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1987 242ls 454 magnum prop performance

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1987 242ls 454 magnum prop performance

Old 06-30-2020, 05:00 PM
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Default 1987 242ls 454 magnum prop performance

I currentlyhave a 1987 242 ls with the 454 magnum with a mirage 23p prop. Any suggestions/ comments about this prop and pitch. I believe the max rpm for that motor is 4800 rpms. Right now the highest is 4300 reps. Iíve read other post on off shore and some owners believe a 17 pitch would be better but my concern is over reving. Also does anyone have any comment/ suggestions about Four blade versus three blade. Iím very new at this I/O and big block boating. The motor appears to run well.

As always any help is appreciated.
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Tony S




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Old 07-01-2020, 06:55 AM
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The 21p mirage plus would be what came on that setup to get 4800 rpm.

Personally I would put a 21p mercury revolution on it. The revo (4 blade) planes, turns, and all around handles the boat much better than the m+ will. I've ran quite a few wheels on my 242 and in my experience the revo is the best all around prop. The mirage is a touch faster on the top end, but the handling at all other rpm makes the revo a better option in my experience.
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Old 07-01-2020, 07:13 AM
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Originally Posted by Redneckcustoms13 View Post
The 21p mirage plus would be what came on that setup to get 4800 rpm.

Personally I would put a 21p mercury revolution on it. The revo (4 blade) planes, turns, and all around handles the boat much better than the m+ will. I've ran quite a few wheels on my 242 and in my experience the revo is the best all around prop. The mirage is a touch faster on the top end, but the handling at all other rpm makes the revo a better option in my experience.
i agree with this. I had a 1988 242ss 454 bravo. And the 23 is too much.
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Old 07-01-2020, 07:42 AM
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2 important unique things to keep in mind here. 1987 454 Mag is 330 hp peanut port NOT a Mag. 1987 has an ALPHA drive NOT a Bravo 1.
May want to check with MASI 242 he ended up with a 19 REV 4 prop for his.
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Old 07-01-2020, 07:59 AM
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The 454 330 hp mag/alpha had/has 1.36 gears, instead of the 1.50, too, right ?

Last edited by SB; 07-01-2020 at 10:49 AM.
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Old 07-01-2020, 08:28 AM
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Originally Posted by SB View Post
The 454 330 hp mag/aloha had/has 1.36 gears, instead of the 1.50, too, right ?
Yes sit that is correct.
Hence even a smaller pitch is in order. i.e. 19 Rev 4-4 blade and easy out of the hole, please.
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Old 07-01-2020, 08:29 AM
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Both great points above! Tony, do you have an alpha or has someone swapped it to a bravo? What is your gear?
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Old 07-01-2020, 07:53 PM
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When i had my 242 it did have the Alpha 1.5 ratio some will come with 1.32 gears, Gary i can`t remember what size the rev was never got to try it, but i would try one four blade is the way to go in my opion. Good luck
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Old 07-01-2020, 08:11 PM
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Max RPM for the 87 454 Mag (330 HP) is 4600. The 88 and above is 5k.

You do not want to run the 330 over 4600 for too long. The rods and especially the rod bolts are the weak link and do not tolerate high RPM.

In my opinion youíre probably propped about right. Are you trimming it out? Dropping to a 21P Mirage Plus will probably put you right at 4600.

My 89 242 454 Mag came with a 23P Mirage per the factory invoice... the drive and prop had been stolen when I got it... I went with the same prop and ran 56-58 4700-4800 depending on the weather.

** I would verify the RPM with a digital tach. The old VDO could be off.
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Old 07-02-2020, 06:31 AM
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All 454 mags in 87 to 90 where rated at 365 hp at the prop.
the 1988 bravo 1.5 330 hp 242 would do 54 mph on the speedo mirage plus 21p. 50 ish radar Per factory.
the mag would do 52 radar factory. Mirage plus 23p. Alpha 1.5
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