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Old 08-21-2013, 11:04 PM   #41
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I replaced a Lehman 6 with a JD 4. The JD is smoother. It was a pleasant surprise. The JD is a modern engine with higher pressure injectors and electronic controls.

I was worried about vibration when I installed the 4. I had no reason to be.
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Old 08-21-2013, 11:49 PM   #42
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Last boat show I was at the JD dealer was claiming that the Tier 3 4's were now smoother than the 6's. This came about after CAD work and balance shafts. And delivered 235HP, presumably M5 mode. The key is the power of CAD.
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Old 08-22-2013, 07:06 AM   #43
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Originally Posted by capt jerry View Post
here is a smoothyBIGGEST ENGINE
Thanks for the link Capt Jerry...interesting

This is what I got out of it....
A single unit and single screw design has also proved over time to have a longer life span than double or even quad screws. Longevity of this engine design is based on less moving parts equals less stuff to wear out, which makes sense when you think about it.

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Old 08-22-2013, 07:16 AM   #44
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>I think the biggest problem with the Wankel engine is that it has a power stroke on every revolution,...that's just not fuel efficient.<

Fuel economy was not the demise of the rotary , the huge volume of combustion chamber made too much polution for the Air Police.

Perhaps with a urine tank they will be able to pass todays specks.
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Old 08-22-2013, 07:59 AM   #45
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>I think the biggest problem with the Wankel engine is that it has a power stroke on every revolution,...that's just not fuel efficient.<

Fuel economy was not the demise of the rotary , the huge volume of combustion chamber made too much polution for the Air Police.

Perhaps with a urine tank they will be able to pass todays specks.
Another interesting Wankel link. I for one always did like the ideas behind this motor.
The Last Mazda Wankel Engine Has Been Built

Yes it did run into pollution problems'
"The down side is that Wankels are always a bit more fuel-gluttonous than a piston engine, and almost always have dirtier exhaust. Poor fuel economy and more polluting are pretty much the only strikes you need against you in our modern age, so the mainstream Wankel is going away."
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Old 08-22-2013, 11:29 AM   #46
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Very very much like a 2 stroke Brian. And I like them both a lot.

The inline 6 is a great engine for trawlers and many cars. But the long heavy crank, overall length, the fuel efficiency of fewer cylinders, the popularity of FWD and all the advances that makes all engines smoother means four cylinder engines will continue to be more popular.
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Old 08-22-2013, 01:49 PM   #47
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hereWorld's smallest supercharged four-stroke V8 engine now in production is a few more
? World smallest V12 engine - YouTube
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Old 08-22-2013, 03:10 PM   #48
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>and all the advances that makes all engines smoother means four cylinder engines will continue to be more popular.<

I would disagree, as modern diesel engines with electronic fuel injection can shut down as many cylinders as are not required.

A shut down to 3 cylinders would still be smooth , a shut down of a 4 might be much harder to get smooth.

Cost is always a factor , so for big mileage cruisers a 2 speed tranny , and the repairability of a mechanical injected engine would be a valid choice.

Other choice could be two 3 cyl engines mounted on LST style tranny , run one or both as desired.

The 3-71 would be a great engine for most 40ish cruisers , but there SO DAMN HEAVY!

But at least they are cheap.
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Old 08-22-2013, 03:59 PM   #49
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Shutting down cylinders is not very effective as all the moving parts for the dead cylinders are still moving and causing a lot of lost power.

"Other choice could be two 3 cyl engines mounted on LST style tranny , run one or both as desired."

That would be much better.
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Old 08-22-2013, 04:06 PM   #50
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yrs ago I was on a 58 Viking and it had mann engines 12cyl at below 1500 rpms it would run only on six cyls any thing higher the others would kick in. MANN GRANADES I know the spelling is wrong
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Old 08-22-2013, 04:29 PM   #51
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Other choice could be two 3 cyl engines mounted on LST style tranny , run one or both as desired.
LST?

Do you mean a combining gearbox with CP wheels? Seems like a bit of overkill for a toy boat, doesn't it?

Or do you mean a honking great Falk reverse/reduction gear with air clutches?
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Old 08-22-2013, 06:50 PM   #52
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the exp. I had with lst engines were not hooked to a tranny but 4 engines hooked up to a gear box and they had a varable picth props you good run 1 or 2 or 3 or 4 engines and only 2 engines had starters you started the other 2 buy throwing in the clutchs,that was a long tme ago. but those were the days my freind
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Old 08-22-2013, 09:05 PM   #53
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.............means four cylinder engines will continue to be more popular.
Huh?
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Old 08-22-2013, 10:18 PM   #54
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What do you mean "Huh?"

I thought I pointed out some of the advantages of 4 cyl engines in the near future. Of course I'm talking about engines in general .. not boat engines.

I think you mean that you just disagree.

Do you think 6 cyl engines are going to become more popular than fours?

Why?
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Old 08-23-2013, 06:14 AM   #55
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<Shutting down cylinders is not very effective as all the moving parts for the dead cylinders are still moving and causing a lot of lost power.>

Dont let the folks with 2 engines that try to cruse cheap know that the second engine has internal HP costs!!!!
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Old 08-23-2013, 08:51 AM   #56
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FF it would seem the second engine would have HP GAINS as the single running engine would be running much harder and in a more efficient mode because of it.

But then the second engine does cause efficiency losses as the weight of that engine and all associated equipment is dead weight to be carry across the water.

FF I have the feeling I may not be understanding your post.

But re the OP it looks to me like if one considers basic engines only w/o any high tech features that would make it smoother, engine vibration is dependent on how many cylinders it has. This of course would include 90 degree V type engines and exclude V type engines w other angles of cylinder inclination.
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