Crownline 225 CCR is slower than expected!!

[cableguy1979]

I have a 1996 Crownline 225 CCR with a 454 Mag. To give a little on the history and clarify Ill make it brief. I bought the boat from a friend as i knew it but it had a bad valve guide i had to replace and had to put a new lower Bravo on the boat which came with the boat. Rebuilt the floor, new carpet and took it to the water. Bought a mercury 14 1/4 x 18p 4 blade cast prop. took it to the lake and tested everything out. Boat seems to be doing fine. Takes off fine, planes and cruises seemingly normal but took it slow. I then decided to buy a stainless prop Laser II 14 1/4 x 25p 3 blade prop. Boat is kinda sluggish taking off unless I use the trim tabs to get it up and it does fine. I decided to test top speed with GPS. 55 mph at 5000 rpm. Put the 18p 4 blade back on 45 mph at 5700 rpm. Boat doesn't feel like i remember. To many RPM's and not enough speed to be gained. The guy I bought it from says the boat does 68 mph on a 21p prop. After all the research I've done the 454 mag with a Bravo in a 22.5ft boat should do around 64 mph. What can cause this to happen? I haven't tried a 21p prop yet but the laser II 25p should be best case top end I would think. If it was the coupler Id expect burning rubber, rpm raising to high, If it was a spun prop hub something very similar with RPM. If something is slipping its doing it evenly enough I cant notice through the full RPM range. He gave me a 24p 4 blade Bravo prop that needed redone and said boat ran 64 mph with cooler and two people with that prop. Can there be anything else causing it to drop 10 mph surely with a 25p 3 blade prop 55 mphs isnt top speed. I know of the same exact boat with a 5.7 that does 52 mph. Ive read similar boats with a standard 454 runs 55 mph with a 21p but ive got almost another 100 hp on those with the 454 Mag. This engine is a rare option in this small of a boat. No wet foam, rear bench and sun deck is out of the boat, No odd noises or smells. Could something in the upper clutch be slipping? I dont expect the motor is a problem since its turning 5700 rpm. The lower unit I put on shouldn't have the gear ratio in it as its in the upper I think and its original to the boat. Any help or test?

 

[roffey]

I did a quick search on google and we all know how reliable that is, lol. Mr. Google reports with a 21 inch prop you should do 62 MPH. I once had a spun prop and it feels like a bad clutch, it just revved up and did not get on plane. I would think 5700 RPM is to high so you would need more pitch? I know I'm not helping you with any useful information so I'll just sit back and let others answer your questions.

 

[alldodge]

Try using the return key some more to help us read your comments, there all mushed together

Max WOT should be 4800 unless you have changed things. The TBV ignition should be hitting the rev limiter

Might need a new tach, and are you using a GPS for speed?

 

[wahlejim]

Exactly what did you do to rebuild the floor? Why did it need rebuilding? What all did you inspect while rebuilding?

 

[cableguy1979]

Yes to GPS for speed. I have been told the rev limiter on this boat is around 5800. Ive also been told 5100 from the manual. Either way I dont believe the tac is off but Ill find out. There was no doubt she was turning pretty hard. Although mine is a 1996 454 MAG EFI/MP i read the older mags didnt have a rev limiter. Previous owner said hes heard it hit the rev limiter before. I dont know but will find out. Either way the top speed with a 25p prop is 55 and seems a bit slow to me. Like the comment above I would expect it to be 62 with a 21p prop. Is there anyway the 25p could be over propping it causing it to lose top end?

 

[alldodge]

I have been told the rev limiter on this boat is around 5800.

They where lying to you, the 96 MPI 454 has a WOT of 4600-5000 and rev limiter by the ECM around the 5150.

And Knot 4 Me has some good comments at OSO
https://www.offshoreonly.com/forums/general-q/362921-crownline-225-ccr-454-mag-slow.html#post4706272

 

[alldodge]

A 21 I can see 60 mph, but a 25 would just lug the motor and keep it from reaching WOT. If it did reach WOT rpm would cause me to wonder if there is to much trim and the prop is ventilating

 

[cableguy1979]

Thats exactly what it seems like. The prop may be ventilating and is probably the best advice yet. Maybe thats the case and the 21 will help. I will try it but if I put the 21p on and its 52 mph WOT is there a possibility im looking at gear ration in the upper having been changed? How many gear ratios did they make for a bravo one for the 454 mag efi/mp

 

[alldodge]

In order to determine if its slip or other we need good numbers.
Drive ratio
GPS speed
Prop pitch
RMP

As example my 300 hp 454 Rinker with 3-blade 21 pitch prop and 4800 rpm (1.5 ratio B1) will just hit 60 mph. Put these numbers in the prop slip calculator it comes to 6%, which is dang good for a 4200 lb cuddy.

http://bblades.com/propeller-slip-calculator/

Your boat shows up as 3900 lb

 

[cableguy1979]

Ok I will put a 21p on it and get all the numbers above.

 

[alldodge]

Ok I will put a 21p on it and get all the numbers above.

Before you take the run find out where the trim is when the vent plate is dead even and level with the bottom of the keel. Do one run at WOT with the trim at this point and record the numbers.

My guess is you should have a 1.5 drive

 

[cableguy1979]

Ok ill give it a try this weekend.