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@gummy8879 avatar
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2009 Stella, 2001 Honda Helix
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@gummy8879 avatar
2009 Stella, 2001 Honda Helix
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UTC quote
Throwing around some ideas for some further performance upgrades. I got the 23/64 upgear kit with the intention of upgrading the rest of the engine to "grow into" its new tall gearing. More power was always in the books but while I had the case open for a rebuild and the kit was on sale, I threw it in early. Here's what I have planned out so far, ordered loosely in stages. My current setup is in my post signatures.

1. Swap out SIP Road 2 for a Polinibox, Case/cyl matching + little PnP and case work especially around the intake. Definitely opening up the ports if nothing else at first.

2. Replace the castiron Super G for a VMC Stelvio aluminum kit. MRP 30mm RD350 pattern reed intake + Keihin PWK28 carburetor.

3. 60mm full circle crank + appropriate spacer. If I go down the longstroke path, I will most likely get a VMC Crono if I ever have to replace the Stelvio.


My minimum end goal is a reasonably reliable, touring-capable 18-21hp. Few questions to pick your minds with:

-Should I do anything to upgrade the ignition system? CDI, stator, etc.
-Am I playing with fire by wanting to do this with a LML case?
-I know Dellorto carbs are popular for standard sidedraft carb swaps, but I am partial to PWKs. Good idea?
-Is a SI 24/24 with a bolt-on venturi worth considering? I assume that the LML single reed becomes a bottleneck much faster than a standard vespa's rotary valve intake.
-Am I being realistic?
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you need to move to a decent clutch to keep up. VMC Molle is what I suggest.
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76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 79 P200E, 66 Lammy S3
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18 HP is easy on LML cases.

Get the Mazzi P200 bell crank & conversion little end bearing, a base spacer, PWK 28, and a better pipe than the Polinibox. The RD350 reeds let it breathe like it wants to.

The Polinibox runs out of RPM's too soon. You should be good for power up to 8,000+ RPM's with no loss of low end. Instead, look at something like a Megadella or one of the BigBox'es. SIP or BGM will both work.

You'll need a better clutch, like Gick said. Any of the upgraded Cosa2's are good up to 27 or 28 HP, which is also about the absolute max you might see from this build. I'm curious to try out one of the new SIP smallie-style clutches for largeframe. Dunno if you feel like being the crash test dummy for one of those, though.

Static timing ignition will work just fine. Variable timing will get you incremental benefit before you get into the power curve, but also a first kick start damn near every time, even dead cold, no choke. Slightly more skill required to set it up, but even that can be pretty easily overcome with an adjustable timing light.

Port timings will be essential to making it all work. Diligent assembly and no air leaks will be essential to keeping it working.
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What about a sip road 3.0 ?
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Lucky
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ferriswolf wrote:
What about a sip road 3.0 ?
It will get you more top end RPM's than the Road 2 and an extra HP. The peak power moves down, too.

Screen cap is of comparative dyno's from SIP's video. Polini 177, but otherwise stock:
SR2 in green, SR3 in red
SR2 in green, SR3 in red
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2009 Stella, 2001 Honda Helix
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I considered the Road 3 too but the poor ground clearance concerns me a little.
chandlerman wrote:
Get the Mazzi P200 bell crank & conversion little end bearing, a base spacer, PWK 28, and a better pipe than the Polinibox. The RD350 reeds let it breathe like it wants to.
Whats the difference between a P200 crank and a longstroke 150 crank? And do you think bell cranks are better for reeds? I understand the idea of crankcase stuffing and keeping velocities up inside, so I assumed a full circle crank + careful porting is the best combo.
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Lucky
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gummy8879 wrote:
I considered the Road 3 too but the poor ground clearance concerns me a little.
The Road 3 is almost the same clearance as a stock pipe. It has much better clearance than any of the BigBoxen.
gummy8879 wrote:
Whats the difference between a P200 crank and a longstroke 150 crank? And do you think bell cranks are better for reeds? I understand the idea of crankcase stuffing and keeping velocities up inside, so I assumed a full circle crank + careful porting is the best combo.
The P200 crank has a 110mm rod instead of a 105mm rod. Stock stroke on both the P200 and 125/150 is 57mm. 60mm is a long stroke. If you really want to go wild, you can do a 62mm stroke, but that will require modifying the crank case to fit it.

The longer con rod gives you better geometry, plus effectively infinite control over your port timings. The bell will give you better low-end power, but will still produce peak power put to almost 10,000 RPM's with the right top end.

Rob Hodge put me up to trying the P200 crank in a 150 almost yen years ago now, and I've been a fan ever since. The Germans have also discovered them for their 150's, too, with very respectable results.
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chandlerman wrote:
The Road 3 is almost the same clearance as a stock pipe. It has much better clearance than any of the BigBoxen.




The P200 crank has a 110mm rod instead of a 105mm rod. Stock stroke on both the P200 and 125/150 is 57mm. 60mm is a long stroke. If you really want to go wild, you can do a 62mm stroke, but that will require modifying the crank case to fit it.

The longer con rod gives you better geometry, plus effectively infinite control over your port timings. The bell will give you better low-end power, but will still produce peak power put to almost 10,000 RPM's with the right top end.

Rob Hodge put me up to trying the P200 crank in a 150 almost yen years ago now, and I've been a fan ever since. The Germans have also discovered them for their 150's, too, with very respectable results.
so if you installed a p200 crank and packed the cylinder up 5mm the timings would stay the same? is there any advantage to that in itself or does that come when you modify the cylinder?
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UTC quote
The geometry is different, so the timings will be a little different, but you also get a lot more crank case volume, so more mixture to pump.
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chandlerman wrote:
The geometry is different, so the timings will be a little different, but you also get a lot more crank case volume, so more mixture to pump.
Thank you for that explanation.
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UTC quote
Be careful though. Too much empty crankcase volume and you get less pumping and cylinder filling. The less crankcase volume you have, the better the piston is at squeezing the fresh charge into the cylinder on the downstroke. Think of it like blowing through a really wide straw, a normal straw, and a little coffee stirrer straw. Too big and you get less air velocity for the same air pumped through. Too small and its restrictive.

The theory behind full circle crankshafts is that they "stuff" the crankcase volume and keep everything flowing fast. Looks like bell cranks are the way to go on largeframe engines solely because of the intake design (as these were designed to be rotary valve originally). All 2 stroke nowadays have full circle cranks for this reason.
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chandlerman wrote:
,The longer con rod gives you better geometry, plus effectively infinite control over your port timings. The bell will give you better low-end power, but will still produce peak power put to almost 10,000 RPM's with the right top end.
This is very interesting! My Stella currently has 5,000 miles on the crank and I'll be replacing everything soon. I'm thinking BGM 177 with electric start and I'll have to look at what crank to get. Hmmmm....
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Lucky
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qascooter wrote:
This is very interesting! My Stella currently has 5,000 miles on the crank and I'll be replacing everything soon. I'm thinking BGM 177 with electric start and I'll have to look at what crank to get. Hmmmm....
I have a BGM177 on the Stella motor in my GL which has all the goodies. With the uprated reed block & reeds, plus side draft carb, things can get real expensive real quick. Especially since you're going to need an upgear and stronger clutch to go with it...
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chandlerman wrote:
I have a BGM177 on the Stella motor in my GL which has all the goodies. With the uprated reed block & reeds, plus side draft carb, things can get real expensive real quick. Especially since you're going to need an upgear and stronger clutch to go with it...
Yeah, Ka-Ching! I like the idea of a VMC Molle clutch. Is that the RD350 reed block you used?

And while I'm dreaming - a 28mm SmartCarb would be pretty cool!
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gummy8879 wrote:
Be careful though. Too much empty crankcase volume and you get less pumping and cylinder filling. The less crankcase volume you have, the better the piston is at squeezing the fresh charge into the cylinder on the downstroke. Think of it like blowing through a really wide straw, a normal straw, and a little coffee stirrer straw. Too big and you get less air velocity for the same air pumped through. Too small and its restrictive.

The theory behind full circle crankshafts is that they "stuff" the crankcase volume and keep everything flowing fast. Looks like bell cranks are the way to go on largeframe engines solely because of the intake design (as these were designed to be rotary valve originally). All 2 stroke nowadays have full circle cranks for this reason.
Careful what you read. Vespa crankcases are small to start with. All original blocks were designed for small capacity cylinders, in the days when high case compression was considered good. Decisions should be made depending on the upgrades and application. Vespas don't have a one size fits all option.
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UTC quote
gummy8879 wrote:
Whats the difference between a P200 crank and a longstroke 150 crank? And do you think bell cranks are better for reeds? I understand the idea of crankcase stuffing and keeping velocities up inside, so I assumed a full circle crank + careful porting is the best combo.
Most modern 2 strokes use full circle cranks. On the Vespa or even LML reed case the path for the gas is fairly well blocked when using a full circle. Hence the popularity for bell or cut cranks... even Kingwelle use them and they're about as high end as you can get.
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qascooter wrote:
Yeah, Ka-Ching! I like the idea of a VMC Molle clutch. Is that the RD350 reed block you used?

And while I'm dreaming - a 28mm SmartCarb would be pretty cool!
I have an MMW reed block with VForce4 reeds. It's a fair amount smaller than the full-on RD-350 reeds that I have in my Smallie, but it only has two petals, not four like the VForce, so I'd need to calculate total area to really have a number.

I'm pretty sure I have spares of both lying around for comparison, assuming I think of it next time I'm in the workshop.

And I'm really curious to try out one of the new SIP Supersport clutches, too.
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chandlerman wrote:
And I'm really curious to try out one of the new SIP Supersport clutches, too.
It may interfere with the pinion for the oil injection cog. don't like the idea of removing material off of it as you only have so much before you get to the circlip. You could remove material off the screws on the backside of the clutch; don't like that idea either. If i have to do either to prevent interference, then it's just not worth it.

If you are not running autolube, then that's not a problem i reckon.
⚠️ Last edited by GickSpeed on UTC; edited 1 time
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Lucky
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UTC quote
GickSpeed wrote:
It may interfere with the pinion for the oil injection cog. don't like the idea of removing material off of it as you only have so much before you get to the circlip. If you are not running autolube, then that's not a problem i reckon.
True. They basically state it's really only for pre-mix bikes in the body of the description, even if they do so in the most convoluted way possible.
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chandlerman wrote:
True. They basically state it's really only for pre-mix bikes in the body of the description, even if they do so in the most convoluted way possible.
agree. if you are indeed running some big setup with a sidedraft carb, then this clutch would be to the way to go.
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gummy8879 wrote:
Be careful though. Too much empty crankcase volume and you get less pumping and cylinder filling. The less crankcase volume you have, the better the piston is at squeezing the fresh charge into the cylinder on the downstroke. Think of it like blowing through a really wide straw, a normal straw, and a little coffee stirrer straw. Too big and you get less air velocity for the same air pumped through. Too small and its restrictive.

The theory behind full circle crankshafts is that they "stuff" the crankcase volume and keep everything flowing fast. Looks like bell cranks are the way to go on largeframe engines solely because of the intake design (as these were designed to be rotary valve originally). All 2 stroke nowadays have full circle cranks for this reason.
I faced this issue when my LML crank blew at 4,500 miles. I ended up shying away from the full circle cranks because the flanges are reputed to block flow at high rpm. Because I wanted to keep a 57mm stroke, I ended up with a Worb5 flowed crank, which is working out pretty well (around 8,500 max rpm). A bell crank might have been even better but, as far as I could see, the minimum stroke on those was 60mm, which did not really suit the cast iron Malossi 177 kit I already had.
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UTC quote
I ran that Worb5 flowed crank in some of my earlier builds. I still have it on a shelf, I think. It was a solid product.
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