ESE's works engine tuner

[teriks]

Yes of course you can do this and it will if done correctly to suit the engine speed and chassis as Wobbly says above,
But while this no doubt works it only works over a narrow rev range because it just moves the out of balance forces to another rev range rather than lessening them over the whole spread of engine revs as a balance shaft so effectively does.

I never understood this talk about balancing for a certain rpm. In my world, as long as we disregard everything around the crank there is one optimum balance factor to minimize the forces on the crank bearings.
The frequency and magnitude of the forces for sure varies with rpm, but how does the optimum balance factor for minimum vibrational forces vary?

For sure, in the real world you have to consider resonances in the full assembly, I guess mainly the frame in the case of bike, and as been stated previously in the thread in witch direction the vibrations have the least negative effect etc. I guess this is where the "balance for at certain rpm" comes into the picture, right?

[husaberg]

I never understood this talk about balancing for a certain rpm. In my world, as long as we disregard everything around the crank there is one optimum balance factor to minimize the forces on the crank bearings.
The frequency and magnitude of the forces for sure varies with rpm, but how does the optimum balance factor for minimum vibrational forces vary?

For sure, in the real world you have to consider resonances in the full assembly, I guess mainly the frame in the case of bike, and as been stated previously in the thread in witch direction the vibrations have the least negative effect etc. I guess this is where the "balance for at certain rpm" comes into the picture, right?

I am certainly no physicist and I have never questioned why, but my best guess would be combination of the different primary balance factor actually moves the rpm range so that the secondary forces won't coincide with the primary imbalance force felt at the rev range where the normal operating range occurs, plus also as you mention moving it out of the range where the frame resonates with the engine.
I based these assumptions on having noticed when engine manufactures have spec'd rev ranges, different frames and different engine inclinations for the same engines this resulted in different primary factors being recommended (old pommy shitboxs)
All I know for sure is when we talk about balance factor or oils it always ends in a disagreement on here. likely because the vibrations are generally not measured, so the end up being assessed by people which are subjective.

less speed variation on a rotation cycle leads to a less disturbed flow

difficult for me to explain in English

Less collapse of the flow established.
No idea but my own assumption was based on a even fire 4 cylinder bike that fires every 90 degress (early NSR) making less peak power as it is made to fire progressively more to that of a twin (in pair every 180 ie two up refered later to as a screamer) or more big a single (big bang) when each of these changes occurred the engines also lost over rev.

[Greg85]

There are several factors at play with removing the balance shaft ( apart from the balance factor ).
First is that if the engine is re balanced correctly, there will be no discernible vibration,there are millions of single cylinder engines running around that dont make the rider loose
concentration due to bad vibes.
Then there is the issue of inertia.
The balance shaft runs at crank speed so in effect adds to the rotational inertia of the engine.
Loosing the balance shaft will change that inertia considerably.
There are two schools of thought on this.
Of course basic physics says a low inertia system will accelerate faster,but in a 2T it has been well documented that high inertia cranks make way more overev power.
Take a stock RS125 Honda and remove the flywheel, suddenly it wont rev at all.
That is why HRC and VHM offer high inertia option cranks for total loss use.
And take a look at the amount of Mallory on the periphery of an Aprilia or TM125 kart crank - they didnt add all that heavy metal,to make the engine slower at the rpm its used at most.

hi wobbly good job for tm and sharing your tests...we're talking about high inertia crankshaft and tm crankshaft ,I analyzed that of the tmkz10c maneton 22, weight of the two half cranks 2066g,weight of the complete connecting rod 260g,complete piston(original tm)176g,a total weight of 2502g.comparing that of the modena it makes 2760g complete without piston saying high inertia as much!!effectively it seeks much further the power compared to the tm ,I think the weight influence on the acceleration of the crankshaft? the balancing factor that depends or one wants the power...?a compromise for the use of the engine

[Frits Overmars]

Removing the balance shaft... moves the out of balance forces to another rev range.

The proportion of horizontal to vertical balance forces won't change with the revs, but the vibration frequency will, and at a certain rpm it may coincide with the natural frequency of the handlebars or footrests, messing up feedback and causing rider fatigue, or with the natural frequency of the frame, causing it to crack, or with the natural frequency of the float system, messing up the carburation.
I would never remove the balance shaft from any engine. I would however make sure that it doesn't double as a cream whipper.
We once worked on a Cagiva engine, used for 125cc production racing in Italy. The rulebook said no touching of the 'thermal parts' but it didn't say anything about sliding a nice round tube over the half-round balance shaft that was immersed up to its neck in gearbox oil. Making it round was good for over 1 hp.

To an extent there is the stored energy which you have done work to accelerate... overrev important in higher gears takes a while to expend. As the combustion efficiency fails and pipe cools surely the power collapsing with that much drag on it couldn't be compensated by the stored energy?

Any form of stored kinetic energy can only be made to work when you try to slow it down. For rotating energy in an engine this means that you turn it to use when you shift up. But if stored energy in a rotating mass would increase the rpm of that mass, it would mean augmenting the very amount of stored energy, something that is not going to happen in this universe. Try to imagine a motorcycle on an inertia dyno, putting a lot of rotating energy into the dyno drum. If the bike chain breaks during a test, do you think the drum rpm will increase because of the energy stored in it?

...talking about high inertia crankshaft and tm crankshaft ,I analyzed that of the tmkz10c maneton 22, weight of the two half cranks 2066g, weight of the complete connecting rod 260g, complete piston(original tm)176g,a total weight of 2502g. comparing that of the modena it makes 2760g complete without piston saying high inertia..

So the Modena engine has more inertia than the TM engine? You may well be right Greg, but you cannot establish that through weighing.
Scales can determine mass, but they cannot determine how far from the center of rotation the bulk of that mass is concentrated.
Take a look at the Aprilia crankshafts below. There is a lot of tungsten concentrated near their outer diameter. Now think of a crankshaft with even more tungsten,
but concentrated on a smaller diameter. It will certainly be heavier than the pictured crankshafts, but it may well have less inertia.

Frits has always criticized my blatant uselessness in applying rules of thumb to the duct geometry based on the bore size and the port effective area.
He is of course annoyingly correct, the whole process should be tied to the Blowdown STA.

Don't be so hard on yourself Wob. I wrote that the blowdown STA approach may be theoretically correct, but that your method has practical value because STA cannot be measured; it has to be calculated, whereas your method only requires measuring, which is much easier to apply for those wo do not have access to a sim program.
By the way, your remark "He is of course annoyingly correct" makes me wonder: did you ever talk to my ex-wife?

[jbiplane]

Hello
Hi Niels
What is prop diameter ...

We tried it with 680mm propeller. Seems this exhaust have at least 2 resonance rpm. At a moment I have no idea how simulate Bi-resonator
in 1d... May be Engmod2t can be used by some trick?

Thanks TZ350

Very clever piece of work, I like it. Love that exhaust, brilliant idea.

My friend was inspired by this idea tried make the same shape on inline 500cc Rotax 503 and got good propeller trust from a first try.

[peewee]

As I scored 98% in Scholarship English I rarely suffer from anomia,so expanding commensurate ( yea that's in google ) by adding ly makes it a " doing " word for you hillbilly folk ie
the act of making something commensurate.

But getting back to important shit - Frits has always criticized my blatant uselessness in applying rules of thumb to the duct geometry based on the bore size and the port effective area.
He is of course annoyingly correct,the whole process should be tied to the Blowdown STA.
Thus we would have an exit geometry that is related to the power achievable , of a certain swept volume , at a certain rpm.

Once some clever fuck with more time and intellect than I , looks seriously into this , then the theory could easily be extended to a new relationship that ties the Blowdown capability to the volume of available
cool plugging charge needed, to support the bmep being produced.

That would be a cool Masters or PhD project , if 2T technology was even remotely interesting or relevant ,to engineering students focused on the future electric shitter everything - no " engines " involved.

maybe somebody, anybody, has a general idea how long the exh passage should be ,in relation to bore diam on our oversqaure shitboxes. even if theyre a mile off, a ballpark would be great. hell even a wild guess. its not like the consequence would be 10hp loss i wouldnt think. my peanut brain is telling me, alittle too long would be better than too short.

[Frits Overmars]

maybe somebody, anybody, has a general idea how long the exh passage should be ,in relation to bore diam on our oversqaure shitboxes. even if theyre a mile off, a ballpark would be great. hell even a wild guess... alittle too long would be better than too short.

If the exhaust duct can contain a volume equal to the cylinder capacity of the engine, it will be long enough. Wild enough for you?

[Muhr]

We once worked on a Cagiva engine, used for 125cc production racing in Italy. The rulebook said no touching of the 'thermal parts' but it didn't say anything about sliding a nice round tube over the half-round balance shaft that was immersed up to its neck in gearbox oil. Making it round was good for over 1 hp.

That one I loved smart! trying to figure out any engine that has the balance shaft down in the cream that i can add this to. have to think about it for a while

[Vannik]

If the exhaust duct can contain a volume equal to the cylinder capacity of the engine, it will be long enough. Wild enough for you?

I was thinking along those same lines - are we equally wild?

[Frits Overmars]

That one I loved smart! trying to figure out any engine that has the balance shaft down in the cream that i can add this to. have to think about it for a while

Like this one, Muhr? There are a lot of these around, and they're supposed to be competition engines .

I was thinking along those same lines - are we equally wild?

It's either that, or equally crazy, Neels .

[Greg85]

The proportion of horizontal to vertical balance forces won't change with the revs, but the vibration frequency will, and at a certain rpm it may coincide with the natural frequency of the handlebars or footrests, messing up feedback and causing rider fatigue, or with the natural frequency of the frame, causing it to crack, or with the natural frequency of the float system, messing up the carburation.
I would never remove the balance shaft from any engine. I would however make sure that it doesn't double as a cream whipper.
We once worked on a Cagiva engine, used for 125cc production racing in Italy. The rulebook said no touching of the 'thermal parts' but it didn't say anything about sliding a nice round tube over the half-round balance shaft that was immersed up to its neck in gearbox oil. Making it round was good for over 1 hp.

Any form of stored kinetic energy can only be made to work when you try to slow it down. For rotating energy in an engine this means that you turn it to use when you shift up. But if stored energy in a rotating mass would increase the rpm of that mass, it would mean augmenting the very amount of stored energy, something that is not going to happen in this universe. Try to imagine a motorcycle on an inertia dyno, putting a lot of rotating energy into the dyno drum. If the bike chain breaks during a test, do you think the drum rpm will increase because of the energy stored in it?

So the Modena engine has more inertia than the TM engine? You may well be right Greg, but you cannot establish that through weighing.
Scales can determine mass, but they cannot determine how far from the center of rotation the bulk of that mass is concentrated.
Take a look at the Aprilia crankshafts below. There is a lot of tungsten concentrated near their outer diameter. Now think of a crankshaft with even more tungsten,
but concentrated on a smaller diameter. It will certainly be heavier than the pictured crankshafts, but it may well have less inertia.


Don't be so hard on yourself Wob. I wrote that the blowdown STA approach may be theoretically correct, but that your method has practical value because STA cannot be measured; it has to be calculated, whereas your method only requires measuring, which is much easier to apply for those wo do not have access to a sim program.
By the way, your remark "He is of course annoyingly correct" makes me wonder: did you ever talk to my ex-wife?

hi frits thanks to answer ,yes then the modena has the heaviest crankshaft weighed 2760g without piston after the crankshaft tm without piston 2326g, the masses concentrated side opposite maneton 2 tungtstene 13mm, that of the middle17mm tungsten and the others alu, a total of 370g added weight,how should I go about calculating the tm balance factor? I would like to modify the one of the modena, the idea of aprilia was to concentrate the maximum of mass opposite to the throttle for a better acceleration interesting the photos thanks

[Frits Overmars]

how should I go about calculating the tm balance factor?

Crankshaft balancing has been covered here some time ago. I'm sorry I can't point you to the exact page, but maybe you can find it by searching for the pictures I used:

[Grumph]

I would never remove the balance shaft from any engine. I would however make sure that it doesn't double as a cream whipper.
We once worked on a Cagiva engine, used for 125cc production racing in Italy. The rulebook said no touching of the 'thermal parts' but it didn't say anything about sliding a nice round tube over the half-round balance shaft that was immersed up to its neck in gearbox oil. Making it round was good for over 1 hp.

Thanks Frits - for giving me something to think about. Not in relation to 2T's but the ever more common balance shafts in 4T's. Another way to consider reducing windage in the crankcase....

How'd you secure the overlay tube ? Shrink and spotweld ?

[F5 Dave]

. . .

Any form of stored kinetic energy can only be made to work when you try to slow it down. For rotating energy in an engine this means that you turn it to use when you shift up. But if stored energy in a rotating mass would increase the rpm of that mass, it would mean augmenting the very amount of stored energy, something that is not going to happen in this universe. Try to imagine a motorcycle on an inertia dyno, putting a lot of rotating energy into the dyno drum. If the bike chain breaks during a test, do you think the drum rpm will increase because of the energy stored in it?

. . .

Thanks the dyno analogy made that part real clear .
But it still leaves me in the dark why over rev is detrimentallly affected by too light of rotational mass.

[wobbly]

Ha,ha,yes Frits I keep in touch with your ex wife on Tinder.

In relation to the duct volume - I am about to receive a new casting from TM that I designed with the Wobbly duct exit configuration and ears of the Aprilia.
Once I have done the dyno work to optimize the exit and spigot etc,I will measure the volume.
At least that will show the ratio that a full noise square 125 likes,but still leaves the bmep out of the equation.
As I said before, the greater the bmep,the greater the volume of cold plugging mixture is required.
This makes wild guesses even less relevant when comparing say the near 15Bar of an RSA vs the 12Bar of Robs GP-NSR110.