Alpha drive for a V8 whats the ratio?

[ColoradoJim]

Good Morning.
I'm trying to understand the gear ratio on my boat so that I can find a replacement propeller. Boat came with a Mercury Marine Mirage Plus # 48-889620 18P. Right Hand. I think the diameter is 15". This is the Flo Torq II Hub System 835257K1.

My spare propeller is a Michigan Match Aluminum 031052.

I have a 2010 Chaparral 21.5 SSI
5.0 (3.05 Chevy)
Model 5.0 MPI
Drive S/N 1A242230
Alpha One Gen II

Book states my horsepower is 260.

Scott's post indicates my engine s/b 230 HP and the 260 HP s/b the 5.7.

So, I'm confused.

I would like to know the gear ratio (1.47 or 1.61). But what I really need to know is a replacement stainless steel propeller.

My b-e-a-u-t-i-f-u-l stainless found bottom in the 1000 islands last summer. I finished last season using the Michigan Match aluminum spare and the performance simply is not the same..

Thank you in advance for any guidance.

Jim B

 

[Bondo]

Ayuh,..... Welcome Aboard,..... I moved yer post to the prop forum,as that's the basis of yer question,.....

How did the boat behave with the old prop,..??
What was the rpms at Wot,..??

How does it behave with the current prop,..??
What are the rpms at Wot with it,..??
What's the pitch of this prop,..??

 

[Scott06]

A 5.0 mpi is 260 hp Gear ratio will be stamped on the outdrive by the lube vent plug. Willing to bet it is a 1.62:1

In addition to bondos comments if you were happy with the performance and it hits 4800 rpms or so at wot get the same prop.

if you are looking to change the performance let us know what are u looking to do

 

[jimmbo]

I suspect the WOT Range for the Fuelie 5 liter, is 4800 - 5200 rpm. Mercury was placing that Info on the Flame Arrestor Decal

 

[Fun Times]

Serial number 1A242230 shows the drive to be an MERCRUISER ALPHA 1.62:1 DRIVE, model number 5121300TS.

 

[QBhoy]

Rpm range is 4600-5000 and limiter is around 5100/5150 rpm.
You can rarely get a 1.47 ratio on an mpi 5.0, but most would be a lower ratio, I’d think.
Your horsepower is 260hp

 

[ColoradoJim]

Unfortunately I do not have data in order to answers the moderators questions. Boat is in storage and the stainless prop is toast. So I'm unable to recreate the RPM, WOT, etc

However, The stainless prop (Mercury Marine Mirage Plus # 48-889620 18P) was a home run. Efficient, fast on plane, no cavitation. Excellent in all respects.

The Michigan Match with the same geometry (18P Ø15-1/2") simply doesn't accelerate as well as the stainless. Presume the aluminum is deflecting. Maybe not. But it's obvious the engine RPM "holds" as the prop fights to grab enough water to move the boat forward.

My goal is to replace the Stainless propeller with something as close as possible.

Any suggestions?

Thank You,

Jim

 

[jimmbo]

2 or more Props with the same Dia and Pitch, can result in very different Performance. Blade shape, Blade area, Blade thickness, Rake and Cup are the reasons for the difference in performance. As for "aluminum is deflecting" go clamp a Visegrip on a Blade and see how much it flexes. That is just a Marketing Gimmick that has sold many Stainless Props. If there is any Deflection, it is likely in the 1/100" range. Water will adapt far sooner than the Metal will Flex

 

[Scott06]

However, The stainless prop (Mercury Marine Mirage Plus # 48-889620 18P) was a home run. Efficient, fast on plane, no cavitation. Excellent in all respects.

Any suggestions?

Any suggestions?? get another mirage or get yours fixed by a prop shop. If you don't have one near you try Prop MD they have a very efficient and reasonably priced mail order repair service.

As Jimbo lays out when you get into it there is more to it than diameter and pitch. There is no comparison between a Michigan Match, which is as basic as prop can be, and a good SS prop.

If you are one of the folks who has found a prop they are happy with the performance why are you looking to change it ? You are not going to spend less than half the price on an AL prop and be happy with the performance