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| I have a 2001 Lund 1675 Explorer with a 75 merc 2 stroke. Best boat ever, motor is average and starts hard. What to replace with 75 Yamaha but it is 100 lbs heavier than my current Merc. Although Yamaha F70 is the same weight as my current Merc. Not a big speed guy can I get away with the F70 and not loose much performance? Will at times have 3 guys in boat.
Thanks,
Larry
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Posts: 32935
Location: Rhinelander, Wisconsin | Your hole shot and top end will suffer, but the motor should run the boat OK if you maximize the propping. |
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Posts: 1663
Location: Kodiak, AK | What's that hull rated for? That's my first thought. I'd consider the 75 and take the 100 lbs. I'm not a speed demon either, but I went through sorta the same thing a couple years ago; going from 2 to 4 and looking at weights and hp's and I'm glad I maxed it out and my boat runs better than it did before the repower, with the extra weight. The 70 would run that boat, but I think you'd be missing too much going down in hp being used to what you're used to now. My Dad has a 50 on a 1660 ProV and it runs it, but within most situations, I'll take hp over weight....most situations, not all. Especially if the hull is rated for more.
But prop geometry and even prop material can make a big difference.
Edited by esoxfly 10/15/2011 12:10 PM
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Posts: 32935
Location: Rhinelander, Wisconsin | I believe the 100 additional pounds on a boat that size will cancel out any advantage 5 hp offers. |
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Posts: 3508
Location: Elk River, Minnesota | Hiya,
I would bet that there will be a significant decrease in performance by going to the 70hp yamaha. Engine displacement is less in the 70hp along with the added weight... SWorrall is right on that a pitch change downward will be needed and both top end and low end performance will suffer greatly.
I would also agree with fly here...if you can go to more hp (or at a minimum more displacement) I think you would be much happier.
no doubt that the 2 stroke engine has a much better power to weight ratio than the comparable 4 stroke, but things keep improving... but as fly did, he maxed out his hp and loves his rig. I just went through a 2 stroke repower on mine, went from 69 cid in my former yamaha to 104 cid in the equivalent hp johnson... HUGE difference, even though I added close to 100 pounds of weight. 2 stroke to 4 would need even more displacement to get the same performance...
Steve |
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Posts: 1663
Location: Kodiak, AK | sworrall - 10/15/2011 1:24 PM
I believe the 100 additional pounds on a boat that size will cancel out any advantage 5 hp offers.
I expected you'd disagree with me. That's cool. In my opinion, having messed with more than one smaller Lund and 16-17' tin boats in years gone by, which I humbly believe does make me at least somewhat quallified to throw my .02, 5 hp is a more significant percentage of that boat's max rating, than say on a 620. On a 620, sure ditch the hundo pounds for the measly 5 hp, but 5 hp is a decent swing on a 75 hp boat. A hundred pounds is a full livewell and a battery...that's manageable weight to work with. Weight yes, but managable. Guys in 450 lb flats boats mount 75 lbs of dual PP to their sterns and they get by. If the weight is doing you good, it's worthwhile IMO. It's "earning it's keep." |
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Posts: 742
Location: Grand Rapids MN | I have a 2001 Tracker Targa 17WT that had a 75hp Merc carb 2-stroke motor. I didn't have any issues with getting it started and it wasn't a bad motor but I did upgrade. Anyways, you're not really comparing apples to apples with those motors. Not just rated hp and weight but power curves as well. As everyone knows 2 strokes have more torque which creates the hp lower in the rpm range.
As far as pure performance I would agree with esoxfly with the 75hp 2-stroke. May be heavier but the power curve and higher peak power will make up for it. But consider all the things you would like to have in a motor and then choose. I bought a 115 merc 4-stroke and even though it won't quite match up to an Opti other factors led to me choosing that motor. I will say they seem to take a little more tweeking on setup and proping to get the most out of it. Really sensitive to changes for sure.
Good luck man...
Edited by Targa01 10/15/2011 11:00 PM
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Posts: 743
| I have a Lund 1600 Explorer. I repowered from a 2003 Merc 60 2 stroke to a 2008 4 stroke. I actually gained 1 mhp with the switch, not at all what was expected. why don't you put a 75 Merc on it? You might actually get on increase in performance like I did.
It's possible that these new boats with the wider transoms might be designed to run better with more weight on the transom.
Edited by KSauers 10/16/2011 9:35 AM
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Posts: 32935
Location: Rhinelander, Wisconsin | Just a point. HP is measured and listed at the prop now, not the crankshaft. If a motor is putting out 70 at the prop or 75 at the prop, top end will be faster with an exta 5 hp by about 2 mph if the prop they spin is the same and the motor weighs the same. Add 100 pounds, lose speed at about 3 mph on that boat all things considered. Don't know enough about the Yammys to know if they both spin the same prop, that will make a difference. Hole shot with more displacement may be offset by the extra 100 pounds, one needs to prop accordingly which then causes...loss in top end. I'd get in touch with Yamaha and ask them, they might be a little stronger in actual hp at the prop on the bigger block and dead on on the 70, which would cause me to lean toward the bigger motor. |
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Posts: 258
Location: Mayville, WI | The Yamaha 75 spins a 13.25x17 prop while the 70 spins a 13.625x14. Unfortunately, there aren't any performance bulletins for Lund boats on Yamaha's website and they don't have one for both the 75 & 70 on the same hull for boats that might compare to your Lund (I only glanced through Alumacraft).
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Posts: 131
| i heard that you can remove the air restrictor from the yamaha f75 you get a yamaha f90.i heard it was located in the airbox.just something i heard  |
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Posts: 46
Location: Hayward, WI | The F70 is the same displacement as the 50 & 60. The F75 & F90 are about 37 ci larger. The problem is that you get 369# with a bigger 4-stroke. I would always max out a 4-stroke when going from a 2-stroke if the weight is more. I could never see going past a 60 Yamaha in a 4-stroke vs the weight difference. A F60 and F50 are 237# but the F70 is 257# and the F75 & F90 are 369#. So, I believe the 60 then comes the 90. For the 130# weight, you are getting an extra 30hp. An Optimax 75 weighs in at 375# with the 4-stroke slightly more at 399#. Also, the Opti 90 is tahe same weight as the 75 @ 375#.
So the F70 would work but I would put a 90 on it if it would work!!
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Posts: 311
Location: Ontario | I have a 2004 1675 Explorer that's rated for 90hp, and I have a 90hp 4stroke Yamaha on the back. The boat will do 46mph if I need it to, will troll down to 1.3-1.4mph and uses basically no gas when I travel on plane at around 23mph. Unless you're restricted by hp, I would max out the horsepower your boat is rated for. My old boat was a 17' Lund dlx with a 75hp 2 stroke Merc and there's no comparison in any category as a boater or fisherman. I can't think of anything worse than having to shell out for a boat with an underpowered motor based on local lake hp regulations. Probably the nicest thing about my 90 is running on plane and having a conversation using your 'indoor' voice. very smooth and quiet. Not sure how important hole shot is to a wknd fisherman in the 2strk vs 4strk debate, mine sure makes it out of the hole fine. My 90 weighs 385lbs dry. It's a perfect match for the 1675 IMO. |
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