gear ratios

9

91rr

Seaman
Joined
Apr 21, 2011
Messages
55
What is a common gear ratio for a 19ft deep v with a 260hp 350? I have an 86 Cobra with high altitude gears, 1.49:1 I think. What would be the effect of running that low of a ratio compared to a higher one? Can the ratio be easily changed? Or should I just bite the bullet and get the SEI conversion? But then that brings me back to what gear ratio should I look at?
 
9

91rr

Seaman
Joined
Apr 21, 2011
Messages
55
Re: gear ratios

Nobody? Come on I know there are people out there running 5.7's with Cobra outdrives. What gear ratio are you running?
 
Howard Sterndrive

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
Re: gear ratios

if you get the SEI conversion, the ratio for a 5.7 is 1.5:1, same as what you report having now. are you having issues?
 
9

91rr

Seaman
Joined
Apr 21, 2011
Messages
55
Re: gear ratios

Howard Sterndrive said:
if you get the SEI conversion, the ratio for a 5.7 is 1.5:1, same as what you report having now. are you having issues?
Click to expand...
The main issue I have it just seems to under powered even though I just dropped in a brand new 5.7. I replaced an 86 5.0 because I just thought it was getting tired. On the bottom end I noticed a tremendous improvement but I really only gained about 400 rpms and about 3mph on the top end. I am only getting about 35 mph @ 4400 WOT. Everything forward of the fuel tank is new to include, carb, fuel pump, and dissy. I even ran from a separate fuel source to eliminate problems with the tank. I figured the only 2 things left are the outdrive ratio or the fact that I live in Denver and the dang altitude is just robbing the heck out of my HP.
 
Howard Sterndrive

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
Re: gear ratios

I suspect altitude has a lot to do with it. Anyone with a propshaft dyno around your area? Could dyno it.
that is awfully slow for a 19 footer though.

My take on high altitude drive ratios: if a dealer runs out of propeller options at high altitude, they can regear because once you get into 13p or 11p props, you lose a lot of efficiency at higher speed (I *think*)

if you can get wot rpm with prop swap and you're still using 15P 17P 19P or 21P (i.e. efficient pitch propellers), then a different ratio isn't going to improve anything.
 
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