1.5:1 vs 1.8:1 question

T

thatguy

Seaman
Joined
Jan 4, 2009
Messages
69
I have a question about drive ratios.

I am going to be re powering my boat in the coming months. One of my considerations is that I am going from the 205 hp 4.3 V6 to a 325 hp 5.7 V8. I have been told that i want to go to the 1.5:1 ratio in the drive. I have no problem with this at all. I have a 1.5 alpha 1 unit in storage from my last boat.

My question is, can the larger motor be coupled to the 1.8;1 ratio drive and have a steeper pitch prop be attached to the drive?

This is just a thought that i have, what do you guys have to say?

Tom
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: 1.5:1 vs 1.8:1 question

Nope.
Assuming you are taliking big blocks, With the 1.8 gear ratio, a steeper prop would ONLY work for top speed, if you ever got it on plane. The pitch would be so steep that you would have no hole shot at all. Along with not being able to find a prop with enough pitch to keep the rpms in range. That is why they have different gear ratios. To keep within a working pitch range.

Moving this to the prop forum for better explanations of pitch and gear ratios.
 
G

gemcitypos

Cadet
Joined
Sep 23, 2008
Messages
20
Re: 1.5:1 vs 1.8:1 question

I am finishing up the close to the exact same repower on my boat. However, I put a 260 HP 5.7 in. And an Alpha Drive, if I am not mistaken is only rated to 300 HP.

I used a 23P SS prop on a 1.8.1 outdrive and was 4800 rpms @ WOT. Am now starting to work on the performance issues i.e. holeshot etc. So it can be done. Yet to be determined if you can get the correct performance though.

Hope this helps and good luck.
 
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