[Technique] Help me...power curve!

Hi!

These are the power curves of 2T minibike engine!
Red is my engine... black is another engine...
these minibike not have gear-box, but have centrifugal clutch.
The clutch coupling point is 8500-9200 g/min

I have deliberately removed the horses power because in this forum there are people that I do not want too see...

My pilot, last year run with engine that have the black curve...and now run with engine that have the red curve.

contrary to the graphic my engine is very strong in out for the curve, but missing rpm-out!
wanting to sacrifice the max power...you think it possible to extend my curve?

I did a test by lowering the stage, but I just lost power everywhere...

sorry for my english!!!





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no power values
no torque values
not even a little information about the differences between the engines .....


how would you like to have a good answer

Stephane a écrit:

no power values
no torque values
not even a little information about the differences between the engines .....


how would you like to have a good answer

you're right, but I would not write the power ... "i want" some idea for increase the utility of my curve.

bore: 40mm
stroke: 39.7mm
piston rod: 76mm
crankshaft weight: 724 g
crankshaft balance:14g

these are the drawing the transfer port of my cylinder.
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These are the engine black curve

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If you need the values ​​of force and torque, i send to for private message! i prefer not publisher!!

Between the clutch engagement point and 11.300 rpm the black power curve has more power everywhere, which shows in the dark blue time line at the bottom of the graph. The higher maximum power of the red curve comes too late to compensate for the time that was lost below 11.300 rpm. Simply put: the black curve is more suited for this bike.

Another thing: your auxiliary exhaust ducts deviate from the drawing. Correcting this may improve overrevs.
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Frits Overmars a écrit:

Between the clutch engagement point and 11.300 rpm the black curve (IAME) has more power everywhere, which shows in the dark blue time line at the bottom of the graph. The higher maximum power of the red curve comes too late to compensate for the time that was lost below 11.300 rpm. Simply put: the black curve is more suited for this bike.

Another thing: your auxiliary exhaust ducts deviate from the drawing. Correcting this may improve overrevs.
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I have seen this difference, but i thought my solution is more best... i thought wrong!!!
I am interested to understand how IAME solution ( auxiliary exhaust) could be better !!!

These are the IAME port in PLAN VIEW

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This is my exhoust port modify!

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SB07 a écrit:

Stephane a écrit:

no power values
no torque values
not even a little information about the differences between the engines .....


how would you like to have a good answer

you're right, but I would not write the power ...

yes, i've understood that, but i don't think that putting your specs will help someone to copy your engine !
so without head volume / head shape / squish gap / diagrams / exh pipe dimensions .... etc, it will not be easy to help you

Citation :

"i want" some idea for increase the utility of my curve.

well...
as you said that the black curve was better i'd say "return to black cuve specs"

-> couldn't you tell us more without a "if i tell you that, after i'll have to kill you"
=> what have you change between black and red ?


for the shape of the aux exhaust duct : if you change the cross section , you change the speed of the gas flow.
and i'd say that it's not very good to decrease so much the cross section in an area wich is so close to the port

Stephane a écrit:

-> couldn't you tell us more without a "if i tell you that, after i'll have to kill you"
=> what have you change between black and red ?


for the shape of the aux exhaust duct : if you change the cross section , you change the speed of the gas flow.
and i'd say that it's not very good to decrease so much the cross section in an area wich is so close to the port

Hy Stephane!!! you and I have the same name

The black curve is not my engine, but is IAME engine....
my engine is red curve and is on prototype.
I have not modified an existing engine, but I created a new engine

My engine in this moment works with a cylinder build with this technique:

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[img][Vous devez être inscrit et connecté pour voir cette image][/img]

I did not understand what you mean by these words:
for the shape of the aux exhaust duct : if you change the cross section , you change the speed of the gas flow.
and i'd say that it's not very good to decrease so much the cross section in an area wich is so close to the port

i mean that the area of the auxiliary duct should -at least- be the same along the duct
but on your engine the area keep on decreasing as it comes to the main exaust duct

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i'd also said that the shape of the main duct should be changed : B should be greater than A to let the gas expand (i don't know the width of your port, but lets say that B should be wider of 5 mm compared to A)



ca you give us a side view of the vinamold and it's angle from the piston ?

Stephane a écrit:

i mean that the area of the auxiliary duct should -at least- be the same along the duct
but on your engine the area keep on decreasing as it comes to the main exaust duct

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i'd also said that the shape of the main duct should be changed : B should be greater than A to let the gas expand (i don't know the width of your port, but lets say that B should be wider of 5 mm compared to A)



ca you give us a side view of the vinamold and it's angle from the piston ?

the exhoust port in the photograph, modified by you, is IAME motor.
Yuo can see my exhoust port in the 3D drawin
IAME motor exhaust port presents an unfavorable section exchange rate respect mine, but IAME works better
For other drawings you must wait until this evening

your opinion is in conflict with Frits Overmars opinion?

You get high power, within a narrow RPM range, like drag racing engines. I don't known much about 2 strokes, but if you want to broaden this RPM range, without loss of max power, you will probably need some more tricks (exhaust valves, variable length intake, and so on). You could also adjust the coupling point of your clutch, and adjust the secondary transmission. But a bike with such a narrow power band motor will probably be quite difficult to drive.

Thieu a écrit:

You get high power, within a narrow RPM range, like drag racing engines. I don't known much about 2 strokes, but if you want to broaden this RPM range, without loss of max power, you will probably need some more tricks (exhaust valves, variable length intake, and so on). You could also adjust the coupling point of your clutch, and adjust the secondary transmission. But a bike with such a narrow power band motor will probably be quite difficult to drive.

my clutch is adjustable, but when attack point is more of 9500g/min the clutch life is very very short.
Systems as exhaust valve, electronic ignition, variable length intake...are prohibited.
i can work on exhaust system; intake diameter; crankshaft weight and crankshaft balance...

I lowered the cylinder changing only the phases, without changing squish and compression ratio... but the result has been power loss anywhere... the curve is shifted downward...

For shifted the curve to the left, i have added 5mm between collector and expansion.

SB07 a écrit:

I have deliberately removed the horses power because in this forum there are people that I do not want too see...

SB07 a écrit:

For shifted the curve to the left, i have added 5mm between collector and expansion.

SB07 a écrit:

(...)
I lowered the cylinder changing only the phases, without changing squish and compression ratio... but the result has been power loss anywhere... the curve is shifted downward...
(...)

Without "active" devices, this will always be what you'll get. The "total" power you can get from a given engine is limited. Either you get very high power, at high RPM, on a limited band of RPM, or you get a wider band, with less power, at lower RPM. The max torque available on an engine is more or less a function of the displacement (or a function a the quantity of burnt fuel on each turn, to keep things simple). The power is the product of the torque by the rotation speed. If you want high power, high torque, on a wide range of RPM, increase the displacement (american way) or the maximum rotation speed (european / japan way).

You will also have to optimize the volumetric efficiency. If your engine is very very efficient, that will mean that the chosen parameters will only be the good ones within a very narrow range. You can then increase the fuelling, and then the torque, and so the power. If you "losen" your optimization, and choose a set of less optimal parameters, the max efficiency will be lower than previously, but the "optimal" band will be wider, consuming less fuel, but giving less power. You can't have your cake and eat it.

Either you adjust you power band, or you adjust you transmission. Having more power, you can have a longer ratio. But having less torque in the low RPM range, you will have to clutch at quite much higher RPM (above 10 000RPM, from what I see, to the cost of a clutch...) Perhaps an alternative clutch could be a solution?. It will need some tests to get the right compromise.

Thieu a écrit:

SB07 a écrit:

(...)
I lowered the cylinder changing only the phases, without changing squish and compression ratio... but the result has been power loss anywhere... the curve is shifted downward...
(...)

Without "active" devices, this will always be what you'll get. The "total" power you can get from a given engine is limited. Either you get very high power, at high RPM, on a limited band of RPM, or you get a wider band, with less power, at lower RPM. The max torque available on an engine is more or less a function of the displacement (or a function a the quantity of burnt fuel on each turn, to keep things simple). The power is the product of the torque by the rotation speed. If you want high power, high torque, on a wide range of RPM, increase the displacement (american way) or the maximum rotation speed (european / japan way).

You will also have to optimize the volumetric efficiency. If your engine is very very efficient, that will mean that the chosen parameters will only be the good ones within a very narrow range. You can then increase the fuelling, and then the torque, and so the power. If you "losen" your optimization, and choose a set of less optimal parameters, the max efficiency will be lower than previously, but the "optimal" band will be wider, consuming less fuel, but giving less power. You can't have your cake and eat it.

Either you adjust you power band, or you adjust you transmission. Having more power, you can have a longer ratio. But having less torque in the low RPM range, you will have to clutch at quite much higher RPM (above 10 000RPM, from what I see, to the cost of a clutch...) Perhaps an alternative clutch could be a solution?. It will need some tests to get the right compromise.

my engine, in max power is very very bad...
I sacrify my max power for stretch the range...but I do not know how to do....

SB07 a écrit:

my engine, in max power is very very bad...
I sacrify my max power for stretch the range...but I do not know how to do....

Unless the curves are drawn using different scales, your engine has higher max power.

And, for the second question, I won't help you, I know nothing about 2 strokes, sorry...

Thieu a écrit:

SB07 a écrit:

my engine, in max power is very very bad...
I sacrify my max power for stretch the range...but I do not know how to do....

Unless the curves are drawn using different scales, your engine has higher max power.

And, for the second question, I won't help you, I know nothing about 2 strokes, sorry...

The curves are drawn with identical scales, and my engine is more powerful to other engine ... but other engine have better use!!! (for my speciality)

First of all, you have to test different exhaust configurations(volumes and lengths) after you can optimise by intake ducts coupled with resonator chambers at orthogonal angle
Other ways are to fine tune the spark advance, the conrod length,etc