Tue Nov 09, 2021 10:12 am

Ossessionato
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Tue Nov 09, 2021 10:12 am linkquote
Quote:
So to check that, if I take the inlet's opening time in °, 113.55, and subtract the closing time in ° of 61.8, I get a distance of 68.55. That is "B" in the drawing below Sime previously provided.
Hmmm.
Houston, we mY have a problem.
113.55-61.88 = 51.67.

Like trying to learn to ride a really powerful scooter.
I keep dumping it.
Will just keep getting on until I tame it - then ride around proudly with all the scratches (and one arm).
Tue Nov 09, 2021 11:09 am

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Tue Nov 09, 2021 11:09 am linkquote
charlieman22 wrote:
Well, at least now I know what kind of math it is...
some trig, numerical integration... the rest is book keeping.
Tue Nov 09, 2021 11:40 am

Hooked
1984 PX(BGM187)EFL
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Hooked
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Tue Nov 09, 2021 11:40 am linkquote
I'll have another go, but I'm really trying not to get too involved; I was just responding to your request for a refresher on Inlet timings. There's been a couple of posts while I was composing, so maybe you've spotted some of it now anyway, but I'm posting as is to get it off my desk....

Firstly, because it's bugging me, "Sip says" isn't very convincing; I'd measure your crank to confirm those timings if I were you.

That aside, in the above calcs you've used 130 in crank and 180 target, so that leaves 50 in pad. That means that Io – Ic should be 50, but at first you have 113.55-61.8=51.75, which makes an Id of 130+51.75=181.75.
Jack posted earlier that Id 175 would be OK, as would Ic 60ATDC, but you're still using 180, and, I think, still getting yourself muddled too because you also stated 'B' (pad opening) as 68.55, at which point I thought best not to try to follow your calcs (your 'B' should have been 180-130=50).
Jack also posted that if you set the Io for MHR, but then used the Crono, you'd just have a small overlap, which wouldn't matter for the Crono (and it's a running in set up anyway). I took that to mean stick to TD126.5 no overlap, not 122.9 for Io setting out.

Still using Td=126.5, and still setting Io from there, and before your first post today, I had this from Jack's suggestions:

175º Id ≈ Ic 58º ATDC – actual pad opening (≈45º) and Ic depends on precise crank timings.
177º Id ≈ Ic 60º ATDC – actual pad opening (≈47º) and Ic depends on precise crank timings.
180º Id ≈ Ic 63º ATDC – 180 is not required (because it's a wide pad the ATDC can be kept low, which is good for this engine).

No decimal places given there because it can only be approximate until:
1) Io position is agreed and fixed (fix transfer measurements/timings for Tc and decide overlap with Io).
2) Crank timings (125/-5º, 130º) are confirmed as checked by measurement, not Sip website.

Although it's not precise until those two points are firm, it does give you a target for Id and ATDC, with a 2º margin for error to satisfy both, which will be OK for running in set up. All you've got to do is fix/confirm Io, fix/confirm Id (175-177º) and/or Ic ATDC (58-60º), check crank timing to determine pad opening (≈45-47º) to fix Ic, get it checked here, and cut it.

Abbreviations I've used here (as requested):
ATDC = After Top Dead Centre
BTDC = Before Top Dead Centre
I = Inlet/Intake
T = Transfer
E = Exhaust
o = opens
c = closes
d = duration

(Edit re: the posts above and below this - it's actually just addition and subtraction - of angles)

Last edited by sime66 on Tue Nov 09, 2021 11:47 am; edited 1 time in total
Tue Nov 09, 2021 11:43 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella
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Lucky
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Tue Nov 09, 2021 11:43 am linkquote
oopsclunkthud wrote:
some trig, numerical integration... the rest is book keeping.
Yup. If you were trying to calculate the intake opening size as a function of time, *that* would be calculus, but I don't think you're going there...yet. (Although if you were, you'd need to be going 88 mph to get there)
Tue Nov 09, 2021 1:23 pm

Molto Verboso
2007 Stella 225
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Molto Verboso
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Tue Nov 09, 2021 1:23 pm linkquote
I'm putting in reeds when I split my case this is giving me a head.
Tue Nov 09, 2021 1:31 pm

bodgemaster
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bodgemaster
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Tue Nov 09, 2021 1:31 pm linkquote
Quote:
... it's actually just addition and subtraction - of angles
No sorry ... when you start saying things like this "is good for this engine" or that "will be OK for running in set up" you're going way beyond just adding and subtracting angles.
Tue Nov 09, 2021 4:09 pm

Addicted
Too Many piles of Junk that need too much work and too much money
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Tue Nov 09, 2021 4:09 pm linkquote
Birdsnest wrote:
Head hurts trying to keep up... I'm sure this is making me smarter by degrees but it is sure making me feel exponentially more stupid. Fun to watch/read along regardless.
The amount of work and calculating and sheer creativity going on here is just....intense. I am frequently having to just 'skip ahead' a bit just to keep up.

keep up the good work
Wed Nov 10, 2021 3:55 pm

Ossessionato
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Wed Nov 10, 2021 3:55 pm linkquote
- Appreciate you guys putting up with the orchestra tuning part of the program.
Sounds like hell - but good things to come with shiny pictures and machined bits.
- Sime - thank you. I will have a good look through all this and get a better handle on it using your notes to figure out where I went off the trail. I will fire up the bat signal if in trouble again. Thanks for the teach a man to fish lessons.

There is some method to my madness.
Without going into all details - there are trade off's with the numbers Jack proposed, and the concept of avoiding any overlap between transfers and inlet being open.

Benefits
Lower end power/torque.

Compromises
1. Shorter overall inlet duration time
2. Inlet duration will be pushed to favor Ic side rather than Io side - which works against mid and low end power.

My project is focused on enlarging the inlet through width - but length is good too.
If I punt on avoiding overlap of the inlet and transfers - I can have:
1. Significantly larger inlet duration
2. That duration will occur meaningfully earlier.

What that would look like on the Crono
- 180 inlet duration
- 123° Io (10 degrees overlap of transfers by... my calculations...)
- 73 Ic

All this can be verified on the cases - but gist is, I am weighing the trade offs of allowing overlap of the transfers and the inlet/ combined with the Crono cylinder's timings/ to provide a larger charge in the cases and more overall power.


Bell's chart shows the advantage of earlier duration of the inlet on mid power.

Wed Nov 10, 2021 4:03 pm

Lucky
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Lucky
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Wed Nov 10, 2021 4:03 pm linkquote
Still seems like a lot of work to justify that new rotary pad instead of just slapping in some reeds and going crazy with the Dremel.

Seriously, I've enjoyed the hell out of following along, even if I usually just go to reeds and focus on blowing up cylinders.

And Sime, thanks for throwing in the glossary. It's helpful both for Future Self and for folks who are reading to learn.
Wed Nov 10, 2021 11:11 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Jet Eye Master
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Wed Nov 10, 2021 11:11 pm linkquote
charlieman22 wrote:
What that would look like on the Crono
- 180 inlet duration
- 123° Io (10 degrees overlap of transfers by... my calculations...)
- 73 Ic
Think this has got confused. If Io + Ic = duration, where do you get 180 from? Is 196 duration when added together.
Thu Nov 11, 2021 12:44 am

Hooked
1984 PX(BGM187)EFL
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Hooked
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Thu Nov 11, 2021 12:44 am linkquote
Jack221 wrote:
Think this has got confused.
Certainly true, but I did agree with the last bit:

Pad degrees = Io – Ic = 123-73 = 50
Crank degrees (Sip says) = 130
Id = 130 + 50 = 180

He's talking about angles, and you're thinking 123/73 timing.
(and I haven't checked where the 123 from).

CM2; if you want I'll check it when the transfers, Io & Id are chewed over and agreed, until then I'm just popping out for cigarettes...
Thu Nov 11, 2021 1:22 am

Hooked
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Thu Nov 11, 2021 1:22 am linkquote
chandlerman wrote:
Still seems like a lot of work
Chandlerman, it really isn't, normally.

All you have to have is Transfer timing, know the Tc/Io overlap, Inlet duration and ATDC you'd like to achieve (those three rely on Jack's input here), and the crank timings; those dictate the Io position on the pad and the pad opening degrees. If they all fit (on the pad and within the parameters of the design targets) then cut it, if they don't, decide where to tweak or compromise...
Other than unilaterally changing the targets, the biggest confusion is between actual timing and angles, and that's just being careful with the numbers, sketching stuff out, and double checking; especially checking before posting, which I think is the main cause of the impression of confusion and difficulty here, because it spreads confusion - you need your waders to go back and find if numbers are correct or not.

The maths really isn't complicated; it's all the other mud, most of it unnecessary, you need the waders for.
Thu Nov 11, 2021 3:10 am

Ossessionato
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Ossessionato
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Thu Nov 11, 2021 3:10 am linkquote
Don't trust what SIP says…
Thu Nov 11, 2021 3:45 am

Hooked
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Hooked
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Thu Nov 11, 2021 3:45 am linkquote
SaFiS wrote:
Don't trust what SIP says…
I have made that point, but so far CM2 has offered no actual measurement, hence "Sip says"

As I'm posting again, and on the subject of measurements, I wonder if there's another reason CM2 doesn't like the first Io number we reached on Nov 8. CM2, I believe you've already made a 'conservative' cut in the pad? What are the angles for the opening already there? Is your current-cut Io position and pad opening OK for the calcs? Or is there already a Tc-Io overlap?

You reposted my sketch from p20 on the previous page (Nov 9); if you've made a cut, with reference to that sketch, what are:
A:?
B:?
Thu Nov 11, 2021 6:14 am

Lucky
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Lucky
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Thu Nov 11, 2021 6:14 am linkquote
sime66 wrote:
Chandlerman, it really isn't, normally.
...
The maths really isn't complicated; it's all the other mud, most of it unnecessary, you need the waders for.
Agreed. I went through this exercise when I built my Sprint's motor and wasn't all that bad other than the VERY nerve-wracking part when I did the actual cutting.

I feel confident when it comes to measuring and selecting port timings, but I also tend to avoid messing with those other than adjusting overall height to get the timings I want.
Thu Nov 11, 2021 8:06 am

Ossessionato
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Thu Nov 11, 2021 8:06 am linkquote
Sime - appreciate that you are putting in the knowledge/explanations.
Don't want you frustrated - think the following will help clarify & be helpful for all following.

While it may appear I'm ignoring Jack's numbers, I'm actually paying extra attention to the details. For example - Jack noted that keeping transfers closed with inlet open has marginal improvement. It's A method - but not absolute.

Jack's numbers are optimized - but they are optimized for two key parameters as fixed.
1. Transfers closed when inlet opens - to provide torque/mid range
2. MHR transfer timing - which is high.

So its a short late duration.

Those are the inherent compromises due to locking in the above two parameters - Jack speak up if you disagree.
Because:
1. MHR relatively high transfer timings are forcing late duration
2. High transfer timings + avoiding any overlap of inlet opening = shorter than desired duration.

So I've brought two means for us to find room to move.
1. Bell's chart showing early inlet duration = mid and low end is another solution to the goal - different than holding transfers closed - but similar benefits.
2. Crono cylinder is taller and has lower timings - opening our envelope for shifting the inlet duration earlier - and possibly still having no overlap.
3. Consideration of allowing overlap of inlet and transfers

Simple terms: I am questioning if 180 or perhaps 190 inlet opening, shifted meaningfully earlier - is a better solution than avoiding overlap/living with smaller inlet opening/ having that duration occur later in the cycle.

For everyone.

One of the things that was clear from looking at MHR and Crono dyno charts.
There is a huge jump in HP due to reeds - and that can be assumed is due to the inlet opening/ size of charge.
My thinking is - let's talk about how we get more out of the rotary.
This project is about optimizing that.
Maybe we fall half way to reeds...

Also - since this is a conceptual discussion - I don't care if the SIP numbers are dead on.
We can assume they are for this discussion - then get to the nitty gritty of careful measures to execute the actual motor once we've beaten up the concept.
Sime's tutorial on how to figure the numbers is essential to the exercise.

Sime - I am on the run - but saw you asked what my A and B are in my example.
I will get those for you and post. There is no overlap of inlet and transfer even with the MHR currently - so we have room to grind. I just don't want to do it until we have above discussion - as I think it may be better to be grinding Io than Ic and that has to be determined before I move.
Thu Nov 11, 2021 10:04 am

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Thu Nov 11, 2021 10:04 am linkquote
I would not think of inlet opening in terms of duration, but rather treat the open and close separately and let the duration be what ever it comes out to be.

on the opening side, opening the inlet at transfer close is a safe bet. you could open earlier and that would benefit some RPMs but likely kill others. so, half of the timing is now known.

On the closing side you are in a race against the rising pressure in the crank case. when the crank case pressure goes above the intake, the flow will start to reverse. after that, any additional duration is not helpful.

ps. I know there are way too many cooks in this kitchen, hoping the result is a nice fusion.
Thu Nov 11, 2021 3:43 pm

Jet Eye Master
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Thu Nov 11, 2021 3:43 pm linkquote
I'm with OCT. No overlap on Io and 60 degrees on Ic. Job done.

If the MHR pulls the rig with the higher TFR, it will have way more power than the Crono, even with its longer inlet.
MHR does need the exhaust moved up to as near to 185 as you dare (although I would just put it at 190).
Thu Nov 11, 2021 5:39 pm

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Thu Nov 11, 2021 5:39 pm linkquote
Quote:
I would not think of inlet opening in terms of duration, but rather treat the open and close separately and let the duration be what ever it comes out to be.

on the opening side, opening the inlet at transfer close is a safe bet. you could open earlier and that would benefit some RPMs but likely kill others. so, half of the timing is now known.

On the closing side you are in a race against the rising pressure in the crank case. when the crank case pressure goes above the intake, the flow will start to reverse. after that, any additional duration is not helpful.

ps. I know there are way too many cooks in this kitchen, hoping the result is a nice fusion.
Well - this is all about fusion. Good input. Thanks!
Quote:
I'm with OCT. No overlap on Io and 60 degrees on Ic. Job done.

If the MHR pulls the rig with the higher TFR, it will have way more power than the Crono, even with its longer inlet.
MHR does need the exhaust moved up to as near to 185 as you dare (although I would just put it at 190).
I'm down with raising ex. port timing on MHR.
Torn about the conservative Io/ total duration.
OCT's point on limit of gulp size the cases can accommodate makes sense.
In my case (and cases) I have some additional capacity from the 62mm crank/ lifted cylinder.
How to calculate optimal inlet duration is a mystery.
I suspect the 170ish inlet duration, is less than complete fill.
Lacks balance.

How can one calculate the amount of time you need open to fill the case with a charge?

(Of course - if I ran it with the expansion pipe - I would have some sucking on the chamber to help it fill...)

Thanks for the input gents.
All appreciated and helpful.
Back in front of the rig Saturday.
Will ponder.
Other opinions/insights/challenges/ welcome.
Thu Nov 11, 2021 6:18 pm

Ossessionato
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Thu Nov 11, 2021 6:18 pm linkquote
Quote:
CM2; if you want I'll check it when the transfers, Io & Id are chewed over and agreed, until then I'm just popping out for cigarettes...
Chuckled.
Will post when Io/Ic are agreed targets.
Quote:
He's talking about angles, and you're thinking 123/73 timing.
(and I haven't checked where the 123 from).
123 was theoretically 10° of overlap of inlet and transfers if I used the Crono. I then added 180 I think (chosen based on past experience) and calculated the Ic from that (and the 125/-5 crank).
Quote:
CM2; if you want I'll check it when the transfers, Io & Id are chewed over and agreed, until then I'm just popping out for cigarettes...
Chuckled.
Yes.
Would be great.
Will do my best to focus on angles and duration degrees difference...
Should get there this weekend.

BTW - not in front of the motor now - but have the Io and Ic you asked about previously (basically A & B from your prior sketch from page 20).
Io 108.5, Ic 85.5 (A) so I suppose that makes B 23 - which physically appears to allow the transfer to close by a few degrees before the inlet opens.

Oh - and CM1 - you posted a question about the 62mm crank on the 57mm MHR kit. What you can't see in that picture is the fat stack of packers under the cylinder to lift it up high enough to have only -2.3pbt.



Fri Nov 12, 2021 8:14 am

bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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bodgemaster
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Fri Nov 12, 2021 8:14 am linkquote
Quote:
How can one calculate the amount of time you need open to fill the case with a charge?
Yes 👏👏.

From Jennings:

" If there is a rule, it is that the point of opening for rotary valves is best established right at the point of transfer-closing if you want a very broad range of power. On the other hand, maximum power is obtained by opening the intake port somewhat earlier: from 130- to 145-degrees before top center, which means that the intake and transfer ports have overlapping open periods. This presupposes that the engine will have been fitted with a proper expansion chamber.

" ... intake-open timing is very closely tied to the exhaust system's pulsing and the overall flow characteristics of the transfer ports. A few hours work with an oscilloscope and pressure-transducers would get you right on target, because you would then know with a high degree of certainty the precise point at which crankcase pressure did in fact fall to atmospheric, but few people have that very expensive equipment and most will have to achieve the same result through a laborious process of cut-and-try. The same kind of cut-and-try in fact, as is needed to locate the optimum point for intake-closing."
Fri Nov 12, 2021 8:29 am

Ossessionato
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Fri Nov 12, 2021 8:29 am linkquote
SoCal - good stuff.
Thanks!

I was kind of surprised no one brought up the expansion pipe as means to deal with overlap.
Quote:
This presupposes that the engine will have been fitted with a proper expansion chamber.
Reason being - it provides some sucking on the case that will help.

My thinking is this right now.
I have two builds on my hands with the parts I have.
1. Current - transfers close when intake opens - box exhaust - Crono cylinder. Crono gives me lower transfer timings, which in turn allows for:
a. earlier inlet opening
b. longer inlet duration
c. lower timings (123-179 out of the box, or perhaps 123-181 after I open up the ex. ports a little.)
2. MHR build for second motor. Reeds (no timing issues) 60mm crank, 185-190 inlet timing, expansion pipe. And of course - I have a second scoot frame hanging on the wall that might house one of these motors...

Crono is apparently on my home office desk - took 2 days from order to delivery from SIP to California - go figure. I plan to put this on the motor and look at what the inlet timings truly are with my transfers around that 123 mark.
Fri Nov 12, 2021 11:27 am

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Fri Nov 12, 2021 11:27 am linkquote
to give an idea of what the pressure in the crank case is doing i got out the simulated oscilloscope. examples, not set to your specific engine, and not perfectly tuned.

first graph:
the red box outlines the intake event with the left side aligned to TPC and the right set to 60° ATDC (240° on the graph x axis).

at 5-6k rpm and lower this is where the case goes below atmospheric, but from 7k on up it happens sooner.

second graph:
Even though the crank case goes above atmospheric at about 30° ATDC, the ramming of the air in the intake is keeping up with it up until about 70° ATDC.

agree with jack on an intake close at ~60° ATDC being a reasonable value.

one other thing to consider is that the intake does not open and close instantly. the longer the pad opening in the case is, the slower it opens and closes. The case needs to have at least the area of the carb, but making it longer than that gives you less duration at full open. But that assumes you are willing to cut the crank, and that may or may not be in the cards.


crank case pressure from 5-10k rpm


crank case pressure vs intake pressure at 8500 rpm

Fri Nov 12, 2021 3:56 pm

Ossessionato
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Fri Nov 12, 2021 3:56 pm linkquote
OTC,
Wow.
So my takeaway:
For this rotary build - you like 60 ATDC.
To avoid confusion: you're referring to a 60 degree angle from TDC for the inlet close - as opposed to any sort of timing reading. I believe Jack was saying same - tho there was some dialog about confusing duration timing with angle-from-TDC? Or do you mean 60 duration timing close when including the cranks influence on opening time (125/-5 if you spec)
Fri Nov 12, 2021 4:23 pm

Ossessionato
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Fri Nov 12, 2021 4:23 pm linkquote
Sitting on plane responding on phone.
Re reading my last post/OCT's prior post as well.
Feel like I understated the wow part.

So if I followed - what you are showing is that these modeled cases would draw fuel/air thru carb even past point of atmospheric pressure - I think due to momentum of air flow.
So the 60 ish close is roughly where your estimating the intake of fuel air would run out of steam? And jack presumably is saying same.




[/quote]
Sat Nov 13, 2021 8:23 am

Ossessionato
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Sat Nov 13, 2021 8:23 am linkquote
Using this method for determining my timings on the Crono: BGM 177 port timing

Ginch struggled with the same thing - Sime created a sketch & explanation.
Will take final timings for both MHR and Crono (using this method) t'day and see what we have.
Sat Nov 13, 2021 10:46 pm

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Sat Nov 13, 2021 10:46 pm linkquote
Had time to fit both cylinders and carefully measure.
Spoiler alert - MHR is probably not going to work/long shot.
Close measure of transfers with cylinder on cases gives me 130.83 (45.27mm with -2.3PBT).
Too high.

How can it move from 126 to 130?
CM - what are you smoking over there?
Well: yes.

Measuring port hight with veneer calipers (back side cut off to fit in cylinder) consistently Gives about 1mm shorter measure than using piston to align with port top with everything assembled.
That's 4° of difference in duration.
I can get tight ranges with any single method.
But each method delivers different tight ranges.

So time to move on.
MHR is going to go on a reed motor and do just fine.
Crono is going to be this build.

let's have a look at those Crono numbers!
(Vernier caliper depth rod method and Lambretta port calc site)
No base gasket = 113.2/173
(needless to say - vernier calipers are about 1mm lower...)

Then added 1mm base:
116.6/ 176.8
Using Buzwangle digital measure of open and close as a double check:
116.5/176.6
PBT is 1.3

Those are some pretty tight correlations.
But these timings are still a bit low.
I'm thinking to add another 1mm to base as starting point.
Should give 121.6/180.5/29.45 (PBT goes to 2.3)
Lil concerned its not going to give enough revs - but that is probably getting up to the top of where the Polini box is best/ bottom of where the pipe would start to work.
Jack?

With 121.6, if I calc Io (which will also be Transfer close for me aka Tc)
360-121.6/2 = 119.2 target for Io.
Assuming my SIP Says Full Circle Crank™ is truly -5, then the angle on my pad relative to TDC, that I need to cut to is 114.2 (119.2 - 5) Edit - that was incorrect. pad should be cut at 119.2 in this example to have transfer and inlet not overlap.

Ok - hang on to your hats - I am gonna try something here.
It could get ugly.
Full face shield is recommended.
Using reverse osmosis to calculate inlet duration with above numbers:

114.2 - X = 60 (Jack & OCT's recommended Ic)
X then = 54.2
54.2+130 (SIP Says Crank™) = 184.2
That is my inlet duration.

Since my transfer duration is the control - it makes some sense to focus on this as primary target.
So if I wanted to hit 125 as optimal, then lift cylinder 2.7mm
This would give PBT of 3.0
Transfer duration would then be 125
Ex. port duration would be 183.1
Inlet opening would be/remain at:
360-125/2 =117.5
117.5-5= 112.5 (angle from TDC pad is cut to)
112.5-x=60
x=52.5
130+52.5=182.5 inlet duration

If I needed more ex. I would then grind ex. port ceiling.
Think that's right.
As I lift the cylinder - my inlet has to get shorter and my inlet duration thus goes down.

Note: the crank is pressed in to the case and I want to take it in and out a limited number of times.
When it comes out - I can do a rubbing - though it is full circle so ill have to sort out how to do an accurate measure.


To get the most accurate measure with the depth rod of the calipers, I ground it down to ensure it was on the edge of the piston


Big picture


Ex port set up - kinda cool looking


Apparently they are using the Braille method for creating the chamfers at the factory.


But they made some mighty big transfer ports - for which my cases have plenty of meat to marry up to. 🙂



Last edited by charlieman22 on Sun Nov 14, 2021 6:51 pm; edited 1 time in total
Sun Nov 14, 2021 2:36 am

Jet Eye Master
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Sun Nov 14, 2021 2:36 am linkquote
Crono is a bit rough. Some gentle work with a diamond bit might be a good idea. Can you do a port map of it? Ex port looks really curved.

The vernier in the port is the most accurate. Only interested when it is open to the roof and not the chamfer. The gas getting past the chamfer will just squirt upwards and mix with the exhaust gas. Sure you re zeroed your vernier before measuring depth? Otherwise wtf.

The Crono might be better on the rig anyway. Not going to be so fast, so shorter duration will be better.
If Io is 117 and Ic is 60 the duration is 177. If the crank is 130 then the inlet is 47 of the 177. This is how it works. The piston port degrees and inlet rotation degrees are the same degrees.
177 degrees is quite enough. The Crono and Polini box will be all out by 7000rpm anyway. Might just make 20bhp.
Sun Nov 14, 2021 5:53 am

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Sun Nov 14, 2021 5:53 am linkquote
Quote:
Crono is a bit rough. Some gentle work with a diamond bit might be a good idea. Can you do a port map of it? Ex port looks really curved.
Diamond bit is the plan then - or fine sand drum.
Crono's design is impressive but it's finish is less so.
All stud's and their nuts need to have thread's chased due to coating.
It should clean up tho.
Port map to follow.
Quote:
The vernier in the port is the most accurate. Only interested when it is open to the roof and not the chamfer. The gas getting past the chamfer will just squirt upwards and mix with the exhaust gas. Sure you re zeroed your vernier before measuring depth? Otherwise wtf.
You answered your own question I think.
The chamfer of the piston is about 1mm.
That's the consistent difference in amount of the measures.
The measures are quite consistent within the methods.
Quote:
The piston port degrees and inlet rotation degrees are the same degrees.
.
This is true only if the cut of the crank doesn't go past TDC.
On mine, the cut on the crank is -5 (in theory), past TDC.
So when the transfer closes (say 117°), its another 5° before the inlet opens at 112°.

Back on page 20... Sime posted a pic and a check.
He was talking about a different calc so ignore the "55".
Quote:
The /55 you'll have is 'E' + 'F' - 'A' = 123+3-71 = /55
It's the degrees ATDC at which the crank closes the opening on the pad (Ic), not where the pad Ic is BTDC
(E) crank cut after TDC + (F) crank cut before TDC - (A) inlet closing degrees from TDC.
Using my crank, it would be 5+125 - 60 = 70
Giving me 112/70/182 in your example of 117 transfer opening, 60° inlet closing angle on pad.

It's more than just the inlet opening - its the combo with the crank which has a cut past TDC.
Time for the Sime bat signal.
Quote:
177 degrees is quite enough. The Crono and Polini box will be all out by 7000rpm anyway. Might just make 20bhp.
All the GSF Dyno's I've seen suggest about the same. I'd like to creep up past that tho - but will likely need more revs. I've got the pipe of course - but it's louder than I'd prefer. Might have to shop for a box that is more suited to a bit more revs - or put up with the louder pipe once run in a little...



Sun Nov 14, 2021 7:51 am

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Sun Nov 14, 2021 7:51 am linkquote
Jack - stolen from FB Freakmoped - who's measures are somewhat less precision than mine sometimes (FM - if you're reading - you can yell at me over a beer sometime in Viena for that!)

Note his was not symmetrical.
Mine has some weirdness on the sides of the small auxiliary ex ports - that might be there to avoid short circuit - or might just be sloppy work.

Pic of mine below as well





Sun Nov 14, 2021 8:30 am

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Sun Nov 14, 2021 8:30 am linkquote
the mismatch in size is caused by the core not being perfectly aligned to the bore when cast or machined. the aux ports are likely the same shape/size, just shifted in the bore.
Sun Nov 14, 2021 10:33 am

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Sun Nov 14, 2021 10:33 am linkquote
Quote:
the mismatch in size is caused by the core not being perfectly aligned
Makes sense.

Wonder if you have any thoughts or modeling related to the double split port ex. like this one.
There is a lot of info we can glean from the internet.
I am posting some of the castings below - so everyone can see what the shapes are of those ports.
You can see the auxiliary ex. ports (as shown previously - are limited in width due to the intrusion of the stud bays.

Jack suggested in his prior post that there might be some meat on the bone from a shaping perspective.
Here are some castings showing how the ex. ports are shaped.


Top view


Side


Front


Isometric


Ex has a flange added past these castings


Flange is tapered down - appears to be completing the taper you see in


Taper looks a bit like OTC shaping? Perhaps they have been following Overmars also?

Sun Nov 14, 2021 11:11 am

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Sun Nov 14, 2021 11:11 am linkquote
Wobbly has the definitive design on this:

Wobbly on Exhaust Port Duct Design.pdf

good to see they are following it for the most part.
Sun Nov 14, 2021 9:07 pm

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Sun Nov 14, 2021 9:07 pm linkquote
If you are the last person standing - reading this thread - you're are the winner!
Congrats - and apologies.
Calc dive is almost over.

Fit my cylinder with lift and got some results.
Here is where I'm at.
2.15 base
Gives 122.5/180.2
That also works out to about a .80 squish with no head gasket.
That 180 ex. duration is about most I can harvest from my box exhaust I think as well.
All adds up to a good max setting for box.
That matters - because I want to cut the inlet pad opening Io to match max box set up.
I can always lower the cylinder - without creating overlap - in this manner.
And if I ever go pipe - I can lift the cylinder a bit/ live with some overlap as pipe will suck.
So to speak.
So this is the balance point for transfer duration.

Re-read Jack's comments/ my response and calcs.
My calc's are in error.
We are also still having a disconnect between pad cut angle and duration time of combined pad and crank I suspect.

For 122.5/180.2 the transfers close at (360-122.5/2) = 118.75
Inlet pad will be cut to open at 118.75.
If I cut the inlet pad to close at 60° (Jack and OTC's number?) the length of the inlet would be (118.75-60) = 58.75
Add that to my SIP Says™ crank's 130° and I get (58.75+130) = 188.75 inlet duration.
This would be stated as ~ 119/70/189

On the other hand - if Jack and OTC meant that the /xx number was to be 60, then the calcs would look like this:
For 122.5/180.2 the transfers close at (360-122.5/2) = 118.75
Inlet pad will be cut at 118.75 (same as above)
To get the second number in the stated timing to be 60, I would need to make the cut on the pad at 70. (E+F-A = second number. See drawing below)
Now the pad is cut at 118.75 to open and 70 to close.
Thats an opening of 48.75.
Add my crank's 130 to that and I get 178.75
This would be stated as 119/60/179

Ok - trail is here for me to follow in future.
But now a discussion on how open that inlet pad should be.
OTC - Jack - given how well this cylinder performs with reeds - why wouldn't I assume the larger duration would be inside the envelope of what volume the cases could hold?
When you guys gave 60 previously - did you mean the cut on the inlet pad at close - or did you mean the 60 of 119/60 above?

For future CM22. Here is what you have to remember.
1. The second number of the duration, the /XX, can be calculated using E+F-A.
2. The first number can be calculated by:
A. knowing your desired duration, and subtracting #1 form it
B. Using 360-transfer duration/2, if you want to open the inlet when your transfer opens.
Think its as simple as that.



Sime's drawing


Jack - are we going to let the German's win the war?! Let's make this thing thump! Would this shape answer your prior round question better? (timing remains 180/ all ports are brought up to 180 across top)



Last edited by charlieman22 on Sun Nov 14, 2021 10:19 pm; edited 1 time in total
Sun Nov 14, 2021 10:18 pm

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Sun Nov 14, 2021 10:18 pm linkquote
I'd just put the crank in the case with a degree wheel and position the crank at 118.75° BTDC and scribe a line on the pad along the opening edge of the crank. then rotate it to 60° ATDC and scribe a line on the pad based on the closing edge of the crank.

removes a bunch of intermediate measurements
Sun Nov 14, 2021 10:25 pm

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Sun Nov 14, 2021 10:25 pm linkquote
Chuckled.
Yes.
But I wrote a book and finally left the formulas that make sense to me in bold in 3 sentences.
So either will get me there I suppose...

From your suggestion -my question is answered: You were referring to its duration timing of 60 - not 60° on the pad...
Sun Nov 14, 2021 11:16 pm

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Sun Nov 14, 2021 11:16 pm linkquote
charlieman22 wrote:
From your suggestion -my question is answered: You were referring to its duration timing of 60 - not 60° on the pad...
I would not call the 60° a duration or an angle on the pad. it's the crank position (60° ATDC) at intake close.

The duration of the intake is 118.75 BTDC + 60 ATDC = 178.75° (note no BTDC or ATDC) as you have deduced. These are your targets to hit independent of the crank web or pad geometry.

I would not trust any number quoted on scooter parts without verifying it.



Sun Nov 14, 2021 11:34 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX125 and some motorbikes
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Posts: 3050
Location: London UK
Sun Nov 14, 2021 11:34 pm linkquote
Saves me typing. Use a degree wheel for cutting the pad. 119/60 two lines, make a hole in the middle.

With the exhaust port, keep the arc but put it in the right place. Each port shouldn't have a curved top but all three should use a common arc. Take the centre port up to 185 leave the outer edge of the aux ports where they are. Draw the arc across all three, cut and blend. Radius the corners. The port must open at the centre first then get wider and wider.
Mon Nov 15, 2021 12:01 am

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Mon Nov 15, 2021 12:01 am linkquote
OTC - good clarification.
Very helpful.
Thanks for sticking with.
Quote:
I would not trust any number quoted on scooter parts without verifying it.
Seems to be a popular opinion...

I have stuck with the SIP Says (and given it a ™) to denote it is just a place holder while I sorted out the how-to. Would have been 6 pages instead of 3 if that was also a variable...

I will look at scribing the pad for synchronizing it's opening with the transfer's closing.
That will limit any measuring variance.

Thanks.
-CM
Mon Nov 15, 2021 7:40 am

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Molto Verboso
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Mon Nov 15, 2021 7:40 am linkquote
oopsclunkthud wrote:
I'd just put the crank in the case with a degree wheel and position the crank at 118.75° BTDC and scribe a line on the pad along the opening edge of the crank. then rotate it to 60° ATDC and scribe a line on the pad based on the closing edge of the crank.

removes a bunch of intermediate measurements
I found using a degree wheel helped with my understanding not smart enough for buzzwangle
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