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If I'm running max about 4600 rpms on a pair of new Alpha MR drives with 21p Laser-II drives. I have thru hull exhaust with a pair of built up 302's.
The boat leaps on plane even though a heavy 25ft boat.
Question I have, If the max HP can be reached in the 5000rpm range. Should I pitch down to 19's...? Initial thought would be the obvious, going to 19's I loose speed but pick up RPM or is it a wash with no real gain.
If I hit the gas hard on the 21's I can cavitate the props a bit once I bolted on the alum. heads.
OR is this where lab finishing props come in? Or 4 blade Mirage props. Any thoughts?
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I have always had the best luck turning higher RPMS.. the motor runs better and there is just not that much stress on the system.. Also if you talk to some prop guys, you may find that when you downsize the prop, spin it a little faster you may go faster depending on what the boat needs.. You may need some bow lift ,transom lift, slip or less slip.. Those things can be labbed into the prop..
good luck
I know on my OB... we tried 5-6 props before we decided on one for the Parker 300.
If you talk to a prop guy.. they will usually let you try different ones before purchase.
good luck
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If I'm running max about 4600 rpms on a pair of new Alpha MR drives with 21p Laser-II drives. I have thru hull exhaust with a pair of built up 302's.
The boat leaps on plane even though a heavy 25ft boat.
Question I have, If the max HP can be reached in the 5000rpm range. Should I pitch down to 19's...? Initial thought would be the obvious, going to 19's I loose speed but pick up RPM or is it a wash with no real gain.
If I hit the gas hard on the 21's I can cavitate the props a bit once I bolted on the alum. heads.
OR is this where lab finishing props come in? Or 4 blade Mirage props. Any thoughts?
You want to prop your boat for were your max Hp is at the engine rpm so yes you would want to prop it for 5k. you may go faster with the 19 pitch props, or you may not, or you might see the same speed. You will probly get better fuel consumption
