Squish band

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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.
 
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.
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.

248002_5001724204300_1029217642_n.jpg
 
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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.
-Fred
 
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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.
 
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.
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.


428032_10200108602021231_480102620_n.jpg


944388_10200108602061232_1598872913_n.jpg
 
>"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
 
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Here is a graph from Blairs book that shows the combustion happening up to 30 degrees ATDC:
comb-burn.jpg
 
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.
 
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 they all 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.

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