difference with a 225 hp jetboat powerhead vs a 2.5 outboard

[Yubz]

Hi,
Here is my story, I baught a 225hp powerhead of a jetboat and it fits a lower unit !
So on my boat a have a jetboat powerhead on a lowerunit.
It's a hydrostream Valero.

The engine is a mercury, I have no idea about the tuner or whatever it is !
I run a 28inch chopper at 5000 RPM and it is very hard to go higher 70 mph
I run a 21 inch alum prop and it's had to get more than 5500 RPM 55 mph
I run a 23 inch Hi Five prop and it's hard to get more than 5300 RPM 60-65 mph

My question is, about the porting, does it makes a difference on the torque or the High rpm.
I don't have any picture yet.
But I want to know, what do you think about this kind of configuration !?
about the porting and etc ...

[wired247]

Jet motors often have rev limiters. Might want to check there first.

[Motv18]

The amount of drag from the boat is changing with the different speeds generated by the different pitches on your props. Common in v's "go faster less wet more pitch." You can climb a v without a flat dead rise clear up on its ass with enough power.

[Yubz]

So relatively to the engine, does it makes some difference !? about the porting and everything ?

[tlwjkw]

About tha only difference in tha rotating assembly is tha crank splines. ..

[wired247]

Not on the outboard jets. Same splines.

[tlwjkw]

Not a sport jet?

[Dave Strong]

Regardless of the power head those #'s don't make sense. Do you have a hyd jack plate? If you can turn a 28 chopper to 5000 you should turn a 23 High Five to well over 6000. JMO.

Dave

[Dave Strong]

Wired could be on to something with the rev limiter.

Dave

[wired247]

They make sense if you figure the outboard jet motors have rev limiter modules.

[tlwjkw]

'nother ? What block assy do they use ta get 225 with a pump? Same as 240 SJ?

[wired247]

I don't know.Ii still havent figured out what the OP has. If its is a 225 3.0 outboard powerhead it could have a rev limiter with an outboard jet. They didnt make a 225 outboard jet in 2.5 liter. They did make a 240 I/O jet which is the same thing as a 225 promax more or less BUT it has different splines. The 200/140 outboard jet is the same powerhead but he is claiming a 225. That makes me think he has a 3.0 225 outboard jet.His description of what he actually has sucks. At least where I'm at its easier to find 2.5 outboard jet motors and convert them to prop lowers than it is to find good 2.5 prop lower motors.

[Yubz]

I Will hâve dyno number this week and i hâve mwv 6 carbs i am not à super pro about it and if i hâve à 3 liter engine, it was fitting the Alien cowl of bob

[Yubz]

I hâve à hyd jack

[wired247]

I Will hâve dyno number this week and i hâve mwv 6 carbs i am not à super pro about it and if i hâve à 3 liter engine, it was fitting the Alien cowl of bob


You have 3.0 liter 225.

[Yubz]

thanks to you all for your help ! it was very helpfull !

Hubert

[Kevin Turner]

They didnt make a 225 outboard jet in 2.5 liter. They did make a 240 I/O jet which is the same thing as a 225 promax more or less BUT it has different splines. The 200/140 outboard jet is the same powerhead but he is claiming a 225.
Although rare, there were a few 2.5 carb'd / 225 HP Sport Jet power heads

[Yubz]

which year was it !?

[wired247]

Don't confuse outboard jet powerheads like you have with inboard jet powerheads which you don't have.

[Kevin Turner]

which year was it !? If your question was directed toward me; MY-2000 / I could be wrong, but I can't recall seeing a OB Jet limiter kick in below 5600 /

[Yubz]

good inpupt ! I am still waiting for dyno numbers !

[KIRCHNER]

you say you can run 70 @ 5000! w/ 28p your # dont seem correct. and a 21 only turns 5500? somethings off.... try a 24 0r 26 chopper.

[cdubya]

Have you verified the tach is reading correctly?