Maxum 2400 SCR 1999 Prop Selection

[afirststep]

I just bought a 1999 Maxum 2400 SCR with a 5.0L Mercruiser. (Wife loves loves the upgrade from a W/A and head!)

With two people the boat runs WOT at 4100RPM at 36MPH with a 14.5X17P 3-blade Michigan AL prop. (prop rebuilt recently.)

With 6 people and 35 gal fuel, the boat will not make it past about 3400RPM and not get up on plane. (Yes I tried to use the trim tabs and engine trim to get on plane. Also shifted people forward...)

NOTE: trim tabs work, Compression 190-195psi all cylinders, rebuilt 2bbl carb, fresh fuel (Blue enzyme and ethanol Stabil added), fuel pump pressure check OK, new fuel filter/separator, boat hull is clean (Trailered).

I was debating with my boat buddy if a SS 14.5X15P or 14.5X17P would be better. Since the top end should be 4400-4800PRM, I have 300 RPM to give to the 15P prop. It would improve the hole shot and allow the boat to get on plane easier and with a bigger load. He says that a 17P SS will not flex and would solve the high load hole shot problem and retain maximum cruise efficiency. We were also debating putting a fuel injection add-on to boost the HP from 230 to 10-20HP more....

Help! Is it possible to rent props to try both pitches (15P and 17P) out before purchasing? Can anyone make an educated guess which way to go? (Are we both wrong?)

Thanks!

 

[QC]

Re: Maxum 2400 SCR 1999 Prop Selection

Welcome aboard. Thanks for the info. You should have a 1.62 gear ratio and it looks like all of your numbers stack up. Cool

I just bought a 1999 Maxum 2400 SCR with a 5.0L Mercruiser. (Wife loves loves the upgrade from a W/A and head!)

Congrats.

Are we both wrong?

You're closer to right.

He says that a 17P SS will not flex and would solve the high load hole shot problem and retain maximum cruise efficiency.

Backwards. Stainless does not flex so hole shot is usually worse . . .

Some prop shops (this place included) have prop "loan" programs to help you get it right. I think the 15 is probably the way to go. That is a big load for a 220 5.0L. While EFI would help, there are a whole bunch of other reasons (search I/O section) including cost and possible legal and safety issues that will make this impractical.

Please report back with any details. Also, find any weight that you don't absolutely need and chuck it

 

[John_S]

Re: Maxum 2400 SCR 1999 Prop Selection

Instead of the pricey fuel injection, consider an Edelbrock Performer Intake and 1409 4brl carb. You will get another 20HP. That is about the extent of the "cheap" HP. A good winter project if you have someplace to work on the boat. Save yor pennies for a 350 or 383 reman down the road.

 

[afirststep]

Re: Maxum 2400 SCR 1999 Prop Selection

QC, Thanks for the reply.
I am confused about the less flexing and worse hole shot. Could you please explain why? Maybe the term hole shot is confusing me.
Novice, Andrew...

 

[QC]

Re: Maxum 2400 SCR 1999 Prop Selection

Yeah, no prah dude . . .

If the blade flexes under acceleration (at full load too) it is effectively "flexing" to less pitch, so it it may act like a 16 1/2 pitch instead of a true 17 with no flex (stainless). So the 16.5 would have better hole shot (acceleration from a stop, getting on plane etc.) than the same prop if stainless because it's effective pitch is lower than it's static pitch. A little counter-intuitive, but true. Like slightly gearing down.

Keep asking, we'll all answer what we can.

 

[afirststep]

Re: Maxum 2400 SCR 1999 Prop Selection

John_s,

Thanks for the reply. I looked up the intake and carb. Great suggestions.
I also found that some people only changed the carb and got better results. I guess they also need a mounting adapter and fuel line re-routing. Could I just change the carb? (I have Rochester carb...)

Thanks, Cadet Novice.

 

[John_S]

Re: Maxum 2400 SCR 1999 Prop Selection

John_s,

Thanks for the reply. I looked up the intake and carb. Great suggestions.
I also found that some people only changed the carb and got better results. I guess they also need a mounting adapter and fuel line re-routing. Could I just change the carb? (I have Rochester carb...)

Thanks, Cadet Novice.

You should have a 2brl Mercarb (similiar to Rochester, but only one idle mixture screw). While some Volvo's have a 4brl intake manifold with a plate to run a 2brl, Mercuiser didn't do that. You will need a 4brl intake for vortec heads. They have a Performer eps that should work great on a 5.0L. If you are raw water cooled and boat in the salt, you would need to find a marine version.

 

[afirststep]

Re: Maxum 2400 SCR 1999 Prop Selection

I looked into the 4bbl carb and the need for a new manifold. Well, $500 gets both. :facepalm: I will save pennies for the upgrade since the 14.5x15 prop did the trick. Thanks for the advice.

Instead of the pricey fuel injection, consider an Edelbrock Performer Intake and 1409 4brl carb. You will get another 20HP. That is about the extent of the "cheap" HP. A good winter project if you have someplace to work on the boat. Save yor pennies for a 350 or 383 reman down the road.