Opinion on upgrade from 50 hp to 75 hp

[judavis126]

Have a Lowe stinger 170. Im thinking of upgrading from the 50 hp Mercury 2-stroke to a 75 hp 2-stroke. Will this make a noticeable differce in the ride and speed. Do you think the upgraded power will be noticeable. Whats your opinion on the upgrade.

Thanks

 

[DJ]

Re: Opinion on upgrade from 50 hp to 75 hp

You will definetely notice the additional 25 ponies. I can't speak to speed increase but the hole shot will be better.

 

[judavis126]

Re: Opinion on upgrade from 50 hp to 75 hp

Does anyone know if the bolt holes will match up or where to find that kind of info on the net.

 

[Silvertip]

Re: Opinion on upgrade from 50 hp to 75 hp

Depends on the years of the engines for the bolt holes. I swapped a 50 Evinrude for a 75 Merc on a boat similar to yours and yes, you will notice a difference -- a lot of difference. Better hole shot, better cruise, and better top end. Ride won't change much because that's more a function of the hull than the engine. However, the 75 will hold the bow up a little better so there will be less hull in the water at top end with proper trim. When you make the swap, add Nauticus Smart Tabs and you will transform the boat to a real performer.

 

[DJ]

Re: Opinion on upgrade from 50 hp to 75 hp

Does anyone know if the bolt holes will match up or where to find that kind of info on the net.

Somewhere, in the mid eighties-I think, the bolt holes for all the major brands became the same.

 

[AGENT 37]

Re: Opinion on upgrade from 50 hp to 75 hp

I wouldn't expect much difference in ride going from a 50 to 75 2 stroke. But if you went from a 2 to 4 stroke I bet that you'd notice a difference in ride. I have a home built 18' welded aluminum boat and recently replaced my 70 2 stroke with a 100 4 stroke. The ride has changed drastically with the added weight; when I come out of the water the stern settles faster which gives me a smoother ride. I tend to run hard in rough water and with the lighter 70 the bow used to come down really hard and pound through the waves. The angle of attack utilizes my deep V hull a lot better now. The difference in hole shot, top end speed, and fuel economy is night and day. I gained about 18 knots on top end, the hole shot tends to move unsecured things in the front of the boat to the back very quickly, and can run better speeds at lower RPM which comparatively uses less fuel. I wouldn't be surprised if you get better fuel economy with the larger 2 stroke motor as long as you don't constantly run at WOT. I've found that to be a challenge though, having more HP I still use every bit of it anytime the conditions allow!

 

[Silvertip]

Re: Opinion on upgrade from 50 hp to 75 hp

Actually, at WOT a two stroke and 4 stroke of the same horsepower on the same boat will burn very nearly the same amount of fuel. I will not go into more detail here as there are plenty of posts that concur, including a fuel economy study i did on 75 motors some time back. it's all a matter of physics -- it takes so much fuel to make so much horsepower.

 

[AGENT 37]

Re: Opinion on upgrade from 50 hp to 75 hp

If you read my post again you'll see that I wasn't talking about the difference between the 2 and 4. Just that a boat that is under-powered and run to the floor generally burns comparable fuel to a suitably powered boat run at lower RPMs. My 2 stroke 70 went through the fuel because I had to run it constantly at WOT. My 4 stroke 100 does a lot better because I don't have to run near WOT to produce the same performance. I've found the same result in 2 strokes that I've had in the past too. A bigger motor just doesn't have to work as hard. But that's not the topic of the started thread..... Go with the upgrade to 75, it'll pay off.

 

[rndn]

Re: Opinion on upgrade from 50 hp to 75 hp

50% more power, go for it!!

 

[MikDee]

Re: Opinion on upgrade from 50 hp to 75 hp

Yes! Do It!,,, Weeee! are we havin fun now?

 

[scoutabout]

Re: Opinion on upgrade from 50 hp to 75 hp

My dad bought a Wilker Galaxie 15 back in the early seventies with a Merc 40 on it. It was noisy, underpowered, and guzzled gas moving that deep v hull around. Then we upgraded to a Merc 70 in the mid eighties and it was night and day...except for full economy, which stayed about the same. Big engine working easy versus small engine at WOT.

To paraphrase that well known saying. "No one at the end of their life ever said I wish I had spent more time at the office...or kept the smaller motor..."

 

[achris]

Re: Opinion on upgrade from 50 hp to 75 hp

To paraphrase that well known saying. "No one at the end of their life ever said I wish I had spent more time at the office...or kept the smaller motor..."

Don't mean to hijack the thread... but I am one who has changed from a 'smaller' engine to a bigger one and regrets it.

Just to answer the original poster's question... On a boat that size Upgrade to the bigger engine, definitely!

On to my story. I had a Mercruiser 165 in the boat for the first 8 years that I owned it. Changed that to a 4.3LX, making 180 propshaft hp. That engine was great, but suffered from one problem that annoyed the living daylights out of me! The carb dribbled after shutoff. It would flood the engine and cause hard starting. I couldn't fix it, even had carb experts and the manufacturer deny the problem existed. A year ago I changed the engine to a 4.3MPI, making 220 propshaft hp. Fixed the dribbly fuel system problem, but I now have too much power. With the old 4.3 the torque curve appeared to be flatter and the engine was untroubled at most revs. I could easily choose a cruising speed and the boat would run on that speed happily. With the new engine I have trouble maintaining a steady speed if the engine is under 3000rpm. It will either die in the arse and slow right down (11 knots) or try and build speed and make the ride too harsh. I have tried fiddling with props and load distribution, all to no avail. I am currently running a 17" prop. That seems to give the best performance, but I still have to ride the throttle when trying to maintain anything in the 16-20 knots range. At WOT the rev limiter is pulling up at 5200rpm (40 knots). If I put the 19" prop on then my WOT is right on 4700 (recommended 4400-4800), but she will not hold a speed of less than 22 knots (3000rpm) without the risk of dying off. I put all this down to being 'outside the torque curve'. And I really wish I had my old motor back!!

0.02

Chris............

 

[MikDee]

Re: Opinion on upgrade from 50 hp to 75 hp

AChris, do you have a hydrofoil, trim tabs, or a Stainless steel prop? all of these items help you stay on plane easier, and hold your boat at your throttle setting much better so I've found. It's almost like having cruise control! You probably have an idea of how the frst 2 work, but I think less flex in the SS prop equates to less slip, and more grip on the water at all speeds.

 

[achris]

Re: Opinion on upgrade from 50 hp to 75 hp

AChris, do you have a hydrofoil, trim tabs, or a Stainless steel prop? all of these items help you stay on plane easier, and hold your boat at your throttle setting much better so I've found. It's almost like having cruise control! You probably have an idea of how the frst 2 work, but I think less flex in the SS prop equates to less slip, and more grip on the water at all speeds.

I currently have a 17" Vengence SS on. I have tried 3 blade and 4 blade ali props. I have tried SS Laser II, Offshore, and Vengence. Any I've missed?

No foil... Refuse to have one. Period. Too damn dangerous. I may go to tabs one day....

I'm going to talk to the engine supplier when I get home and see if we can change the ECM set up to flatten out the torque curve. I would be willing to sacrifice top speed to get the mid range a bit better.

Chris..........

 

[AGENT 37]

Re: Opinion on upgrade from 50 hp to 75 hp

How big is your boat? Trim tabs may or may not help..... Do you feel that it is an issue of the hull settling or the engine loading up?

 

[AGENT 37]

Re: Opinion on upgrade from 50 hp to 75 hp

Trim tabs are worth the trouble for all the reasons that they are useful.

 

[achris]

Re: Opinion on upgrade from 50 hp to 75 hp

How big is your boat? Trim tabs may or may not help..... Do you feel that it is an issue of the hull settling or the engine loading up?

It's definitely an engine problem... The previous 2 engines (165 and 4.3LX) didn't create the same problem. The last one was exactly the same weight. Both 4.3 litre. I have a friend who had the same hull with a Mercruiser 470 and he said tabs definitely benefited.

Chris.............

 

[whofan]

Re: Opinion on upgrade from 50 hp to 75 hp

I have a 1650 Lund Fisherman that came with a 1999 Johnson 50hp 2 stroke. I traded it for the same motor in a 2000 70 horse. I can cuise at 3/4 throttle with the 70 at what was wide open with the 50. You will see a difference and maybe even save fuel with less throttle.

 

[steelespike]

Re: Opinion on upgrade from 50 hp to 75 hp

It appears the 170 is rated at a 75 hp max.and weighs close to 1,000lbs dry.
Go for it Set up carefully and driven within the 50s speed range it will use close to the same fuel and not work as hard.Then you'll still have that extra boost when you need it.