Offshoreonly.com - New Prop starting point

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Do yourself a favor, call Brett @ BBlades tell him your set up, he has a great testing program that's a lot cheaper than just guessing at buying and trying props, that can get costly very quick, what you think "should work" on paper often times does not work in real life.

What is the diameter of your current props? Some model info on them would be nice. Run what you have for a base line test, it'll only cost you fuel.

Get these numbers. It's the way to really give some good advice, no matter if you get it here or call Brett.

Max inteded rpm for your new power.
Max rpm with new power and current props
Top GPS speed with current props.
Drive ratio.
Props make/model/pitch/diameter

Good luck with it.

Quote:

Originally Posted by Griff (Post 3646588)

All props are not the same. Trying to compare completely different props based only on pitch does not work.
Your numbers are all over the place if you just look at pitch. If it spun 23's at 4600 and you were only spinning 21's at 4200, then the engines would have been down on power around 100hp each from when it was original or something else was wrong. Were they 3 or 4 blade cleavers...big difference.
Exactly what 21" props were you using???
You boat, being older probably has a deep X dim and will probably run the fastest with some Mirage plus props, but it may porpoise easily.

You did not say if you switched cams??? I hope so, because if not, I highly doubt you'll gain more than about 40hp.

Some box stock 23's should be a good starting point and will get you a baseline.

Going from 4200rpms to 5000rpms takes at least 100hp gain(per engine).......and that is with the same props.

Not quite sure I will buy 40hp per side. I have done all the homework.....I have many articles with dyno pulls that show going from the crappy stamped steel rockers with 1.47 ratio to full roller 1.6 alone bump hp by 36-41hp, all by themselves.

More importantly, what about props causes a boat to porpoise?? I noticed that when I switched props at certain speeds it does porpoise much easier, but either a lil tab or trim takes care of the issue. Curious because if I was to run 3 blades the mirage + is what I would go with.

Mirage Plus props are bow lifting props. They will try to lift the bow and without enough speed or power, the boat will porpoise. It can be controlled with the correct trim and tab.

A switch from 1.50 to 1.60 rockers does about the same thing as upping the cam one size. No way it will increase the engines hp by 15% with just that change. With your rocker swap, you might see a 60hp gain.