Prop Size ? for single engine 454 MPI ?
 

I have a 99 Donzi 28ZX with a single 454 mpi engine. It is currently running a Hydromotive 4 blade 20 prop. Does anyone have any recommendations for maybe going to a larger prop to gain a few more MPH ? Thanks

Re: Prop Size ? for single engine 454 MPI ?
 

Need some more information. How many RPM do you get spinning the 20 Hydro? How fast are you currently going? Does it ride bow high or stern high (hydro's normally carry the stern if I remember correctly)? How is the handling?

Labbing a prop usually gives you another 200 rpm or so... but if you are already at redline with the 20 Hydro, you might have to have them add an inch of pitch when they lab it to bring the rpm's back down, which results in more speed.

There are some merc. dealers who have specially painted (blue) loaner props. Or ask some of your friends with performance boats if you might borrow their prop for one spin around the lake. I'd think that if the 20 hydro works, you might like a 22 Merc. Bravo One prop (especially a labbed one).

'Foul

Re: Prop Size ? for single engine 454 MPI ?
 

Like Waterfoul said we need a little more infomation about your boat.

What is your WOT RPM and MPH (gps)?
What prop and pitch are you running currently?
What is your gear ratio?

I am sure with a little information we can take a step indialing you in.

Julie

Re: Prop Size ? for single engine 454 MPI ?
 

We have had great success on ZX's with Lab Finished Bravo 1's

Echoing everyone else, we need to know the current rpm and speed of your rig to determine the correct pitch to work with.

Re: Prop Size ? for single engine 454 MPI ?
 

Ok, sorry for the delay. I had to get the boat back in the water.

I took it out with 3 people and 90 gallons of fuel and it ran consistently 58mph (speedo) at 5200 RPM's.

Let me know what other information you may need.

Thanks

Re: Prop Size ? for single engine 454 MPI ?
 

Sounds like you are under propped to me... Need more pitch... possibly a 22" or possibly even a 24" labbed Bravo One. By yourself and with less fuel you are going to be banging the rev limiter...

Also ask yourself, how will you be doing most of your boating? Light fuel? You and one other person? Or will it be heavy fuel, big cooler of refreshements, and several friends? If it is the latter, you are about right on... maybe have your prop tuned down a few hundred rpm to say, 5000 rpm with a loaded boat?? There are several reputable prop shops advertising here on OSO that can "work" your prop for you.

'Foul

Re: Prop Size ? for single engine 454 MPI ?
 

Assuming that you have a 1.5 gear ratio then it appears that you have 12% slip which is not bad for a 4B propeller. I agree with Foul that you need a taller pitch propeller.

Are you able to put full trim into her as well as full throttle? This will help us to determine exactly how tall of a pitch you may need. Additionallly how is the attitude of the boat? Do you like the way she feels or carries?
What are your goals? This information will help us to provide you with propeller suggestions.

Julie

Re: Prop Size ? for single engine 454 MPI ?
 

These guys are right. A little more info as to your goals and a prop suggestion can be made.

So far I like Waterfouls suggestion on the 24 Bravo 1 Lab. It has been a good match for your rig in the past.

Re: Prop Size ? for single engine 454 MPI ?
 

Normally I will have probably (4) people and at least 1/2 a tank of fuel.

Definetly have hit the rev limiter if I try to trim it up all the way. When I have a full tank and 4 people I can trim it up a little more but in only one instance have I been able to trim it up all the way without hitting the rev limiter and that was with a full tank of gas and 5 people.

With (4) people and it trimmed up a little it runs great, gets up on plane quickly....no complaints so far. Just looking for a little more top speed.

Re: Prop Size ? for single engine 454 MPI ?
 

As the boat sits deeper in the water you could trim it farther.

If you go up in pitch and Lab Finish to regain the rpm, your peed should follow.