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Thread: I don't get it

  1. #1
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    Default I don't get it

    Ok bj29v3 stock motor 2x2s2p 6000mh.
    with stock prop got 41mph
    with s&b octura x642 got 45.1mph.
    then with a s&b x440/3 got 40mph.
    what am I doing wrong here.
    everything moves freely, strut is about 1/8 off the deck aka table.
    when I went to the 3 blade I changed the timing to 7.5 as recomended here or should I only change it if Im running 6s?
    any suggestions ?

  2. #2
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    not bad speeds considering only 4s .if your looking for more speed you need more voltage or more prop .the v3 is different then the v2 bj .i never owned a v2 but people reported speeds of 50+ on 4s with the v2 .just not so with the v3 .
    my best on 6s with a cnc 440/3
    this would add quite a bit of heat so this prop on 6s was only good for a few passes .this prop adds about 4-5 mph but heats everything up .


    ps- yes you should only change timing if running 6s .lowering the timing lessens the amp draw and in turn the watts go down a little so less speed .if you had no heat issues on 4s with the 3 blade then the higher timing would have been fine .
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  3. #3
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    ok then I will reset my timing back to 15 and try again on 4s with the 440/3.
    my temps are great since I up graded the cooling.
    motor temp 98
    esc 101.

  4. #4
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    45mph is a great run on 4S with an x642. Yes, no need to drop timing on 4S, definitely leave it at 15*. Not entirely sure the 440/3 will net you a gain in speed as the 2 blade is more efficient. On 6S, the 440/3 is a lot of fun.
    Vac-U-Tug Jr (13mph)

  5. #5
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    Props are like Gears. A 642 has more pitch than a 440/3. (440/3 or 440/2 same pitch) 40mm=1.57"x1.4"(pitch)= total pitch 2.198"
    642 (42mm=1.65"x1.6 pitch)=total pitch 2.64"

    Every time that prop rotates it moves total pitch. (less some slip)

  6. #6
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    Quote Originally Posted by photohoward1 View Post
    Props are like Gears. A 642 has more pitch than a 440/3. (440/3 or 440/2 same pitch) 40mm=1.57"x1.4"(pitch)= total pitch 2.198"
    642 (42mm=1.65"x1.6 pitch)=total pitch 2.64"

    Every time that prop rotates it moves total pitch. (less some slip)
    But RPM also factors in too. I don't have personal experience running the 440/3 on 4S to give the OP hard facts on comparisons at that voltage, but on 6S, the 440/3 was nearly 10mph faster than a 642 on my V3.
    Vac-U-Tug Jr (13mph)

  7. #7
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    Robert, props are a very complex thing and a science on it's own. That's why certain people like dasboata for example, specialized in props..it's uses, for what boat a certain prop is good for, how it behaves. . .etc. But a couple of things to remember, the 3 blade props will get you greater acceleration or greater hole shot because it produces more torque than two blade props. But in exchange you will suffer with top end speed where the 2 blade will have less torque when you punch it from a dead stop compared to a 3 blade but will have greater top end speed. Also, a 3 blade prop will draw more amps so hotter gear. That's why if you use, for example, an X442 and you want to use a 3 blade, it is wise to go at least two prop sizes to a 3 blade 440/3 to decrease certain problems like heat for one. But really it's not as simple as that. There's a lot more to that but just a couple of things to remember that's all. Guys like Chris most likely read and studied the behavior, make up and more things about props combined with years of experience to have the knowledge and understanding that makes them gurus with "prop science". That's why two props, exactly the same, one professional prepped form Chris compared to just a normal balanced and sharpened prop from a non professional will have a great significant difference in performance.

  8. #8
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    I agree Bp9145 I've read many posts and articals on prop mods, detounging, cupping ect but just do,t have the proper tools to play around such as the cupping items need to do the work properly but all and all good info thankyou.

  9. #9
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    ok I went back to where I was when I hit 45mph on 4s with an x642, did it again and lost major speed then I realized that the liner was coming out and pushing on the collet, does this make sense? what do I do know? remove Teflon liner or glue it in, this must be the problem. BJ29v3 stock motor.
    Also do you round the leading edge of the rudder?

  10. #10
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    I've done two things to keep liners from popping out:
    1) pull the liner, clean the outside of any grease, clean the brass stuffing tube of any grease, wrap the last inch or so of the liner with a few wraps of plumbing teflon tape and slide back into the tube. This has proven to be extremely reliable for my problematic liners
    2) pull the liner out a few inches, clean off any grease, smear a little silicone caulk on the exterior, and slide back into the stuffing tube.
    Vac-U-Tug Jr (13mph)

  11. #11
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    Or you can take out the liner all together as some people believe there is no need for a liner. .there's debate thread on this, or put one of these on it
    https://www.ebay.com/itm/Shaft-Tube-...AAAOSwZd1Vbw7V. . .
    this is also available on OSE store........https://www.offshoreelectrics.com/pr...d=aero-sts-250

    if you get one of these you can grease your shaft without having to take it out. . .but I've done something like Ryan's way and also works well, but definitely do not glue it in.

  12. #12
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    Or another way is take a small piece of water cooling tube/hose, about 1/2 inch and put the stuffing tube trough and leave enough of the cooling tube to cover about !/4" of the prop shaft and this will also help with water coming in through the stuffing tube. . . essentially think of it as joining the stuffing tube and the prop shaft inside the cooling hose. Any of these will fix your issues. . .

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