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Thread: I am looking for a propeller suggestion for 21 Cougar MTR

  1. #1
    RUNWME
    My wife has a 21 Cougar MTR with modified 2.5 Mercury and using Mad EFI adjustable injection. Compression is 160 lbs. I have a 10 inches of setback and CLE gearcase.
    She spins a 28 3 blade Mazco cleaver 7000 RPM at 86.5 mph on gasoline and the same prop 8000 RPM at 101 mph when using a alcohol/nitromethane mix
    This combination seems ok for top speed, but it turns WAY too many RPMS for my comfort level. On our family/play/ski boat. In addition it doesnt get on plane very well (blowing out prop)
    I would like to max RPMS to be 7000 at 100 mph and was thinking a 30-32 pitch prop would be perfect.
    Would a cleaver or chopper style get max speed and drivability for her Heavy Cougar tunnel? A friend has a new Spinelli 30 pitch over hub 4 blade chopper style prop that he feels might do the job.
    Please give me suggestions on a prop. No one around me runs a prop that big that I can try, so I will be most likely ordering one and hoping for the best.
    Thank you
    David

  2. #2
    HavasuDreamin'
    RUNWME:
    This combination seems ok for top speed, but it turns WAY too many RPMS for my comfort level.
    In addition it doesnt get on plane very well(blowing out prop).
    I think you have a good all around prop. You can hit 7K on gas and go to 8K on alcohol. That is right in the range you should be in. The 2.5L Hi Perf. motors are designed to turn 7,500 RPM. Why do you want to spin less than that on alcohol and only spin about 6K on gas. If you go to a 30" prop, or 32" prop, your acceleration is going to be for sh*t and the boat will be extremely sluggish out of the hole. Sure it will bring your RPM's down when running alcohol, but it is going to be a slug on gas.
    You will not find a good all purpose prop for your rig. There is too much of a discrepancy in HP when you run gas vs. alcohol, thus you need multiple props! I would spin a round ear 26" chopper on gas. You could try either a 3 or 4 blade. This will give you good acceleration, better out of the hole, and decent top end. With a 3 blade 26", look for RPM's in the 7,600 range. With a 4 blade 26" look for RPM's slightly less than that.
    Keep the 28" and throw it back on the rig when you run alcohol.

  3. #3
    RUNWME
    Where we ride is on a river with 4-5 mile stretches. When we race, its almost never acceleration, its first one to the next sandbar 5 miles away. My system is set up with 2 15 gallon fuel tanks. I have gasoline in one and alcohol/nitromethane in the other with an electric diverter valve. Running down the water, I can swtich fuel systems on the fly and rotate the enrichment knob on the dash to keep EGT down as I go over to alcohol/nitro for higher speeds. When normal cruising, I just switch back to gasoline.
    I feel that I need to lower the RPMS while on nitro because I am not over 7k for short 1/4 mile bursts, I may be in high RPMS for several minutes covering ground.
    If the best answer is leave it alone, then that may be the path I follow. The combination is certainly acceptable.
    But if I can get longer engine life with a bigger prop and less rpms then I would give up some of the acceleration for longer engine life.
    Thanks
    David

  4. #4
    HavasuDreamin'
    Well that changes my repsonse a bit, but not much. I would try out some 30" props, or a 28" four blade. I think a 32" is way too much. A general rule of thumb is that 1" in pitch is equal to 300 RPM's. Thus if you were to swing a 30" three blade, you would be at about 7,400 RPM. Also, a four blade of the same pitch will reduce your RPM's a little as well.
    I would recommend trying some props out instead of buying one and hoping for the best. That could get expensive. As far as suggestions, I would say to try some choppers and E.T. style props because your cleaver is coming in at 12.8% slip. A better number would be 10% or so which would result in about 89.3 MPH.
    Reality is that very few (including myself) can give you GOOD advice because your set-up is quite different from the norm. You will have to experiment to get the best results. If you truly are trying to save on your engine life, ditch the alcohol/nitro mix.
    Good Luck
    HD

  5. #5
    CATDADDY
    i have a 28 lightning et. like new not a scratch.it would be a great prop for your cougar.$550.obo

  6. #6
    Boatmaster
    That 28et is the ticket, there was a guy in speed alley at the BBSP with a 21 running 101 with a 28et. On top of that the price is right.

  7. #7
    RUNWME
    HavasuDreamin':
    Well that changes my repsonse a bit, but not much. [IMG].
    If you truly are trying to save on your engine life, ditch the alcohol/nitro mix.
    Good Luck
    HD Ditch the alcohol/nitro mix? AND have to listen to my wife fussing about the boat not being fast enough? woooah man.. you dont know my wife!
    argue
    Thanx for advice though... CatDaddy you have mail !

  8. #8
    HavasuDreamin'
    RUNWME
    Ditch the alcohol/nitro mix? AND have to listen to my wife fussing about the boat not being fast enough? woooah man.. you dont know my wife! 300X........300X

  9. #9
    COUGARMAN
    A Mazco 4 blade 28 pitch will bring down your rpms while boosting your hole shot and keeping most of your speed.COUGARMAN

  10. #10
    Boat Racer
    Stick with the ROUND EAR style props.... If you want the beast of both worlds.....
    That motor can handle the rpm range you are running, just DON'T lean it out & run a 32:1 mix!!!!!!

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