272 boss prop ?

[toyman365]

Hello, First time user looking for a little input. I recently puchased a 1997 baja 272 with merc 502mpi bravo 1 outdrive. I am currently running a mirage plus 25p at approxamently 4500 rpm , Gps shows my best top speed of 62 , Is this the right prop ? The boat has good hole shot for planning out but will cavitat , I want to still be able to get out of the hole but my top speed seems a little disappointing, any suggestions ?????

 

[steelespike]

Re: 272 boss prop ?

Welcome,I'll try to get you started.Do you know your gear ratio? Usually on the out drive.

 

[Philster]

Re: 272 boss prop ?

It's likely a 1.5 ratio.

My Scarab is 27 feet (26.9) and had the same issue.

Low 60's is what the 502 and Bravo 1 on a 1.5 drive ratio can do on these deep V's around 26-27' in length. You could drop down in pitch to a 23p and raise the RPMs, but top speed might not move by more than 1-2 MPH.

I got my RPMs up and speed up a couple of MPH from going 25p to 23p, but the 50-60 range came alive, so it was worth it. Engine gets up near 4900 RPMs now.

No matter how you slice it and dice it, these 27-foot boats with a 502 are low 60's boats. They just are. 60-65 is the typical/normal range, give or take an MPH for different hulls, conditions, etc.

You might be better off just getting the current prop labbed. It's close enough the way it is. I think I'd look at that since it's already a Mirage Plus and you are at the (bottom) edge of the WOT operating RPM range anyway.

A prop shop can add the RPMs and maybe address the cavitation issue, and you'll get a little more top end. I had a basic Mirage, not Plus, so I didn't opt for labbing. I was better off getting a new Mirage Plus at 23p. I'd have the engine declared healthy and consider labbing if I were you.

 

[toyman365]

Re: 272 boss prop ?

Thank you for your help. Yes it's not confirmed but the origanal boat dealer said it was more than likely a 1:5 ratio. I talked to one prop shop and they said they would'nt recomend labbing or what they called super cupping a mirage plus prop. I have been told it is one of the better props to have but was'nt sure if someone recomended a different brand or style. I had the motor checked and at 300 hrs it was declared very healthy , the thought of a pro charger has crossed my mind but I like the idea of turn key weekend play not weekend mechanic . If you have any recomadations I'm all ears . Thank you toyman365

 

[toyman365]

Re: 272 boss prop ?

Without pulling the gears, I contacted the origanal dealer and they said it was more than likely a 1:5 ratio

 

[steelespike]

Re: 272 boss prop ?

any boat that is in the 60 mph range will take a lot if fiddling to gain a few mph.
I'm no expert but I have seen props respond with more speed and rpm with a little cup removed. You allready have a little cavitation issue so maybe not a good idea.

 

[Philster]

Re: 272 boss prop ?

The 24-pitch Ballistic, 3-blade prop from Michigan Wheel has been suggested more than once when I was hunting around.

I had a chance to get the Mirage Plus from my rack neighbor, but I was very tempted to get the Ballistic prop.

Cavitation issue: If you are confident that you manage the drive trim properly, then when hunting or asking about a prop, you should mention it. I find my boat sensitive because these big V's are dependent upon proper trimming. The deep V allows you to move the drive way up, so it's more prone to cavitate.

Shallow hulls and lesser V's don't require the trim so far up, so when they slow, it doesn't have as far to come down, or need to.

That's my two cents on cavitation. Make sure you consider the range the drive moves and how far/often it needs to come down to avoid having the prop cavitate.