Posts: 3479
Location: Elk River, Minnesota | Hi again...
Same response here as over on MH... The extra 1/2 will cut down on your RPMs somewhere around 200 or so and, you may get better handling. If you go stainless, you will gain durability, and with the prop options out there, plenty to try to find a prop that best matches your driving style.
I went and worked your numbers...
5400 RPM with a 21 pitch prop and a 2.33 gear ratio gives you a theoretical speed of 46mph. You are getting 42 which is rougly a 9% slip of the prop. (very respectable). But...your motor has an RPM range that is maxed at 5750. I feel you are over-propped by just a touch. Now...If you go to larger diameter, this slip might drop to say 8%, but you will also lose the approximate 200 RPMs which is going in the wrong direction. Theoretically here again, you will now have a motor that produces only 5200 rpm, and 40...maybe 41 mph.
If you are running aluminum currently and you switch to a stainless, in most cases the recommendation is to go down 2" in pitch because of the minimal amount of flexing the prop blade made of steel has as compared to aluminum. If you make a diameter change AND go to steel, you will be well under your RPM range now......somewhere around 400 or so...
I will say this...from your other post on MH, a diamter was never stated, and I made a poor assumption about the pitch...my fault there and my apologies to you. Your's would be higher due to the gear ratio at 2.33:1 as compared to many others at 2:1.
My gut tells me a switch to a steel would help out, but keep as close to the same diameter as possible...and I feel you might want to be prepared to drop in pitch as well...overall I think You've got great numbers right now in terms of slip...just a little low on RPM...
I have heard the lazer is not a very good prop, but the mercury Tempest and vengeance have gotten some very good reviews. I don't know sizes available, but it's a start. I still feel if you can get a Michigan Ballistic in your hands to try you will be quite happy, but then again, testing the props is what you will need to do...
On my 90, the ballistic didn't lose any RPM's from my stock aluminum, but it hooked up much better, and I was able to raise the motor up two holes for a better top end, and it also lowered the front of the boat during hole shot...
Steve
Edited by VMS 2/1/2008 9:15 AM
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