3LikesHow come this hasn't been done successfully?
07-07-2012, 11:45 AM
#61
oh bouy
engines run and make us happy , what more do we need ?
compression and compression ratio are two separate things
our engines are very dependant on a few things
compression: measured in p.s.i., created by the friction fit of the piston/liner,
no "blow by" or leaking of compressed material in the combustion chamber which causes ill running and lack of tunability (send to Ray A if this happens) and bearing clearances , if loose and excess clearance they will annihilate all other components inside engine from moving too much , bearings are important , loose bearings cause excess crankpin wear which transfers to rod and then to wristpin and piston
crankcase pressure and its ability to seal , a well sealed crankcase is a must , high end engine manufacturers put orings in certain locations which create good seals and also provide a front bearing which has a very good sealing capability , also a must in offroad with our varying engine rpms and crankcase pressures both positive and negative . (onroad is very different)
high quality fuel which in order to maintain your engine properly should include a minimum of 3% castor oil in its oil package , if you pay for your engines you will choose a fuel which has castor , full synthetic fuels will ruin your engine in a much shorter time but will provide more power as you must lean the engine so far just to get the synthetic oils to burn through , completely different flashpoints and molecular structures between synthetic and castor
anyway my .02$ ,LOL
engines run and make us happy , what more do we need ?
compression and compression ratio are two separate things
our engines are very dependant on a few things
compression: measured in p.s.i., created by the friction fit of the piston/liner,
no "blow by" or leaking of compressed material in the combustion chamber which causes ill running and lack of tunability (send to Ray A if this happens) and bearing clearances , if loose and excess clearance they will annihilate all other components inside engine from moving too much , bearings are important , loose bearings cause excess crankpin wear which transfers to rod and then to wristpin and piston
crankcase pressure and its ability to seal , a well sealed crankcase is a must , high end engine manufacturers put orings in certain locations which create good seals and also provide a front bearing which has a very good sealing capability , also a must in offroad with our varying engine rpms and crankcase pressures both positive and negative . (onroad is very different)
high quality fuel which in order to maintain your engine properly should include a minimum of 3% castor oil in its oil package , if you pay for your engines you will choose a fuel which has castor , full synthetic fuels will ruin your engine in a much shorter time but will provide more power as you must lean the engine so far just to get the synthetic oils to burn through , completely different flashpoints and molecular structures between synthetic and castor
anyway my .02$ ,LOL
Last edited by houston; 07-07-2012 at 06:10 PM.
07-07-2012, 05:53 PM
#62
Tech Regular
All there is is compression ratio.
"Compression" is a bad or short or popular or whatever nickname to blow-by. You are calling that compression, and it is not.
This thing measurable as psi by removing the plug and putting a gauge, is not compression, it is just a resultant of the blow-by at a given compression ratio.
In other words, if you measure a given non-operating chamber pressure, and then you change your shim setting, you'll get a "new" higher presure reading. Is your sleeve condition any different? no. is your blow by any different? no. Your compression ratio is different, thats all.
And this thing you are calling "compression" is hugely over-hyped, I've seen countless engines that have incredible blow-by or "low compression" and run like f***!
OS anyone? Compression ratio and sleeve roundness is what you really want.
Again, blow-by, the thing you feel when you spin a flywheel and say - "huh, this engine is shot", is not a good or complete equation to the condition of the sleeve and piston, overall shape of the sleeve/piston is much more important.
Blow-by is aproximately constant, varies with temp, ok, but when you get to operating temp, other than in the straightaway you are approx. at the same temp. And it is constant.
The amount of air/fuel that "fits" between the sleeve and the piston IS CONSTANT, it is allways the same, (ok, at a given temp, but lets use a set temperature for this case), but the amount of time that the piston is giving the air/fuel mix to escape from the chamber is alway changing, the higher the rpm, the less time this mix has to slip through the cracks, so your resultant efficiency can only get better as rpm rises, basically if the engine starts and is able to ile at operating temp, it has enough of this so called "compression" to run with the best of them.
But, the shape or state of the sleeve is a real concern. When we intend to run an engine at a given temperature basically we are telling the engine to operate from 0deg to whatever we like to run.
Any metal goes through a lot of changes in a temp rnge so big, nd if an engine is able to make good power at 200deg witha given setup and with another you are asking it to make good power with a different setup, what's different in the engine? nothing! so the sleeve and piston are suffering bigtime.
Lets use 240deg. if we measure 240 at the outside of the engine, can you imagine whats the temp inside? in addition there is a side of the engine that always gets the hot gases, so the exhaust side of the sleeve - IS HOT!!! And at the same time is the side that has the less material to discipate this heat! can you guess if there is a side of the sleeve that expands more than the other? its litterally changing the (round) shape of the sleeve.
The sleeve and piston are made of different materials, they will expand differently! All this adds up. plus you get a part of the piston that is wearing faster due to more carbon deposits and softenned by excessive heat and has the sleeve on the other hand wanting to separete from it becase of its over expansion. Or even already deformed from countless 300deg runs. It can only take it for so long...
If we had rings, this would be a hole different story...
This parts are made as perfectly round as possible (piston and sleeve), when they "over expand" due to operating temperature they can only work to a certain point. As soon as the piston cannot cover the space the sleeve is openning as it expands, we get all this trouble we talk about.
Richen the lil bastards to 210-230, and double or tripple your engine life. Thats it.
Last edited by maxflo777; 07-07-2012 at 07:11 PM.
07-07-2012, 05:57 PM
#63
i just want to know how these engines are ignited...
07-07-2012, 06:14 PM
#64
No rings
Fuel is also a huge part of the equation , or the amount/type of oil in the fuel that is
The oil package in the fuel changes the volume of the combustion chamber by how much it fills the chamber with on each stroke
These engines are so f'n simple its ridiculous , they often get made too complicated
Fuel is also a huge part of the equation , or the amount/type of oil in the fuel that is
The oil package in the fuel changes the volume of the combustion chamber by how much it fills the chamber with on each stroke
These engines are so f'n simple its ridiculous , they often get made too complicated
07-07-2012, 08:50 PM
#65
Agreed!
I couldn't agree more...
No rings
Fuel is also a huge part of the equation , or the amount/type of oil in the fuel that is
The oil package in the fuel changes the volume of the combustion chamber by how much it fills the chamber with on each stroke
These engines are so f'n simple its ridiculous , they often get made too complicated
Fuel is also a huge part of the equation , or the amount/type of oil in the fuel that is
The oil package in the fuel changes the volume of the combustion chamber by how much it fills the chamber with on each stroke
These engines are so f'n simple its ridiculous , they often get made too complicated
07-08-2012, 07:02 AM
#66
Tech Fanatic
No rings
Fuel is also a huge part of the equation , or the amount/type of oil in the fuel that is
The oil package in the fuel changes the volume of the combustion chamber by how much it fills the chamber with on each stroke
These engines are so f'n simple its ridiculous , they often get made too complicated
Fuel is also a huge part of the equation , or the amount/type of oil in the fuel that is
The oil package in the fuel changes the volume of the combustion chamber by how much it fills the chamber with on each stroke
These engines are so f'n simple its ridiculous , they often get made too complicated
The words speak for them self.
Compression RATIO: The Ratio of volumes between total volume above piston at BDC / volume above piston at TDC.
In our two strokes this is uncorrected compression ratio.
For corrected use the same formula but use volume when the piston has closed the exhaust.
Our un-ringed engines rely on hydraulic seal when compressing the gases.
This is not blow-by in it´s right term, blow-by is burning gases during the power stroke that escape.
Both the hydraulic seal and the blow-by is not constant over temperature alone as the viscosity of the seal (oil) is not only affected by temperature but also pressure in our engines.
If there´s a pressure that counts it´s BMEP.
07-08-2012, 07:21 AM
#67
OK, I'll explain it one time more and I'm done.
All there is is compression ratio.
"Compression" is a bad or short or popular or whatever nickname to blow-by. You are calling that compression, and it is not.
This thing measurable as psi by removing the plug and putting a gauge, is not compression, it is just a resultant of the blow-by at a given compression ratio.
In other words, if you measure a given non-operating chamber pressure, and then you change your shim setting, you'll get a "new" higher presure reading. Is your sleeve condition any different? no. is your blow by any different? no. Your compression ratio is different, thats all.
And this thing you are calling "compression" is hugely over-hyped, I've seen countless engines that have incredible blow-by or "low compression" and run like f***!
OS anyone? Compression ratio and sleeve roundness is what you really want.
Again, blow-by, the thing you feel when you spin a flywheel and say - "huh, this engine is shot", is not a good or complete equation to the condition of the sleeve and piston, overall shape of the sleeve/piston is much more important.
Blow-by is aproximately constant, varies with temp, ok, but when you get to operating temp, other than in the straightaway you are approx. at the same temp. And it is constant.
The amount of air/fuel that "fits" between the sleeve and the piston IS CONSTANT, it is allways the same, (ok, at a given temp, but lets use a set temperature for this case), but the amount of time that the piston is giving the air/fuel mix to escape from the chamber is alway changing, the higher the rpm, the less time this mix has to slip through the cracks, so your resultant efficiency can only get better as rpm rises, basically if the engine starts and is able to ile at operating temp, it has enough of this so called "compression" to run with the best of them.
But, the shape or state of the sleeve is a real concern. When we intend to run an engine at a given temperature basically we are telling the engine to operate from 0deg to whatever we like to run.
Any metal goes through a lot of changes in a temp rnge so big, nd if an engine is able to make good power at 200deg witha given setup and with another you are asking it to make good power with a different setup, what's different in the engine? nothing! so the sleeve and piston are suffering bigtime.
Lets use 240deg. if we measure 240 at the outside of the engine, can you imagine whats the temp inside? in addition there is a side of the engine that always gets the hot gases, so the exhaust side of the sleeve - IS HOT!!! And at the same time is the side that has the less material to discipate this heat! can you guess if there is a side of the sleeve that expands more than the other? its litterally changing the (round) shape of the sleeve.
The sleeve and piston are made of different materials, they will expand differently! All this adds up. plus you get a part of the piston that is wearing faster due to more carbon deposits and softenned by excessive heat and has the sleeve on the other hand wanting to separete from it becase of its over expansion. Or even already deformed from countless 300deg runs. It can only take it for so long...
If we had rings, this would be a hole different story...
This parts are made as perfectly round as possible (piston and sleeve), when they "over expand" due to operating temperature they can only work to a certain point. As soon as the piston cannot cover the space the sleeve is openning as it expands, we get all this trouble we talk about.
Richen the lil bastards to 210-230, and double or tripple your engine life. Thats it.
All there is is compression ratio.
"Compression" is a bad or short or popular or whatever nickname to blow-by. You are calling that compression, and it is not.
This thing measurable as psi by removing the plug and putting a gauge, is not compression, it is just a resultant of the blow-by at a given compression ratio.
In other words, if you measure a given non-operating chamber pressure, and then you change your shim setting, you'll get a "new" higher presure reading. Is your sleeve condition any different? no. is your blow by any different? no. Your compression ratio is different, thats all.
And this thing you are calling "compression" is hugely over-hyped, I've seen countless engines that have incredible blow-by or "low compression" and run like f***!
OS anyone? Compression ratio and sleeve roundness is what you really want.
Again, blow-by, the thing you feel when you spin a flywheel and say - "huh, this engine is shot", is not a good or complete equation to the condition of the sleeve and piston, overall shape of the sleeve/piston is much more important.
Blow-by is aproximately constant, varies with temp, ok, but when you get to operating temp, other than in the straightaway you are approx. at the same temp. And it is constant.
The amount of air/fuel that "fits" between the sleeve and the piston IS CONSTANT, it is allways the same, (ok, at a given temp, but lets use a set temperature for this case), but the amount of time that the piston is giving the air/fuel mix to escape from the chamber is alway changing, the higher the rpm, the less time this mix has to slip through the cracks, so your resultant efficiency can only get better as rpm rises, basically if the engine starts and is able to ile at operating temp, it has enough of this so called "compression" to run with the best of them.
But, the shape or state of the sleeve is a real concern. When we intend to run an engine at a given temperature basically we are telling the engine to operate from 0deg to whatever we like to run.
Any metal goes through a lot of changes in a temp rnge so big, nd if an engine is able to make good power at 200deg witha given setup and with another you are asking it to make good power with a different setup, what's different in the engine? nothing! so the sleeve and piston are suffering bigtime.
Lets use 240deg. if we measure 240 at the outside of the engine, can you imagine whats the temp inside? in addition there is a side of the engine that always gets the hot gases, so the exhaust side of the sleeve - IS HOT!!! And at the same time is the side that has the less material to discipate this heat! can you guess if there is a side of the sleeve that expands more than the other? its litterally changing the (round) shape of the sleeve.
The sleeve and piston are made of different materials, they will expand differently! All this adds up. plus you get a part of the piston that is wearing faster due to more carbon deposits and softenned by excessive heat and has the sleeve on the other hand wanting to separete from it becase of its over expansion. Or even already deformed from countless 300deg runs. It can only take it for so long...
If we had rings, this would be a hole different story...
This parts are made as perfectly round as possible (piston and sleeve), when they "over expand" due to operating temperature they can only work to a certain point. As soon as the piston cannot cover the space the sleeve is openning as it expands, we get all this trouble we talk about.
Richen the lil bastards to 210-230, and double or tripple your engine life. Thats it.
These engines are ignited by compression, the piston moves up, compressing the air/nitro mixture, igniting, and pushing the piston down.
When an engine is worn, it has less compression, it cannot compress the fuel mixture to a pressure or specific psi that it used to be able to when the engine was newer.
The compression ratio represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity.
07-08-2012, 08:01 AM
#68
It is compression, same thing as with a normal car. If you want to check the compression of the engine, you remove the spark plug, install a gauge, turn over the engine and that will give you the compression of the engine.
These engines are ignited by compression, the piston moves up, compressing the air/nitro mixture, igniting, and pushing the piston down.
When an engine is worn, it has less compression, it cannot compress the fuel mixture to a pressure or specific psi that it used to be able to when the engine was newer.
The compression ratio represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity.
These engines are ignited by compression, the piston moves up, compressing the air/nitro mixture, igniting, and pushing the piston down.
When an engine is worn, it has less compression, it cannot compress the fuel mixture to a pressure or specific psi that it used to be able to when the engine was newer.
The compression ratio represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity.
Engines are made to have compression, people don't say I have 10 psi of blowby. I think you're misinterpreting how the vocabulary is used and measured. If you'd like to measure blowby then you would be more interested in a cylinder leak down test.
07-09-2012, 05:09 AM
#69
Tech Rookie
the glow plug uses platinum...either plated or pure wire.
when hot, it reacts with methanol and oxygen, causing combustion. the paltinum is a catalyst and is unaffected by the reaction. timing is governed by temperature and compression.
the nitro methane just lets you stuff more methanol into the cylinder without the required amount of air...think of it as a liquid supercharger! its surprisingly hard to light when by itself. 98C is its flash point i believe.
can take some work, getting to know what fuel to use with how many shims under the head with what number plug at what humidity to get optimum performance! a true feat of juggling
but...all this talk of compression and blowby....WTF? ok, a stinking big fat diesel. i cant turn that over by hand. if it had this so called "blow-by" then yes, i would be able to. blow by is air blowing by the piston. logical huh? i cant turn it over though because its compressing air! this takes pressure! or an increase in temperature! boyles law! temperature, volume and density!
because it has no (minimal actually, theres no such thing as perfection) blowby, it compresses. if the air were "blowing by" it wouldnt be compressing anything and id be contemplating rebuilding the bloody thing!!!!
same as any bloody engine. compression is air being squeezed into a smaller volume. end of lesson.
its impossible to make an engine last forever.
as stated, us maniacs rev the lil titties off these engines! alloy expands! brass expands! steel expands! all at different rates! the high silicon piston will expand at a completely different rate to the low silicon crankcase! even though both are an aluminium alloy! they accelerate, they decelerate! fatigue! all materials have a fatigue limit when abused! intergranular growth at elevated temperatures! formation of corrosive byproducts! look at yourself when you complain about things not lasting forever! WORMFOOD! or did you freeze at 16?
the machinery required to work to superfine tolerances cost millions! how many people do you know make, FROM SCRATCH, race-worthy engines? you need damn sophisticated machinery! i know, from experience, its hard to finish grind 3/16 rod to within half a 10,000" consistently, across a whole day. its actually bordering on impossible. you have to know exactly when to start leaning on the machine, and how hard to lean to keep the size within tolerance! and no cnc machine can do that! they have definite, fixed increments of feed! unlike a person going a "smidge past" the mark...
the expansion and contraction issue strikes even during manufacture! controlled temperature rooms, machine coolants at fixed temperatures that arent allowed to vary by .5 degree... the machines themselves change size!
including design, marketing, logistics... im amazed they dont cost over 1000 already! even the guy at the hobby shop has to make a profit or he has to close the doors! which is happening all around here lately...
when hot, it reacts with methanol and oxygen, causing combustion. the paltinum is a catalyst and is unaffected by the reaction. timing is governed by temperature and compression.
the nitro methane just lets you stuff more methanol into the cylinder without the required amount of air...think of it as a liquid supercharger! its surprisingly hard to light when by itself. 98C is its flash point i believe.
can take some work, getting to know what fuel to use with how many shims under the head with what number plug at what humidity to get optimum performance! a true feat of juggling
but...all this talk of compression and blowby....WTF? ok, a stinking big fat diesel. i cant turn that over by hand. if it had this so called "blow-by" then yes, i would be able to. blow by is air blowing by the piston. logical huh? i cant turn it over though because its compressing air! this takes pressure! or an increase in temperature! boyles law! temperature, volume and density!
because it has no (minimal actually, theres no such thing as perfection) blowby, it compresses. if the air were "blowing by" it wouldnt be compressing anything and id be contemplating rebuilding the bloody thing!!!!
same as any bloody engine. compression is air being squeezed into a smaller volume. end of lesson.
its impossible to make an engine last forever.
as stated, us maniacs rev the lil titties off these engines! alloy expands! brass expands! steel expands! all at different rates! the high silicon piston will expand at a completely different rate to the low silicon crankcase! even though both are an aluminium alloy! they accelerate, they decelerate! fatigue! all materials have a fatigue limit when abused! intergranular growth at elevated temperatures! formation of corrosive byproducts! look at yourself when you complain about things not lasting forever! WORMFOOD! or did you freeze at 16?
the machinery required to work to superfine tolerances cost millions! how many people do you know make, FROM SCRATCH, race-worthy engines? you need damn sophisticated machinery! i know, from experience, its hard to finish grind 3/16 rod to within half a 10,000" consistently, across a whole day. its actually bordering on impossible. you have to know exactly when to start leaning on the machine, and how hard to lean to keep the size within tolerance! and no cnc machine can do that! they have definite, fixed increments of feed! unlike a person going a "smidge past" the mark...
the expansion and contraction issue strikes even during manufacture! controlled temperature rooms, machine coolants at fixed temperatures that arent allowed to vary by .5 degree... the machines themselves change size!
including design, marketing, logistics... im amazed they dont cost over 1000 already! even the guy at the hobby shop has to make a profit or he has to close the doors! which is happening all around here lately...
Last edited by headsmess; 07-09-2012 at 05:47 AM.
07-09-2012, 05:27 AM
#70
i actually know how its ignited.. the term i was looking for is compression ignition... seeing that maxflo said its not compression... so i was looking for some other terminology..
but you are right with .. WTF
but you are right with .. WTF
07-09-2012, 07:03 AM
#72
Tech Regular
Hmm sarcasm?
It is compression ignition, of course, like a diesel engine.
but the reason it starts is becouse of the compression ratio.
It is still only because of a ratio. In thermodynamics, when you study the different power/thermal cycles, there is only compression ratio.
Yes, blow by is what's stated above, basically the same thing I mean. And with enough of this "leakage" the engine won't be able to make a "compression ignition", ok.
But still this leakage, like I mentioned is overrated, the shape and condition of the sleeve is much more important.
If the sleeve has good roundness and the leakage is not bad enough that the engine idles at (a fair) operating temp, the engine can be a great performer. Obviously having all other components in good shape.
But this can "feel" as a shot engine if the flywheel is spun.
That is all I'm sayin'.
In other words, speed as in rpm is part of this equation.
I whole completely agree with all on the fuel part of it. I was considering all things being equal.
Last edited by maxflo777; 07-09-2012 at 07:14 AM.
07-09-2012, 08:15 AM
#73
HAHAHAHAHAHAHA, I love this thread!
07-12-2012, 10:08 AM
#74
Compression is still measured in Psi and is quite variable by engine speed and efficiency.
Compression ratio is a ratio and is fixed. Well.... not quite. Compression ratio varies with engine RPM as well. The conrod can stretch and contract quite a bit at high rpm's and different temps. F1 rods can stretch many mm's.
You can make a 4 stroke engine with a 14.6:1 compression ratio have the exact same compression as an engine with a 11:1 compression ratio.
Just increase the valve overlap until the compression bleeds out the exhaust some. Huge lopey cams are why we can run monstrous compression ratios on gasoline drag race engines. Put a small cam on those race engines and they'll detonate hard.
Compression ratio is a ratio and is fixed. Well.... not quite. Compression ratio varies with engine RPM as well. The conrod can stretch and contract quite a bit at high rpm's and different temps. F1 rods can stretch many mm's.
You can make a 4 stroke engine with a 14.6:1 compression ratio have the exact same compression as an engine with a 11:1 compression ratio.
Just increase the valve overlap until the compression bleeds out the exhaust some. Huge lopey cams are why we can run monstrous compression ratios on gasoline drag race engines. Put a small cam on those race engines and they'll detonate hard.
