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Old 10-26-2010, 02:21 PM   #31 (permalink)
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Quote:
Originally Posted by Laurentiu View Post
Here's a video of it working . I'm not too technically inclined so I don't know if they reach TDC at the same time, it just look as if they are moving in perfect tandem.
Yes, it does appear that both pistons move in tandem, but don't fire at the same time.

EDIT: Ha! Euromodder, you beat me by a few seconds

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[Old] Piwoslaw's Peugeot 307sw modding thread

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Old 10-26-2010, 02:24 PM   #32 (permalink)
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Quote:
Originally Posted by Laurentiu View Post
Here's a video of it working . I'm not too technically inclined so I don't know if they reach TDC at the same time, it just look as if they are moving in perfect tandem.
If they didn't reach TDC at the same time you'd have an uneven firing pattern, like a Harley-Davidson twin.
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Old 10-26-2010, 02:31 PM   #33 (permalink)
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The straight twins I'm familiar with incl. CB450 have pistons going up n down in unison whilst firing non simultaneously. This is how you get even firing pulses; if they fired together what would be the point? Make a big single then.
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Old 10-26-2010, 09:54 PM   #34 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
The straight twins I'm familiar with incl. CB450 have pistons going up n down in unison whilst firing non simultaneously. This is how you get even firing pulses; if they fired together what would be the point? Make a big single then.
An opposing twin that is balanced makes no conter movement or vibration when both OPPOSING cylinders fire as they counteract each others momentum, a Single would make a hopping action having another single fire at the same time 180 deg opposite would cancel it out.

BMW motorcycles occasionally did this.
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Old 10-26-2010, 10:12 PM   #35 (permalink)
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What about the "Twingle" engines ?
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Old 10-26-2010, 10:46 PM   #36 (permalink)
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You can see the cam lobes on the 4-valve cyls aren't lined up so it doesn't have simultaneous ignition.
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Old 10-27-2010, 08:27 AM   #37 (permalink)
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each pot fires 360deg apart from each other, bang creates suck and blow creates squeeze.
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Old 10-27-2010, 08:49 AM   #38 (permalink)
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Quote:
Originally Posted by rmay635703 View Post
An opposing twin that is balanced makes no conter movement or vibration when both OPPOSING cylinders fire as they counteract each others momentum

BMW motorcycles occasionally did this.
BMWs opposed twins fire 360 deg apart from cyl to cyl., otherwise there would be two simultaneous bangs and then a crank rotation with no power pulse.... just like the 360 deg parallel twins.

http://www.animatedpiston.com/BMW.htm
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Old 10-27-2010, 10:27 AM   #39 (permalink)
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each pot fires 360deg apart from each other, bang creates suck and blow creates squeeze.
Hey, thanks, great explanation
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Old 11-20-2010, 10:48 AM   #40 (permalink)
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The 2-cyl engine in the Fiat 500 has gotten decent reviews in the couple of English language reports I've read:

Quote:
...the more constant flow of air keeps the small turbocharger spinning, pushing power up to 84bhp, and just under the magic 100bhp-per-litre mark. Not bad for such a small, yet refined engine.

What’s it like to drive?

Just like a normal 500. [...] Around town, if you keep below 3000rpm, the engine doesn’t feel greatly different to the 1.4. But once you breach that rev threshold, you get an interesting motorbike-esque thrum from under the bonnet. The noise can be a bit tiring on the motorway, but it keeps up with traffic. On a more interesting road, it’s actually pretty good fun, thanks to the 107lb ft of torque, as long as you keep the engine buzzing away under the bonnet.
From: Fiat 500 TwinAir two-cylinder turbo review | evo

Quote:
On the road, the 500 TwinAir is deeply impressive. Only at idle and under full acceleration are you truly aware of the engine's twin-cylinder format, and even then the noise is gruffly enjoyable and the balancer shaft keeps things four-cylinder smooth. We were able to cruise quietly at 90mph, more conscious of wind than engine noise, though other testers complained of a 'drone' which suggests some variability among early-build cars.

[...]

In summary, the TwinAir shows that amazing advances are possible in the practical efficiency of small cars, and it makes an invaluable addition to Fiat's small-car range — already the lowest-polluting in Europe — that other manufacturers must surely envy. For potential customers it’s a great ownership proposition, and a lot of simple fun.
From: Fiat 500 TwinAir - Road Test First Drive - Autocar.co.uk

We'll never see it in North America.

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