1980 Larson Wildfire 5000

[romanowichm]

Hello everyone, this is my first post to SNF. Been here quite often over the past few weeks. Very nice site, love all of the pics.

My father has given me his boat. It is a 1980 16.5ft Larson Wildfire 5000 with a 1979 Mecury 115 inline 6. We bought it new in 1980 and have used it for skiing for 27 years. It has the 25in long shaft a 17 P prop on it. That old Merc has some great holeshot and will pull quite nicely when skiing.

My question is, when pulling up slolumn skier, it takes a little bit. I would like to get some more pulling power out of the boat. The max rating for the boat is 115. Better high-end would also be nice. Ultimately, I would like to throw a 150 on it, and maybe move to a 19P prop. After doing some reading on this website, there seems to be alot of discussion regarding the older inline 6's. Can I get more power out of the existing motor without spending too much? If I put a 150 on it, am I going to get that much more power out of it? I read on 1 post that the older 115's actually had 150HP at the crank.
I am also a little worried about the age and hours of the motor. One of the upper cyclinders was corroded by rust about 6 years ago, my parents had the cylinders honed out to remove as much corrosion as possible. The technician charged us $1500.00 for the procedure. He told us that it was from using cheap oil. We have used only Quicksilver since then. Motor has been running fine. Starts every year and will pull my 205 LB butt out of the water way better than my uncles 17Ft Chettah with 150 Black Max on it. (He also has a 17P prop). Any suggestions would be greatly appreciated.

[j_martin]

Welcome to the board.

The rust in the cylinder was probably caused by condensation during winter storage. You'd also be amazed at the damage a mouse can do if he get into a cylinder , or even the exhaust chest, and makes it his outhouse. The greatest danger our motors face here in the North is winter storage.

Back in the 70's and 80's, when BASS sanctioned tournaments were limited to 115 hp, some of the guys were hanging a 150 inline on hydrostreams and putting a 115 cover on it. They were downright scary to ride in, especially on the river dealing with barge wakes. That might be where the 150 at the crank 115 story started.

Even with a 150 on a fish and ski boat, I use different props for fishing and skiing. I use high fives for both, but I go down in pitch for skiing. It only takes a couple of minutes to change it, and it's good to be taking them off and on frequently, keeping the prop shaft well greased anyway.

hope it helps
John

[DEYS]

The old in-lines are a good motor, but pretty much next to nothing you can do to get more power. The old 90 and 115 were the same motors with different decals. The 90 was prop rated and the 115 was crank rated....same motor. The 140 is basically the same motor with different carbs & porting and is crank rated.

I have a similar boat as yours. I have 3 props, a 15, 17 and 19 pitch. Depending on the intended use for the day I will run a different prop. Sking all day I use the 15 and it absolutly jerks the skier out of the water. The 19 is for fishing and crusing only and will barely pull a skier out of the water (won't do it with a bunch of peeps in the boat either). The 17 is great for "all-round" use, as it will pull a skier and criuse at a decent speed, but it does neither thing well.

The best thing for that engine is premium gas & oil and a selection of props. And put a new impeller in it every season or two depending on use. For the price one a season is a good idea. Another trick with a boat like this to get more speed / better hole-shot, is to lighten the load. If your just sking on that day, leave the fishing gear at home and a few buddies on the dock. It's surprising how much of a difference 25 pounds of dead-weight makes on boat performance. And polish the bottom of the boat at least once a year, clean & smooth is faster than dirty and dull.

[romanowichm]

Thanks for the info guys. Tell me the difference between a 5 blade and a 3 blade prop. Will I get better hole shot with a 17P-5Blade than a 17P-3Blade? If so, why? Same question for top-end. Which will give me better top end?
You've stated that the 90 and 115 are the same, just where they rate the HP is different, given that statement, then a prop rated 150 should definitely give me better pulling power AND top-end, right. There is that thing about insurance though........maybe I need to find an older inline 150 powerhead?

[jay1]

BEST WAY I COULD DESCRIBE... A 17p prop travels 17 inches in one revalution.. a 19p travels 19 inches, and so on.. a 3 blade 19p takes three swipes in 1 revalution to travel 19 inches .a 5 blade takes 5 smaller bites to travel the same distence in one revalution.....

[j_martin]

5 blades gives you a better bite, especially at hole shot time, and also in turns when it might partially surface. It also runs much smoother. You gain in hole shot and driveability, and lose a bit in top end. Not much, though. Pitch is pitch, the definition of how far the propeller wants to go through the water in one revolution. Pitch the prop how the motor wants it, that is to run near the top end of maximum WOT rpm. That will vary with load and use.

The difference between stainless and aluminum is great. The condition of the prop is major, also. A few nicks in the prop can cause significant loss of performance, especially if they aren't deburred. (filed smooth)

The 5 blade prop (high five), if it weren't ventilated, would bog down terribly, and possibly even hurt your engine when taking off. The holes allow exhaust to break it's traction in a controlled way, allowing the engine to spool up into the power band. When you're cruising, the flow of water effectively closes the holes.

On the 150 horse powerhead. If you're overpowering your boat, this trick will get by the casual water cops, but if you get into an accident, they'll tear it down and figure it out. You don't have a speed demon there anyway, so I'd rig it so it does it's job comfortably, and enjoy it. If you want to go fast, you need a better hull to start with, and a bigger engine, and..................................well:
B ring
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A nother
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hope it helps
John