Big Pitch Drop?

[jmarty10]

Here is my setup:
1. 2008 Larson 180 - 18 foot fibergalss i/o witha 4.3l 190 hp TKS, alpha one. Dry weight= 2300lbs
2. Running a factory mercury alum prop that is 14-1/4 x 23p prop
3. WOT with about 650 lbs aboard = 4700 rpm going about 47 mph

I have been pretty satisified with the performance as prop stays in RPM and speed range. My question is? I have a couple of old 14X17p alum props from the old boat. What will be the effect in dropping the pitch by this much? I have been considering getting a 4 blader to help with hole shot when tubing and staying on plane longer. Will the 17p do this. Also, given the above what pitch is recommended on my rig when going to a 4 blader?

 

[86 century]

Re: Big Pitch Drop?

The general rule of thumb is 200rpm per inch of pitch. This will very due to differences in design from one manufacturer to another.

Going to a 17p will most likely put your wot rpm way above max for your eng.


In most cases going from three to four blades you would go down one inch in pitch.

23p-3blade = 22p-4blade Again prop design will effect you rpm as well so these are not hard and fast rules more like loose guide lines.

 

[Tail_Gunner]

Re: Big Pitch Drop?

You say you have a TKS alpha if so is this a description

TKS 4.3L V-6​

• Both the TKS and MPI Mer Cruisers use the same 4.3-liter V-engine block. With a modest 9.4:1 compression ratio, it will run on 87 octane pump gas. The TKS delivers 220 horsepower at 4,400 to 4,800 rpm. The primary difference between the two engines is their aspiration. The TKS uses a multi-port fuel injection system. With all other components and specifications being the same, the TKS's fuel injection system provides slightly more head flow and better aspiration, delivering more power and fuel economy.

• 
  If that description is correct you have a bad speedo or something is not right...A 18' glass boat with a 220hp v6 should be above 50mph...You may want to post the gearing stamped on the leg of the outdrive....might want to check your tach to...:redface:....I seem to be on a tach rage
  

 

[jmarty10]

Re: Big Pitch Drop?

The TKS is the 190 hp. Where did you get this from? All my docs, manuals and test specs on the boat list the TKS as 190 hp.

 

[Tail_Gunner]

Re: Big Pitch Drop?

http://www.ehow.com/list_7687350_alpha-one-43l-v6-specs.html Opps guess i should have sourced the real source...

http://www.mercurymarine.com/engines/inboards/sterndrives/tks4-3l_features.php

I wouldnt drop below a 20 or 21....17 she'd scoot pretty go from 0-35