Modern Vespa

I speak for at least some of us in saying.. too late. Thoroughly confused for a while.

OCT - thank you.
I have some insights from this - but first I wanna see all the numbers.
Looks like somehow the chart dropped off the 119/60/179 HP readings in the 13mm and 14mm groups.

Before I respond - do those exist?

Swiss.
Will do a little break down of Patric's diagram that might help.
Your response was pretty good chuckle over here.

OCT - second question(s):
- Circled angle is 65 in this drawing. Expected it to be either 60°. Is that correct?
- Opened the link - cool! could not quite sort out how to rotate just the crank?

I only ran a subset in the 15, 17mm width. let me run the rest.

"Circled angle" is A in your diagram, right?
This is dependent on E (-5°) and F (130°), I pulled these values off the info on the SIP crank. the web interface is not that good, if you have fusion (free for limited use) you can download it and it works better

I'll download so I can play.


Ok. The sip crank I have (sip says…) is 125/-5 rather than 130.

Yes. That is angle A from my drawing.

Here's a really good spreadsheet based STA model that is very up to date with the state of the art. It also produces a printout of the cylinder wall to guide the cuts. has a well written manual too.

https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1131193744#post1131193744

After some phone calls and discussion sorting out all the angles, what the crank measures, where the cases are currently... we came to the following numbers to run.

Note:
* due to the chamfer on the edge of the crank the max width of the port is kept to 14mm

OTC - many thanks for taking the time to do this.
Couple observations then.
- I look at the HP numbers in this chart as relative to ea. other rather than precise predictions for what I will achieve. I expect to be closer if not above 20.
- However - the 5K-6K RPM ideal for peak HP - leaves me in a bit of a quandary. That suggests I should be tuning all components (box exhaust, cylinder, etc.) for this lower rev range. Challenge is - I prefer to peak closer to 8K/ 8500 RPM for my riding style.

Have decided I will be a bit more aggressive with the inlet duration - taking it to 185 - while taming the cylinder to about 180 ex. duration rather than 185. I think that will be a good balance for me. I could even drop the cylinder down to 177 if I wanted to see if that produced more power as the calc's suggest it would - but it would be all in by ~6500 Im guessing.

Ok - off to grind and shape.
Need to fabricate a new intake manifold as well.
Pretty pictures to follow.

Good, cause I only come here for the pictures - wait, wrong forum! Ha!

All in by 6500 would be great, what are your exact numbers? I still have a virgin P200 with a Pinasco cylinder and 60mm crankshaft, waiting for me to do some grinding.

Do you have the numbers for a P200 rotary pad width?

Seeing differences in inlet widths and HP numbers relative to each other is great.

What would you need to do to show a set of reeds in this setup for a relative comparison? I would love to see a set of RD350 reeds in comparison. A set of Vforce 4 reeds would be great also. I could buy a set of each if you would need measurements from them.

https://www.mrp-racing.de/MRP-Reed-Valve-System-PX-RD350-30mm-CNC-Edition-with-RD350-reed-and-carb-rubber

🙂 Christopher:
- Mine is a P200 rotary pad - as I modified my 150 cases. I am using a P200 crank as well - so my numbers would be similar to yours. You can reliably expect the 14mm wide pad opening, from OTC's calcs, as a highly achievable one (P200 crank will be 16.5ish after you account for it's chamfers).
- What his calcs suggest is, that with a rotary pad, and inlet duration of less than 190, the motor will produce its highest POTENTIAL HP at about 6500.

By potential - I mean - you can put a cylinder on it with raised ports so that it peeks at 8000RPM. However, on the same motor, if you brought that cylinder down to timings more appropriate to 6500 RPM - you will actually make more HP.
I went and found some dyno tests - and posted below.
Compares the Polini box with higher and lower cylinder timings.
Seems to confirm OTC's calcs.

The reason for this, I think, is that your rotary opens and closes. You need time and area for that to occur. The rotary is open longer at lower RPM. Balancing that though, at some point, there is too much pressure in the cases to fill them any more - OTC estimated that to be about 8 with a modern cylinder.

So below 6500 (as an example), the rotary is open longer in time, but BMEP is limiting factor/ is too high to use all the open time. Above 6500, pressure is low enough to handle more fuel air being packed in, but your rotary is closing too fast to fill it to the max.
OTC can comment on whether the above stands the test of reason. He and I discussed the results and I think this was his view.

Now - whether you believe those calcs to be accurate is another thing. I suspect they are - relative to ea. other - but I have some skepticism about their accuracy from an absolute value perspective.
I am basing that on what I've seen over on the German scooter forum.
These guys are maxing out about 20HP (around 6500 RPM) with rotary valve.

The only advantage that I bring vs them at this point, on my build is:
A. 62mm crank.
B. A full P200 width pad (they are all stock 150 width and probably about 12mm wide to my 14).


This shows 117/124 vs 124/180. Looks like there is more in it in this case with the lower timing.

Question:
Squish.
I have it at .8, which the GSF wiki says makes it 11.7:1
If I move to .1, would give me 11.3:1
What is too high?
What are the trade offs of more or less squish?

It would be great to see calculations with a reed valve, seeing numbers with a wider opening makes me think a reed may produce more. The difference between a 14mm and 17mm is about 20%.

Re-post incase this got lost:
Question:
Squish.
I have it at .8, which the GSF wiki says makes it 11.7:1
If I move to .1, would give me 11.3:1
What is too high?
What are the trade offs of more or less squish?

Last two pieces of fabrication.
Timing indicator plate - will make more sense when finished & new intake manifold.
Manifold welding is a bear.
So hard not to warp anything.
Tight angles and what not.

Moved carb to a 37° angle to buy just a touch, and shaped the manifold to go from partially ovalized to round.


Found a piece of scrap steel and surfaced both sides

cut and welded a few bits of steel tubing... Tho not shown shown here - while hot - I squeezed the end to ovalize it a bit - so it takes on the shape a bit like what OTC drew - and transition from carbs round outlet to intake's elongated radiuses rectangl

bit of nip and tuck and its all settled in nice and tight. Can just pull the choke - no touching of the cylinder fins, etc.

This will make more sense when its complete...

Do you mean from 0.8 to 1.0?

Calculations not my strong point...
1.0
🙂

Squish gap

Thanks.
Had seen that previsously. But the mind wonders:
What are the practical results of to much or too little MSV ?
How does one recognize they have gone too tight on squish or too high in compression ratio?

Blair says to aim for a MSV of 15-20 m/s, later work by Aprilia goes much higher, but that's in race bikes.

Pro (in the right range):
the turbulence caused by squish works to prevent detonation and speeds up the burn rate, both are good things. The small gap between the piston and head is too small for the flame to burn into so the piston can transfer some heat to the head in the squish band.

Con (MSV to low):
Possible detonation, slow burn rate requires more ignition advance, larger gap between piston and head holds more unburnt fuel.

Con (MSV to high):
Gas trapped at the farthest edge of the squish band may not be able to move out through the gap and may detonate at the edge of the piston. If the squish gap is too small the piston will hit the head.

Too little MSV creates less power and what doesn't turn into power turns into heat. Not great. Too much MSV, detonation, way more heat, damage, cost, embarrassment, piston hole.....all totally avoidable if you listen to the engine crying for help.

Compression: All the regular and exotic looking heads we buy and the ones sold with kits, from any scooter shop, are all reasonably vanilla. MSV is within limits (or way under), average squish band or less, low ish compression.
Serious but still usable compression is around 14:1 or 8:1 trapped, on 95RON pump gas. Depends on what type and how much cooling. Ignition timing is important. Jetting is critical. Budget matters. Under 12:1 or 7:1 trapped is considered safe enough for the general public.

Manifold looking very professional. You could sell those.

Reeds will absolutely produce more power, because they're pulling in all the air that the carbs and reeds can handle, which if you're using a ginormous carb and VForce4 reeds, is a LOT.

The basic theory still holds true, but you can also get to higher RPM's because you're not losing the intake duration due to the valve closing off when BMEP is below maximum.

I'm looking at the calculations and estimated carburetor size and a 14mm carburetor can't even use the 30mm carburetor I have now to it's full potential. Has me thinking my rotary valve is going bye bye.

one reason I was interested in running the numbers and seeing what we could get from the rotary is reliability. On distance runs reeds are a bit of a gamble and I've been thinking of a 150-175cc rotary based bike that could do 3000+ miles at ~80mph with nothing but a tire change or two.

one thing that is working against the specific time area here is the "specific" part. That divides the time*area by the displacement.

Sounds like someone's contemplating a cannonball...

What about finding or fabricating spring steel reeds like on an LML, but to fit a VForce4 cage? Those things last forever, but are going to lose some (lots? most?) of the performance benefit, too.

Depending on how it tested out in the real world, that could be an interesting compromise.

Houston... we have a problem.

With intake fabricated (tks Jack), and inlet optimized for shape - I was ready to assemble.
Of all the mods I've made - the one that has left me the most uncertain was the inlet pad.
The original version was just bonded in - and then I promptly failed it with heat.
Then I welded in a solution - which was super solid - and re-cut - which was great - except...

Once I cut the fat inlet hole in it - the bottom portion was so narrow - and the material so thin - it just seemed wimpy.
And when I filed the final width of the inlet - I could hear the pad I put in vibrating.

I based my solution off of Joe Cassola's (saint's) but modified.
He strictly bonded - and I chose to weld.
The picture ( below ) of his is thick - but once its cut down - its only about 1mm.

I should have better anticipated that issue.
When bonded as he did - that 1mm is a non issue - you have a laminated component.
But when welded at the ends - the middle area is free floating.
That was a non issue before I cut the inlet hole - but once cut - not so good.
¯\_(ツ)_/¯

Observation:
Every year that goes by - the less patient I am with paying job - the more patient I am with the scoot.

I am regrouping on this one and considering my options.
Have to say - though the process - one thing that has been bugging me:
When your pad is ACTUALLY .05mm away from the crank - it is incredibly hard not to score it when assembling the engine!
(Try pulling a crank in and keeping it aligned by .05mm while simultaneously not allowing it to turn at ALL. wholly cow - its a sensitive one.)

Option under consideration.
Considering going back to the fully boned solution - but without milling.
Rather than using aluminum - moving to stainless. A kind of skin on the epoxy.
I could make some tabs that sit down into the epoxy to help it say put with some mechanical lock.

A flexible epoxy in this case - two different substrates - would make sense.
Joe chose one that while not terribly high heat - was excellent for peal and had some flex.
I would bond it in place with the crank in position and a .05 (.04?) offset created by a shim - no cutting or post processing.
Mind wonders: If 1.25mm is the min at .05mm, would 1mm at .04MM be equally as good?

That's why they call it R&D...
Below - some pictures of the carnage.


That little gap is the pad unattached to the cases. Had not anticipated how thin the pad would be after I cut it down. Futile effort to tack the pad can be seen as well.

The removed pad after grinding out the ends. Pained me - but you can see just how thin the pad was after machining down. Feel like a mold in place solution may be more attainable for accuracy for me

dang it charlie it is still going good you will impress us with the solution. I do feel better about the bajaj now headlight still not working but the steering might be tight now. Looking forward to what you come up with.

When you pull the crank in the open section of the crank should face the pad... but with the fancy pants SIP crank I guess that does not help.

Dude, what a bummer. I thought you were onto something. Oh well, live and learn.

And for what it's worth, it's damned impressive, like off the charts impressive what you've been making happen.

I can remember your first post, and was thinking "this dude just needs to buy a hack and try it out".

Little did I know you were that one and a million (billion) that pulls rabbits out of your ass, er, hat, consistently.

Looking forward to the solution, and like I said - damned impressive...

It was so close. I think I would have run it. Filled the gaps with some chemical and see what happened. Do admire the determination to get it perfect though. Next version will be way better. Not sure what it is but way better.

Thanks you guys.
Appreciate that.

I really want to see what I can get out of a rotary - but I also want it to be durable.
Painful to walk backwards - but gotta post the losses as well as the wins.
This one elicited an out loud yell in the garage.
Makes me laugh at myself as I type.

OCT - I took to inserting the crank away from the sharp edge of the inlet - but you end up spinning it a little to get the piston in the cylinder, checking TDC, adjusting inlet... .05mm is really (really!) close. No way to do the inlet work without turning the crank...
Killed me to see those gouges.

I feel like I got caught between solutions with this last effort.

The welding method can work - but I need to have the inlet cut first - so I can weld by coming in from the top of the inlet. This will work if I do it before I cut the pad.

The bonding method can also work - but if I am bonding - I want to take advantage of how the material conforms and not have to try and do a perfect cut afterwards.
Saints does a nice job - using a specialty boring machine.

To me - the two advantages of bonding I see are:
- You should be able to make it conform exactly to the shape of your crank for a perfect clearance everywhere.
- It opens the door to using different materials - more durable against wear than aluminum.

I'm going to play with some very thin stainless steel.
I'll use Saint's chosen epoxy - it has good elastic properties appropriate to using different materials in a single sandwich like I am thinking.
In the end - I'd love to come up with a fix that is universally doable.
Let's see how this fairs.

If I do go back to welding - this time I will weld that edge that lifted as noted above. The upside to welding is the heat tolerance once complete...

I may be confused cause I haven't followed this modification as religiously, but in your initial attempt that was following saints version, what was the heat from that caused it to delaminate?

Second attempt you just welded it on ends? Or bonded then welded ends? If you bonded and welded, the heat from the weld would cause the central area to delaminate.

I would assume that bonding alone would be fine cause where is it getting serious heat from? Boring it out to a specific gap I didn't think creates enough heat, nor would dremeling the new opening. And when the crank is in and engine running, I wouldn't think the rotary pad is getting heated enough from the case being indirectly heated from the cylinder.

Forgive me if I'm just missing a step or process that caused the excessive heat on new rotary pad.

Hey Swiss - so the original attempt was bonded - and the heat that failed it was my torch!
Why was I using a torch?
I was using a slightly tighter then normal press fit of the main bearing to the bronze seat in the case (which I fabricated).
I needed to get the cases quite warm to open them sufficiently to press the bearing in.
If I had done ALL welding repairs first - I could have inserted the main bearing - then done the bonding as the last step - after all the more significant heating had been done - as I am proposing now.
It's not that I didn't consider this - it was more that I wanted to have something that would stand up to multiple builds/ heating/fixes/torching/welding/ etc.

The welded version was only at the ends and the top edge - not the bottom edge.
I didn't account for how thin it would become after cutting.
When I first welded it in - I thought - oh - the curve will keep its shape nicely - and I will have it welded on three sides - no problem.
But after I cut the pad back - I was struck by how thin it had become.

Jack - my first thought was same as yours.
Leave it alone - its going to run fine.
But I knew I was dealing with some weird clearances in that thin area - and I have only 1.25mm of overlap - so having that part flutter around wasn't good.

I tried to bond it in place overnight - but it was slightly bridged - and the bond was poor.
Last thing was to attempt a high wire weld - where I heated the thick part and just let it creep up on the thin - but the thin just ran away from the heat.
You can see it almost tacked one little spot - but damage was done to the surface.

With stainless steel having a different expansion rate than aluminum, will that cause a bonded pad to come loose? The case will be expanding faster than the pad. Dissimilar metals is how a bimetallic thermometer works.

Fuckstockings. Sorry to see this....

Hey thanks though for the continuing education. FWIW your stumbles are making us all smarter and your determination inspires. Sorry it went all pear shaped, but excited to see the next iteration.

Doesn't also marrying two dissimilar metals result in corrosion? I thought that chemical bonding was a better solution to prevent corrosion.

Material science is not something I'm knowledgeable in, just been obsessively reading up on and watching lots of videos on Tesla's material science for their giga casts and how they will build the cyber truck which will marry stainless steel with their custom aluminum alloys.

Thanks BN.

Christopher - the dissimilar metals is the question mark.
I don't anticipate it will turn inside out tho!
I do expect some differential.
The coefficient of linear expansion of casted aluminum is about a 11 to 12 (ppm/f°)
304 SS is closer to 9.6.

I'm using very thin SS - for its flexibility so it doesn't want to rip away from the epoxy.
I'm also using an epoxy that is designed for joining dissimilar substrates and has good elongation.

Will it work?
Well - first I have to see if I can even execute it well without gluing the crank - or my fingers - in place.
Then I will warm (note - not scorch...) the cases with the crank in and see if I get any weird binding or loose my clearance tolerances.

You might want to look for a better performing epoxy.

Loctite's Hysol 9394 appears to have slightly better hi-temperature strength than the 9460 product.

Good thought SoCal - I'll touch base with the loctite guys again/ look at the TDS.
Thanks.

This is gonna have to get back burnered until early next week - much as I hate to do it...
Will give me some time to ruminate on a range of solutions.