EXTREME1
RCTalk Talkaholic
get the most out of your engine
Ignition timing is done by headshims and glowplug.
Lower compression will give a later ignition
colder plug will give a later ignition.
(by the way: less nitro will give a later ignition as well)
later = more rpm but less power
sooner = more power but les rpm and a hotter engine....
Colder plug with higher compression will keep the timing the same but the higher compression will give more power, the colder plug can give an unstable engine....
Porttiming can be changed mechanical.
Higher ports by grinding the ports out
Higher ports can also be made by adding a modified headshim under the edge of the sleeve
lower ports can only be made by taking off some material from under the edge of the sleeve.
Higher exhaust will give more rpm but lower power, lower exhaust will give more power but les rpm. Widening the exhaust will give more rpm without affecting the power.
Take care with positioning of the sleeve that you change the headshims as well.
Changing crankshaft timing can do a lot to get more power or more rpm, it can only be done by grinding,
A big win can be found in the timing of the crankshaft. Take away about 0.2mm of the side that is closing the intake from the carburator so it closes a bit later, it will give a better responding and more powerfull engine.
The squish area are normally placed in the outer circumference of the combustion chamber and are machined smooth. The squish area could be a band or a tapered area or two bands on opposite sides. The squish area are either flat or angled depending on the profile of the piston crown. They are machined smooth to a high degree of finish and set up in design with a close tolerance between combustion chamber and piston at TDC preventing contact.
In principle, the piston on the upward stroke causes the compression to progressively increase. Nearing TDC, the gases around the squish band and the piston crown are pushed towards the center scoop causing Turbulence which in turn improve flame propagation as ignition has occurred before TDC and greatly reduces Pinging and Detonation. Thus, present day two stroke combustion chambers are hemispherical or the "top hat" type with a circular or partial squish band and are machined smooth with no sharp edges.
Two stroke engines have lesser volumetric efficiency due to the obstruction in the ports and short time/area available in the intake and transfer phase. Due to the size, shape and angles of the ports the charge is in a higher state of turbulence entering the cylinder than four strokes and requires far lesser ignition advance to operate efficiency irrespective to combustion chamber design.
The concept of a portion of the combustion chamber at close proximities to the piston crown at TDC came to be known as "squish" area or "squish" band earlier referred to as quenched area. In principle, the trapped charge between the piston crown and the squish area nearing TDC starts to be injected towards the main scoop of the combustion chamber causing turbulence prior to ignition greatly reducing detonation and pinging. Higher compression ratios are possible with squish bands resulting in improved engine efficiencies. Turbulence in the charge is also caused by inlet ports, their shapes, angles and surface finish. They greatly help to keep the air-fuel mixture bonded and in a homogeneous state at the point of entry.
Ignition timing is done by headshims and glowplug.
Lower compression will give a later ignition
colder plug will give a later ignition.
(by the way: less nitro will give a later ignition as well)
later = more rpm but less power
sooner = more power but les rpm and a hotter engine....
Colder plug with higher compression will keep the timing the same but the higher compression will give more power, the colder plug can give an unstable engine....
Porttiming can be changed mechanical.
Higher ports by grinding the ports out
Higher ports can also be made by adding a modified headshim under the edge of the sleeve
lower ports can only be made by taking off some material from under the edge of the sleeve.
Higher exhaust will give more rpm but lower power, lower exhaust will give more power but les rpm. Widening the exhaust will give more rpm without affecting the power.
Take care with positioning of the sleeve that you change the headshims as well.
Changing crankshaft timing can do a lot to get more power or more rpm, it can only be done by grinding,
A big win can be found in the timing of the crankshaft. Take away about 0.2mm of the side that is closing the intake from the carburator so it closes a bit later, it will give a better responding and more powerfull engine.
The squish area are normally placed in the outer circumference of the combustion chamber and are machined smooth. The squish area could be a band or a tapered area or two bands on opposite sides. The squish area are either flat or angled depending on the profile of the piston crown. They are machined smooth to a high degree of finish and set up in design with a close tolerance between combustion chamber and piston at TDC preventing contact.
In principle, the piston on the upward stroke causes the compression to progressively increase. Nearing TDC, the gases around the squish band and the piston crown are pushed towards the center scoop causing Turbulence which in turn improve flame propagation as ignition has occurred before TDC and greatly reduces Pinging and Detonation. Thus, present day two stroke combustion chambers are hemispherical or the "top hat" type with a circular or partial squish band and are machined smooth with no sharp edges.
Two stroke engines have lesser volumetric efficiency due to the obstruction in the ports and short time/area available in the intake and transfer phase. Due to the size, shape and angles of the ports the charge is in a higher state of turbulence entering the cylinder than four strokes and requires far lesser ignition advance to operate efficiency irrespective to combustion chamber design.
The concept of a portion of the combustion chamber at close proximities to the piston crown at TDC came to be known as "squish" area or "squish" band earlier referred to as quenched area. In principle, the trapped charge between the piston crown and the squish area nearing TDC starts to be injected towards the main scoop of the combustion chamber causing turbulence prior to ignition greatly reducing detonation and pinging. Higher compression ratios are possible with squish bands resulting in improved engine efficiencies. Turbulence in the charge is also caused by inlet ports, their shapes, angles and surface finish. They greatly help to keep the air-fuel mixture bonded and in a homogeneous state at the point of entry.
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