95' 150 Rude, foot gear ratio question

[SparkieBoat]

I have this motor on a 17' McKee Craft, I have heard of many people with 150s on boats much bigger than mine running 21-23 pitch props spinning 5500-6000 RPMs, I have a 14x19 prop and spin around 4200 RPMs at WOT at about 34 MPH. I just tried it out with a 15x17 and got it to 37 MPH at 4800 RPMs. Motor seems to be running fine, checked all plug wires, great thick hot blue 1/2" streaks, carbs all cleaned and working fine, seals/gaskets all good. New fuel pump. I am wondering if a previous owner could have put a foot on this motor that has a higher gear ratio. How can I check my gear ratio and what is it supposed to be??? Hopefully I can check ratio without pulling the foot off. I defiantly believe that this is not the original foot it has the four bolt bearing carriage instead of the tabs and the internal water screens.
Thanks Sparkie

 

[SparkieBoat]

Re: 95' 150 Rude, foot gear ratio question

ok I did some research..it seems that the V-6 came with a 1.86/1 gear ratio and the V-4s came with a 2.25/1 gear ratio..I did some math with 37 MPH at 5000 RPM and came out with 2.175 so if I am off 1 or 2 miles per hour ( I used the old MPH gauge installed on the boat , not a GPS) it could easily be the 2.25/1 V-4 foot on my motor..so I think I answered my own question. But any further input would be appreciated.

 

[SparkieBoat]

Re: 95' 150 Rude, foot gear ratio question

darn I am stumped again, I have been looking at this gear ratio thing backwards.
I ran some more math.. a 2.25/1 with a 17 pitch prop @ 5000 RPM should be moving at 35 MPH. A 1.86/1 with a 17 pitch prop should be moving 43 MPH @ 5000 RPM. So if I do have a V-4 prop with a 2.25/1 ratio my V-6 150 should need a higher pitch prop than what would be used with a 1.86/1 ratio. I turned my fly wheel around less than 2 full turns to rotate my prop one full turn..so I think that I do have the 1.86 gears. Now I am back to wondering why my motor will not spin these low pitch props much faster..I should be able to spin a 21 pitch prop over 5K easy

 

[SparkieBoat]

Re: 95' 150 Rude, foot gear ratio question

I found a really cool site.
http://go-fast.com/Prop_Slip_Calculator.htm