increasing top speed

[smike26]

I have a 16ft Glastron Carlsong '78 with a 115hp Merc. I have read of people getting 60mph+ with this configuration, I only get about 35mph. What are some methods for increasing my top end. My prop is pitched correctly but needs to be replaced do to wear. I run premium fuel at 50:1. Motor seems to be strong, compression is at about 90psi on all six. I have gone through full range of trim with no improvement.

 

[Texasmark]

Re: increasing top speed

90 is low. I ran a 18 ft Ranger Fisherman with a 115 at 55mph, 24 pitched prop. Premium fuel means nothing to me. Did mine on regular (87 octane).<br /><br />Sounds to me like you are suffering from Glastron hull drag problems, but 35?<br /><br />Get some decarb.<br /><br />Mark

 

[79Merc140]

Re: increasing top speed

I have a 1996 Glastron GS-160 with a 1979 140 tower that is equal to todays 115's, and at 6,000 rpm's I am doing about 55+ (17P alluminum 3 blade).<br /><br />What is your Wide Open Throttle rpm? Should be as close to 5,500 as possible (A little over is fine) with just you in the boat.<br /><br />Craig

 

[studlymandingo]

Re: increasing top speed

35 sounds waaaaaay low. What is the prop pitch and your WOT RPMs? Maybe you have a lot of water weight in the hull. The compression sounds a bit low too.

 

[phatmanmike]

Re: increasing top speed

most good strong inline mercs have compression #s up in the 125, 135, even 150 range.<br /><br />my last 1150 had over 160!<br /><br />do a decarb, make sea foam your new lover !<br /><br />how far down is the motor mounted? do you have trim stabs? do you have a jack plate? is the bottom of the hull clean and smooth? what pitch prop do you have? what are your WOT rpm's? what does your boat weigh? whats your favorite color? how much weight can a sparrow carry?<br /><br />these are all serious questions!~

 

[Chris1956]

Re: increasing top speed

Mike, I think it will be hard for you to get 60MPH. However you should get into the 50s with that setup. I will guess not all of your cylinder are firing due to a bad ignition system, water in the cylinder, bad link and sync or carb issues.<br />I recommend a prop in the 19-21" pitch range, which should be optimum.