RE: 2 cycle vs 4 cycle

RE: 2 cycle vs 4 cycle
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RE: 2 cycle vs 4 cycle - 4/26/2006 2:23:47 AM

khodges

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quote:

ORIGINAL: e-dave

Gotta agree, they sound about as much like a Merlin as a Saito 100 sounds like the Lycoming AEIO 540 in an Extra.

yeah, but my Saito 1.00 with a straight pipe sounds like a Ducati racebike comin' down the front straight at Daytona W.F.O.

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RE: 2 cycle vs 4 cycle - 4/26/2006 2:29:35 AM

Rebellion

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quote:

ORIGINAL: khodges

quote:

ORIGINAL: e-dave

Gotta agree, they sound about as much like a Merlin as a Saito 100 sounds like the Lycoming AEIO 540 in an Extra.

yeah, but my Saito 1.00 with a straight pipe sounds like a Ducati racebike comin' down the front straight at Daytona W.F.O.

Yes, and my SS piped Jett 50 sounds like----
That's one of the things I like about a high revving two stroke, they sound like nothing else.

All a matter of personal taste I guess.

< Message edited by e-dave -- 4/26/2006 2:51:15 AM >

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RE: 2 cycle vs 4 cycle - 4/26/2006 2:49:01 AM

loughbd

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Now you take one of my OS 4 cylinder 4 Cycles in a Cub or my Five cylinder OS FF300 in a Fleet Biplane and you get a more realistic sound than a scrreaming 2 cycle or gasoline engine sounds like a Rolls merlin. By the way someone awile back mentioned a Packard Merlin. Now THAT would be a rare engine. Rolls Merlin or Rolls Griffin I will believe but a Rolls packard?? Nope.

Oh and turbines sound like a small vacuum cleaner.

< Message edited by loughbd -- 4/26/2006 2:54:18 AM >

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RE: 2 cycle vs 4 cycle - 4/26/2006 2:55:25 AM

loughbd

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A Jett sounds like a big Cox 049. Two cycles sound like two cycles. Whiney obnoxious noice. That's why we got kicked out of so many flying sights.

Here's a question, would you rather wake up Sunday morning to the sound of some guy using a chain saw or a guy moving his lawn with a Briggs and Stratton powered lawn mower?

< Message edited by loughbd -- 4/26/2006 3:00:44 AM >

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RE: 2 cycle vs 4 cycle - 4/26/2006 3:43:02 AM

mrbonk

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I've got both and I don't understand what all the fuss is about. They've both got applications that they're more suited to.......just depends what you want to use it for. I *love* the torque and the sound that my YS 4 strokes produce though......I can't imagine flying my Ultimate Bipe with anything else

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RE: 2 cycle vs 4 cycle - 4/26/2006 5:33:46 AM

loughbd

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Here's a little item for you. A four cycle engine does not have more torque than a two cycle. It has a higher BEMP, brake effective mean pressure. A two cycle firing every stroke has more torque.

< Message edited by torque wrench -- 4/26/2006 1:02:15 PM >

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RE: 2 cycle vs 4 cycle - 4/26/2006 1:02:09 PM

Hobbsy

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quote:

ORIGINAL: loughbd

Here's a little item for you. A four cycle engine does not have more torque than a two cycle. It has a higher BEMP, brake effective mean pressure. A two cycle firing every stroke has more torque.

ORIGINAL: loughbd

Actually it's BMEP, BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

< Message edited by torque wrench -- 4/26/2006 1:05:46 PM >

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RE: 2 cycle vs 4 cycle - 4/26/2006 1:18:10 PM

mrbonk

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quote:

ORIGINAL: loughbd

Here's a little item for you. A four cycle engine does not have more torque than a two cycle. It has a higher BEMP, brake effective mean pressure. A two cycle firing every stroke has more torque.

Doesn't the 2 stroke have to be doing more revs to produce the same torque? I was always lead to believe that the 4-stroke would produce better torque at lower revs, making it more suitable for swinging larger diameter, lower pitch props.

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RE: 2 cycle vs 4 cycle - 4/26/2006 1:28:32 PM

Hobbsy

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I know that there are examples of the opposite, for example my MVVS .91 is real torquer but my ABITAR 1.20 fourstroke is a revver, it will turn a 14x6 APC at 12,000 plus but can't handle a 15x8.

As you say the general rule is that the fourstroke will have a broader torque band.

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RE: 2 cycle vs 4 cycle - 4/26/2006 1:48:27 PM

aussiesteve

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BHP = torque (ft/lbs) x rpm / 5250

If a 2 stroke delivers more torque - why do they need to rev higher to produce the requisite horsepower to suit the engine load (created by the propeller)?

It would appear that the original question has worked. For most people there is very little practical difference - it is mostly personal preference based on the sound. The exeptions being true 3d (4 stroke) - or genuine top end speed (2 stroke) otherwise it is probably much of a muchness. -

1 lb of fuel will only contain a set amount of potential energy - it's how efficiently the engine transfers that into kinetic energy that makes the difference. - This is why, displacement for displacement, different engines have different power outputs - it's all about engine efficiency which is controlled by many factors.

BTW - BMEP is controlled by a large number of factors - most of which are to do with engine design - I would just about guarantee that, size for size and cycle for cycle, an older style of engine will produce a lower BMEP than one with later more efficient designs (Schneurle porting for instance). this also applies to combustion chamber design, valve timing atc and is a fascinating science all of it very own.

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RE: 2 cycle vs 4 cycle - 4/26/2006 3:24:40 PM

Sport_Pilot

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quote:

If a 2 stroke delivers more torque - why do they need to rev higher to produce the requisite horsepower to suit the engine load (created by the propeller)?

In most 2 strokes the torque is going down well before it reach's peak HP. The four stroke is limited in top RPM because of valve float, and no company as yet has tried the stiffer springs, roller tappets, overhead cam, etc, so that they will reach the same RPM. At the lower RPM many of the two stroke will attain a higher torque than an equivelant displacement four stroke.

BTW I think Hobbsy's formula is an approximation as it doesn't take in account all of the possible rod, crank, stroke and length combinations. Also I think that displacement is for one power stroke. For a four stroke the power stroke is followed with a no power intake stroke so the torque measured by a dynometer will be about half of his calculated figure.

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RE: 2 cycle vs 4 cycle - 4/26/2006 4:20:53 PM

loughbd

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Yeah Dave,

I knew it was BMEP. Just didn't engage brain at the time. It will stir up a can of worms though, you watch.

< Message edited by loughbd -- 4/26/2006 4:24:05 PM >

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RE: 2 cycle vs 4 cycle - 4/26/2006 11:50:16 PM

Ed Cregger

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Well put, Steve.

I love ALL IC engines, even a Ueda .55. You had to be there.

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RE: 2 cycle vs 4 cycle - 4/27/2006 1:16:56 AM

XJet

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Ah, now there's a name I haven't heard in a *long* while.

My most cantankerous engine was an original OS Pet. They were horrible things -- really loud (when you could get them to go) and difficult as hell to start. They'd either be dry or flooded -- with little ground inbetween.

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RE: 2 cycle vs 4 cycle -