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03-23-2018, 08:45 AM #15000 RPM
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Switching to a raker, should I let it vent?
So I just got a 24pitch raker to go on my 120 evinrude. I have my jackplate buried at the bottom so I can trim all the way up without venting my 18 that was on it. Should it vent with a raker or stay buried?
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03-23-2018, 11:10 AM #2Team Member
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It simply depends on what the holeshot is like . I know back in the day the raker 24 was superior to anything else on my Starflite 21 with 225 omc . I made custom insert to fine tune the bleed holes
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03-23-2018, 12:09 PM #35000 RPM
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No no, not the vent holes. I mean should I raise my jackplate up so that it surfaces some at full trim?
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03-23-2018, 12:58 PM #4'71 Glastron V153 - Composite rebuild - Unceremoniously wrecked
'81 Baja 15 SS - "nine-paged" '77 140
'81 Carlson C500 Metric - Currently in foster care
'70 something Speedcraft - Allison 16R clone - Undergoing restoration
'79 Carlson CVZ 19 - Far back burner
WALK TALL AND CARRY A BIG BILGE PUMP
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03-23-2018, 01:33 PM #5
I loved my Raker props. I ran a 24p on my GT150 set-up and an 18 on my 90 before that. They carried the bow really well and delivered almost SRX performance without all the hassles of using over-hub props on holeshot.
The correct height of the prop has a direct dependency and relationship to the amount of set-back you have and need. There is an excellent guide to Pad-V Bottom boats, set-up, chine-walk, bow-steer, driving, and trim here - The the book used to get shipped with every new Allison, but as you'll see - it's not been updated to include the newer and heavier DFI's and 4-Strokes. Gordon
http://forum.allisonowners.net/index...book-pdf.8793/
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03-23-2018, 01:54 PM #6
Raker is a better all around performer than a SRX. Just not quite as fast.
'71 Glastron V153 - Composite rebuild - Unceremoniously wrecked
'81 Baja 15 SS - "nine-paged" '77 140
'81 Carlson C500 Metric - Currently in foster care
'70 something Speedcraft - Allison 16R clone - Undergoing restoration
'79 Carlson CVZ 19 - Far back burner
WALK TALL AND CARRY A BIG BILGE PUMP
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phillnjack liked this post
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03-23-2018, 04:33 PM #7
I ran a 26 on the Baja. 1.4 mph slower than a 25 SRX. Ironically, as best we can tell. The Raker is faster, so far, than the SRX. On the 16R.
Last edited by 71V153; 03-23-2018 at 04:36 PM.
'71 Glastron V153 - Composite rebuild - Unceremoniously wrecked
'81 Baja 15 SS - "nine-paged" '77 140
'81 Carlson C500 Metric - Currently in foster care
'70 something Speedcraft - Allison 16R clone - Undergoing restoration
'79 Carlson CVZ 19 - Far back burner
WALK TALL AND CARRY A BIG BILGE PUMP
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03-23-2018, 05:47 PM #8
And you can pull a lil bigger wheelie with a Raker ...
'71 Glastron V153 - Composite rebuild - Unceremoniously wrecked
'81 Baja 15 SS - "nine-paged" '77 140
'81 Carlson C500 Metric - Currently in foster care
'70 something Speedcraft - Allison 16R clone - Undergoing restoration
'79 Carlson CVZ 19 - Far back burner
WALK TALL AND CARRY A BIG BILGE PUMP
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03-23-2018, 08:47 PM #95000 RPM
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The prop that was on this boat before was an 18 pitch. After the slight mods I did to the motor it has a bunch more power. I really never thought it could get on plane with a 24 but it gets up pretty good. Im more than a little excited to see what it does. I still have the timing turned down to 14 degrees.
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03-24-2018, 09:16 AM #10Team Member
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I had a 23 DAH SRX and a 24 Raker on a 16' Baja/115HO. They ran almost the same, from hole shot to top end. I've sold the motor so if anyone needs an almost new 24 V4 Raker...
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71V153 liked this post
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03-27-2018, 06:01 PM #11'71 Glastron V153 - Composite rebuild - Unceremoniously wrecked
'81 Baja 15 SS - "nine-paged" '77 140
'81 Carlson C500 Metric - Currently in foster care
'70 something Speedcraft - Allison 16R clone - Undergoing restoration
'79 Carlson CVZ 19 - Far back burner
WALK TALL AND CARRY A BIG BILGE PUMP
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03-27-2018, 08:56 PM #125000 RPM
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04-06-2018, 05:45 PM #135000 RPM
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Ok, so I had the ting raised up a few inches to let it vent and as soon as it surfaces the revs go up but I don't gain any speed. actually lost 5 mph off the top. but since I have no idea what I'm doing, Ill ask a few more questions.
after it vents and revs up, should it take right off or take a while to build speed from that point? Ill be honest, I didn't let it go for very long. It just seemed to stall out at 50mph at 5600 r.p.m.
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04-06-2018, 11:42 PM #14
Wolf, no. You've got cavitation - your prop is spinning in a mix of water and air. The air is getting in the blades from being too high for the set-up, it's not getting laminar flow to the blades, or you've got a hub that is spinning inside the hub. Is there a possibility of trying another comparable prop?
I ran Rakers for more than 20 years. Great "do everything prop" when chosen in the right pitch and set-up. Ski, wake-board, tubing, running, fishing - the Raker did them all. Nail the throttle.....motor revs to 2,500~3,000 and the vent holes allow a small amount of slip, but I never hit 4,000 rpm until the boat "breaks over" (that moment when the boat is out of the hole and the drag on the hull is greatly reduced). The prop then bites and moves the boat with about 85% efficiency. I have never, ever had my boats cavitate wildly as you describe. Something is wrong. Gordon
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04-07-2018, 12:02 AM #15
Wolf, as a modified 120 looper, your rpm should easily push the 6,000 mark - especially with a cavitating/slipping prop. Horsepower is a calculation so it can only go up if one or both factors of torque (twisting force) and/or rpm goes up. Torque increases are harder to make since those require significant changes that produce more air and more fuel inside the combustion chamber. What goes in, must also come out so that function has to be changed as well. RPM is a lot easier and often relates to turning a smaller prop for more performance everywhere.
Horsepower = RPM x Torque / 5252
5600 is not at all what I'd expect to see in a looper. I could turn 6,200 with my old GT150 and those heavy cross-flow pistons after some reeds and tuning. I only did it when I needed to impress.
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