Modern Vespa

boosting velocity into a plenum is counter productive. you trade pressure for velocity but when you dump that into a plenum the velocity is lost to turbulence.

An alternate hypothesis for why it tapers in that 8mm space:
1. The area in the casting at the exit of the reed block must be large enough to house the reed block.
2. Because of the reed stops, walls, and bridges, the effective flow area at the end of the reed block is less than the total area of the casting.

Hypothesis: To reduce the losses due to the area change the manifold can reduce in area to more closely match the flow area.

Ok - Know this is hitting plaid levels of nerdy.
Ginch your going to love this... its full of cut and paste from my Ai queries (only way I can digest some of this).
Editors note: This is probably why they gave us the "Just Walk Away" button... So this sent me back to more carefully check my modeling.
Here is a sliced view of the areas as you move down from the nose of the reed.
(I also show the 8mm Patrick referenced, for clarity)
Screenshot 2026-08-29 at 12.16.35 PM

So on double check, the Quattrini is in fact intentionally necking down the opening area.
The velocity increase appears to be real/intentional.
I have to believe that it is a feature not a bug. This seems like it's in tension with the idea that velocity is helpful here.
So what's going on? Maybe two things are occurring at once.

Here's a possibility: The plenum is not steady state. It's pulsing.
Once the charge column has real momentum, it keeps flowing into the crankcase for a brief moment even as the driving pressure differential starts to fade, packing in extra charge right at the closing window of the reeds. I think this "super packing" (my term) is a known principle in 2 stroke pipes as well.

The trade-off comes down to how the air decelerates:
Useful Ramming: Velocity converts cleanly into static pressure, packing more air molecules into the crankcase.
Turbulent Loss: Velocity is lost to chaotic, swirling eddies

In a pulsing two-stroke engine, high intake velocity is the carrier of mass momentum—and momentum is what creates dynamic supercharging in Quattrinis design.
This is why I don't want to mess with the last 20ish mm of inlet as it reaches the cylinder.
I'm assuming he is getting some "useful ramming" net positive over the "turbulent loss", so I am re-utilizing that part.

Sounds like you are getting there! This is great, a lot for me to learn here.
Velocity increase, I think you got that right. The first time I really gassed it, the Quattrini M200 totally blew my mind. A Jet Engine sensation and sound is as close I can describe it. Riding a jet engine!

Well you lost me, Nerdyman22. I'm with Socalguy, I think he had physical restrictions that makes ideal geometry impossible. Much like the welded intake picture earlier - if it won't fit, change it until it does.

Here's a thought along those lines - make the absolute ideal manifold, and cut your side panel to suit.

I think that one thing that's being forgotten here is just how good the M1XL is.

I'm talking third gear power wheelies and sub-six second zero to sixty with my 230lb fat ass on the back.

If Max ever does an updated version, I'll be all over it, but in the meantime, this cylinder is on another level from every other small block kit on the market. The only competitors I've ever ridden... were smallie Quattrini kits.

Well you two have good company.
OCT also not buying my theory on velocity.

I'm curious why Max made certain choices.
- Reed pulled out
- Angled back
- Not feeding transfers directly.

Space explains the tilt - so I see some "physical restriction".
Maybe he wanted height for bigger carb too.

But both those could have been done without pulling the reed out of the cylinder.
*If he had stuffed it in there like Rotax/moto, it would have blocked less cooling air path and made more space.
Pulling it out looks very purposeful to me - and not for space.

I get y'all are skeptical. Chuckled.
You can take the boy out of tune, but you can't take the tuner out of the boy.
Off to force-feed a V4 in this thing in search of just that much more.

also consider constraints of needing most of the same molds to work with the non-direct induction version. Specifically Boyesen ports feeding the transfers could likely work, but making cores that play nice with both versions of the casting would be a pain.

Good thought.
Perhaps that was the reason for the closed off section - tho they must have had some kinda collapsing core to allow the shape they ended up with?

Maybe it's about high end power.
Chandler, does below match or conflict with your experience?

If you believe what I read…

Sliding reeds toward carb (same total tract length) affects torque:

Reed valve splits the tract into two separate systems (reed→cylinder vs carb→reed) that are isolated from each other when the reed is closed.

Reeds closer to cylinder = shorter reed-to-cylinder length = sharper response, tighter reed timing, usually better low/mid torque.

Reeds closer to carb = longer reed-to-cylinder length = more dead crankcase volume at low RPM, softer bottom end, often stronger top end.

How much more is it exactly?

And if you do all this super-fine tuned machining, and it goes like wow! ... what percentage are you going to attribute to Ned, and what percentage to Max?

And if it goes like wow! ... are you sure it wouldn't be wow + 7.3% if you had have left it alone?

Inquiring minds would like to know.

Are the musings above about space to fit under the panel, or increase power utilising the new block?

If its just about space with a power increase, couldn't you just turn the manifold and the associated part after the reeds 180 degrees?

This would allow fitment and negate most of the modifications necessary to fit the carb and reed assembly


My pondering based on probable lack of understanding of what's being discussed

Between those two, I'd say Option A, sharper response...better low/mid torque. It pulled power wheelies up to third gear if I didn't have my mass up over the bars. Still revved way out, too, though.

I'm still dreaming of the day that Max releases an updated "S" version of it, similar to what he did with the M1L60S and M200S.

*Who's Max? At this point - even I have to consider "what's it about"?!
It's largely about fitting a state of the art reed to the kit.
"Largely" rather than "mostly" because it's also about the process.
HOW I fit the reed itself will affect the characteristics.
Spinning the manifold: Considered. not ideal. it leaves a nasty internal edge at transition from manifold to cylinder, that can't be ported as there is no meat on the cylinder and manifold has internal area pointing wrong direction. Also doesn't fit the reed I want to shoe horn in. Yeah - that caught my eye. Interesting. Would have thought perhaps it was more about the top end power. Was that with pipe or box?

*Depending on how I execute the V4, I may still be in position to swap one intake/reed for the other - with just a few cap head screws. That would be fun - as of course I'm interested. But I'm going to optimize for for the V4, so if that means scrapping the comparison; so be it.

OK, I'm gonna say it. Time to get the show on the road.

Put the V4 on the shelf for now. Bolt up the stock reed cage and see how the engine runs. The reeds are going to add what? a tenth of hp?

You can mess with a different set of reeds downstream. It's the middle of summer fercrissakes. The unicorn needs to be ridden.

I'm waiting on the CM22 proprietary nuclear fusion power plant design. Look, look… If he doesn't get the unicorn into actual orbit by the next ROM this will have to be considered a failure at some level.

CM2 right now...

I've definitely had Michael J Fox's look on his face while following along with this…

Hold onto Your butts. We're gonna see some serious Sh*t

Is it the last minute already!!?? You can't just jump to the end like that... first he has to create a machine that can build a can-making machine, then....

Hope you didn't jinx it!!

There are no jinx'es in CM2's world. Only opportunities to learn more machining techniques.

You grossly overestimate my jinx power.
Fortunately for all of us, Ned learned a long time ago not to listen to me.

Oh, don't you worry your pretty little cylinder heads!
As soon as I can shake my day job duties which have me up in LA a lot right now, y'all are in for a treat.

And when I say y'all, I mean all y'all.
Weather your in the: "just make the biggest hole you can" crowd, or the "just get it done" group, or the "you can't do it better than Max" gang, or even if you are in the just get it done group but also biggest hole you can curious, I assure you I will propose something that is likely to prove you mostly right.

And of course for the "I'm just enjoying the ride" crowd, my brothers, there should be plenty YouTube Darwin Award winning entries, so prep your popcorn. Few more days and I am back in the shop.

In the mean time, here is one of the concepts.
Careful look will illuminate.

Yay! Don't let that damn side panel hold you back!

I'm both "Make the biggest hole you can" and "Just get it done" at the same time.

I still think that if you don't build it stock, test it, then swap to your customization, you'll never know how much (if) what you did made it better than stock.

And, yes, I know that's definitely counter to "just get it done."

Go big or go home!

Ginch, you were so close with that choice of picture...

I bet you could. Just not by guessing, even if it is informed guessing. Absolutely this. Choices were limited when I filtered it for orange!!

You found the Key to the Secret?!?!?!

I don't think you are giving this guy the proper credit.
Can we just pause for a moment on that corner cut out?
Wow.
[url=https://flic.kr/p/2sAmMZ3]

The Quattrini cylinder is already highly optimized.
Often in cases like this, its more about trade offs.

There are 3 items I see that I wanted to tackle.
1. Cooling air flow
2. Allow for a modern reed (broader power band)
3. Cylinder stud hole small ID

Patrick mentioned production constraints related to another feature.
Got me thinking: maybe they undersized the stud holes because of issues with wall thickness. They come really close to the delta shaped inlets.

No matter the reason, I don't like the small size.
It limits expansion before seize, and stud holes should not be counted on for alignment. That's the skirt's job.
So easily fixed. Check.

My design concept addresses 1&2.
Before you start throwing tomatoes, I am well aware it raises a risk of undesirable turbulence.
With that in mind, I've done what I could to minimize/ only testing will tell if it creates issues or not.

The concept: if I spin the reed 90°, I could create a design that harvests the concave side of the reed to diminish air flow path intrusion.
To do that, I need to create a transition of flow from North/South, to East/West.
The idea is to do that in as compact a height as possible, without creating transitions at greater than 60° included angle (the sum of both sides of my taper).
I didn't quite get there, but the intake is expanding in width as it is narrowing in depth - so this is where I landed.
[url=https://flic.kr/p/2sAsKZP]

The "transition area" is where the flow will change from N/S to E/W. It is about 15mm tall. Some additional porting can help reduce the "included angle" to minimize turbulence.

And here is the pay off.
Now using the modern reed.
If I shape my intake as a net fit to the concave side of the reed.
Red dotted line for accentuation purposes.
[url=https://flic.kr/p/2sAsece]

As for height of carb, it's probably not that evident without looking at how I measured up for it.
Below is the stock manifold. The intake is angled upwards.
That's probably because they didn't want to make a tighter bend.
The carb in this picture is sitting at the lowest point possible.
You can see from the angle of the intake, if I attach the carb, it will poke the nose up in the air.
This is where I want to run my bell mouth.
Its close call on if it will fit under my cowl/ interfere with airflow.
[url=https://flic.kr/p/2sAspz3]

And here is how I created the fit for my model.
You can see there is a gap between the rubber 90 and the reed.
This is most of the space I need for my transition area (though it will be below rather than above the reed).
[url=https://flic.kr/p/2sAuJQH]

I get that the only way to know what I am or am not getting is to compare the two in the end...
But if I don't do the porting now, it would mean pulling motor back out, tearing down, porting and replacing.
By porting now I obviously avoid that.
However - I need to know what I am porting and where - and there are more subtleties to that than may meet the eye.

I am off to the shop to do some metal cutting.
The set ups and execution are their own thing.
Perhaps I'll touch on that in next post with some evidence of just how pear shaped it can go...

So let's call the above "Concept A".
I've got another but first I need to see what's actually cuttable on my mill.

Once the part is designed, you have to create the cutting programs.
Its in the same software but its like the difference between turning wrenches and riding.
Its just a whole different set of skills.
So in the background, I am on a super steep learning curve(s).

Because this thing has a negative draw (taper in then taper out). and I am cutting it from billet, I'm going to need to seam it somewhere.
Kinda like motor cases... 🙂
I can split it up a seam or at the hourglass "waist".

It's debatable which one would be best.
The "waist" might be simpler, but would require deeper cutting.
I decided to try the tall seem.
I've added material above and below the final part, and put dowel pin holes in.
This will allow me to align the two sides while I weld them together.
Then I'll machine away the extra material top and bottom which will also give me flat gasket surfaces.

Time to try some cutting to see what some of these programs produce, and what it's like to cut billet aluminum.
First up: square up the stock.
[url=https://flic.kr/p/2sAyau6]

Including the end, which will allow me to reference this off a stop I set up in next step. This will make keeping its position when rolling it to the different cutting sides.
[url=https://flic.kr/p/2sAyawv]

Then I drilled some holes that will serve for alignment pins. I discovered a "peck drilling" feature that was super cool way to set it up so it clears the chips between drilling in "pecks".
Below you can see the steel lock I have set up to give me an end stop.
[url=https://flic.kr/p/2sAyaub]

With the reference holes drilled, I cut the front pocket out. This is where the reed will live.
[url=https://flic.kr/p/2sAwGeV]

Then with a flip of the stock, I took a shot at the back. There were a few programming errors but I managed not to trash the part - still usable if not elegant. This is after the "roughing cut" and before I played with any finish cuts to clean up the steps.
[url=https://flic.kr/p/2sAwcav]

Last up were the sides. As more and more work goes into the part, it gets a little puckering - as the possibility that the cutting tool just whacks through a wall you didn't anticipate. (trust me...)[url=https://flic.kr/p/2sAyawk]

And this is the (mostly finished half). [url=https://flic.kr/p/2sAwXDi]

So I'm able to create the half - if imperfectly.
I've corrected some of the more egregiously erred programs.
Forgot the reed at the shop - so will have to wait til then to do a fi test.

I left the mine craft tapers on the side, no need to fully refine the part.
Managed to experiment a little with some of the other surfacing finishes.
Have a much better sense of what and were the levers are for refining.

Are you using M7 or M8 studs?

I've been waiting patiently for you to get to this part of your build. Digging it.

Std M7 (bit longer than stock).
This is what I posted back in March in my failed run up to the rally. Chandler initially told me about it...
So naturally I was skeptical.
Measured them for myself...
To my surprise, they were about .2mm (IIRC) under the VMC and BMG size.
🙂

Not much to report today - but I have this vid of the mill doing the auto "pecking" I previously mentioned.
It's a little OCD moment of zen for me - so sharing it here for your joy.
(note the way it creates a precision pre-drill nib before shooting down into the material).
Kinda makes me tingle.

https://youtube.com/shorts/Np7Wuyc1wNc

Pity. If they were 8 you can get a stud made for a different series (Quasar iirc?) that is thinner in the middle. Maybe you can get that lathe start paying its way* and turn up some special M7 studs.




* kidding

Interesting. SIP says "The reed valve supplied with the Quattrini can be used as a reed valve or models from Tassinari or Reed Valve. "

https://www.sip-scootershop.com/en/product/intake-manifold-quattrini-m1xl_17981169?usrc=Engine%2C+Gaskets

I have one. It fits perfectly.

https://www.sip-scootershop.com/en/product/reed-valve-block-tassinari-vforce-3_27422000

me too