Squish band

Discussion in 'Performance Mods' started by jaguar, May 20, 2013.

  1. jaguar

    jaguar Well-Known Member

    In "Advances in the Design of Two-Stroke, High Speed, Compression Ignition Engines" it is written that with a squish band there is more heat loss due to swirl. [which brings more burning fuel in contact with metal.] Heat is what causes expansion of gases to push against the piston so it equates to say that heat loss, without regard to other factors, reduces power. The advantage of swirl is better mixing and flame propagation. But in a small engine there is usually already enough mixing due to its high intake/transfer turbulence. When I tested a head on my 55cc that had a squish band the power output was less. This most probably is only the case for small engines since larger engines need help with fuel/air mixing, and flame speed increase is helpful because of larger distances from spark plug to cylinder wall.

    This is not to say that a good cylinder head with a squish band will never improve power. There are always many factors at play in 2 strokes. Increasing the compression can give as much as a 5% boost in power. But it is my opinion that these small engines will do better without a squish band. I don't remember where I read that small engines have more intake/transfer turbulence but I did read it.

  2. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Your opinion is just plain wrong.
    you haven't tested "your theory" in real life and you don't know what you are doing.

    At the races we have a dyno and a properly shaped squish band definitely increases
    power significantly.

    CR Machine is making the best head on the market right now and they are working closely with Arrow Motorized cycles.

    I am not saying that because they are a sponsor at the races and give out heads as prizes.

    They got the best design with lots of cooling area, correct squish band and they come in 3 head sizes to work with motors in various states of tune and the CR Machine heads look great too.

    Last edited: May 20, 2013
  3. crmachineman

    crmachineman Member

    Do some research!

    Mr Jaguar. Wow! What you wrote didn't even touch on what the function of the squish band is for! Sorry, but you don't have a clue.

    You are a novice posing as a someone with understanding and authority.

    The squish band has nothing to do with initiating a swirl or anything like that.
    The shape of this kind of combustion chamber is designed to trap the air/fuel mixture closely around the spark plug, so the mixture will be burned as quickly as possible.

    A quick completion of burn is the key to preventing detonation.
    The farther the flame front must travel in order to complete the burn, the more time it will take, and as pressure is rising, so is the temperature of whatever fuel mixture is yet unburnt.
    There is a point in temperature when this unburnt mixture will spontaneously ignite which is harmful to the engine.

    There are other nuances about this combustion chamber design which I don't feel I need to get into.

    You and your opinion is on one side, and the rest of the world is on the other. Haven't you ever looked at a 2 stroke moped combustion chamber?

    Do you really think it was just some arbitrary reason that all the best ones incorporate generous squish bands?

    Why don't you go and race against some competent teams with your non-squish band head and see what happens? If you manage to finish the race, you'll be dead last.
    Last edited: May 22, 2013
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  4. jaguar

    jaguar Well-Known Member

    It could be that you are right but I did experiment with both designs on my engine and the standard non-squish-band shape gave the better result. I'll bet you haven't done the same test because you don't question things that are generally agreed upon. I question everything.
    I believe the greater power output from your heads is just from the compression increase.
    Prove me wrong. Measure the compression while using a squish-band head and then mill down a standard head to yield the same compression and then run them on a dyno. If you are right then the results will speak for themselves. Until then I will continue with my opinion because it is based on such a test.
  5. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    what head were you using for your experiment?
    The standard piece of crap Chinese one?

    Check out this experimental head from CR Machine.

    Copper inlayed squish band and a compression release.


  6. jaguar

    jaguar Well-Known Member

    >"you haven't tested "your theory" in real life"
    I wrote "When I tested a head on my 55cc that had a squish band the power output was less." I would appreciate it if you would pay attention to what is written before making comments.

    >"The shape of this kind of combustion chamber is designed to trap the air/fuel mixture closely around the spark plug, so the mixture will be burned as quickly as possible."
    When maintaining the same compression ratio between these two types of heads of course it stands to reason that the area at TDC is the same. And the combustion does not all happen before the piston lowers enough to allow much more combustion area than just what the top dome permits. You are way way off from the truth here.

    >"The squish band has nothing to do with initiating a swirl"
    Everything I have ever read about it says that is its principle purpose! The swirl causes more complete mixing of the fuel and air (and trapped exhaust gases).
    Read Graham Bells Two Stroke Performance Tuning
    Last edited: May 21, 2013
  7. jaguar

    jaguar Well-Known Member

    Here is a graph from Blairs book that shows the combustion happening up to 30 degrees ATDC:
  8. jaguar

    jaguar Well-Known Member

    Gordon Jennings - Two Stroke Tuners Handbook
    "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." (he is referring to a head w/squish band being necessary for high compression high rpm engines)

    What I recommend and use is no more than a compression of around 130psi which is right around the mentioned 6.5:1 ratio. If you go over that and have ported the engine to rev up to at least 9,000 rpm then you should use a cylinder head with a squish band. The engine I used to test had a top rpm of around 8,000.

    Since very few people with these engines run higher than 130psi and/or rev higher than 9000 I think my advice concerning squish bands has been accurate for the majority.
  9. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    When are we seeing your motor built on your theories racing against the arrow motorized cycles race bikes?
  10. jaguar

    jaguar Well-Known Member

    maybe never. JNMotors has my top end and torque pipe but is whining now because some of the chrome is flaked off. If we can trust each other we can have an on-line video match. When I get back to the States I will make another 60cc to race and we both can video our rides going from a stop to 1/4 mile. Shortest time wins.
    Last edited: May 21, 2013
  11. crmachineman

    crmachineman Member

    Sure, I've done a lot of research Jaguar. What do you take me for? I manufacture cylinder heads and other kinds of performance enhancing parts for these engines. I certainly don't do this stuff blindly.

    I have spent countless hours building and testing these designs, compared with other designs, etc. When I first started out running these kind of engines, I ran into terrible problems with detonation and overheating.

    If you are putting around at 30 MPH it's probably OK to run stock equipment.

    I started making these cylinder heads because they were necessary in order to do what I wanted to do, which is to travel 40-50+ MPH.

    I have read that book from Jennings. It's very good. If you too have read that book, and understood it, certainly you would have seen then the importance of the squish band.
    You know, it probably does create more mixing of air/fuel mixture, well, the more the better!

    I have made and tested a lot of prototypes. I don't think you have. You shouldn't talk like you are an expert about something unless you really are.

    Large manufacturers guided by proven racing results, who have tried everything under the sun make squish band combustion chamber cylinder heads for small engines.
    This is for a very good reason, because they allow you to run higher compression without the damaging effects of detonation. My god, this is basic stuff here!

    They would never support what you are saying about combustion chambers. You tests were just weak or flawed, or you don't have the capabilities to test different designs.
    You know, you would have to make different cylinder heads to do this. Have you done that? I get the feeling that you don't have the capability to do this.

    I have done this type of research, and you are quite wrong here. I saw some You tube video a while back promoting your Jag ignition box, and it was pathetic!

    That pretty model was revving that sad little engine with a scared look on her face, like, "who is this guy that put me up to this."

    All stock, revving so lamely. Gosh, it was sad. There was no punch there.

    Make an engine and race against a competent racing team and see what happens. If you would like me to continue, I can talk about why using a ignition retard module is a compromise solution to the quest of better performance.
    Last edited: May 22, 2013
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  12. jaguar

    jaguar Well-Known Member

    ok Freddy here goes
    thanks for all the insults. It lets me know what a moral-less person you are.
    Yes I did make my own head with squish band by modifying a stock 55cc head.
    What I have presented is reasons in favor of the argument that a squish band is not helpful for an engine with no more than 130psi and that revs under 9000. You havent presented anything in your defense. That is why you have to insult, because you have no substance. You keep talking about race eninges and for them, of course, it is necessary. And yes heads with squish bands are on most small engines but those engines are much much closer to being a competition engine than a putt-putt Grubee engine. They have much more compression and they rev much higher.
    If your heads bring the compression over 130psi then its cool that it has a squish band. I have no problem with that. I just hope you warn your customers to also change the upper conrod bearing and to be aware that the lower conrod bearing will now have a much shorter lifespan.
  13. HeadSmess

    HeadSmess Well-Known Member

    in my mind, what i know of squish bands and such forth, is that, on the zbox happytime grubee call it what you will, the piston has a fairly large chamfer on it. well, 48s do at least. (just double checked...the 66 has a slight dome but no chamfer)

    just the chamfer alone nullifies any effect generated by the squish band by holding quite a large volume of unburnt, cold, and seperated charge mixture...

    unless you was to skim cylinder down to edge of chamfer plus clearance, then shape head to suit.

    im getting sick of this CC stuff. 48, 50, 55, 60, 66, 70, 80... arrrrrgh!
  14. crmachineman

    crmachineman Member

    Whatever Jaguar. You talk about mods for more performance, then say that squish band type cylinder heads are not important. What?

    Well, they are important and very helpful for real performance benefit for street and racing. That's what racing competition does, it improves design for everybody, allowing higher performance.

    You are talking about higher performance aren't you? Now you are back pedaling, trying to make it seem that the racing scene is a completely far off practice. Well, it's not.

    Lots of people on the street want better performance, and what you are saying about combustion chambers is totally wrong.

    You just don't know what you are talking about. Showing us some boring graph like it's supposed to impress us. Just go away!

    Like, you are right and everybody else is wrong. I don't think so. Look at all the competition combustion chambers. You think that's not important? Well, it is important.

    Either you are into performance, or you are not.

    It's okay that you are happy putting along at 30 MPH with your overheating stock setup, but don't go running your mouth, talking a bunch of lame nonsense that squish band combustion chambers don't help improve performance for small 2 stroke engines.
    Last edited: May 22, 2013
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  15. jaguar

    jaguar Well-Known Member

    I still just hear a lot of wind with no real substance.
    I have given technical reasons and real life experience to back up what I am saying. You just keep on defending race engines. Yeah I am in to performance but since these are usually one speed rides I dont recommend porting them for anything higher than 8000 rpm. And I dont recommend any higher compression than 130 psi, both of which brings the engine into the category of not needing a squish band. But if someone wants 150 psi then I am all for a high compression head with a squish band. That is where machinists like you come in. My initial post was strictly concerning squish bands, not high compression heads with squish bands. So there was never any reason for you to march to war and catapult all the insults you could think of at me. I dont need to insult you back since you are doing a real good job of making yourself look bad.
    Who has got my back is Gordon Jennings himself. He said basically that only a race engine with more than a 6.5:1 compression ratio is in need of a squish band. I rest my case.
  16. Fabian

    Fabian Well-Known Member

    If Honda believes that squish band is important, then it can be taken as "fact" that squish band is important to maximising engine performance.
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  17. Fabian

    Fabian Well-Known Member

    I have purchased CR Machine Manufacturing cylinder heads in both the 2 hole and 3 hole versions. I have also purchased CR Machine Manufacturing modified OEM pistons.

    I have been happy with the results but what i am most happy with is the dramatically improved cooling surfaces with the CR Machine Manufacturing cylinder heads. They have a massive heat sink area compared to other billet cylinder heads that i have tried, enabling an 80 degree (Celsius) drop in peak cylinder head temperature compared to other billet cylinder heads.

    If i had three thumbs, i would give CR Machine Manufacturing a full three thumbs up for his cylinder heads.
    Last edited: May 22, 2013
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  18. crmachineman

    crmachineman Member

    Jaguar. No substance? You are not reading and comprehending what I am saying then.

    I have written about my testing. I put a 1/4 Inch size hole in a piston because of detonation related overheating while running a stock head.

    Since I have started making my squish band heads, those engine problems have completely gone away.

    You are arguing with a manufacturer who naturally has a need to do comprehensive testing.

    You are saying that I am not giving any substance? What do you think I've been writing about?

    Partial detonation occurs with these engines. Your engine partially detonates, I guarantee it. And, according to Jennings, you can't tell by listening to the engine.

    The engine problems I had before I started making squish band type heads was frequent.

    After making the first prototype head with a 6.2 cc combustion chamber (a significant compression increase), compared to the stock 7.2 cc combustion chamber, the engine ran cooler, and I wasn't having frequent bearing failures and piston and cylinder damage.

    I attributed this to the detonation management that a squish band provides for a combustion chamber.

    I make low compression heads which have the same compression as the stock heads as well. In fact, that is what I'm running in one of my test bikes which uses low octane fuel.

    I don't believe that Jennings would agree with you. I also don't agree with those compression ratio numbers you have cooked up.

    Jaguar, I've noticed that you like to fluff up a lot of your theories with a bunch of wordy mumbo jumbo and graphs. That's what a BSer does.

    Take note of what Fabian said: Honda uses that same technology, Honda. So, you are going to argue with Honda? Well then, you are coo-coo!
    Last edited: May 22, 2013
  19. Fabian

    Fabian Well-Known Member

    Someone once said that if Honda has researched and developed an engine design or theory, there is no point in trying to reinvent the wheel over a company that spends 500 million dollars per year on piston engine development.

    Honda only stops development on a particular technology when it has been refined to the point where further development yields no benefits.
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  20. crmachineman

    crmachineman Member

    Totally Fabian. Honda engineering is amazing. Real masters.