jdcorbitt3

I am going to repower a Velocity 22 with about 400hp. I am interested in knowing what my prop rpm should be. I would like to top out between 75 and 85 mph with a Bravo 1

Thank you,

John

throttleup

What is the base motor ie: make and model.

Julie

bbladesprops

Obviously the engine configuration is key.

Here is an example.............

5200 engine rpm with a 1.5 gear ratio turning a 28 pitch propeller with 13% slip nets 80mph.

jdcorbitt3

I am loking at a Merc 502at 5200rpm or using a Mazda 20b with about 7000 rpm.

bbladesprops. It looks, by your example, that a 28 pitch should be turning 3500 rpm at the shaft. I am assuming 15" diameter.

John

throttleup

If it is the mercury 502 then you will need to run at 5000 RPM at WOT. I cannot make a recommendation for the Mazda motor, sorry.

Julie

bbladesprops

Yes, with a 1.5 gear ratio @ 5200 the prop would turn 3467 rpm. The Bravo 1's are 15-15.25" diameter even though they are "all advertised as 15.25" Also, the true pitch is aprox. .75"-1" lower than stamped.

Griff

What rpm you turn depends on what rpm the engine was designed for.

Change the prop pitch acccordingly to put your rpms in the correct range.

What drive???? A bravo will more than likely not like 7000rpms.

jdcorbitt3

With 7000 rpm I will need a 2:1 gear reduction to yield that 3500 prop rpm. Thank you. This is the info I was looking for. I was trying to figure out the prop rpm that most props were most efficient at.

John

mmwalters

Save yourself some heartache a mazda 20d will never make enough torque to push your boat the way you hope. I know it will make plenty of HP but it will not work well in a boat. Stick with the BB chevy

offshorebankin

guessing 28 bravo