Speedmaster RPM Loss going from 1.68 to 1.5
 

Ive gotten mixed answers of a drop in rpm from 200 to 500rpm. I understand if you drop below your powerban it could be more. Im estimating a loss of 300 rpm. Running the same wheel ofcourse. Now going from running a 17X34 3 blade to a 17X34 4 blade will be another loss of 200rpm. Am I wrong ??? Or on the money !!

The math says 600 less rpm's with same prop. Same rpm's with 31.
As you know there are many other variables at work. Unless someone has tried it on your your boat there is no way to know for sure. If you lose 300 rpm's and slip stays the same you MAY go 4 mph faster. If you are determined to go faster its worth a try. Sure would be nice too try someone else's drive. It's a shame testing is so expensive and time consuming.

Adding that intercooler is going to give all the rpm you lost back...:p
I better get a ride next summer...:cool-smiley-011:

Loosing 700 rpm is alot between a gear change and adding a blade ! An intercooler adding between 75 and 100 hp mite bring back 3-400 rpm. Synthetic oil mite be worth another 100 rpm being the drive holds 10 quarts of mud now. Too bad they dont make a drysump number V !!

Gear ratio change will be about 300-400 rpm drop. The extra blade will be in the 150-200 rpm change. Total 450-600 rpm change. But, as stated earlier, too many variables to be exact.

My guess 500 rpm drop.

Try this for just the math, does not look at any of the other variables. It is really just a percentage.

http://go-fast.com/Prop_Slip_Calculator.htm

I have that Calculator in my favorites . Thats kind of like my bible for testing along with weather and water conditions.

So Zup, when are you going to start testing?
It is going to get into the 60s next week...:party-smiley-004:
You want to race?:p