420 over reving?
 

I can spin my twin 454 420hp engines to 5700-5800. I was told most can't and that this was good. Should I have more pitch than a Mirage 23P?


I have a TRS with 1:1 stamped on It! It will hit about 60 MPH in a 357 Formula.

Thoughts?

Re: 420 over reving?
 

Go to higher pitch props. Merc recommends 5100 as top rpms. Valvetrain is not designed for that many r's.

Re: 420 over reving?
 

Just as a safeguard, check your tachs. Even with your drives being 1.5 to 1 reduction your prop slip numbers are all wrong. Did TRS come with a 2 to 1 ratio?

Re: 420 over reving?
 

I would start there!! I used to have one of those engines in my Formula. They are great mills!! You can run 'em all day long at 4000! Are you running stock ignitions?

Re: 420 over reving?
 

Tachs are brand new...wait I don't mean that they can't be wrong butI have owned her for 6 years and original tachs would read the same as the new ones installed this year.

Sorry but you lost me with the prop slip and 1.5: and 2:1 ratio's. Here is some info taken from motor/Tranny

Port Motor
Motor B860992
Tranny# 10-18-014
Tranny Serial# 13681
Tranny Ratio 1 : 1

I am assuming you mean prop slip as in cavitation would be worst case sinerio of prop slip correct?

I have only cavitated the prop a few times and one being with a full tank of gas and 18 people on board. And Yes I had enough life jackets. Ya know when one friend invites one friend who invites one friend...sorry back to the subject.

Tell me more about the 1.5:1 ratio. You mean in the drive corect? the Tranny is a 1:1 tranny but the drive would be like 1.5:1 right?

Ignitiion is stock high perf for back in the day! But tachs do read correctly. I did check them with a cheap dig tach when timing them this summer and tachs were correct.

Re: 420 over reving?
 

Your overreving the motors. Prop up at least 2" to get around 5200. You're also going slow for that rpm and pitch. Could be bad props or the fact you're spinning then so fast.
See attached link. BTW, your TRS are almost certainly 1.5:1.
http://www.go-fast.com/Prop_Slip_Calculator.htm
Gary

Re: 420 over reving?
 

Theoreticly your boat should be going 83 mph at 5700rpm if the props are not slipping in the water. My old Scarab 400 would go 58-60 at 5000 rpm with Hydromotive 23 4 blades. I know that Mirage props on heavy boats tend to slip but you're about the worst i've seen. Try to get a set of 4 blades to see if you can cure the slip problem. You'll probably get some more speed and gas milage also.

Re: 420 over reving?
 

Should I go to 3 blade or 4 blade and 23P or 25P?

Are you suggesting 4 blade 25P prop?

What does going from a 3blade 23P to a 4 blade 23P do for a boat? Just as an example.

Re: 420 over reving?
 

If the prop gets a better bite in the water it'll slow the engine down and push the boat slightly faster. From previous experience I'd say stay with the 23 pitch in a 4 blade. If it doesn't slow the engine enough, it can be worked by a good prop shop. Most people are using Bravo 1 4 blades these days.

Re: 420 over reving?
 

I have a friend that sez he has a prop with Bravo stamped on one side and Mirage on the other and they are 23P.

Mine are Quicksilver Mirage stamped on one side and are 23P.

Are these different mfg or what?

Are they using Bravo1 4 blades on TRS's?