers on it. I have been told its a 15x23 but it does have a c stamped on it.
Carb is opening all the way. Not sure about timing at this point.
It absolutely jumps out of the hole. Lightening fast but peeters out at 4k. Thanks for your continued help

[raritan]

<IMG SRC="http://www.yellville.net/~thomas/auction/PROP.JPG">
The prop on the boat reads as follows
MICHIGAN S M C 295 CUP
I also have another michigan which is marked
15x21

Whats the first one all about. The one on the left is the cup prop

[raritan]

Prop on left is marked Michigan S M C 295 cup
the one on the right merely says 15x21

<IMG SRC="http://www.yellville.net/~thomas/auction/PROP.JPG">

[raritan]

the prop on the boat is marked as follows

Michigan S M C 295 cup
I have another one marked 15x21. which should I use.
Plz go to http://www.yellville.net/~thomas/auction/PROP.JPG
The prop on the left is the "cup" prop

[raritan]

Havent tried the 21 yet. It would require removal of the spacer that sits behind the cupped prop at the line cutter. When the 21P is installed the allen bolt threads wont engage. Do we need the spacer?

[Flash]

I had a 65 Ski sporter also, and it had a 350 with about 300 hp. I tried many props and I found the Volvo stainless high performance 14x25 to work the best. They are expensive but they work great. My 83 18 2+3 with a Volvo 280T and a 260hp. small block worked best with the same Voivo stainless but 14x27 and would spin it 5000. I could never understand why and thought it must be the different gear ratio.

[Looped]

Madpoodle,
I think “Elephant Ears” is a bit of an understatement; this thing is what is attached to my Penta 250:
http://www.donzi.net/photos/ringerc02.jpg
All that this drive/prop is, is an anchor.

Craig

[raritan]

This is really helpful... Please let me have the syntax for posting pics.

[Formula Jr]

The code is in here. (http://www.donzi.net/ubb/ubbcode.html)
Its not standard HTML.



[This message has been edited by Formula Jr (edited 07-11-2001).]

[jkeefe]

With all this knowledge out there, it raises
more questions for me. What if anything
does that dorsel fin do, I had one on and
was told it was more of hindrance than a
benifit? Took it off as soon as I purchased the Donzi. Also what would changing to a
21 pitch prop on a 16' 4.3L alpha do, now
running a 23 pitch mirage? Tach reading
44-46, max for motor 48. jack

[Formula Jr]

Depends on what you want to do. If you just want top speed, you find where on the power curve your engine puts out the most torque and pitch the prop to stay in that "sweet spot". Higher RPM on a boat means very little, taken out of context. An engine builder should have dyno-ed the motor to give you this curve if its been modified. You need a target RPM range and bracket 200 rpm on either side of the curve's top. Shoot for the high side of this bracket and test props with 1/4 tank of gas, and no extra weight. And then play with props till you find the one that is most effecient for your use. My understanding is that a cupped prop is a general use prop - jack of all trades, master of none. Speed props are single (non- progressive) pitch and have some rake to them. Hole shot and top speed are mutually exclusive. The Donzis always had twin personalities and you could tell what the owner was doing just by looking at the prop. Those big Volvo 19" fan props were for skiing, while a raked stainless 23" was for speed. Prop selection is the last in a long list of speed improvements.


The ventalation extension fins act as trim tabs and are only good for getting on plane or maintaining a slow speed plane; ie. skiing. They steal at least 2 mph off top end.



[This message has been edited by Formula Jr (edited 07-12-2001).]

[jengel]

This thread is outstanding. I have that problem. I also have a 1976 16' with a Chevy 350/350 and Volvo 280. I have an elephant ear prop just like the one in the picture! Two! I have a spare that is stamped 14x23.

I don't care about pulling skiers. My kids are 5. Speed is nice but I would like better performance. It is just too hard to steer. When stopping suddenly from WOT the boat lurches from the (sudden lack of) torque. Maybe it is the oversize prop. [relatively low revs (4000), low top speed (50)] Basically, performance is a mess. Help!

[Moody Blu']

SO how do you rake a prop to get more top end?

heres 3 different vovlo props... the stinless prop is rehubbed to fit a volvo drive.
can I get my new prop raked?
its the one on the right.
http://www.donzi.net/photos/props1.jpg

I had a prop on my boat that looked more like a chopper, it hit 5100 rpms at 50mph but was dinged up bad I hit a best of 5300mph@ 53 mph..the "elephant ear prop was supposedly volvos "speed prop"

I am going to send mine out for some improvements....
I think I am definately getting the prop lightened.

[jengel]

Talked to Geoo about it this morning.

Sounds like poor handling can be a result of too much play in the outdrive. He suggested replacing the bushings.

Then, plugging in 1.61 and 14x23 into the prop calculator it seems I am doing a theoretical 54mph with 10% slip for a true 48-50mph. That's at low rpm as I recall. But I gotta go check my figures.

If you ever make it up to the Connecticut coast with the boat I'd like to see you. How about end of August?