Talking Opposed Twin Torque Curves

[Horse Newbie 7,202]

14 minutes ago, kpinnc said:

theory that the belt guard impedes some of the airflow at the rear cylinder. 

Theory…

I think if you keep the fins clean it will get all the airflow it needs… oops…

[Horse Newbie 7,202]

Had to do it…

[kpinnc 13,798]

Just now, Horse Newbie said:

Had to do it…

 

Oh trust me, I have no data to confirm either way. I just think that the fact that it almost always was the back cylinder made most (including me) try anything to save them. The oil filter location was also discussed.

[Horse Newbie 7,202]

After some of the stories I’ve heard on here, I just pray that I have one of those that has 6000 hrs and still no major problems !

[RED-Z06 2,479]

1 hour ago, Achto said:

 

Very good point. Although kinetic energy will not effect an engines HP or torque out put, it will effect it's responsiveness. Garden tractor pullers who run modified engines will ditch the 18lb flywheel on a Kohler K model engine and replace it with a 36lb flywheel. They are not concerned with how fast the engine will respond, they just want it to maintain the max RPM once it gets there. (It's kind of weird listening to them wind down from WOT to idle. It takes a good 20 seconds or more) Racers on the other hand will ditch the cast iron flywheel and switch to a billet aluminum one. They want the engine to respond quickly when they step on the peddle. (Response from WOT to idle is very quick on these engines. Less than a couple of seconds) Kinetic energy can make the same engines with virtually the same modifications act completely different. 

If not indirectly though, a heavier wheel can allow an engine to produce torque.  You can have a 6hp engine run 150rpm with a 250lb 2ft tall flywheel make  180ft/lbs of torque.  Put a 30lb wheel on its not going to do that.

 

When i raced gx200 Hondas we put on a 4lb wheel and the throttle response was insane however it cost us at times, you couldn't lift and coast, you had to ride the brake..stock was i think 7.5lbs, and the idle got choppy.

[RED-Z06 2,479]

1 hour ago, Achto said:

 

Very good point. Although kinetic energy will not effect an engines HP or torque out put, it will effect it's responsiveness. Garden tractor pullers who run modified engines will ditch the 18lb flywheel on a Kohler K model engine and replace it with a 36lb flywheel. They are not concerned with how fast the engine will respond, they just want it to maintain the max RPM once it gets there. (It's kind of weird listening to them wind down from WOT to idle. It takes a good 20 seconds or more) Racers on the other hand will ditch the cast iron flywheel and switch to a billet aluminum one. They want the engine to respond quickly when they step on the peddle. (Response from WOT to idle is very quick on these engines. Less than a couple of seconds) Kinetic energy can make the same engines with virtually the same modifications act completely different. 

If not indirectly though, a heavier wheel can allow an engine to produce torque.  You can have a 6hp engine run 150rpm with a 250lb 2ft tall flywheel make  180ft/lbs of torque.  Put a 30lb wheel on its not going to do that.

 

When i raced gx200 Hondas we put on a 4lb wheel and the throttle response was insane however it cost us at times, you couldn't lift and coast, you had to ride the brake..stock was i think 7.5lbs, and the idle got choppy.

[RED-Z06 2,479]

32 minutes ago, Horse Newbie said:

After some of the stories I’ve heard on here, I just pray that I have one of those that has 6000 hrs and still no major problems !

My 218g went 1800hrs...air filter came loose while disking dry soil and she ate dirt...dusted the rings bad, couldn't keep oil in it.  At the time the only option was $1000 in parts...plus special tools.  If not for getting dusted it probably would still be going...maybe.

[oldlineman 1,495]

Just think hit and miss engines.A lot of torque very little HP. Bob

Edited January 26, 2022 by oldlineman

[sgtsampay 117]

14 hours ago, lynnmor said:

 

The 20 HP Onans have a higher lift on the intake cam lobe.

I also thought the carb was different between to two? Perhaps I'm wrong.

[lynnmor 7,577]

4 hours ago, sgtsampay said:

I also thought the carb was different between to two? Perhaps I'm wrong.

I believe that it had a different number, probably just the jetting.

[Tuneup 1,433]

So, I haven't read yet that an opposed twin gives twice the torque pulses at a given RPM when compared to a single. That stores more 'torque-time' in the flywheel and allows for more work in the crank. It would certainly account for the marketed 'gobs of torque' when the torque values were almost identical. Like my sister, the Lefty, would say, "It's all about the feeling." Yeah, she's a nut. I'd rather have a power pulse at every rotation of the crank than in every other. Still, the rated torque would be about the same, or maybe a bit lower given the smaller piston size and similar strokes for given HP.

 

My Onan 16 never seems to strain and will tug the old machine up a hill at low RPM. That flywheel is a beast. Still, an old Kohler chug is a sound to be cherished.

 

I thought it'd be fun to keep this thread near the top.

[ebinmaine 70,812]

26 minutes ago, Tuneup said:

my sister, the Lefty

Seriously. My father is left-handed. My mother is right-handed. I'm partially ambidextrous.

Fortunately for me I'm also twice as crazy.

 

Back on topic though, I meant to bring up earlier... I see where somebody mentioned that there are different weight flywheels for certain engines. Having taken the flywheel off of my k582 recently I was VERY surprised at how light it was.

 

I'm not going to go searching out a heavier flywheel but it makes me wonder what that engine would be like if it had a great big beefier chunk of iron on the front of it.

 

 

[Tuneup 1,433]

1 hour ago, ebinmaine said:

I'm not going to go searching out a heavier flywheel but it makes me wonder what that engine would be like if it had a great big beefier chunk of iron on the front of it.

 

Well then, let you be the first to extend the input and clamp a 25 lb barbell on that machine! As a teen, I found a very heavy flywheel for my old '60 Briggs 2HP and it would just chug-chug at such a low RPM. I could sit and stare at it and it just amazed my Dad (he could add STP to the Ford but that was the extent of his mechanic talents).

[ebinmaine 70,812]

3 hours ago, Tuneup said:

 

Well then, let you be the first to extend the input and clamp a 25 lb barbell on that machine! 

 

Funny thing is I wouldn't even have to extend it if I put it on the pulley side. There's a ton of extra crankshaft over there. I just wouldn't do it because I'd be afraid of throwing something out of balance inside or outside of the engine.

 

[Greentored 3,220]

As a somewhat blanket statement, cubic inches = torque, and the more cubic inches, the lower the rpm it will make that torque.

While a more 'modern' 30ci ohv twin might make the same torque as a 45ci opposed twin due to its efficiency, its making it at higher rpm, and normally is not going to be as much of a broad, flat curve.

That curve, plus the fact that its 48ci, is what makes a big Onan a torque monster. Linear power.

Would be interesting to see a pull off between identical machines with opposed twin and OHV twin of the same torque rating and buzz em up to their torque peak. Bet it would be a good fight.

Now drop the rpm down to about 2 grand. My money is on about ANY of the oppys dragging the V twin around the yard backwards. 

The lower rpm you go, the more cubic inches rule.

[Greentored 3,220]

As for flywheel weight, I recently swapped the oem wheel on my 'warmed up' 18hp briggs opposed and installed an ARC wheel- approx 8lbs vs maybe 24? The difference in throttle response and acceleration are mind boggling, but it will not crawl through obstacles off idle without stalling. 

The engine isnt making more power, but it feels like it doubled.  Inertia is tricky for seat of the pants, butt dyno comparisons....

 

[ebinmaine 70,812]

1 minute ago, Greentored said:

flywheel weight

Is there such a thing as adding weight to a flywheel? I'm assuming it has to be balanced by a machine shop?

 

[Greentored 3,220]

8 minutes ago, ebinmaine said:

Is there such a thing as adding weight to a flywheel? I'm assuming it has to be balanced by a machine shop?

 

yes and yes, and likely going to. Just havent figured out how to attach it yet

[AHS 1,491]

@Greentored Ok.. adding weight to a 14hp Kohler magnum… Would that create a longer more flat like toque curve? @ebinmaine has seen a snowblower video on my magnum 14 throwing snow 25’! It is harmonious sound at the torque of the motor!!😀

[RED-Z06 2,479]

25 minutes ago, AHS said:

@Greentored Ok.. adding weight to a 14hp Kohler magnum… Would that create a longer more flat like toque curve? @ebinmaine has seen a snowblower video on my magnum 14 throwing snow 25’! It is harmonious sound at the torque of the motor!!😀

Its not going to alter the curve as much as its going to make it more sluggish, but feel more powerful to a load.  Like a truck big heavy wheels and tires...you have to work harder to spin them up and slow them down

[bds1984 1,466]

On 1/26/2022 at 6:58 AM, oldlineman said:

Just think hit and miss engines. A lot of torque very little HP. Bob

They certainly do.  My grandfather restored a 1917 Hercules 1.5 HP engine.  I loved the brass tag on it that proclaimed 1.5 HP @ 550 RPM.  I am not sure what torque values were, but you cannot tell me that having two 50 pound flywheels on each end of the crankshaft didn't influence the power.  Even though it was a hit and miss engine, it was fairly smooth under load.  At twelve years old, I remember really having to "crank" on those flywheels to get her snorting and spinning to life!  This picture isn't that my grandfather had, but very, similar.
 

Edited February 2, 2022 by bds1984

[RED-Z06 2,479]

17 minutes ago, bds1984 said:

They certainly do.  My grandfather restored a 1917 Hercules 1.5 HP engine.  I loved the brass tag on it that proclaimed 1.5 HP @ 550 RPM.  I am not sure what torque values were, but you cannot tell me that having two 50 pound flywheels on each end of the crankshaft didn't influence the power.  Even though it was a hit and miss engine, it was fairly smooth under load.  At twelve years old, I remember really having to "crank" on those flywheels to get her snorting and spinning to life!  This picture isn't that my grandfather had, but very, similar.
 

If not for the flywheels the engine wouldnt operate, they store alot of power in them...but youll see the lack of horsepower if you load it up to an apparatus that needs rpms.

 

Lets say you want to make electricity...you need 3600rpms to make 60hz power so youll need to run a 655% overdrive...thats going to cut your torque by..655%.  Youll only be able to make about 1.1kw or 1100watts...regardless of the huge torque number, horsepower is a formula of torque and speed...no matter how much weight you add to it, the engine still only makes 1.5hp

[AHS 1,491]

@bds1984 My father has a hit and miss engine. It’s an orange one about the same size as that. I’ve always wondered what the top opening is for? Water to cool it?

[oldlineman 1,495]

Yes I believe so. Bob

[ebinmaine 70,812]

5 minutes ago, AHS said:

@bds1984 My father has a hit and miss engine. It’s an orange one about the same size as that. I’ve always wondered what the top opening is for? Water to cool it?

 

2 minutes ago, oldlineman said:

Yes I believe so. Bob

 

That's correct.