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'89 formula 272 sr-1 only 55mph with twin454 ? >

'89 formula 272 sr-1 only 55mph with twin454 ?

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'89 formula 272 sr-1 only 55mph with twin454 ?

Old 06-03-2019, 10:41 PM
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Pat, how did you like the small blocks in that boat? Were they reliable?... lots of torque to push that beast, no?
thanks
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Old 06-04-2019, 07:42 AM
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My 89 272 with 330s ran 64 with 25 mirages at about 4500rpm
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Old 06-06-2019, 01:56 PM
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Originally Posted by lokipk View Post
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.
you boat came from the factory 23 mirage plus. 1.5 :1 bravos. Thats what would work best for you; the 23 mirage plus should put you at 62 ish gps. A 4 blade should be 20 pitch. You have too much pitch for a 4 blade on that combo
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Old 06-10-2019, 11:14 PM
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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.
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Old 06-10-2019, 11:17 PM
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I might try to check the silent thunder before changing props with a light and mirror before messing with props etc.
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Old 06-11-2019, 10:12 PM
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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

Last edited by lokipk; 06-11-2019 at 10:16 PM. Reason: K
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Old 09-03-2019, 07:16 PM
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Following
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Old 09-04-2019, 09:58 AM
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My 1991 272 SR1, has a factory made hook in the hull which limits speed.
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Old 09-04-2019, 04:08 PM
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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.
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Old 09-22-2019, 08:58 PM
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Type error. My props were 23 pitch.
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