Want more performance out of my Mariah

[mikesnowman]

I have a 96 mariah Z200 LTD 20 foot, with a 5.7l mercruiser alpha one. By the book the weight is 2550 pounds. I currently have a 19 pitch "Rapture" which has been reworked. My issue is that the top speed has never exceeded 50 in any conditions. GPS verified. The rpms are almost 5000. From what I can find it seems I should be around 4600-4800. I am fairly convinced that I need a 21 for more top end. Wemainly pull the kids on tubes, and cruise. No skiing yet. I am looking for any prop advice.
Thanks

 

[Bondo]

Re: Want more performance out of my Mariah

Wemainly pull the kids on tubes, and cruise. No skiing yet.

Ayuh,... Stepping up to a 21" might/ will Kill your hole shot...

All you can do it Try it...

 

[jkust]

Re: Want more performance out of my Mariah

Something seems amiss. That is by far the largest I/O in the lightest boat I have ever heard of. Most bowriders that weigh that much will have a 3.0 or 4.3. I can't hardly imagine a 5.0 in there much less being rated for a 5.7. I can get more than 50mph on GPS with a 4.3GL and 2900lb dry weight plus gas,gear and passengers.
What is the rated hp of your 5.7? Is it not a vortec? I can't get past the fact it is a larger v8. If it was a 4.3 I could see your situation. Something besides the prop pitch isn't adding up in my head.

 

[steelespike]

Re: Want more performance out of my Mariah

Problem with changing from a reworked prop is unless you know exacvtly what you have now there is no way to be sure of your results.And if you change brand and or style adds another variable.Assuming same brand not reworked to same brand going to a 21 will generally lower rpm 300 to 400 rpm a rough estimate.
And as suggested may add some speed but will most likely kill your hole shot.

 

[mikesnowman]

Re: Want more performance out of my Mariah

I am only referencing the literature for this boat. It does state 2550 lbs. It is a 5.7l 2 barrel V-8 alpha one. When I bought it the rapture prop on it was vibrating badly so I had it rebuilt. What would a Mercury lightspeed 20 pitch do? I want more top end but do not want to give up much hole shot. I suppose I try to find a good used 21 and see what happens? Any recommendations would be much appreciated.
Thanks

 

[Tail_Gunner]

Re: Want more performance out of my Mariah

This is just a opinion but a 4 barrel carb and a 20 pitch stilletto 4 blade....... Well lets just say youd grin a lot...Raptures are not the best on a I/o

 

[mikesnowman]

Re: Want more performance out of my Mariah

For a 4 barrel (LX) I would need to change out he intake also correct?

 

[Tail_Gunner]

Re: Want more performance out of my Mariah

Take the question to I/O's...But you will have to remove the valve cover and take the head casting number to determine if you have a true vortec head...96 was a crossover year i believe it could be the new head design or the old.

Different intake for both designs anyways you should be delighted with the results if it you indeed have a true vortec head..