conversion for high altitude??

[QXlineguy]

I'll soon be moving from sea level to Colorado. I have a 3.0L Mercruiser/alpha. I have been told that a gear change to compensate for the altitude (6000ft.) is necessary. I looked into the price and found it quite spendy. I currently run a 21in. pitch prop. Will changing to a 20 or 19in. pitch be ok or will I have to bite the bullet and go for the gear change. any suggestions on what to do?

 

[Haut Medoc]

Re: conversion for high altitude??

Welcome to iboats <br />You will need to do some carb adjusting, or fuel delivery modifications, since you didn't post your year I don't know exactly what you have.....<br />Post up your serial #'s & you will get a more definitive reply.....<br />You do not want to run to lean, though....<br />A gear change will not be necessary.... <br />New prop, maybe, maybe not, depends on what you use the boat for.....JK

 

[lilmandavis]

Re: conversion for high altitude??

talk to mile high mariner about that. hes a 3 liter guru!

 

[waterdog85170]

Re: conversion for high altitude??

what part of colorado? as far as gear change you cant do one cause you already have the lowest ratio in your 3.0(we use 6 cyl gears with v8 and 4 cyl gears with v6) drop a prop size and go from there. i have a 3.0/merc myself, if your gonna be close to me, i have a few props we could experiment with.

 

[QXlineguy]

Re: conversion for high altitude??

It's a 2004 model engine s/n 0w009717 drive s/n 0w518591. I use the boat primarily for wakeboarding. So top end speed isn't really a concern. I would however like a decent cruise speed. 25-30mph is what I would like to shoot for. I'll be spending most of my boating time out on Horsetooth lake near Ft. Collins.<br /><br />I originally bought the boat in denver. they changed the gears for me to 2.2:1 no carb adjustment. Then I moved to Seattle and had the gears changed back to 2.0:1. I'm really trying to not have to change the gears again if possible.<br /><br />If a carb adjustment is necessary, where would I find a manual to give me the proper steps on doing it right.

 

[Mile-High Mariner]

Re: conversion for high altitude??

Hold on, there WD - Mercruiser has a 2.4:1 drive ratio conversion for high-altitude 3.0 boaters (QX's quoted 2.2 ratio uses the gears for the conversion they recommend for V6/V8 Alphas), but it really isn't necessary unless you do ALL of your boating above 5,000 feet. QX - you'll benefit from rejetting your carb down one or two jet sizes; you have either 1.55 or 1.60mm jets (Quicksilver OEM, about $3 a set from your local Merc dealer), depending upon the carburetor number (it's stamped on the side of the carb), so you'll be looking for something in the 1.50 range. You'll the technical info in the MerCarb section of the Mercruiser Service Manual (http://www.boatfix.com/merc/Servmanl/13/13B5R2.PDF). For now, make sure you lean out your mixture to prevent carbon build-up. <br /><br />Also, 19" props for use above 5,000 msl is a pipe dream if you want to maintain printed RPM ranges and prevent lugging. You will more likely need to drop to 17" or even 15", again, depending upon your usual operating altitude. I think you'll probably want the 15", since you're more interested in hole-shot; it'll still give you good top end, at least as good as you've stated that you want. I have props ranging from 23" (for use for good top-end at low-alt lakes and at places like Powell) all the way down to 13" (for up at Blue Mesa (~7,500 msl) and higher lakes like Big Creek (~9,000 msl)). Like my tagline says - "Gotta have attitude at this altitude!"<br /><br />Don't bother with the gear ratio conversion. It's expensive, as you've discovered, and will screw you up if you ever want to run down and enjoy a weekend with your friends at Meredith or Pueblo.<br /><br />P.S. - if you want to drop me your e'mail, I'll keep you posted re: the forced-induction project I'm working on for guys like us, with lower-displacement motors operating in high-altitude environments. It's goal is NOT to produce obscene amounts of horsepower (I'm working on a separate 3.0 project that will yield normally-aspirated output in the range of 150 to 185 hp), but to maintain at least sea-level manifold pressure at altitude - effectively, turbonormalizing using a belt-driven supercharger.<br /><br />It's all in the 'tude, dude.....

 

[Capt Ralph]

Re: conversion for high altitude??

QXlineguy,<br />I have a 3.0 in a 18ft bowrider. I was just up at Horsetooth last weekend and managed WOT with a full tank and one other person at about 35mph and 4500 rpms running a 17P aluminum prop. Wake boarding I usually never go above 15-20mph, FWIW mine has always run fine up here with this set-up. <br /><br />-CR

 

[Mile-High Mariner]

Re: conversion for high altitude??

QX - Ralph is doing well with his 17" prop on a lake at ~1900 msl. Your 6000 msl elevation will still call for a lower pitch due to the drop in ambient atmospheric pressure at your altitude. The power loss doesn't really become apparent in these motors until the 20% loss you experience by the time you exceed 5000 msl; at 2000 feet, Ralph has only lost about 8%, which is not really detectable yet. The manufacturer is allowed a quote range of +/- 10% on output, so the 135 hp 3.0LX may be putting out as little as 123 hp or as much as 149 hp to begin with, and the 115 hp 3.0L as little as 104 and as much as 127 hp.<br /><br />By way of clarifying, I'll back up Haut Medoc's post - you DO want to lean out your mixture, but you don't want to run TOO lean or you'll end up burning your pistons or valves. Adjust it carefully, according to book procedures, and keep an eye on it until you can swap the jets.

 

[Mile-High Mariner]

Re: conversion for high altitude??

Wait a minute - Ralph, I just noticed your location ID - you were at Horsetooth up near Ft. Collins and I was thinking of HorseSHOE Res. down in Arizona. Sorry for the mixup - QX: the elevation at Horsetooth is a little over 5000 msl, so Ralph is doing quite well with his 17P at that altitude. It wouldn't surprise me if we discovered that he was running a Stingray returning those numbers, but there are other hulls that will give startlingly better performance that the rest of the pack can't match, and trim and configuration make a big difference, as well.

 

[QXlineguy]

Re: conversion for high altitude??

I took the boat up to horsetooth yesterday and to my surprise, ran better than it ever has. Didn't get it up to WOT due to the rough seas. I'm thinking about putting a 18P four blade on there. Any thoughts on that? I'm taking it up to the lake this evening (depends on the crowd) to give it the test.

 

[Mile-High Mariner]

Re: conversion for high altitude??

I have a 16P 4-blade stainless that I use when I'm up high (higher than Horsetooth, for sure), so your 18P 4-blade should work fine for your purposes. It'll have good holeshot authority and should keep your RPM and speed up where you want to be. Never hurts to give it a try!

 

[Capt Ralph]

Re: conversion for high altitude??

QX,<br />That's the thing about Horsetooth it always seems to be rough water unless you out first thing in the AM or late in the afternoon, and on windy days forgettaboutit!! Let me know if you get that 18P 4 blade.....I haven't seen too many I/O's out here with 4 blade props mostly only bass boats with 200+ HP outboards.<br /><br />Mile High:<br />No Sting Ray hull here....It's a 93' Monterey 180SCR. I'm not sure if these hulls are faster than the rest of the pack but I have only seen one other older Monterey here in CO.<br /><br />-CR