'89 formula 272 sr-1 only 55mph with twin454 ?
06-06-2019 | 12:56 PM
#13
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Joined: Sep 2008
Posts: 460
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I have a '89 formula 272 sr-1 with stock 454 merc 330s and Bravo1 drives... spinning 4 blade 24p bravo props
Gps is 55mph at 4400rpm.
seems a bit slow to me for that set up.
anyone have ideas or different prop setup for this rig ?
any and all input is welcome. This boat is new to me this season. My other boat is a 78 Donzi 21GT with single 330 trs spinning 23inch 3blade cleaver... hits 68 on gps at 4900rpms. Fun, reliable and solid...she's a champ.
the new boat is great size wise, but thought it would be 10-12mph faster...
again thanks in advance for any ideas.
Gps is 55mph at 4400rpm.
seems a bit slow to me for that set up.
anyone have ideas or different prop setup for this rig ?
any and all input is welcome. This boat is new to me this season. My other boat is a 78 Donzi 21GT with single 330 trs spinning 23inch 3blade cleaver... hits 68 on gps at 4900rpms. Fun, reliable and solid...she's a champ.
the new boat is great size wise, but thought it would be 10-12mph faster...
again thanks in advance for any ideas.
06-10-2019 | 10:14 PM
#14
Charter Member
Joined: Jan 2001
Posts: 1,237
Likes: 2
From: south east of dome island
an inexpensive test could be to put the cleaver from the GT on the left drive and keep the 4 blade on the right to check rpm and speed, If rpm on the left is good and speed increases then proceed with a Mirage 23 on right, then match port to it. if rpm is too high on the cleaver side then go mirage plus, in a set, there is about 100-200 rpm drop from standard mirage to plus. mirage non plus is close to the cleaver in rpm.
good luck, Chris
bravo 4 blade= ok all around , best cruise
Mirage non plus thinner blades = best top end
mirage plus, good top end and better planing and cruise than non plus
all based on std drive heights. as you go up everything changes.
oh , also, if props do not help some then sometimes the baffles in the silent thunder can come loose or fail and reduce the power output by restricting exhaust flow.
good luck, Chris
bravo 4 blade= ok all around , best cruise
Mirage non plus thinner blades = best top end
mirage plus, good top end and better planing and cruise than non plus
all based on std drive heights. as you go up everything changes.
oh , also, if props do not help some then sometimes the baffles in the silent thunder can come loose or fail and reduce the power output by restricting exhaust flow.
06-11-2019 | 09:12 PM
#16
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Joined: Mar 2017
Posts: 22
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Thanks for the prop tips!
can anyone explain the difference in hull attitude in reference to twin prop rotation? Meaning spinning in/ towards each other vs. spinning out/ away from centerline?
pk
can anyone explain the difference in hull attitude in reference to twin prop rotation? Meaning spinning in/ towards each other vs. spinning out/ away from centerline?
pk
Last edited by lokipk; 06-11-2019 at 09:16 PM. Reason: K
09-04-2019 | 03:08 PM
#19
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Joined: Sep 2005
Posts: 186
Likes: 1
From: Cincinnati, Catawba Is. Oh
be sure to post your results! I have an 89 272 with 25p Mirage (non plus) and 330/bravo's, tops I've ever gotten is 60 mph. (I rarely get flat enough water for speed runs) I think my carbs need tuned up. plugs showed me running rich. motors got 650hrs.
I feel you on the porpoising. I have to run at least 45mph before I can get the drives or planes neutral, WOT is the the only, and I mean the only, way I can trim up both drives and planes.
I feel you on the porpoising. I have to run at least 45mph before I can get the drives or planes neutral, WOT is the the only, and I mean the only, way I can trim up both drives and planes.
