What harm does lugging do?

[MarkHPCA]

I have read many places that it is bad to lug a motor. If I run my '86 120 looper at a WOT of 5300RPM is this considered lugging? If so what harm is done over time to the motor?<br /><br />How is this different than having a WOT of say 6000 RPM but using less throttle and never going over 5300 RPM?

 

[CATransplant]

Re: What harm does lugging do?

Well, to start with, if your engine is only hitting 5300 RPM, it is not producing its maximum horsepower, rated at the 6000 RPM speed.<br /><br />Bottom line here is that if you have a prop that allows the motor to reach its rated WOT RPM, you will proceed on the water at a faster rate, since your speed on the water is more or less directly related to the RPM of the prop and that prop's pitch.<br /><br />If you can turn a prop at 6000 RPM at WOT, you will be generating more HP from the engine, and will go faster. Going faster is always good.<br /><br />On the other hand, I never run an engine at its maximum RPM, except perhaps in short bursts.

 

[LubeDude]

Re: What harm does lugging do?

Think of it this way. If you have a standard transmision in your car, would you leave it in a gear going up hill that allowed you to just maintain the speed you were at the bottom of the hill with your foot to the floor, or would you shift down so you could lift your foot off the gas a bit and still stay at the same speed? Hopefully you would shift down. Your rod bearings suffer, and you risk excesive carbon built up not to mention preignition problems, none of them a good thing. You are lugging your engine being propped the way you are. You will notice the difference in the engines tone at a criuse speed with a lower pitched prop.

 

[Dhadley]

Re: What harm does lugging do?

Yep, that motor has a bunch left. If youre going to use only 90-100 hp, you could have saved money and bought a smaller motor.<br /><br />Lugging or "overpropping" (btw -- thas a horrible term, you fix it with set up -- not lowering the prop pitch) increases the combustion temps. Not the motor temp (it does somewhat) but the combustion temps. Pistons really dont like that. At all. At some point youll pound out the wrist pins and/or collapse the skirts.<br /><br />The biggest deal is excessive combustion heat promotes coking. That leads to stuck rings, bad idle, lost power and eventually broken rings.<br /><br />Worst of all -- some guy with the same boat and a 90 blows by you. And your friends are always right there and help you remember.

 

[CATransplant]

Re: What harm does lugging do?

"Worst of all -- some guy with the same boat and a 90 blows by you. And your friends are always right there and help you remember. "<br />---------------------------------------<br /><br />And there you have it, Dhadley. That would be horribly embarrassing. A new prop would fix all that, and the guy with the 90 would have Johnson envy when the writer blew by him with his 120. Speed is good.

 

[MarkHPCA]

Re: What harm does lugging do?

OK. I can see how high combustion temps can be harmfull in the long term. Would 5300 be considered on the low side for my motor? What would be acceptable? I am tunning a 24P Raker and getting 60 MPH GPS . I can probably gain a few more RPM by raising my motor a little more, right now the prop shaft is about 2" below the pad and the water pressure is good (28PSI). If I raise it I do notice that the water pressure starts to jump about 5-10 PSI as I go over chop. I was thinking about blocking the top two water intake holes (on on each side). Would this still give sufficient flow or would I have to open up the remaining ones>

 

[moderator1]

Re: What harm does lugging do?

A new prop would fix all that, and the guy with the 90 would have Johnson envy when the writer blew by him with his 120. Speed is good.

Prop is not the fix....set-up, as Dhadley suggested is much cheaper and not only improves performance, it's more fuel efficient as well.<br />Dhadley is a good one to follow....you might be surprised what you will learn...

 

[Dhadley]

Re: What harm does lugging do?

Are you running the V6 style gearcase? Whats the diameter of your Raker?

 

[MarkHPCA]

Re: What harm does lugging do?

DH..<br /><br />It has a V4 gearcase, the prop is 13.5" dia. I am running with 5 1/2" setback on a manual jack plate. The hull is the same as a Hydrostream V-King but with a bow-rider deck. The Vista is the Canadian Edition version of the Hydrostream's Vasseret V- bottom, made under license in Canada.

 

[Dhadley]

Re: What harm does lugging do?

Excellent hull / prop combo. Thats why your numbers are so good. <br /><br />You are correct. Raising the motor is the next step, and youve done the testing that proves what we'd look for. Fluxuating water pressure. And yes, you can fill the top 2 intake holes on each side.<br /><br />We like to do it by threading the holes and screwing in a pipe plug. You dont want it going in too far or sticking out too far. Some people do it with Bondo but I dont like the fact its hard to control how much goes in and it always seems to crack without something as a backer. We do use it to smooth over and blend the outside.<br /><br />Actually there should be enough room at the bottom to add another hole. Youll have to remove the gearcase and pump assembly to look.<br /><br />Also, has the prop been reworked? And just to verify, is the tach set on position 6? What brand tach is it?

 

[MarkHPCA]

Re: What harm does lugging do?

When you say 'I can fill the top two holes' do you mean one on each side or two on each side? I like the idea of threading and pipe plug better than Bondo, easier to remove in the future. Do you think I would have to add another hole or is there enough flow as is (with the blocked holes). As far as I know the prop is standard, it was fixed after hitting a rock a couple of years back but no re-work. The tach is a Teleflex brand, new last year, and is set to #6.

 

[Dhadley]

Re: What harm does lugging do?

You can fill the top 2 on each side. You have a good baseline so just refer to that. Its possible to get enough water from the other 2 on each side (4 total) but if you create another, you can basically raise the motor and leave the intakes lower. So to speak. <br /><br />OK, the prop was reworked but obviously whoever did it had the right pitch blocks. Thats good. <br /><br />If the tach is a T-flex itll be off some,about 3%, but no big deal. If you ever get a chance to try an OMC shop tach or one from Electronic Specialties, do so. The tach you have is fine. We have it as a baseline. The digital tachs I mentioned are within 0.5% or 30 rpm at 6000.

 

[MarkHPCA]

Re: What harm does lugging do?

Can I check the tach by using a pulse generator? If it is set to 6P does this mean 6 pulses per revolution? Also what would be considered a 'not lugging' RPM. They way I figure it as I increase the height the RPM goes up with speed untill I pass 'the sweet spot' and then the speed will not increase anymore and water pressure may drop (assuming it is sucking air). Is this a true assement?

 

[Dhadley]

Re: What harm does lugging do?

That would be correct. That motor should have a rev limiter at about 6200. It may be 6700, it depends on the pack. Youll be surprised how much is left.

 

[MarkHPCA]

Re: What harm does lugging do?

Good info DH.. Thanks. Unfortunatley I wont be able to try anything as the water in the lakes here in Canada is still somewhat 'thick' In about 4-5 weeks I should be in the water. I'll follow up with the results then.<br /><br />Once again thanks all for your inputs.

 

[Dhadley]

Re: What harm does lugging do?

Keep us "posted". That sounds like a fun ride.<br /><br />Better idea -- bring it down here. The water here seldom gets hard. Blown away sometimes, but not hard.

 

[moderator1]

Re: What harm does lugging do?

Problem with your water, DH, is when it blows away, it takes everything with it...

 

[Dhadley]

Re: What harm does lugging do?

But have no fear....it will be right back. And boy does it ever come back! Well, maybe that is the part to fear...