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Hello everyone,

I am the proud owner of a Vespa GTS 250cc. I'm thinking of maybe replacing the cylinder with a larger one.

The easiest solution is a cylinder from Malossi. These are also supplied with a 15mm piston pin for the GTS 250. The "normal" Vespa 300cc cylinders are much cheaper, but you are dealing with a 16mm piston pin. is it possible to make a 300cc or larger fit for the 250 engine? Are there people who have installed this on a 250 engine?

how do you adjust the fuel? with a Malossi ecu unit controller? maybe you have some tips?

Thanks!

Mark
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Malossi do (or did) make a cylinder for the 250. It won't make it a 300, but it is the matching cylinder head with its much larger valves that makes the big difference. Well worth it! The cylinder by itself doesn't do much.
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Thanks Mike for your response. I have enjoyed looking at many of your posts! Can't the standard 300cc cylinder from Piaggio be modified? and how did you adjust your fuel for your new cylinder?
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Mark1985 wrote:
Thanks Mike for your response. I have enjoyed looking at many of your posts! Can't the standard 300cc cylinder from Piaggio be modified? and how did you adjust your fuel for your new cylinder?
The ECU adjusts for the new conditions, up to a point.

I've got a GTS 250 modified with a Malossi head and Malossi cylinder. It's pretty potent, but it's also a lot of money and work to install.

Also, any mod like that is suspect from a reliability standpoint. Not saying the Malossi is unreliable, just saying that a stock GTS 250 is a very, very solid engine that will probably run forever if you keep oil in it.
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jess wrote:
I've got a GTS 250 modified with a Malossi head and Malossi cylinder. It's pretty potent, but it's also a lot of money and work to install.
I have debated this modification for years. As these Malossi parts become more scarce (I think you can still buy the head and cylinder on ebay), I am considering purchasing for a rainy day project down the road before I no longer have the option.

Based on your experience would you do it again?
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Shebalba wrote:
Based on your experience would you do it again?
I wouldn't do it for the same reasons that I originally did it -- to have a fast Cannonball bike. The sweet spot for Cannonball under the current rules is to have a bike that maximizes handicap while keeping you somewhere in the general vicinity of the speed limit. An older 200cc bike would be much more suitable.

Also, the mantra that we learned the hard way over several early Cannnonballs was "Don't bring a quarter-mile bike to Cannonball". And the Malossi head + cylinder definitely makes it a quarter-mile bike. Stock reliability on Cannonball is a far better choice.

There are other reasons to do the swap, I suppose -- I probably briefly had the fastest GTS in America -- and it is scary fast when you finally get all the pieces right (exhaust, etc).

But no, I don't think I would do it again. I gave away the original iron cylinder, so I can't even go back. And I miss that very smooth, very reliable stock bike.

The engine in the GTS 250 is, for my money, the best engine Piaggio have ever produced. I regret messing with it.
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I upgraded both my 2015 and 2018 GTS300s with the full Malossi cylinder/head kit. That gave them a fraction more performance than the current HPE models. They were totally reliable, but I never took them on any cross-country endurance type runs.
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Mike Holland wrote:
They were totally reliable, but I never took them on any cross-country endurance type runs.
After about Day 6 on Cannonball 2012, I ended up with a pressure leak (probably at the head gasket) into the coolant system. Which pressurized the coolant until it came out of the reservoir in the leg shield.

Doh.
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jess wrote:
After about Day 6 on Cannonball 2012, I ended up with a pressure leak (probably at the head gasket) into the coolant system. Which pressurized the coolant until it came out of the reservoir in the leg shield.

Doh.
Yeesh. Hot coolant in the lap will definitely keep you from nodding off while riding.
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I do the Malossi mod from the 244 to the 282, with the head, variator, etc. 4 years ago and +23,000 Km in my MP3 250ie and never regret (reliability point). Is all that I expect come from the factory and more.

It's so true that I once tried an MP3 300 Sport (thinking of a change) and I felt like it was stopped, had no energy, was very boring, it had to be at full throttle all the time and even with that don't have the agility as my modded 250. Even when I bought the MP3 500HPE I felt that the modified 250 ran better and paint me a smile in my face.
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Or just buy a 300.

Sure you can't garner any interest in a build but it's a lot easier.
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Bill Dog wrote:
Or just buy a 300.

Sure you can't garner any interest in a build but it's a lot easier.
It's not the same experience, though. I own a Malossi-modded 250 and a 300. They have very different power bands. And the Malossi-modded 250 is a lot faster.

(Okay, I know nothing of the HPE, the HPE2, the HPE3, or the HPE4, which might well be much faster...)
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>> OP
If an original cylinder and head from the 2012 GTS 300 will fit your scooter, I will offer it to you at a very reasonable price.
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jess wrote:
(Okay, I know nothing of the HPE, the HPE2, the HPE3, or the HPE4, which might well be much faster...)
My HPE2 is equal to my Malossified 300s in acceleration up to 100 kph. Then its power drops a bit. Up my long steep test hill, the modded ones come over the top at 120 kph where the standard HPE2 only achieves 110 kph. Don't know about top speed.
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What a lot of good responses!

As I read it, there are many pros and cons. reliability is of course very important. I assume that the original 300cc cylinder from Piaggio is also reliable?

Is the piston pin thickness the only difference? 15mm for the 250cc and 16mm for the 300cc. Isn't it simply possible to enlarge the existing 250cc crankshafthole by 1mm so that the piston of a 300cc fits? I think the crankshaft on a 300 has a longer stroke. I assume that a 300 cylinder must also be slightly longer?
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Mark1985 wrote:
I assume that the original 300cc cylinder from Piaggio is also reliable?
Yes, but from a strictly theoretical engine design standpoint, the cylinder in the 300 is as close to the hairy edge of destroying itself at high RPMs as you can get. Or at least, that's what I'm told by people with more engine theory chops than myself.
Mark1985 wrote:
Is the piston pin thickness the only difference? 15mm for the 250cc and 16mm for the 300cc. Isn't it simply possible to enlarge the existing 250cc crankshafthole by 1mm so that the piston of a 300cc fits? I think the crankshaft on a 300 has a longer stroke. I assume that a 300 cylinder must also be slightly longer?
This is probably a good theoretical question for oopsclunkthud -- I'll see if I can direct him to this thread.
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jess wrote:
Yes, but from a strictly theoretical engine design standpoint, the cylinder in the 300 is as close to the hairy edge of destroying itself at high RPMs as you can get. Or at least, that's what I'm told by people with more engine theory chops than myself.



This is probably a good theoretical question for oopsclunkthud -- I'll see if I can direct him to this thread.
why is the 300cc more sensitive? Will there really be much difference in reliability between the 250 and the 300? the way I see it now it is a matter of filing the crankshaft to 16mm and installing a 300cc, unless there is a difference in the cylinder. if the 300 is longer, it may be possible to turn it with a lathe (I'm not sure if this is the correct name, because I'm from the Netherlands)
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$new correct cylinder << $modify the rod (good luck) + $wrong cylinder + $decking the wrong cylinder to work with the shorter stroke of the 250

and in the end the ~12cc increase will not give any more power because it's the same valves that have been used since the GT200

The power output is limited by the head/valves and that is basically the same from the GT200 to the GTS300
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oopsclunkthud wrote:
$new correct cylinder << $modify the rod (good luck) + $wrong cylinder + $decking the wrong cylinder to work with the shorter stroke of the 250

and in the end the ~12cc increase will not give any more power because it's the same valves that have been used since the GT200

The power output is limited by the head/valves and that is basically the same from the GT200 to the GTS300
Thank you! 12cc increase is indeed not interesting. So what I understand from your response is that another cylinder head with larger valves from Malossi is much more interesting than another cylinder?
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Mark1985 wrote:
Thank you! 12cc increase is indeed not interesting. So what I understand from your response is that another cylinder head with larger valves from Malossi is much more interesting than another cylinder?
Yes, that will give you much more bang for the buck.

(Modifying a 300 cylinder to work on a 250 is… ambitious, at best)
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Mark1985 wrote:
Thank you! 12cc increase is indeed not interesting. So what I understand from your response is that another cylinder head with larger valves from Malossi is much more interesting than another cylinder?
exactly! but...

The Malossi head with the Malossi cylinder is a straight forward bolt on job.
The Malossi head with a stock cylinder requires machining valve pockets into the stock piston. see: Malossi V4 Head, The Missing Measurements

what are your goals? quicker? higher top speed?

inspiration: GTS Land Speed Record (Post 1358271)
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the problem with the malossi 4v head is its NLA
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oopsclunkthud wrote:
exactly! but...

The Malossi head with the Malossi cylinder is a straight forward bolt on job.
The Malossi head with a stock cylinder requires machining valve pockets into the stock piston. see: Malossi V4 Head, The Missing Measurements

what are your goals? quicker? higher top speed?

inspiration: GTS Land Speed Record (Post 1358271)
my goal is more torque. I don't think top speed is important at all. my Vespa is purely for fun. I already have a Malossi vario, Malossi air filter and a different exhaust.
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Mark1985 wrote:
my goal is more torque. I don't think top speed is important at all. my Vespa is purely for fun. I already have a Malossi vario, Malossi air filter and a different exhaust.
Then what you want is a 300 engine. The whole engine.
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Mark1985 wrote:
why is the 300cc more sensitive? Will there really be much difference in reliability between the 250 and the 300? the way I see it now it is a matter of filing the crankshaft to 16mm and installing a 300cc, unless there is a difference in the cylinder. if the 300 is longer, it may be possible to turn it with a lathe (I'm not sure if this is the correct name, because I'm from the Netherlands)
Both engines, the 250 and the 300, are from the Piaggio Quasar engine family. https://de.wikipedia.org/wiki/QUASAR_(Motor)
Originally designed as a 250cc engine (the "Qua" in the name refers to a quarter liter)
The original 250cc had a 244cc engine with a bore of 72mm and a stroke of 60mm.
Later Piaggio enlarged the engine to a 300.
The 300 cc has a 278cc engine with a bore of 75mm and a stroke of 63mm.
That means the cilinder wall thickness is 1.5mm smaller in the 300 than it is in the 250.
In theory that could lead to a less reliable engine.
I do not think there is a reliability problem because all GTS 300's and also the today HPE 300 engines both in Vespa and in Beverly all have that same engine design.

Wat bedoel je met deze zin?
it may be possible to turn it with a lathe (I'm not sure if this is the correct name, because I'm from the Netherlands)
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PeterCC wrote:
Both engines, the 250 and the 300, are from the Piaggio Quasar engine family. https://de.wikipedia.org/wiki/QUASAR_(Motor)
Originally designed as a 250cc engine (the "Qua" in the name refers to a quarter liter)
The original 250cc had a 244cc engine with a bore of 72mm and a stroke of 60mm.
Later Piaggio enlarged the engine to a 300.
The 300 cc has a 278cc engine with a bore of 75mm and a stroke of 63mm.
That means the cilinder wall thickness is 1.5mm smaller in the 300 than it is in the 250.
In theory that could lead to a less reliable engine.
I do not think there is a reliability problem because all GTS 300's and also the today HPE 300 engines both in Vespa and in Beverly all have that same engine design.

Wat bedoel je met deze zin?
it may be possible to turn it with a lathe (I'm not sure if this is the correct name, because I'm from the Netherlands)
So I'm starting to understand that the 250cc version is a more reliable and perhaps even the best version that Piaggio has released? maybe it would be smart to keep the 250cc after all. I had the idea that converting to a 300cc would not be a huge amount of work and would improve performance. So maybe I shouldn't think of a different cylinder, but of the Malossi cylinder head with larger valves.
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Mark1985 wrote:
So I'm starting to understand that the 250cc version is a more reliable and perhaps even the best version that Piaggio has released?
As PeterCC said, the 300 isn't inherently unreliable. They actually have a good track record. The 250 is more within the safety envelope of engine design than the 300 is, but history demonstrates that Piaggio managed to keep the 300 within the safety margin -- just a bit closer to the edge.

I just personally think the 250 is a better engine. The power band is (for me) more useful. But you said you're interested in torque, and the 300 engine has a nice low-end torque grunt that the 250 doesn't have. So maybe that would be more suitable for you.
Mark1985 wrote:
I had the idea that converting to a 300cc would not be a huge amount of work and would improve performance.
I don't think this can be reasonably achieved. I'm sure there's a maniac machinist out there who is ready to prove me wrong, but the effort is way out of sync with the payoff.
Mark1985 wrote:
So maybe I shouldn't think of a different cylinder, but of the Malossi cylinder head with larger valves.
If you can find one, yes. They don't make them anymore.
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What you gain, what it costs and what you lose is a sucker's bet on this one. There is something to be said for being happy with what you have.
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the reason the 300 makes more torque is because of the longer stroke-- in conjunction with the larger bore, but mostly it's the stroke.

it's pretty much been laid out here, to convert a 250 to a 300 would require the crank, piston and barrel be swapped, or an amount of machine work that isn't economical for the returns.

so, obviously the best path is the aftermarket bits: malossi head & barrel. but, considering neither is made any longer that makes it a little trickier.

so, if you're hell bent on making more power then you're going to have to get creative. which means machine work.

a malossi valve kit and a custom ground cam with a reprofiled piston for additional valve clearance is probably where I'd be looking to start.

but really, the malossi 4V head is the absolute best bang for the buck. even with having to machine the piston.
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looks like there are plenty of V4 heads on ebay
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greasy125 wrote:
(...)
it's pretty much been laid out here, to convert a 250 to a 300 would require the crank, piston and barrel be swapped, or an amount of machine work that isn't economical for the returns.
(...)
I think so too.

And there is good advice in what Abner_Bjorn said:
Quote:
There is something to be said for being happy with what you have.
But if you really need or want more power I would look out for a GTS 300 in good condition and replace the 250.
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thank you all for your good responses! I have plenty to think about. my thoughts are now mainly on a Malossi 4v head, perhaps even in combination with the standard 250cc and adjusting the piston. I'll think about it!

Is the standard ECU able to provide sufficient fuel in all cases? Does the ECU adjust itself when, for example, you install a larger cylinder or different cylinder head?
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ECU compensates up to a point. Let's say it can compensate up to 10%, on a fuel injected engine, before you start to go outside normal fuel mixture parameters and cause issues. For 250cc that means you can go up to 275cc before it cannot compensate any more. Maybe it can compensate up to 20%. Then you'd be good up to 300cc. Or you could get 20% bigger injector, then the ECU will be working in its more normal range. It depends really on how sophisticated your ECU is. How much/many of the engine parameters it is monitoring.
Engine power is a careful balance of everything from the tip of the air intake to the point of the exhaust. Change any one parameter and you might end up with less power. Almost always less reliability and more fuel consumption. And on a scooter you then have to tune your CVT to the engines new power-curve.
It can work. IMHO though, spending money to chase one or two horsepowers is money I'd rather spend on service; better tires, brakes and fuel, even suspension.
The Driving 4 Answers YouTube channel has many videos explaining how engines work. Here he has listed some of the main items affecting power and power curves. (Vespa does not have variable cams)
Forum member supplied image with no explanatory text
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Mark1985 wrote:
Is the standard ECU able to provide sufficient fuel in all cases? Does the ECU adjust itself when, for example, you install a larger cylinder or different cylinder head?
I didn't have to make any ECU or injector changes for my modded 250 with Malossi head + cylinder. The ECU was able to compensate.

On that bike, I also had a PM Tuning exhaust and the Malossi upgear kit. All of these things put together made it quite fast -- but low-end torque wasn't especially pronounced like it is on the 300, since it's still using the stock 250 stroke.
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jess wrote:
I didn't have to make any ECU or injector changes for my modded 250 with Malossi head + cylinder. The ECU was able to compensate.

On that bike, I also had a PM Tuning exhaust and the Malossi upgear kit. All of these things put together made it quite fast -- but low-end torque wasn't especially pronounced like it is on the 300, since it's still using the stock 250 stroke.
Agree 100%, exactly same experience here.

I remember I do the numbers for some conversions in order to check how much is the cylinder capacity and going from a 250 engine (244cc real) to a Malossi 300 (282cc real) is 15.57% more and the injector do a good job
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oopsclunkthud wrote:
looks like there are plenty of V4 heads on ebay
just because they are listed (by 2 separate sellers only) does not make them available.

Motovista has great contacts in Italy and with malossi and he can not get one.
@lars_danner avatar
UTC

Hooked
2014 GTV300; 2009 S50
Joined: UTC
Posts: 163
Location: Anchorage AK
 
Hooked
@lars_danner avatar
2014 GTV300; 2009 S50
Joined: UTC
Posts: 163
Location: Anchorage AK
UTC quote
old as dirt wrote:
just because they are listed (by 2 separate sellers only) does not make them available.

Motovista has great contacts in Italy and with malossi and he can not get one.
Yup. I tried ordering from one of those eBay sellers and after about three weeks they admitted they didn't have the head and refunded my money.
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