help with Bravo 3 to Bravo 1 swap
 

Hello,
I have a 1997 Chaparral 2335 with 2001 Merc 502 (warmed up by Teague to 500 HP) and a Bravo 3, the 26" Merc props have been worked (thinned and cupped) and take the boat to 64 MPH (5200 RPM).

I want more top speed (I am looking for 70 MPH) and I have been told ditching my B3 for a B1 is the first step (anyone agree of disagree?)

To swap to a Bravo 1 and I need help... I assume that the lower unit will bolt right on (right?) but I need help with gear ratio, Etc.
Is the Gear ratio in the upper part or is it in the lower unit (or both?). I have been told that I currently have a 2:1 ratio, what do I need?
Do I simply buy a lower unit (if so what ratio?) Do I have to change the gears in the upper? (am I better off buying a new upper and sell everything I have?)

Suggestions on Prop size? Suggestions on where to get parts? or suggestions on who in the Portland Oregon area would a good place to take it?)

Any help is greatly appreciated
Mike

The upper is the same as a B1 in a 1.50 ratio once you install a B1 lower (that is all you need to do).......not sure where to start for a prop but if your hitting 64 then a 24 to 26 sounds close. Maybe someone with the same boat will chime in.

I assume your looking for more speed at WOT.........you might find 1-2 mph by doing this but will likey LOOSE speed at all other rpms.

I was led to believe that switching from a B3 to a B1 would give me 4-5 MPH more top end.... I know that I am going to lose out of the hole power, but I thought that it was a acceptable l trade off and that the I would have to switch if I ever wanted to break the 70MPH mark. Am I wrong?

The B3 is more effective for hole shots and mid-range while the B1 is better for WOT speed. The B3 tends to create more drag than it can overcome somewhere in the 60-70 mph range. While 4-5 might be possible, my uneducated belief is the difference is much less than that. Now, if your comparing trashed B3 props to new B1 props then you might see a bigger difference and assume the drive is what caused the increase.

If you can spin that 502 5200 rpm with a 1.5 B1 24p you will see close to 71mph.

which lower do I need?
 

What do I need to buy to make it happen? Do lower unit come with different gear ratios? Or are they all the same and the gear ratio is determined by the upper gears?

I am told that i currently have a 2 to 1 ratio if I simply bolt on a B1 lower will I be within a a range that I could get a prop that would take me to 71 MPH?

If you are spinning your engine at it's optimum now, I doubt you'll see a big increase at the sppeds you are running. Yes, drag is less with the B1, but slip will go up also with the B1. I'm in the 2, maybe 3 mph camp- and that's after you play with props, etc.

That thing is big and loaded for a 23 foot boat. Not sure what the dead rise is though. So really you dont have the optimal tool for the job, A legitimate 500 hp should push a 23~24 sport boat to 70. You do realize you will be making trade offs?? With the b1 it will wander more in no wake zones, its liable to lean more, your holeshot will suffer, your cruise will be less efficient and your handeling cous start to get interesting... Do you have decent steering and tabs??

The boat weighs 4870 pounds ready for the river (everything in it, 50 gallons of fuel, 2 bags of ice and 24 beverages).

The dead rise at the stern is 22 degrees, my Billet trim tabs are 12" wide x 16" long and I have stand up bolsters too (not that increases the speed).

I know that this is not the most performance minded boat on the market but it is far from a pig, It is more than 1000 pounds lighter than Sea Rays, Etc of the same size and the quality of construction is great through out (My last boats were Eliminator Daytona and Baja).

I know of a boat of the same model that does an honest 71 MPH (GPS) with a 454 carb motor that is stock expect for the ProCharger that is "supposed to" have 500 HP (rumor has it that a stock 90's 454 carb motor with a Pro charger is actually something like 470 HP)

Do any of you have B3's running at 70 MPH or above? I have been led to believe that B3's just don't work over 65 MPH

Chris has a B3 on one of the batboats and a volvo duoprop on the other, both run well over 70 with 500 hp small blocks, but they are light and stepped. To the point just moving them around the yard the weight difference between a batboat and my 22 (3500#) is obvious.