Re: Closing up the squish band clearance on my modified head! My testing continues...
Honda trx 250R? Or... the three wheeler 250R?
Honda trx 250R? Or... the three wheeler 250R?
Closing up the squish band clearance on my modified head! My testing continues....
- Thread starter joeak47
- Start date
Re: Closing up the squish band clearance on my modified head! My testing continues...
trx, but the liquid cooled atc's used the same motor. i know theres minor difference in some of the years. they are minor and i could probably list every difference from memory if i tried.
there were liquid cooled trikes in 85 and early 86. then they shifted to the trx. thats not to say the air cooled atc's before that werent amazing machines in their time too though.
trx, but the liquid cooled atc's used the same motor. i know theres minor difference in some of the years. they are minor and i could probably list every difference from memory if i tried.
there were liquid cooled trikes in 85 and early 86. then they shifted to the trx. thats not to say the air cooled atc's before that werent amazing machines in their time too though.
Re: Closing up the squish band clearance on my modified head! My testing continues...
Test rode again today. It was 104 degrees ambient temperature.
I'm running .035 to .041 squish clearance and 130 psi compression.
Still using that "cheap cast piston" that everybody loves to hate,and maxima 927 castor at 20 to 1 mix.
The infrared temp gun shows between 330 degrees and as high as 357 degrees after long,long hard runs and heavy loads. I couldn't get it any hotter. The variances in tempuratures are because I was measuring all over the cylinder and head. I concentrated on the top few millimeters of the cylinder and the cylinder head where most heat is created during the combustion process.
No detonation to report what so ever!
I'm machining another head right now. I'm going to up the compression to 160 psi, increase squish to about .045 and go from there.
I might try increasing compression to 180 psi like zedicus is running just to see what happens.
I have lots of extra heads to machine if need be.
I'm curious how much more the increase in compression is going to help the torque?
I'm also curious how far I can take the compression with pump gas.
I love experimenting...Stay tuned...this is getting interesting!
Test rode again today. It was 104 degrees ambient temperature.
I'm running .035 to .041 squish clearance and 130 psi compression.
Still using that "cheap cast piston" that everybody loves to hate,and maxima 927 castor at 20 to 1 mix.
The infrared temp gun shows between 330 degrees and as high as 357 degrees after long,long hard runs and heavy loads. I couldn't get it any hotter. The variances in tempuratures are because I was measuring all over the cylinder and head. I concentrated on the top few millimeters of the cylinder and the cylinder head where most heat is created during the combustion process.
No detonation to report what so ever!
I'm machining another head right now. I'm going to up the compression to 160 psi, increase squish to about .045 and go from there.
I might try increasing compression to 180 psi like zedicus is running just to see what happens.
I have lots of extra heads to machine if need be.
I'm curious how much more the increase in compression is going to help the torque?
I'm also curious how far I can take the compression with pump gas.
I love experimenting...Stay tuned...this is getting interesting!
Re: Closing up the squish band clearance on my modified head! My testing continues...
Joe I would just love to give one of your experimental heads a run.
If you can find a reasonable cost effective way of freighting me one, I am interested in buying one.
Joe I would just love to give one of your experimental heads a run.
If you can find a reasonable cost effective way of freighting me one, I am interested in buying one.
Re: Closing up the squish band clearance on my modified head! My testing continues...
What modifications have you done to your engine so far?
What have you done to the head?
By the way...your 69 years old and ride blasters???
What modifications have you done to your engine so far?
What have you done to the head?
By the way...your 69 years old and ride blasters???
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Re: Closing up the squish band clearance on my modified head! My testing continues...
Maybe I'll just keep my squish band clearance where I have it,or reduce it even more,but decrease my chamber volume to up the compression. Hmmm... I'll decide after my first cup of coffee in the morning. After I finish the coffee,I'll finish the head. I'll possibly have pictures of the head tomorrow plus a ride report with recorded running temperatures. We'll see.
About tempuratures... It seems that alot of people think that my running tempuratures are high. I don't beleive so. I think humidity has alot to do with it too. Like I've stated in other threads the go kart guys run 400 degrees to 475 degrees all the time,under heavy loads,and for long periods of time!!!
I'm safe.
Here is a short read about what Gordon Jennings Has this to say about squish band clearance... I think everybody will find it interesting....especially the last two paragraphs.
By and large, you would be well-advised to ignore the whole business of compression ratios in favor of cranking pressures. There is, after all, a big difference between the kinds of numbers you get by performing the traditional calculations to find compression ratio, and what is happening as the engine turns. My experience has been that you can use cranking pressures of 120 psi without worrying much about overheating anything. Maximum power will be obtained at cranking pressures somewhere between 135 and 165 psi. Going higher with compression, in a conventional motorcycle engine, can give a neat boost in low speed torque, but the thermal repercussions of higher cranking pressures will surely limit maximum output. On the other hand, fan-cooled kart engines perform very well at cranking pressures up at 200 psi, and water cooled engines behave much the same.
One of the most undesirable side-effects that comes with too-high compression ratios is an enormous difficulty in getting an engine to "carburet" cleanly. When the compression ratio is too high, you'll find that an engine's mixture-strength requirement has a sharp hump right at its torque peak that no motorcycle carburetor can accommodate. You'll realize, after working with high-output two-stroke engines, that all of them are to some degree liquid-cooled - and that the cooling liquid is gasoline. It istrue that an over-rich mixture tends to dampen the combustion process, and reduce power, but here again we find ourselves faced with the necessity for finding a balance between evils: We have overheating to rob power on one side, and we can cool the engine with gasoline, but too much fuel also robs power. The solution is a beggar's choice, in which we try to find the cross-over point between overheating and over-rich mixtures.
In an engine intended purely for road racing, with a torque peak virtually coincidental with its power peak and driving through a very close-ratio transmission (enabling the rider to hold engine-speed within narrow limits), making this beggar's choice is a fairly straight-forward proposition: you play with jetting until the motorcycle runs fast. However, road racing conditions allow you to stay right on the mixture-requirement hump; you don't have to worry about what happens two-thousand revs below the power peak, because that's below what you'll use in a race. Motocross racing is another matter entirely, and an engine with a mixture-curve hump will drive you absolutely mad. Jet a motocross engine so that it doesn't melt a piston every time it pulls hard at its torque peak, and (if its mixture-curve is humped) it will be huffing soot and losing power above and below that speed.
The answer to this problem is to iron out that mixture-requirement hump, because no matter how much work you do with the carburetor, it never will be able to cope with the engine's needs. All the carburetor knows, really, is how much air is moving through its throat, and it adds fuel to the air in proportion to the rate of air-flow; don't expect it to know when the piston is getting hot and respond by heaving in some more fuel. How do you get rid of the hump? You do it mostly by substituting a somewhat less effective expansion chamber: one that gives more nearly the same boost all the way through the speed range you are obliged to use by racing conditions, without any big surges. That will result in a drop in peak power, obviously, but you can compensate for it to a considerable extent with the higher compression ratio you previously were forced to forego in the interest of keeping the piston crown intact when the expansion chamber did its big-boost routine. Again, it is all a matter of finding the balance.
No matter what the compression ratio you ultimately use, it will have been influenced much more than you probably suspect by the combustion chamber configuration, and by certain gross characteristics of the head itself. Over the years, I have seen the fashion in combustion chamber forms swing back and forth, hither and yon, with first hat-section chambers in favor and then trench-type chambers, and torus-type chambers and so on and so forth ad infinitum. I was not, and am not, impressed. Combustion chamber form should be established with an eye toward only a very few special considerations, and these cannot account for even half the chamber shapes I have seen. Listed, though not really in order of importance, these are: surface / volume ratio; spark plug location; thermal loadings; and combustion control. We will consider each of these in turn.
Surface to volume ratio is important because even in the part of the combustion chamber fully exposed to the advancing flame front, there will be a mixture layer adhering to the metal surfaces that does not burn. These layers, like that trapped within the squish band, are cooled by their proximity with the cylinder head, or piston, and simply never will reach ignition temperature. And, like the end-gases from the squish band, they eventually find their way out the exhaust port, having taken no part in the conversion of fuel and air into horsepower. Thus, the best combustion chamber shape - taken strictly from the standpoint of surface/volume ratio - would be a simple spherical segment sweeping in a continuous arc from one side of the cylinder bore to the opposite side. No tricky changes in section, no squish bands, no nothing. And that is, in point of fact, precisely the shape employed in nearly all non-squish cylinder heads.
But if you want to use a true (measured from exhaust-closing) compression ratio much over 6.5:1, on a high-output engine, combustion control beyond that afforded by a non-squish cylinder head will be necessary. Considerable variation is possible, but a good rule to follow is to make the cylinder head's squish band about 50-percent of the cylinder bore area. For example, in a 3-inch bore -which has a total area of 7.07-inches2 the squish band would be wide enough to represent an area of just about 3.5 in2. Assuming that you have centered the combustion chamber proper on the bore axis, then your squish band would be a ring having the same outer diameter as the bore, and an inner diameter of just over 2-inches. The combustion chamber itself, to meet the previously-stated minimum surface/volume requirement, would again be a spherical segment - with a radius that provides the total volume, added with that from the clearance space between piston and squish band, to give the desired compression ratio.
The clearance space between piston and cylinder head must be enough to avoid contact at high engine speeds, yet close enough to keep the mixture held there cooled during the combustion process. This vertical clearance between squish band and piston should not be greater than 0.060-inch, and it is my opinion that the minimum should be only barely enough to prevent contact -usually about 0.015-inch in small engines (with tight bearings and cylinder/rod combinations that do not grow, with heat, disproportionately) and up to about 0.045-inch in big engines.
Some disagreement exists as to the validity of claims that the squish band aids combustion by causing turbulence in the combustion chamber as a result of the piston "squishing" part of the charge between itself and the head. I don't know about that, but I do know that holding squish band clearance to a minimum means that there will be the smallest volume of end-gases escaping the combustion process, and that can be more important than you might think. For example, a 250cc cylinder with a full-stroke compression ratio of 10:1 will pack its entire air/fuel charge into a volume of only 28cc by the time its piston reaches top center. Assuming that it has a 3-inch bore, and a 50-percent squish band with a piston/head clearance of .045-inch, then the volume of the charge hiding in the squish area will be in the order of 2.6cc, or almost 10-percent of the total. That can be reduced to 5-percent merely by closing the squish band's clearance to 0.020-inch - and you'll never find an easier 5-percent horsepower difference. True, the difference measured at the crankshaft might prove to be more like 2-1/2-percent, but the addition of those small percentages can make a very large final difference.
Maybe I'll just keep my squish band clearance where I have it,or reduce it even more,but decrease my chamber volume to up the compression. Hmmm... I'll decide after my first cup of coffee in the morning. After I finish the coffee,I'll finish the head. I'll possibly have pictures of the head tomorrow plus a ride report with recorded running temperatures. We'll see.
About tempuratures... It seems that alot of people think that my running tempuratures are high. I don't beleive so. I think humidity has alot to do with it too. Like I've stated in other threads the go kart guys run 400 degrees to 475 degrees all the time,under heavy loads,and for long periods of time!!!
I'm safe.
Here is a short read about what Gordon Jennings Has this to say about squish band clearance... I think everybody will find it interesting....especially the last two paragraphs.
By and large, you would be well-advised to ignore the whole business of compression ratios in favor of cranking pressures. There is, after all, a big difference between the kinds of numbers you get by performing the traditional calculations to find compression ratio, and what is happening as the engine turns. My experience has been that you can use cranking pressures of 120 psi without worrying much about overheating anything. Maximum power will be obtained at cranking pressures somewhere between 135 and 165 psi. Going higher with compression, in a conventional motorcycle engine, can give a neat boost in low speed torque, but the thermal repercussions of higher cranking pressures will surely limit maximum output. On the other hand, fan-cooled kart engines perform very well at cranking pressures up at 200 psi, and water cooled engines behave much the same.
One of the most undesirable side-effects that comes with too-high compression ratios is an enormous difficulty in getting an engine to "carburet" cleanly. When the compression ratio is too high, you'll find that an engine's mixture-strength requirement has a sharp hump right at its torque peak that no motorcycle carburetor can accommodate. You'll realize, after working with high-output two-stroke engines, that all of them are to some degree liquid-cooled - and that the cooling liquid is gasoline. It istrue that an over-rich mixture tends to dampen the combustion process, and reduce power, but here again we find ourselves faced with the necessity for finding a balance between evils: We have overheating to rob power on one side, and we can cool the engine with gasoline, but too much fuel also robs power. The solution is a beggar's choice, in which we try to find the cross-over point between overheating and over-rich mixtures.
In an engine intended purely for road racing, with a torque peak virtually coincidental with its power peak and driving through a very close-ratio transmission (enabling the rider to hold engine-speed within narrow limits), making this beggar's choice is a fairly straight-forward proposition: you play with jetting until the motorcycle runs fast. However, road racing conditions allow you to stay right on the mixture-requirement hump; you don't have to worry about what happens two-thousand revs below the power peak, because that's below what you'll use in a race. Motocross racing is another matter entirely, and an engine with a mixture-curve hump will drive you absolutely mad. Jet a motocross engine so that it doesn't melt a piston every time it pulls hard at its torque peak, and (if its mixture-curve is humped) it will be huffing soot and losing power above and below that speed.
The answer to this problem is to iron out that mixture-requirement hump, because no matter how much work you do with the carburetor, it never will be able to cope with the engine's needs. All the carburetor knows, really, is how much air is moving through its throat, and it adds fuel to the air in proportion to the rate of air-flow; don't expect it to know when the piston is getting hot and respond by heaving in some more fuel. How do you get rid of the hump? You do it mostly by substituting a somewhat less effective expansion chamber: one that gives more nearly the same boost all the way through the speed range you are obliged to use by racing conditions, without any big surges. That will result in a drop in peak power, obviously, but you can compensate for it to a considerable extent with the higher compression ratio you previously were forced to forego in the interest of keeping the piston crown intact when the expansion chamber did its big-boost routine. Again, it is all a matter of finding the balance.
No matter what the compression ratio you ultimately use, it will have been influenced much more than you probably suspect by the combustion chamber configuration, and by certain gross characteristics of the head itself. Over the years, I have seen the fashion in combustion chamber forms swing back and forth, hither and yon, with first hat-section chambers in favor and then trench-type chambers, and torus-type chambers and so on and so forth ad infinitum. I was not, and am not, impressed. Combustion chamber form should be established with an eye toward only a very few special considerations, and these cannot account for even half the chamber shapes I have seen. Listed, though not really in order of importance, these are: surface / volume ratio; spark plug location; thermal loadings; and combustion control. We will consider each of these in turn.
Surface to volume ratio is important because even in the part of the combustion chamber fully exposed to the advancing flame front, there will be a mixture layer adhering to the metal surfaces that does not burn. These layers, like that trapped within the squish band, are cooled by their proximity with the cylinder head, or piston, and simply never will reach ignition temperature. And, like the end-gases from the squish band, they eventually find their way out the exhaust port, having taken no part in the conversion of fuel and air into horsepower. Thus, the best combustion chamber shape - taken strictly from the standpoint of surface/volume ratio - would be a simple spherical segment sweeping in a continuous arc from one side of the cylinder bore to the opposite side. No tricky changes in section, no squish bands, no nothing. And that is, in point of fact, precisely the shape employed in nearly all non-squish cylinder heads.
But if you want to use a true (measured from exhaust-closing) compression ratio much over 6.5:1, on a high-output engine, combustion control beyond that afforded by a non-squish cylinder head will be necessary. Considerable variation is possible, but a good rule to follow is to make the cylinder head's squish band about 50-percent of the cylinder bore area. For example, in a 3-inch bore -which has a total area of 7.07-inches2 the squish band would be wide enough to represent an area of just about 3.5 in2. Assuming that you have centered the combustion chamber proper on the bore axis, then your squish band would be a ring having the same outer diameter as the bore, and an inner diameter of just over 2-inches. The combustion chamber itself, to meet the previously-stated minimum surface/volume requirement, would again be a spherical segment - with a radius that provides the total volume, added with that from the clearance space between piston and squish band, to give the desired compression ratio.
The clearance space between piston and cylinder head must be enough to avoid contact at high engine speeds, yet close enough to keep the mixture held there cooled during the combustion process. This vertical clearance between squish band and piston should not be greater than 0.060-inch, and it is my opinion that the minimum should be only barely enough to prevent contact -usually about 0.015-inch in small engines (with tight bearings and cylinder/rod combinations that do not grow, with heat, disproportionately) and up to about 0.045-inch in big engines.
Some disagreement exists as to the validity of claims that the squish band aids combustion by causing turbulence in the combustion chamber as a result of the piston "squishing" part of the charge between itself and the head. I don't know about that, but I do know that holding squish band clearance to a minimum means that there will be the smallest volume of end-gases escaping the combustion process, and that can be more important than you might think. For example, a 250cc cylinder with a full-stroke compression ratio of 10:1 will pack its entire air/fuel charge into a volume of only 28cc by the time its piston reaches top center. Assuming that it has a 3-inch bore, and a 50-percent squish band with a piston/head clearance of .045-inch, then the volume of the charge hiding in the squish area will be in the order of 2.6cc, or almost 10-percent of the total. That can be reduced to 5-percent merely by closing the squish band's clearance to 0.020-inch - and you'll never find an easier 5-percent horsepower difference. True, the difference measured at the crankshaft might prove to be more like 2-1/2-percent, but the addition of those small percentages can make a very large final difference.
Re: Closing up the squish band clearance on my modified head! My testing continues...
It is for my Sons bike, which is all stock other than a DMC Alien, +4 advance and reed spacer between jug and reeds.
The exhaust port has been polished but not enlarged, and the intake has had all imperfections removed but no porting.
I have been chasing an old jug for a long time now so that he can practice porting before he attacks his good one.
Stock carb #320 main, needle on bottom clip, dual stage reeds, 98 octane, and Castrol R at 25:1
Nothing has been done to his head, as I do not own a lathe, and out where I live in the bush, machine shops are hard to find.
Although he holds his own, he has expressed his desire to get a little more oomph out of the motor. He has a 35mm D slide Mikuni that he is itching to bolt on.
Yup I still ride, but not in competition any more, it hurts too much, arthritus you know. Also I have realised that if I stack it is going to hurt for a lot longer than it used to.
My 15 yr old lad rides pretty good, and I delight in eating his dust, which I may add happens a lot now.
Since the lad took over the Blaster, my ride has been a 250cc 4 poke Chinaman (wash my mouth out with caustic soda) nearly fast enough, but will not jump.
Here in Aussie Blasters are as scarce as hens teeth, and impossible to get parts for at a reasonable price. It is far cheaper to get them from the US and pay the high freight costs.
It is for my Sons bike, which is all stock other than a DMC Alien, +4 advance and reed spacer between jug and reeds.
The exhaust port has been polished but not enlarged, and the intake has had all imperfections removed but no porting.
I have been chasing an old jug for a long time now so that he can practice porting before he attacks his good one.
Stock carb #320 main, needle on bottom clip, dual stage reeds, 98 octane, and Castrol R at 25:1
Nothing has been done to his head, as I do not own a lathe, and out where I live in the bush, machine shops are hard to find.
Although he holds his own, he has expressed his desire to get a little more oomph out of the motor. He has a 35mm D slide Mikuni that he is itching to bolt on.
Yup I still ride, but not in competition any more, it hurts too much, arthritus you know. Also I have realised that if I stack it is going to hurt for a lot longer than it used to.
My 15 yr old lad rides pretty good, and I delight in eating his dust, which I may add happens a lot now.
Since the lad took over the Blaster, my ride has been a 250cc 4 poke Chinaman (wash my mouth out with caustic soda) nearly fast enough, but will not jump.
Here in Aussie Blasters are as scarce as hens teeth, and impossible to get parts for at a reasonable price. It is far cheaper to get them from the US and pay the high freight costs.
Re: Closing up the squish band clearance on my modified head! My testing continues...
Joe, the thing you have to realize about Gordon Jenning's transcripts (believe me I've read them front, back, side to side) is that he was dealing with 2 stroke engines from the 60's and maybe early 70's. He was still dealing with piston ported engines and engines without proper boost ports. Our engines (blaster's) were designed using some of the types of principles he's describing!
Alas, his theories and observations were at a generally lower state of tune. The material choices and construction techniques back then limited a production type engine to roughly 6k rpm while there are blaster's out there that turn over 10k rpm now. When you start talking about the level of engine tune, the operating rpm is a HUGE concern. The faster you turn an engine, the faster a given squish area pushes a charge as a cube of the distance. The squish area for a relatively igh rev engine (8k rpm max rev) HAS to be wider than an engine you aren't operating over 6k rpm because at 6k, the piston isn't pushing the charge NEARLY as fast....
Joe, the thing you have to realize about Gordon Jenning's transcripts (believe me I've read them front, back, side to side) is that he was dealing with 2 stroke engines from the 60's and maybe early 70's. He was still dealing with piston ported engines and engines without proper boost ports. Our engines (blaster's) were designed using some of the types of principles he's describing!
Alas, his theories and observations were at a generally lower state of tune. The material choices and construction techniques back then limited a production type engine to roughly 6k rpm while there are blaster's out there that turn over 10k rpm now. When you start talking about the level of engine tune, the operating rpm is a HUGE concern. The faster you turn an engine, the faster a given squish area pushes a charge as a cube of the distance. The squish area for a relatively igh rev engine (8k rpm max rev) HAS to be wider than an engine you aren't operating over 6k rpm because at 6k, the piston isn't pushing the charge NEARLY as fast....
Re: Closing up the squish band clearance on my modified head! My testing continues...
I am coming into this thread late, and sorry for it. Good points James, also Jenning's average cylinder pressures were lower due to poor porting and fuels were not as good as we have available, no matter how we complain about it. Still his work is an epic!
Back to squish gap, too little risks a collision between head and piston. 10,000rpm in a missed shift involves a lot of force and roller bearings are plenty loose. As well, too little sucks energy out of the crank and turns it to heat compressing the "squirt". How much is enough? Joe is checking it out... I have heard guys running 0.030" on 250MX machines with no troubles. Often they reduce the band width and close the gap for more power at higher rpm.
Hey, just got a head back from the machine shop (backlogged bad), toroidal type chamber mimicking KTM. A bit large at 25cc but will close the squish and see what we get. Not on Blaster yet, I am hugely busy with outside work.
Due to the surface finish textures the KTM water cooled chamber and Blaster modified chamber look a bit different, but they are nearly identical. There is a bit of Blaster conical chamber remaining around the plug and the plug is deeper than I would want it to be. The stock Blaster head is here for comparison.
How to CC? Greased plate and I add water from the sparkplug hole until bottom of threads. Simple.
Hey Joe, excellent stuff guy!
My experience with air cooled sleds tends to bear out what Jennings says, go easy on compression and timing.
I think like SiCivicDude mentions, heat loadings on aircooled engines have to be considered. Sleds run at max throttle and even in the cold air, they die fast when you have it wrong. A lot of what we are doing here has to due with where the heat goes, keeping it off the piston is critical.
About the 20:1 oil. Besides sealing the piston, I wonder about cooling from the liquid taking up heat and the conduction between cylinder and piston? I don't race, don't need that last hp, and don't like too much smoke or a big oil bill so have not played much with oil mixtures lately. Just used to use the injection in the sled and leave it at that.
I am coming into this thread late, and sorry for it. Good points James, also Jenning's average cylinder pressures were lower due to poor porting and fuels were not as good as we have available, no matter how we complain about it. Still his work is an epic!
Back to squish gap, too little risks a collision between head and piston. 10,000rpm in a missed shift involves a lot of force and roller bearings are plenty loose. As well, too little sucks energy out of the crank and turns it to heat compressing the "squirt". How much is enough? Joe is checking it out... I have heard guys running 0.030" on 250MX machines with no troubles. Often they reduce the band width and close the gap for more power at higher rpm.
Hey, just got a head back from the machine shop (backlogged bad), toroidal type chamber mimicking KTM. A bit large at 25cc but will close the squish and see what we get. Not on Blaster yet, I am hugely busy with outside work.
Due to the surface finish textures the KTM water cooled chamber and Blaster modified chamber look a bit different, but they are nearly identical. There is a bit of Blaster conical chamber remaining around the plug and the plug is deeper than I would want it to be. The stock Blaster head is here for comparison.
How to CC? Greased plate and I add water from the sparkplug hole until bottom of threads. Simple.
Hey Joe, excellent stuff guy!
My experience with air cooled sleds tends to bear out what Jennings says, go easy on compression and timing.
I think like SiCivicDude mentions, heat loadings on aircooled engines have to be considered. Sleds run at max throttle and even in the cold air, they die fast when you have it wrong. A lot of what we are doing here has to due with where the heat goes, keeping it off the piston is critical.
About the 20:1 oil. Besides sealing the piston, I wonder about cooling from the liquid taking up heat and the conduction between cylinder and piston? I don't race, don't need that last hp, and don't like too much smoke or a big oil bill so have not played much with oil mixtures lately. Just used to use the injection in the sled and leave it at that.
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Re: Closing up the squish band clearance on my modified head! My testing continues...
Zedicus, can you post all the details of how you run your engine?
Like SiCivicDude alludes to, you can build an engine around one parameter if you want to, so fill us in on all the details.
For example, what are you running for a head? Any pictures of its chamber?
What are you running for a cylinder? Intake Porting? Exhaust porting? Cylinder Height?
You told us FMF pipe and stock can, +4 timing, 0.030" squish gap.
Very interested.
Zedicus, can you post all the details of how you run your engine?
Like SiCivicDude alludes to, you can build an engine around one parameter if you want to, so fill us in on all the details.
For example, what are you running for a head? Any pictures of its chamber?
What are you running for a cylinder? Intake Porting? Exhaust porting? Cylinder Height?
You told us FMF pipe and stock can, +4 timing, 0.030" squish gap.
Very interested.
Re: Closing up the squish band clearance on my modified head! My testing continues...
A heads up for everybody... I screwed up with the values (numbers) in my first post on this head. I appologize for the inconvenience
I have so many notes in my note book on all the head stuff I've been doing that I made the mistake of being on the wrong stuff when I was typing.
Here's the corrected values....
Before I started reducing the squish band clearance on this head ,the squish band clearance was between .066 and .072 thousands (varied because of the cast piston top) and worked awesome compared to the stock head. The head gasket thickness is .031 thousandths,so when I step cut the head the same ammount .031 thousandths, the squish clearance was effectively reduced to .035 to .041 thousandths. This head is now a "holy crap what a difference" head.
Just wanted to correct that before I go any further.
All squish was double checked with the "solder method" to verify.
A heads up for everybody... I screwed up with the values (numbers) in my first post on this head. I appologize for the inconvenience
I have so many notes in my note book on all the head stuff I've been doing that I made the mistake of being on the wrong stuff when I was typing.
Here's the corrected values....
Before I started reducing the squish band clearance on this head ,the squish band clearance was between .066 and .072 thousands (varied because of the cast piston top) and worked awesome compared to the stock head. The head gasket thickness is .031 thousandths,so when I step cut the head the same ammount .031 thousandths, the squish clearance was effectively reduced to .035 to .041 thousandths. This head is now a "holy crap what a difference" head.
Just wanted to correct that before I go any further.
All squish was double checked with the "solder method" to verify.
Re: Closing up the squish band clearance on my modified head! My testing continues...
i will try and pull my head this weekend and post a pick. you guys are gunna poop yourselves. its gut so much we have cut about half way through the bottom cooling fin.
gordon knows his stuff BUT we are in a new world. he is talking about a high output motor at 6:1. we are working on TRIPLING that.
now think about this. say you werent getting detonation due to squish or compression. say you were getting detonation due to a lean condition. well a 2 stroke works on waves and the pressure builds and over time it it actually continues to build as the engine continues to run in its prime efficiency. its like adding a turbo to the PRIME RPM and suddenly your LEAN....
im at work i will go into it more later.
i will try and pull my head this weekend and post a pick. you guys are gunna poop yourselves. its gut so much we have cut about half way through the bottom cooling fin.
gordon knows his stuff BUT we are in a new world. he is talking about a high output motor at 6:1. we are working on TRIPLING that.
now think about this. say you werent getting detonation due to squish or compression. say you were getting detonation due to a lean condition. well a 2 stroke works on waves and the pressure builds and over time it it actually continues to build as the engine continues to run in its prime efficiency. its like adding a turbo to the PRIME RPM and suddenly your LEAN....
im at work i will go into it more later.
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Re: Closing up the squish band clearance on my modified head! My testing continues...
lil more about the motor, 3mm stroke, ported for low end so more of flowed ports, not drastically raised exhaust port or anything. even though this engine does not spin any crazy high RPM i still use v-force 3 reeds with custom port work done on the reed cage. i cannot use dual stage reeds, this engine sucks the small petals off of the blaster dual stage set up.
keihin 35mm a/s carb with a clamp on air cleaner. and the stock can actually flows just as well as most of the standard length end cans. the benefit of using the stock one is the thick steel and extra chamber capacity makes the blaster WAY quieter. now it does not flow as well as a short or drag end can, but then the FMF fatty is not what i would put on a drag set up.
i wish i could post the port timing and stuff. i simply do not remember. its been a while since i had it done.
lil more about the motor, 3mm stroke, ported for low end so more of flowed ports, not drastically raised exhaust port or anything. even though this engine does not spin any crazy high RPM i still use v-force 3 reeds with custom port work done on the reed cage. i cannot use dual stage reeds, this engine sucks the small petals off of the blaster dual stage set up.
keihin 35mm a/s carb with a clamp on air cleaner. and the stock can actually flows just as well as most of the standard length end cans. the benefit of using the stock one is the thick steel and extra chamber capacity makes the blaster WAY quieter. now it does not flow as well as a short or drag end can, but then the FMF fatty is not what i would put on a drag set up.
i wish i could post the port timing and stuff. i simply do not remember. its been a while since i had it done.
Re: Closing up the squish band clearance on my modified head! My testing continues...
BEST ...
Intead of water to cc that chamber,try rubbing alchohol. It works fantastic,because its "Wetter" than water....meaning there is no "skin" like water has (surface tension),so it flows into the smallest of spaces whithout creating/trapping bubbles.
You probably already knew this,but what the hell.
BEST ...
Intead of water to cc that chamber,try rubbing alchohol. It works fantastic,because its "Wetter" than water....meaning there is no "skin" like water has (surface tension),so it flows into the smallest of spaces whithout creating/trapping bubbles.
You probably already knew this,but what the hell.
Re: Closing up the squish band clearance on my modified head! My testing continues...
With the head right side up the bubbles flush out pretty good, whereas when you do it with the old "glass plate with a hole in it" you have to really chase the air out. Also the water works pretty good with the grease as a seal.
Hey, my number is 25cc, nowhere near "bragging" numbers.
I don't want to make that number any larger, do I? All the younger guys will laugh!
Interested in how this works compared to the hemi head Neil currently has on. We'll cc it and solder gap it on disassemble to try to keep the comparison straight. Going by memory I believe we are in the 22cc by 0.060" range.
Hemi head:
Incidentally, the squish band angle on the new head is perfect, and radii sharper (although don't look it in picts) than the hemi head. Joe, from what I saw you have perfection in your hemi design. Ours is a bit sloppy.
BEST ...
Intead of water to cc that chamber,try rubbing alchohol. It works fantastic,because its "Wetter" than water....meaning there is no "skin" like water has (surface tension),so it flows into the smallest of spaces whithout creating/trapping bubbles.
You probably already knew this,but what the hell.
With the head right side up the bubbles flush out pretty good, whereas when you do it with the old "glass plate with a hole in it" you have to really chase the air out. Also the water works pretty good with the grease as a seal.
Hey, my number is 25cc, nowhere near "bragging" numbers.
I don't want to make that number any larger, do I? All the younger guys will laugh!
Interested in how this works compared to the hemi head Neil currently has on. We'll cc it and solder gap it on disassemble to try to keep the comparison straight. Going by memory I believe we are in the 22cc by 0.060" range.
Hemi head:
Incidentally, the squish band angle on the new head is perfect, and radii sharper (although don't look it in picts) than the hemi head. Joe, from what I saw you have perfection in your hemi design. Ours is a bit sloppy.
Re: Closing up the squish band clearance on my modified head! My testing continues...
take the sharp edge off of that on the inside. i know there is gaket area there but you dont want any chance of there bein a sharp edge in the combustion chamber. just continue the cut until its a nice sloped edge.
take the sharp edge off of that on the inside. i know there is gaket area there but you dont want any chance of there bein a sharp edge in the combustion chamber. just continue the cut until its a nice sloped edge.
Re: Closing up the squish band clearance on my modified head! My testing continues...
I just read thru this whole thread. I know this may be apples and oranges but in my mini quad days we built air cooled 2stroke scooter motors and set squish at .017 had 210psi and ran 110 octane. That won a championship.
We ran stock timing. Everyone else said we were full of crap and crazy. They all topped out at 160-180psi but wouldn't tell me their squish measurements.
They also advanced timing and every couple races they were burning pistons in their liquid cooled motors and we ran all season on our air cooled motor running those numbers.
Our motor got almost every holeshot and was crazy on top end with the heaviest rider in the class. I am a fan of compression. Sorry like I said this was apples and oranges...lol
I just read thru this whole thread. I know this may be apples and oranges but in my mini quad days we built air cooled 2stroke scooter motors and set squish at .017 had 210psi and ran 110 octane. That won a championship.
We ran stock timing. Everyone else said we were full of crap and crazy. They all topped out at 160-180psi but wouldn't tell me their squish measurements.
They also advanced timing and every couple races they were burning pistons in their liquid cooled motors and we ran all season on our air cooled motor running those numbers.
Our motor got almost every holeshot and was crazy on top end with the heaviest rider in the class. I am a fan of compression. Sorry like I said this was apples and oranges...lol
Re: Closing up the squish band clearance on my modified head! My testing continues...
I don't think you are full of crap at all. It matches some of my experience and follows with much of old Gordon Jennings advice too. You have a small motor with lightweight components and you are not looking for longevity so you can push the squish to the limit. This and your compression really speeds up the burn, no need of advanced timing, that is for slow burn. A well designed engine should be able to run 180psi on 93 octane, so 210 on 110 octane sounds reasonable.
Actually squish has been a builder's secret for many years. I first heard about it in the 70s in Jenning's book I believe. When I asked about "quench distance" to automotive engine builders, they smiled like I was asking an inside question. Some remained quiet and coy, others bubbled out information like I was suddenly part of the secret brotherhood! Squish or quench has been a little understood and little shared concept for many years.
For automotive engines I've used much tighter squish gaps, 0.030" to as tight as 0.020" on 350cid engines. Makes a heck of a difference on the power output and detonation resistance. Tightening up on quench allowed me to run as much as 10.5:1 compression ratios on regular fuel in the years we could not get premium at the pump.
Another guy who was an early proponent on intelligent quench design was Larry Widmer in NASCAR, big block Ford and Honda engines. Larry's basic idea was to squeeze the mixture to a tiny ball in the hottest part of the cylinder head. He was running incredible compression ratios of usually more than 14:1 and up to 22:1 in some cases, and very retarded timing compared to his peers. If the burn is sped up, you do not need the timing advance. In Widmer's cylinders, the mixture would almost ignite itself at full power.
So how much squish/quench is too much in our engines?
I really don't know yet. I have always erred on the side of reliability on my bikes.
I don't think you are full of crap at all. It matches some of my experience and follows with much of old Gordon Jennings advice too. You have a small motor with lightweight components and you are not looking for longevity so you can push the squish to the limit. This and your compression really speeds up the burn, no need of advanced timing, that is for slow burn. A well designed engine should be able to run 180psi on 93 octane, so 210 on 110 octane sounds reasonable.
Actually squish has been a builder's secret for many years. I first heard about it in the 70s in Jenning's book I believe. When I asked about "quench distance" to automotive engine builders, they smiled like I was asking an inside question. Some remained quiet and coy, others bubbled out information like I was suddenly part of the secret brotherhood! Squish or quench has been a little understood and little shared concept for many years.
For automotive engines I've used much tighter squish gaps, 0.030" to as tight as 0.020" on 350cid engines. Makes a heck of a difference on the power output and detonation resistance. Tightening up on quench allowed me to run as much as 10.5:1 compression ratios on regular fuel in the years we could not get premium at the pump.
Another guy who was an early proponent on intelligent quench design was Larry Widmer in NASCAR, big block Ford and Honda engines. Larry's basic idea was to squeeze the mixture to a tiny ball in the hottest part of the cylinder head. He was running incredible compression ratios of usually more than 14:1 and up to 22:1 in some cases, and very retarded timing compared to his peers. If the burn is sped up, you do not need the timing advance. In Widmer's cylinders, the mixture would almost ignite itself at full power.
So how much squish/quench is too much in our engines?
I really don't know yet. I have always erred on the side of reliability on my bikes.
Re: Closing up the squish band clearance on my modified head! My testing continues...
lets all pitch in and someone can put together an engine just to blow up? i will donate a carb and some intake stuff.
we can maybe make an entrance form and submit our geusses and the winner get to keep the blown up motor or something?
lets all pitch in and someone can put together an engine just to blow up? i will donate a carb and some intake stuff.
we can maybe make an entrance form and submit our geusses and the winner get to keep the blown up motor or something?
Re: Closing up the squish band clearance on my modified head! My testing continues...
oh also the smaller the bore and stroke the tighter the squish and compression can be, so a CR80 will never compare to a CR500. and really no engine will compare identically to a different size or even rather its water or air cooled. so we need to actually do our testing on a blaster engine.
the knowledge gained can be used as a guide for testing other engines, to to be perfect the full procedure would need done on any other types of engines you wanted tested. sayy a yz490 or something also?
oh also the smaller the bore and stroke the tighter the squish and compression can be, so a CR80 will never compare to a CR500. and really no engine will compare identically to a different size or even rather its water or air cooled. so we need to actually do our testing on a blaster engine.
the knowledge gained can be used as a guide for testing other engines, to to be perfect the full procedure would need done on any other types of engines you wanted tested. sayy a yz490 or something also?
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