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Only hitting 45-50 at max RPM for 454 mag

Nuke

New member
just picked up a 97 253 convincor with a 454 mag/bravo 1 over the winter. The boat has 620 hours on it and I’m running a 23p mirage prop. It’s the 365 hp mag motor.
Everything I’ve read says I should see at least 60 out of the boat. I ran it the other day and according to my tach I was at 5100 rpms only going 54-55, and when I brought it to 4500 rpm which is essentially the max for the motor, it slowed me down to 50-51.
If I’m cruising at 3k rpm, or about 30 mph, anything other than full down on the trim will cause a cavitation.
Am I being unrealistic with this boat or am I propped wrong/spun hub? Something doesn’t seem right
 
just picked up a 97 253 convincor with a 454 mag/bravo 1 over the winter. The boat has 620 hours on it and I’m running a 23p mirage prop. It’s the 365 hp mag motor.
Everything I’ve read says I should see at least 60 out of the boat. I ran it the other day and according to my tach I was at 5100 rpms only going 54-55, and when I brought it to 4500 rpm which is essentially the max for the motor, it slowed me down to 50-51.
If I’m cruising at 3k rpm, or about 30 mph, anything other than full down on the trim will cause a cavitation.
Am I being unrealistic with this boat or am I propped wrong/spun hub? Something doesn’t seem right
What is the final drive ratio, 1.5? If it is 1.5, then the prop slip is 26% at 5100 rpm and 55 mph if your tach is accurate. The slip typically decreases the faster you run. At 4500rpm, and 51mph the prop slip was 22% (if the tach was accurate). I find that unusual, unless you were trimmed too high at 5100 rpm causing more slip. Is the prop in good shape? If 4500 rpm is the max range, you might want to try a Bravo 1 four blade with at least 24P. If your tach is accurate and you can really turn a 23Mirage at 5100, a 26 Bravo would likely still run 4500 rpm, but I think the slip will come down with that prop so it might not turn quite that high. It is a guess but I would try and get my hands on a 24 or 26P Bravo 1, and try it and then you can decide if you need the other pitch Bravo or not. I'm sure some other members with a similar boat / engine combo will let you know what they are running.
 
I would just point out that there are a lot of unknown variables to consider when making comparisons but agre somethings not right. Start by verifying that your tach is correct and speeds are in gps. Has the prop you are running been worked? How many hours on motor and is compression good? Does it need a tune up? Is trim gauge/ sender accurate? Depending on conditions and how boat is loaded you should be in low 60’s. You need some chop to get some air under the hull. I’d say Merc is conservative on wot range. There should be rev limiter at 5150 or so. I would expect a good 23 Mirage Plus should be about your best top end speed prop choice, but many run bravo or hydromotive for better handling. I doubt it could swing a 26 bravo with that power. Good luck with it
 

miller

Active member
And usually cruising a 3k should be around the 40mph mark instead of about 30. Definately need to confirm your drive ratio.
 
And usually cruising a 3k should be around the 40mph mark instead of about 30. Definately need to confirm your drive ratio.
I used to own a 496Mag 230SX Stingray with a 1.5 drive ratio. With a 23 Mirage (not a Mirage Plus), 3000 = 37mph, 4000=52mph,4500=59 mph, and 4950=65mph. All values were GPS. The last two values were with about 10.5% slip. With a 25 Mirage Plus it ran 4750 at 67 mph. That does not meant the Checkmate will do exactly the same with a 1.5 drive ratio because the slip numbers might be different. Some members with the same boat can give you their slip numbers, top end and rpm. Again like many have pointed out, accurate tach readings, GPS readings and drive ratio are required.
 

PA-Checkmate

Active member
Something doesn't add up? Wonder if the prop was reworked at sometime and didn't work out well. Can u try another prop from a friend? Just doing the math a 23P prop should be good for 60-63. I also had 502Mag 230SX Stingray similar to Glenn and would run 64 with 23P mirage I now have 270 w/496HO and currently just put on BBlades worked B1-24p
 

PA-Checkmate

Active member
Had BBlades lab my bravo-1 24 pitch and barrel shortened, but only been out 2 times so still figuring it out. Here is what I can say... with 60+gal fuel, 2 riders I now hit the limiter(beeping) at 67mph. Most noticeable improvement is when under about 45mph I don't need to use tabs to control porpoise along with less positive needed.

270 Convincor w/496HO
 

miller

Active member
Nice, thanks. The bravo prop on my old 251 really makes it lean to the starboard bad. Running a 25" rev4 right now. Would love to trim off some of the barrel to gain some bow lift..... but Im too chicken.
 
I used to own a 496Mag 230SX Stingray with a 1.5 drive ratio. With a 23 Mirage (not a Mirage Plus), 3000 = 37mph, 4000=52mph,4500=59 mph, and 4950=65mph. All values were GPS. The last two values were with about 10.5% slip. With a 25 Mirage Plus it ran 4750 at 67 mph. That does not meant the Checkmate will do exactly the same with a 1.5 drive ratio because the slip numbers might be different. Some members with the same boat can give you their slip numbers, top end and rpm. Again like many have pointed out, accurate tach readings, GPS readings and drive ratio are required.
Sorry, I made a typo. My Stingray had a 25P Mirage Plus, not a 23P.
 
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