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Motorsport Scooters wrote:
The extra power in two strokes comes from twice as many combustions. They fire every time the piston comes up instead of every other time in a four stroke. In Moto GP they race 500cc two strokes versus 1000cc four strokes.
That said the scavenging efficiency (how well it clears and fills the cylinder) of the four stroke is almost twice as good as a two stroke. The magic of the two stroke was in tuning the sound propagation through the engine. As soon as this moved from art to science it was picked up by the four stroke designers.
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UTC quote
Motorsport Scooters wrote:
The extra power in two strokes comes from twice as many combustions. They fire every time the piston comes up instead of every other time in a four stroke. In Moto GP they race 500cc two strokes versus 1000cc four strokes.
Many singe cylinder 4 strokes fire on every stroke, both the compression and the exhaust stroke. Alot of times its called the wasted spark.

There's really 2 reasons this happens. One (the official explaination) is "To burn residual hydrocarbons and further reduce emissions". Two (the real reason) it's cheaper to time the CDI (or other mechanism) to fire on every revolution.
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haven't decided yet (GT or GTS?)
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UTC quote
Not since like 1999. The last 2-smoke 500cc Gran Prix machines competed against the new-skool 990cc four-stroke machines for one season, and I'm pretty sure that was either 2000 or maybe 2001. They made just as much power as the four-strokes, but only because they were at the end of their life cycles and highly refined, compared to the spankin' new and as-yet-untried four-strokes.

The 990s got so light in the next few years, and were so routinely topping 200mph that for this season, displacement for the MotoGP (as the premier class of world racing is now called) is 800cc. But since FIM gave the manufacturors 2 or 3 years heads-up notice, they've had time to develop the new bikes, which, you guessed it, already do 200mph, and are, um...even lighter. They can't accelerate as fast though. And they're no good for city commuting (have you seen the abysmal under-seat space on those things?!) No, I came from motorcycles, and I may go back, eventually, but for now, you can keep 'em.

I just have to still decide between a GT or a GTS.
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Molto Verboso
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UTC quote
Beans tuning......
Forum member supplied image with no explanatory text
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That's why there are two cylinder motors...like in the Ducati Multistrada with 620 cc.
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There are a handful of ways to replace displacement:

1) Weight reduction and aerodynamic improvement. Efficiency is the art of doing more with less, and Lotus and others have worked on this philosophy.

2) Force more air (and fuel) into the cylinder. Superchargers and turbos can very effectively make up for lack of size.

3) Drop the number of strokes. 2 strokes make more power. So do Wankel rotaries.
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Bryce-O-Rama wrote:
There are a handful of ways to replace displacement:

1) Weight reduction and aerodynamic improvement. Efficiency is the art of doing more with less, and Lotus and others have worked on this philosophy.

2) Force more air (and fuel) into the cylinder. Superchargers and turbos can very effectively make up for lack of size.

3) Drop the number of strokes. 2 strokes make more power. So do Wankel rotaries.
You can try to save weight in a scooter. Not much there to begin with, so good luck.

You can increase the air/fuel volume of your existing engine by rejetting the carb, modifying the air intake and adding a modified exhaust. This would be a viable option except for the electronic engine controls. The electronic auto choke makes performance tuning the carb very difficult. Other than that, a turbo or supercharger is impractical.

I wish we could go back to 2 strokes. They were easier to maintain, easier to tweek and in most cases delivered superior performance over the current 4 strokes.

I'm really trying to point out that there is a physical reason that a 150cc 4 stroke scooter is not going to keep up with a 200cc or a 250cc 4 stroke.

There are a myriad of options that you can purchase and install on a small displacement engine to boost the available power. Some work well, others don't work at all. But there is NO magic mod that will unlock free power (not like there were in the 2 stroke days at least). Modding a 4 stroke is expensive and the results are often marginal, requireing further modding. It almost becomes an addiction.. 'One more $200.00 part and I'll finally be happy..'
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Skrapiron wrote:
You can try to save weight in a scooter. Not much there to begin with, so good luck.
Weight savings are difficult on a scooter. They're also difficult on people. Windscreens do make a nice top speed difference.
Skrapiron wrote:
You can increase the air/fuel volume of your existing engine by rejetting the carb, modifying the air intake and adding a modified exhaust.
Modding the air intake on Modern Vespa 4-strokes really isn't even an option due to having CV-style carbs that need specifically tuned airboxes.
Skrapiron wrote:
This would be a viable option except for the electronic engine controls. The electronic auto choke makes performance tuning the carb very difficult.
I don't understand either of these statements. What are the electronic engine controls that limit tuning? Rev limiter? How does the electronic auto choke hinder tuning? When it's off it doesn't play any role in the carb at all.
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LX150
Oh ok this is now the GTS is always gunna be better than the LX150 thread...

The GTS is faster than the LX150. Well unless it blows the exhauset gasket and melts the rear brake line... That happend to another friend of mine in Sacramento. "Ron" Glad he was thinking and was able to stop with his front brake.

I think the choice of the LX150 should be around town use. Only two up once in a while. They are great for moving around in garages and easy to park. Lighter. Even fun to ride.

The GTS I see as somthing you could Ride to a Rally in semi comfort.
Having both of them i felt was a waste of resources. If I had to choose one the GTS would be the winner.

However Riding a kitted little two stroke is a shit load of fun. Having that shit eating grin on my face is to me whats its all about...
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Re: There's no replacement for displacement:
Skrapiron wrote:
3 oz medicine cup. This is approximately the size of a 50cc piston. Approximately 5 hp.
6 oz can of tomato paste. This is approximately the size of a 150cc piston Approximately 12 hp.
12 oz can of soup. This is approximately the size of a 200cc piston. Approximately 23hp.
16 oz can of beans. This is approximately the size of a 250cc piston. Approximately 25hp.
28 ouce can of tomatos. This is approximtely the size of a 450cc piston. Approximately 35hp.
I'm not sure about the size of the pistons when compared to each other, but the displacement (which is what's implied by the title) is much less than indicated by the cans.

For the 50 we're looking at a shot glass, and the 150 through 250 are all covered by the difference between a bit more than 1/3 of a can of Coke and 2/3 of a can of Coke. (The 400 is a Coke and a shot! ) So the above illustration is somewhat deceptive as far as displacement, especially since it is volume (liquid oz) as compared to weight (mass) which is what cans of food are measured in.

I know, being anal again, but I did want to give a better perspective.

50cc = 1.7 fl oz (US)
150cc = 5.1 fl oz (US)
200cc = 6.8 fl oz (US)
250cc = 8.4 fl oz (US)
400cc = 13.5 fl oz (US)
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UTC quote
Motorsport Scooters wrote:
In Moto GP they race 500cc two strokes versus 1000cc four strokes.
...and as long as we're setting the record straight... in 2007 the FIM changed the rules so that MotoGP is now 800cc fourstrokes. The first year of transition where 500cc 2-strokes ran against 1000cc 4 strokes was very interesting, though.

EDIT: Nicky Hayden on pole for the MotoGP of Estoril tomorrow!!! W007!
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I like my can of beans! It is pretty peppy.

But the RPM argument is also valid. My R6 is a 600cc bike, and the Duc is a 900, but the R6 will smoke the Duc once it reaches 10000 RPMs. But until you get to about 7000 it's pretty weak sauce. The Ducati is much better for day to day riding as it has tons of torque down in the real world RPM range.
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I replaced my GT125 top end with a Malossi 210 expecting at least some better torque for overtaking.......nah just the same, maybe even worse at top end!
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I have 100 foot pounds of torque on my FJR and it is very usable riding 2-up at very low RPMs. It also makes it so I do not need to downshift on the freeway when I need to pass someone. You just roll on the throttle and away you go. I prefer the Vespa for everything but long distance rides.
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UTC quote
Michael Moore wrote:
I like my can of beans! It is pretty peppy.

But the RPM argument is also valid. My R6 is a 600cc bike, and the Duc is a 900, but the R6 will smoke the Duc once it reaches 10000 RPMs. But until you get to about 7000 it's pretty weak sauce. The Ducati is much better for day to day riding as it has tons of torque down in the real world RPM range.
Yeah, but my chicken soup smells better than your beans!
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UTC quote
I'm with you Bryce-o-rama, I am with two strokes and the answer to your prayers came from Aprillia and their Direct Injected two stroke.

It's a pitty that Aprillia didn't increase the displacement and didn't achieve commercial success. But there is an answer to two stroke spewing raw fuel mixture into the environment: Metering the fuel injection when the exhaust port has shut and not mixing oil and gas for lubrication. They even achieve less CO at idle and less Nitrus Oxides during operation than four strokes, no valve adjustments nor extra weight, just clever electronics in a simple motor. I call this Clever!

Commercially speaking you can find Direct Injected Two Stroke engines in outboards such as Evinrude FICHT now owned by Bombardier and their Evinrude ETec and ORBITAL part of Brunswick and their Mercury outboard branded OPTIMAX.
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UTC quote
Raisin Hell wrote:
You can hop up a Subaru, but it'll never be an Audi.
Yeah, the Subaru will probably stay reliable. Laughing emoticon
rbruce63 wrote:
I'm with you Bryce-o-rama, I am with two strokes and the answer to your prayers came from Aprillia and their Direct Injected two stroke.

It's a pitty that Aprillia didn't increase the displacement and didn't achieve commercial success. But there is an answer to two stroke spewing raw fuel mixture into the environment: Metering the fuel injection when the exhaust port has shut and not mixing oil and gas for lubrication. They even achieve less CO at idle and less Nitrus Oxides during operation than four strokes, no valve adjustments nor extra weight, just clever electronics in a simple motor. I call this Clever!

Commercially speaking you can find Direct Injected Two Stroke engines in outboards such as Evinrude FICHT now owned by Bombardier and their Evinrude ETec and ORBITAL part of Brunswick and their Mercury outboard branded OPTIMAX.
The Ditech system that Aprilia uses is from Orbital. Piaggio was using it prior to their purchase of Aprilia and selling it under the name Purejet. Peugeot was using it on the Looxor 50 and calling it TSDi.

I'm a big fan of DI two strokes. I think they're great. They are more expensive to build than carbureted four strokes, so it's unlikely we'll see many of them. It's a real shame that Piaggio didn't use this system on their 125 and 180cc 2 strokes that they used in the Gilera Runner.
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