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Squish and Quench or Quinch

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This will be a supplementary discussion to the various other threads on improving combustion chambers or the benefits of a 4-valve head, etc.  Using a topic title specifically for this subject will attract folks from other forums who can share their knowledge, even if it is from another engine design.

I have been reading allot on the interweb lately about this subject.  Seems to be a factor some consider to be a crucial foundation element while others aren't even aware what it is or does.

From what I've gathered, done properly can mean running lots more compression than with it wrong.  I'm wondering just how much proper squish, quench, quinch can do for a CRF230F?

It all comes down to the burn.  To be efficient it must be fast and complete.  If it is then less timing advance is needed and more compression ratio can be used.  Small engines have the advantage of small bore diameter which means less distance for the flame front to travel which means faster burn.  Proper squish creates turbulence and eliminates small pockets where air/fuel mixture or fuel droplets can hide.  It also reduces the Combustion Chamber volume.

Since the 230F engine uses a 2-valve hemi or hemispherical combustion chamber, finding the ultimate design or shape will not send me to discuss tech with our more modern DOHC 4-valve pentroof brethren.  No, we must go and seek the advice of the more ancient horsepower junkies like the American V8 tuners, Yamaha SR500 affectionados and even......gulp......them Harley fellers.  If'n it ain't a pentroof design, some body has probably looked into improving the CC.  

I've searched to find a bore diameter vs. flame front speed relation or a distance from the spark plug the combustion chamber walls need to be at a maximum but haven't found anything discussed that way.  I'm wondering if say a 67mm bore is small enough already that just eliminating the large OE squish gap, something around 0.080", will be enough to deter detonation with say 12:1 and pump gas?  Will a 0.035 squish gap on our hemi head be enough or will we need to make the CC smaller, shorten the distance the flame front has to travel?

Is the actual shape of the CC important?  I have found that shallow CC are bad for turbulence and our good friend Mixxer suggested something with Hockey Puck dimensions is desirable, a 1:3 height:width ratio.  What about the actual shape of the CC?  The heart shape is popular on 2-valve wedge CC but a Hemi isn't a wedge.  I've found more of the bath tub shape but all of the discussions have been on engines with LOTS MORE BORE DIAMETER and some with an intake valve diameter close to the bore size of the 230F.  So they needed to make the CC smaller as well as optimize the squish band.

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My hunch is the operation of a chamber is more dependent on its geometry than its size. So hemi is hemi, etc.  Unfortunately the hemi shape seems to be the most sensitive to detonation. I'm sure Honda had specific goals when it designed the 230 chamber,  I suspect one goal was operation on  3rd world roads  with low octane gas, hence the 9:1 CR and large squish gap. Small squish gaps generate more turbulence but they also  hide mixture, and piston domes interfere with flame propagation.  Lots of little details: Since we can't change included valve angle we are left with squish band and piston dome. Pete told me that cutting the intake valve relief on a high compression piston leaves a small island near the spark plug that interferes with flame travel. I removed it on my last 218 build because I thought the slight loss of compression with a 11:1 piston was OK running the stock cam. What is interesting is that engine has ping events under the same conditions as my XR218 (that has a different carb and cam, both with 0.040" squish gap).  Slightly off topic but food for thought: A TT member posted  a dyno developed ignition advance for a modded 230 engine and when I compared the two curves the difference in timing where the ping events occur was 4 degrees. I could fix the ping with 3D ignition map; problem is the XR200 uses a mechanical advance that limits tuning and I suspect that the Honda CDI units with electronic timing are also 2D. So if I used  3D spark timing I could increase timing for more torque at speeds lower than the ping, reduce timing in the region of the ping, and adjust for WOT HP.

 

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1 hour ago, Chuck. said:

My hunch is the operation of a chamber is more dependent on its geometry than its size. So hemi is hemi, etc.  Unfortunately the hemi shape seems to be the most sensitive to detonation. I'm sure Honda had specific goals when it designed the 230 chamber,  I suspect one goal was operation on  3rd world roads  with low octane gas, hence the 9:1 CR and large squish gap. Small squish gaps generate more turbulence but they also  hide mixture, and piston domes interfere with flame propagation.  Lots of little details: Since we can't change included valve angle we are left with squish band and piston dome. Pete told me that cutting the intake valve relief on a high compression piston leaves a small island near the spark plug that interferes with flame travel. I removed it on my last 218 build because I thought the slight loss of compression with a 11:1 piston was OK running the stock cam. What is interesting is that engine has ping events under the same conditions as my XR218 (that has a different carb and cam, both with 0.040" squish gap).  Slightly off topic but food for thought: A TT member posted  a dyno developed ignition advance for a modded 230 engine and when I compared the two curves the difference in timing where the ping events occur was 4 degrees. I could fix the ping with 3D ignition map; problem is the XR200 uses a mechanical advance that limits tuning and I suspect that the Honda CDI units with electronic timing are also 2D. So if I used  3D spark timing I could increase timing for more torque at speeds lower than the ping, reduce timing in the region of the ping, and adjust for WOT HP.

 

Good info and good real world results.

From what I'm finding, a small 0.035" squish gap will not hide fuel mixture but gaps larger will so a small squish gap will help resist detonation.

I always assumed the 230F hemi design was an old design Honda still likes to use.  A modern design with small squish gap will be less prone to detonation on any quality level of fuel than a hemi design as long as the timing is not advanced.  Squish and chamber size are what allow the mixture to burn more quickly so less timing advance is needed and less should be used to keep residual heat lower and move peak cylinder pressure closer to TDC.  If we optimize squish and chamber size but we don't retard the timing then we won't take full advantage.

Have you ever seen a CRF230F ignition map?  Not sure I have but maybe the map BBR had shows it.  I'm thinking the OE 230F CDI box might be just the ticket for more compression, especially since folks are running a ProCom with higher than OE compression.  Go back to the OE box and bump compression instead.

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My OEM box pings the same as my procom using reg. fuel pings in the upper mid but with a lazy bottom end compared to the procom. I also thought I could go back to the OEM box but the curve is to slow joe!

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If you want to check the curve and total timing use a programmable timing light.

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On ‎1‎/‎31‎/‎2018 at 4:37 PM, ricky racer said:

My OEM box pings the same as my procom using reg. fuel pings in the upper mid but with a lazy bottom end compared to the procom. I also thought I could go back to the OEM box but the curve is to slow joe!

Ping is a symptom of too large of a squish gap.  A smaller CC and squish gap of 0.035" will need less timing, leave less residual heat in the cylinder and move peak cylinder pressure closer to TDC, all of which is GOOOOOD !

 

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Ok, another thing.  The most turbulence the squish gap creates will be at TDC.  This burn will start anywhere from 20degrees to 30degrees before TDC.  The turbulence will happen after the burn has already started.  Just thinking out loud here.

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  Ok, I'm gonna jump in. I saw/read a fascinating article about this where 'someone' was cutting a small, tapering groove in a fairly tight (.025"ish) squish area aimed to shoot a jet of mixture straight at the spark plug. They claimed a reduction of spark lead and better/more complete combustion due all the reason we're discussing here. Thought I might try it on the 230 head I'm going to have welded up in the next day or so. Probably need a dyno to quantify the results, which I ain't got. Interesting to contemplate though. Kevin Cameron mentions in his writings a bike (Lucifer's Hammer, a Harley) that had such a sweet chamber that it made the best power (and ran much cooler to boot) with only 23 degrees of spark lead. Now that sounds nice, don't it?  

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The Singh Groove gets lots of opinions posted all over the interweb.  Might be something I'd try after getting the CC smaller.  Not sure why they want to aim the jet of mixture at the spark plug, the ignition event happened about 20 to 30 degrees earlier and the flame front is already moving away from the spark plug by the time the piston reaches TDC and the squish gets to squishin'.

Your basic squish and quench get my attention because all of the modern high performance engines use it and are able to run 13:1 compression on pump gas.  Even an ol'skool 2-valve head can benefit from this tech with the proper mods.  A Hemi with large included valve angle is designed to flow well, we just need to eliminate the areas on either side which give the flame front a larger distance to travel.

Edited by MetricMuscle
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Another thought relative to the squish band not influencing initial combustion because ignition begins so far before the squish band is active.
So any turbulence present at ignition must be residual from the intake process.  So that means another variable in turbulence is port flow.
Well documented in 2Ts but I haven't heard much about it for hemi combustion chambers.  

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11 hours ago, Chuck. said:

Another thought relative to the squish band not influencing initial combustion because ignition begins so far before the squish band is active.
So any turbulence present at ignition must be residual from the intake process.  So that means another variable in turbulence is port flow.
Well documented in 2Ts but I haven't heard much about it for hemi combustion chambers.  

The squish band does create turbulence, which is always a good thing, but more importantly it eliminates nooks and crannies which are the right size to hide fuel mixture and cause detonation.  Even though it doesn't provide maximum squish turbulence until 25 to 35 degrees after ignition, this is lots closer than intake port turbulence which stops somewhere around or slightly after BDC, ~150degrees before the ignition event.  The compression stroke is what precedes the ignition event so this is when turbulence needs to happen.  Maybe the piston is moving enough faster than the flame front so those 25 to 35 degrees aren't an issue.  I've read on turbo forums where high levels of boost can extinguish the spark so maybe adding turbulence after the flame front has started is actually better, fan the flames as it were. :)

 

Edited by MetricMuscle
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14 hours ago, MetricMuscle said:

Ping is a symptom of too large of a squish gap.  A smaller CC and squish gap of 0.035" will need less timing, leave less residual heat in the cylinder and move peak cylinder pressure closer to TDC, all of which is GOOOOOD !

 

My squish is .035" I get that your into this as your learning new stuff BUT you will only get the 230 to maybe a true 11-1 static cr and be tolerant to 92 octane with all your mods unless you use a cam with much more overlap but then you will sacrifice bottom and in cooler temps with slightly rich jetting. It is air cooled and will be prone to more detonation as cyl. head temps rise above optimal. I have chose to use rather high cr with a small cam(st2.5) to create a real monster down low and understood going into the project I would need to use race fuel. I just think that after all the mods it will not be as octane tolerant as you hope. I am excited though as I love this stuff. please hurry up as I cant wait for the end result!!!!!

 

13 hours ago, MetricMuscle said:

Your basic squish and quench get my attention because all of the modern high performance engines use it and are able to run 13:1 compression on pump gas.

I think the fact that modern bike are liquid cooled has more to do with them being able to use high compression ALSO the cams they use have a lot of overlap much more high performance grinds than what most of us are using in our 230's. put a small 220* at .050 in a 450 with 13-1 and you will see its not so octane tolerant :) 

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I would like to add that all the things we do to our engines really add up and makes ones engine stand above the rest!!!!!!! Everyone that has rode my 230/251 is blown away with how much more power/torque it has over stock and how much better it handles :) I have even run into other (highly modified)lol 230's and they don't stand a chance! Keep up the good work as everything makes a difference! this reminds me that I need to try a bigger head pipe!

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Come on Ricky?
Really?
Your sandbagging us.
Geez, get Er done already...

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3 minutes ago, adnohguy said:

Come on Ricky?
Really?
Your sandbagging us.
Geez, get Er done already...

I did just get a 2005 cr85r shock on its way for the next step in suspension. just need to order a gold valve and spring from Cannon Racecraft. Still looking for some xr400r forks. My current setup is really good but needed modern components so I could purchases some Gold valves :) 

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11 hours ago, ricky racer said:

It is air cooled and will be prone to more detonation as cyl. head temps rise above optimal.

 

11 hours ago, ricky racer said:

I think the fact that modern bike are liquid cooled has more to do with them being able to use high compression

It is my understanding that liquid cooling is superior because it maintains engine heat better and depending on the engine design, air cooled can "out cool" a liquid cooled engine but this is often a bad thing.  Liquid cooling can be better if the design of the engine is not conducive to air cooling like inline 4-cylinder engines.  Oil cooling can often make up for what an air cooled engine lacks in both ability to cool and maintaining the proper temp, not over cooling.

 

11 hours ago, ricky racer said:

ALSO the cams they use have a lot of overlap much more high performance grinds than what most of us are using in our 230's.

This is definitely a reason an engine tolerates such high CR at low rpm but something has to work it's magic as the revs go up.

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I finally got my head to the welder and picked it up yesterday from him.  This is pre machining.

 

108.jpg.6fe523c9ad563cd8f556bd30d4eae3d3.jpg116.jpg.6d8949a55544e32864c0c32a4b58863d.jpg105.jpg.443f19060229aef5f0520f76b90eca43.jpg

 

I'm going to try to get over to the shop where my buddy works and start shaping things.

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Posted (edited)

OK, as far as shaping goes, I'm looking at both of these.  Doogee, would you say that the 38degree angle is close to what you went for?  It only needs to be as wide as the valve has lift.

5aa002248319d_Doogeeunshroudingtheory.jpg.28eee718ba72aa63344f680bb927b8fa.jpg5aa00248a96a0_ZEROSHROUDCONDITIONVALVESEATANGLE.jpg.1974307cc35c260d88c0d2a018a1afcf.jpg

Does the exhaust valve need the same angles?

Edited by MetricMuscle
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Posted (edited)

    Now that's what I'm talkin about:applause:

I started at more of a 45 deg. angle and then curved it down a little steeper toward 50-55. I was trying to hit a compromise between keeping a shallower slope (45ish, curving gently to maybe 50) and removing the least amount of material to keep the chamber as small as possible. The head looks very nice by the way. Was that a new head? The reason I ask is because the welds look a little cleaner than mine did. Mine had been run and my welder said that contamination was probably actually 'cooked' down into the casting. I see you also went down a little closer to the plug hole. As far as the exhaust port goes, that's just the way I've seen it on virtually all the good heads that have that style of chamber.

 Maybe someone else will want to give this mod a go. Might have to start a "brotherhood of the traveling plugs"  :smirk:

Edited by Doogee57
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