Our latest spec reed-valve crankshaft - (Malossi 221cc)

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OzOAP
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It was just an idea as we were building engines at work with lighter and lighter flywheel/clutch assemblies and heavier front pulleys. This is car engines btw.
I was fully aware of the clutch problems associated with HP4/1kg flywheels on P Range/T5 engines. If the clutch is heavier than the flywheel, then the clutch will start acting as one, so whilst modifying the crank for the TS, I slung the parts on the scales. The thinking being that if they weighed the same 'statically' as the flywheel is further out on the taper and larger diameter it would be heavier than the clutch "dynamically" (when its spinning).
Nothing is proven, it is all theory that was thrown around the workshop one afternoon, but then some of the best ideas are.
As a side note, we all know how crap P Range clutches are due to the way they run at engine speed, but the TS has had over 10k miles of torment and hours of dyno running with no problems. Early 7 spring, 3 plate type.
Adam_Winstone
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How much benefit does a dyno show for any such shaping? Is there anything to suggest that the flow is where any such benefit comes from, or whether the reduced primary compression might be the beneficial element? Looking at how such a crank might work, does the flowing of the webs allow the motor to draw in as much mixture as is required to equal out the negative crankcase/cylinder pressure... or would a more traditional square cut web (with longer than std timing) act as a propeller/fin to actively drag mix into the crankcase?

This is me trying to get my mind around whether the motor will best benefit from flow, pull or push. I imagine that they all play their part but do dyno results support the reality of the theory?

Thanks in advance.

Adam
OzOAP
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Ideally, bike on dyno, optimize, power run, split casings, change crank, repeat.
Time consuming.
Wether or not the market is there for top spec reed 210/220s is difficult to say.
Adam_Winstone
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Hi Oz,

Yep, I understand that development (best done with single/small changes and lots of dyno time) is a time and finance hungry process but I was just wondering what people may already know from previous tuning experience, i.e. fit a 210 gain X, fit a reed with no additional work (gain nothing?), fit a standard straight cut crank and gain Y, fit a flowed cut crank and gain Z. Does a dyno actually show any benefit in fitting a flowed crank or is the benefit from extended inlet duration alone?

I know that plenty of people do fit flowed cranks but I tend to do this sort of modification just because it seems right (common sense) to do so...but then again, for decades people talked of the need to polish ports, whereas today's trend is for a satin/smooth (but not polished) surface. I'm just wondering if flowing really does offer much over just extending durations?

Food for thought... for me at least!

Ta

Adam
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sean brady scooters
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you may not be aware Adam but i have been tuning vespas for nearly 35 years now ,and for the past 8 years or so dan has been dynoing them and so we have amassed and collected all sorts of data regarding these in general .
In the light of this we know what to expect from any particular set up considering whether its rotary valve /std or modified /cut this way or that way or both ,reed valved or not ,kitted and which kit and on all sorts of different pipes etc etc .
The results that we are getting now speak for themselves , and we are constantly improving and refining these things as we go on ..
crank wise/flowing ..just look at what pinasco are making now along with what SIP /worb 5 and so many others are producing ..whether for rotary or reeds .
Ours is just a further extension of that and it works for us .
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sean brady scooters
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rather good results on this I think :) (see our seperate post) 31bhp /23ftlbs torque
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hendy
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Mass removed from the outside of a spinning mass has a much greater effect on the second moment of mass which is the term used for inertia of something that spins rather than goes in a straight line.

For example if you had an imaginary flywheel of 2m radius with its mass concentrated in 2 areas: 1kg 1m from the centre of rotation and 1kg 2m from the centre. This object has a second moment of mass of (1*1^2)+(1*2^2)=5Kgm^2. If you remove the mass closer to the centre this reduces to 4kgm^2, whereas if you remove the mass at the edge it drops to 1kgm^2. Even if you haven't got a good feel for this principle you can see that removing mass from the edge is much more significant, in this example it's the same mass (1kg) but 4 times more significant.

Now, the fastest spinning thing in an engine is the crank and its energy is the product of its second moment of mass and the square of its rotational speed. So to accelerate a crank from 2000 to 3000rpm requires the energy in it to increase by a factor of 4 BUT to go from 8000 to 9000rpm it increases by 17. In other words it needs 3.25 times more energy for the same speed increase.

Sorry to blather on but I've tried to keep it as brief as I could. And sorry for thread hijacking but it was relevant to the crank discussion.
cartmel808
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Great work there Sean... & a cracking result! ;)
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sean brady scooters
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the fastest thing spinning in a pe/px vespa engine is not just the crankshaft though is it ?
the clutch spins also at crankshaft speed as well as does the flywheel :)
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hendy
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If you say so. I'm going to stick my neck out and say you know more about vespa engines than I do :D. Especially as I've never touched one since I was 18, and unfortunately that wasn't recently.

Just in case you misunderstood me, I wasn't correcting anyone, just trying to explain the principles.

Anything that spins is subject to these laws, but the faster they spin, and the higher their second moment of mass, the more they influence performance.

I would guess the clutch is less significant, in this respect though. I'd guess a clutch including all it steels, plates etc weighs about half what the flywheel does and that it's about the same diameter? If that's the case, Then it has about half the inertia the flywheel does. Still very important, just less important than the crank.

Without a cad model it's tricky to work out the value unless it's simple textbook examples like the one I used but when you get used to them you can make a decent estimate especially for comparative purposes.
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