proper rpm range

N

Newportme

Petty Officer 2nd Class
Joined
Aug 15, 2005
Messages
113
Hello,

I am an outboard owner, however my BIL has an I/O it is a 1996 mercruiser 4.3l v6. He would like better hole shot the boat takes a while to plane but I don't know what the wot rpm range should be the boat only runs around 3000-3200 right now. This is about half what I am used to but I am ignorant about I/O's. I believe the prop is a 21 pitch I'll check again but I need to know the rpm range to get him in the ball park.

Thanks
Bruce
 
NHGuy

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Re: proper rpm range

I believe you want 4200 to 4600 RPM for that motor. If the boat's not bottom fouled, waterlogged or overloaded and it's running right; then it's time for a lower pitch prop. Quite a lot lower.
 
Bondo

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,095
Re: proper rpm range

Newportme said:
Hello,

I am an outboard owner, however my BIL has an I/O it is a 1996 mercruiser 4.3l v6. He would like better hole shot the boat takes a while to plane but I don't know what the wot rpm range should be the boat only runs around 3000-3200 right now. This is about half what I am used to but I am ignorant about I/O's. I believe the prop is a 21 pitch I'll check again but I need to know the rpm range to get him in the ball park.

Thanks
Bruce
Click to expand...

Ayuh,.... His motor should be seeing 4400/ 4800 rpms at Wot.....

I'd make sure the Motor is up to snuff, before I went screwin' with changin' the Prop though....
 
N

Newportme

Petty Officer 2nd Class
Joined
Aug 15, 2005
Messages
113
Re: proper rpm range

Thanks so much guys, now I might be able to get him headed right. The motor runs like a top, the boat just takes forever to plane and "sounds" bogged down at wot. I just didn't know if that was "normal" nearly all of my experience is with outboards.
 
N

Newportme

Petty Officer 2nd Class
Joined
Aug 15, 2005
Messages
113
Re: proper rpm range

Guys I spoke with my BIL and the outdrive is an alpha 1 model# of464700 can you tell me the gear ratio so I can figure what pitch prop to try. The prop on it now is 21 pitch I believe he needs to drop to a 17 or a 15 any suggestions? boat is a 20' parker cuddy.

Also the boat is dry and clean bottom with paint boat lives on trailer.

Bruce
 
N

Newportme

Petty Officer 2nd Class
Joined
Aug 15, 2005
Messages
113
Re: proper rpm range

He switched to a 15 pitch and could not believe the difference planes much quicker. his rmp is 4750 with 1 person no gear so he should be good with normal running
Thanks for the info

Bruce
 
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