Prop Suggestions?
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Prop Suggestions?

  1. #1
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    Default Prop Suggestions?

    Hi All,

    I just built a new engine and have done some testing with it, it is a vortec 350 with a smaller cam (224/224 .503/503 @ 1.5) and this thing seems to run really well.

    It is is a 1980 Bahner 20' sport cruiser with a MC-1 drive. I know im overkill for the drive i just want to get through this summer and plan on buying a new alpha this winter.

    I took the boat out this sunday to lake perris to break it in and see how it will run, and i was surprised for sure

    With the 19 pitch stainless prop i currently have i was running 5100 easily and was not trimmed out yet. At 5100 RPM i was running 56.9 mph on GPS, it felt like it was still pulling but if you know lake perris you know there is not much room.

    I would like to "prop it down" to a max RPM of around 4600 to try to save the drive as well as get some more top end, I found a used Mirage Plus 23 pitch for sale that i might pick up, would this be a decent prop? Any other suggestions?

    I plan on keeping my 19pitch for skiing and tubing as it did excellent with these two activities.

    thanks!
    Steve

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  3. #2
    ptc
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    Using this theory of operation:

    Pitch is defined as "the distance a propeller would move in one revolution if it were moving through a soft solid, like a screw through wood." For example, a 21-pitch propeller would move forward 21 inches in one revolution. Think of a propeller as you would a car's axle ratio. The lower the ratio, the more pulling power from a standstill. The same is true with a prop. The lower the pitch, the better your hole-shot. However, this comes at a price: top speed. The lower pitch makes the engine reach maximum rpm at slower speeds.

    Conversely, a higher pitch will deliver greater top speeds, but slower acceleration. Be aware that lower-horsepower engines can bog down if fitted with a propeller with too high a pitch and diameter, and that can wear heavily on internal engine parts. If you're changing pitch on a recreational boat, remember that each inch of pitch is worth about 200 rpm. Lowering the pitch will increase rpm and vice versa. For example, going from a 23 pitch to a 21 pitch will increase engine rpm by about 400 revolutions.


    A 23 pitch prop would be about 4,300 rpm based on your 19 pitch info....
    Last edited by ptc; 06-05-2013 at 08:23 AM.
    1975 Sanger True Flat - 496 BBC
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  4. #3
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    Quote Originally Posted by ptc View Post
    Using this theory of operation:

    Pitch is defined as "the distance a propeller would move in one revolution if it were moving through a soft solid, like a screw through wood." For example, a 21-pitch propeller would move forward 21 inches in one revolution. Think of a propeller as you would a car's axle ratio. The lower the ratio, the more pulling power from a standstill. The same is true with a prop. The lower the pitch, the better your hole-shot. However, this comes at a price: top speed. The lower pitch makes the engine reach maximum rpm at slower speeds.

    Conversely, a higher pitch will deliver greater top speeds, but slower acceleration. Be aware that lower-horsepower engines can bog down if fitted with a propeller with too high a pitch and diameter, and that can wear heavily on internal engine parts. If you're changing pitch on a recreational boat, remember that each inch of pitch is worth about 200 rpm. Lowering the pitch will increase rpm and vice versa. For example, going from a 23 pitch to a 21 pitch will increase engine rpm by about 400 revolutions.


    A 23 pitch prop would be about 4,300 rpm based on your 19 pitch info....

    That is what i figured. it looks like a 21 may be in order.

    However i have done some more work on the boat and it seems to be runnning much better so i need to head out again with the 19 and see where i am at

    thanks!

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  6. #4
    21' Bahner Sport ATKpilot's Avatar
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    Quote Originally Posted by steves86ta View Post
    That is what i figured. it looks like a 21 may be in order.

    However i have done some more work on the boat and it seems to be runnning much better so i need to head out again with the 19 and see where i am at

    thanks!
    Hi, I have the same boat, same year as you. I am running a 21 on it with very good results, I also run a 22 Merc. Enertia prop as well with very good results. It is fairly mild 350 with thru hull exhaust etc. The prop that I use for my everyday prop is a worked Michigan Wheel Apollo, I love this prop as it does everything I want well. This is my top speed with the 21 prop 61.0 flat on GPS with two people and 3/4 tanks gas. I can't remember the RPM but I think it was around 5K, it had a little left but that is where I stopped, so the slip numbers are pretty good. Make sure you use a GPS when prop testing or else it is a waste of time. As for the drive, don't worry about that, just keep the oil changed and don't hammer it out of the hole and you'll be fine.

    I have a crap load of pictures of my entire build from rock stock buying from the original owner until now, PM me if you have any questions.


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    Last edited by ATKpilot; 06-10-2013 at 08:06 PM.

  7. #5
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    Quote Originally Posted by ATKpilot View Post
    Hi, I have the same boat, same year as you. I am running a 21 on it with very good results, I also run a 22 Merc. Enertia prop as well with very good results. It is fairly mild 350 with thru hull exhaust etc. The prop that I use for my everyday prop is a worked Michigan Wheel Apollo, I love this prop as it does everything I want well. This is my top speed with the 21 prop 61.0 flat on GPS with two people and 3/4 tanks gas. I can't remember the RPM but I think it was around 5K, it had a little left but that is where I stopped, so the slip numbers are pretty good. Make sure you use a GPS when prop testing or else it is a waste of time. As for the drive, don't worry about that, just keep the oil changed and don't hammer it out of the hole and you'll be fine.

    I have a crap load of pictures of my entire build from rock stock buying from the original owner until now, PM me if you have any questions.


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    Hi ATK!
    It does indeed look like the same boat, if you dont mind, how is your interior setup? Any pics?

    As far as my prop goes i have done some research and come up with some interesting information

    Like i said it ran pretty well, but just had no low end, really struggled pulling a skier up and just really had no throttle response, when it would get to breath she would run pretty well, but i just figured she had more in her. After trying to blame the timing or stock Qjet i started doing some research.

    After i found a magazine did an almost identical build as mine, even down to the cam (same duration/lsa but just a little more lift) and read its numbers 447 [email protected] and 445 ftlbs @4400 but pretty flat from 2800 up i knew something was wrong.

    After some investigating, i found that the #1 intake valve rocker nut was backed off all the way, which chances are i never adjusted it, though unlikely its plausible. Or it backed off (1 in a million chance).

    So after replacing the rocker nut and double checking the rest of the valves, and the addition of a holley 750 double pumper and an HEI distributor locked out at 32* of timing. It fired up in less than a half a rotation.

    It sounds WAY WAY nastier, has 100% better throttle response, and really revs hard now. So im going to say that my numbers from before (yes on GPS) are going to be null and void now. With the changes ive made (i.e. carb, hei and all 8 cylinders) im really expecting a big difference. I will be heading out to Elsinore this Saturday to get the carb and timing dialed in, as well as do some more speed runs. Ill be taking both the 19 pitch prop i already have, and i have borrowed a friends 24 pitch Bravo 1 4 blade so i can get an idea of where i may be sitting.

    Im sort of expecting that the 19 will end up being way small and will probably spin to 6 k fairly easily. So we will see, ill update the post afterwards. I really have no idea what the 24 will do, but it wont hurt to try it out.

    Heres a link to the mag build if your curious (and i found this after my build by coincidence)
    Vortec Small-Block Build - Popular Hot Rodding Magazine

    PS Any chance i can get some pictures of how your Exhaust is setup? I have purchased the center risers and plan to convert mine to thru hull just havent had the money/time and really havent planned it all out yet

    Thanks again
    Steve

  8. #6
    21' Bahner Sport ATKpilot's Avatar
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    Quote Originally Posted by steves86ta View Post
    Hi ATK!
    It does indeed look like the same boat, if you dont mind, how is your interior setup? Any pics?

    As far as my prop goes i have done some research and come up with some interesting information

    Like i said it ran pretty well, but just had no low end, really struggled pulling a skier up and just really had no throttle response, when it would get to breath she would run pretty well, but i just figured she had more in her. After trying to blame the timing or stock Qjet i started doing some research.

    After i found a magazine did an almost identical build as mine, even down to the cam (same duration/lsa but just a little more lift) and read its numbers 447 [email protected] and 445 ftlbs @4400 but pretty flat from 2800 up i knew something was wrong.

    After some investigating, i found that the #1 intake valve rocker nut was backed off all the way, which chances are i never adjusted it, though unlikely its plausible. Or it backed off (1 in a million chance).

    So after replacing the rocker nut and double checking the rest of the valves, and the addition of a holley 750 double pumper and an HEI distributor locked out at 32* of timing. It fired up in less than a half a rotation.

    It sounds WAY WAY nastier, has 100% better throttle response, and really revs hard now. So im going to say that my numbers from before (yes on GPS) are going to be null and void now. With the changes ive made (i.e. carb, hei and all 8 cylinders) im really expecting a big difference. I will be heading out to Elsinore this Saturday to get the carb and timing dialed in, as well as do some more speed runs. Ill be taking both the 19 pitch prop i already have, and i have borrowed a friends 24 pitch Bravo 1 4 blade so i can get an idea of where i may be sitting.

    Im sort of expecting that the 19 will end up being way small and will probably spin to 6 k fairly easily. So we will see, ill update the post afterwards. I really have no idea what the 24 will do, but it wont hurt to try it out.

    Heres a link to the mag build if your curious (and i found this after my build by coincidence)
    Vortec Small-Block Build - Popular Hot Rodding Magazine

    PS Any chance i can get some pictures of how your Exhaust is setup? I have purchased the center risers and plan to convert mine to thru hull just havent had the money/time and really havent planned it all out yet

    Thanks again
    Steve
    steves86ta sounds like you got it sorted out, I think you're right though, that 19 will be way too small. I'll post up some pics of the exhaust and the interior. My new interior is supposed to be ready to pick up this Friday so I will take some pics of it. I am not sure where to post them though since this doesn't seem like the right section for that stuff.

    here is a sneak peak of my new interior that the upholstery shop sent this afternoon
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    Last edited by ATKpilot; 06-18-2013 at 07:24 PM.

  9. #7
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    Quote Originally Posted by ATKpilot View Post
    steves86ta sounds like you got it sorted out, I think you're right though, that 19 will be way too small. I'll post up some pics of the exhaust and the interior. My new interior is supposed to be ready to pick up this Friday so I will take some pics of it. I am not sure where to post them though since this doesn't seem like the right section for that stuff.

    here is a sneak peak of my new interior that the upholstery shop sent this afternoon

    Hi ATK,

    I sent you a PM with some questions i have about your Bahner. If you dont mind taking a look and helping me out that would be great. You can also email me at [email protected]

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