Squish Band Width

[Marty Davis]

.21 Head Buttons

I am interested in the various squish band widths that different head buttons have. Can anyone measure some some of them and post here. Just post the engine, if it is stock, etc, maybe the Orlic and the Keeley buttons too.

Thanks,

 

[Terry Keeley]

All our Turbo Heads were made with 65-70% squish area. ^_^

 

[Jim Allen]

.21 Head Buttons

I am interested in the various squish band widths that different head buttons have. Can anyone measure some some of them and post here. Just post the engine, if it is stock, etc, maybe the Orlic and the Keeley buttons too.

Thanks,

Marty,

Greg Settles has been making toroidal head buttons for his ,21 size engines for some time now. Squish band areas are in the 40 to 45% amounts & the chambers are cut at an angle in a similar fashion as we discussed before. I think he said, he uses Rossi tubro plugs because of their steeper angle on the bottom.

Jim

 

[dwilfong]

Let me put some light on the nomenclature of how we refer to the squash band size.

I have bin trying different % of band and was confused on what was what.

There is % of the total area of the bore dia. and there is % of the bore size.

example 1.14 bore. 50% of the bore is is .570 chamber making the band .285 that is 75% of the total area. Hope we can all get on the same page. Made for some very interesting head buttons.

50% area dose not work.

Believe me I found out the hard way!

David

 

[Ian Inverarity]

50% area dose not work.

Believe me I found out the hard way!

David

David,

50% area squish band works fine for me and a few people I have made head buttons for or designed head buttons for. Some other factor would have been an issue for you. This is what makes testing head button design difficult, any change affects multiple aspects.

 

[Jim Allen]

"Let me put some light on the nomenclature of how we refer to the squash band size.

I have bin trying different % of band and was confused on what was what.

There is % of the total area of the bore dia. and there is % of the bore size.

example 1.14 bore. 50% of the bore is is .570 chamber making the band .285 that is 75% of the total area. Hope we can all get on the same page. Made for some very interesting head buttons.

50% area dose not work.

Believe me I found out the hard way!

David"

David,

Calculate the bores total area (A = 3.1416 X R X R) = 1.0207 sqin for a 1.140" bore DIA

50% = .5103 sqin

.5103 sqin = 3.1416 X R X R

.5103 sqin divided by 3.1416 = .1624 sqin = R X R

.4030" = RADIUS of 1/2 of the bore's area

.4030" X 2 = .8061" DIA of 1/2 of the bore's area

1.140" minus .8061" = .3338"

.3338" divided by 2 = .1669" of squish band width for a bore that is 1.140" DIA; not .285".

Jim Allen

 

[Bart Drieghe]

Jim and /or Marty( or anyone else who knows ) ,

how much is the squish band width related to the percentage of nitro being used in the fuel ? Or doesn't this make a difference ? ( would surprise me but still .. )

Regards ,

B

 

[Jim Allen]

Jim and /or Marty( or anyone else who knows ) ,

how much is the squish band width related to the percentage of nitro being used in the fuel ? Or doesn't this make a difference ? ( would surprise me but still .. )

Regards ,

B

There doesn't appear to be a relationship between the percentage of nitro & the squish band width. I used nitro contents as high as 80%, but the squish band was always 50% of the bores area.

 

[Bart Drieghe]

Thanks Jim !!

 

[Marty Davis]

I am not sure about this at all (the assumption that nitro content makes little difference)..... I am curently testing 3 different head buttons with the exact same volume, just different percentage squish band percentage. I am POSITIVE that squish velocity is the controlling factor in excess detonation. It is especially bad in the small engines with no excess horsepower. You have to ask them to put out more than they want and the result is detonation. The controls of squish velocity are in 2 classifications: The first are those items that affect SV tremendously with only a very small change and those that change the SV only a little bit with changes.

The first group is Squish Width, Squish Angle, Peak RPM, Head Clearance.

Those that fit into the second group are Compression Ratio, Exhaust Duration

It is really a balancing act with SV. If you get it too high, the engine will detonate, too low and the engine will not have good low end power.

 

[Jim Allen]

From my testing, the most important factor in controlling detonation is the head shape. This is the reason I adhere to the 50% number with the deck closed to the maxium. Also in many two stroke engines detonation problems are the results of poor port geometries, but are seemingly corrected with excessive squish band widths & high deck clearances.

I think it is very difficult to correct a detonation problem in an engine that has already been built. Why did those holes keep appearing in the pistons of certain CMB engines? Did this happen because they were pushed to hard or was there something else wrong?

Jim Allen

 

[DickJones]

I am not sure about this at all (the assumption that nitro content makes little difference)..... I am curently testing 3 different head buttons with the exact same volume, just different percentage squish band percentage. I am POSITIVE that squish velocity is the controlling factor in excess detonation. It is especially bad in the small engines with no excess horsepower. You have to ask them to put out more than they want and the result is detonation. The controls of squish velocity are in 2 classifications: The first are those items that affect SV tremendously with only a very small change and those that change the SV only a little bit with changes.

The first group is Squish Width, Squish Angle, Peak RPM, Head Clearance.

Those that fit into the second group are Compression Ratio, Exhaust Duration

It is really a balancing act with SV. If you get it too high, the engine will detonate, too low and the engine will not have good low end power.

Marty, look at available fuel delivery at critical RPM's such as the last 5000 R's, glow plug temp and how it reacts at critical RPM's, also look at the OS 21 with head clearance of .002 to .004 thos before it will really turn on.

Just my 2 cents worth

dick

 

[DickJones]

From my testing, the most important factor in controlling detonation is the head shape. This is the reason I adhere to the 50% number with the deck closed to the maxium. Also in many two stroke engines detonation problems are the results of poor port geometries, but are seemingly corrected with excessive squish band widths & high deck clearances.

I think it is very difficult to correct a detonation problem in an engine that has already been built. Why did those holes keep appearing in the pistons of certain CMB engines? Did this happen because they were pushed to hard or was there something else wrong?

Jim Allen

Jim

I was able to look at quite a few of these engines with holes in the pistons, these were the pistons that were dished, after taking out the dish there was only .061 thosands of material left right in the center of the bowl, just not enough material to survive very long before the material became to soft.

JM2CW

 

[Jim Allen]

From my testing, the most important factor in controlling detonation is the head shape. This is the reason I adhere to the 50% number with the deck closed to the maxium. Also in many two stroke engines detonation problems are the results of poor port geometries, but are seemingly corrected with excessive squish band widths & high deck clearances.

I think it is very difficult to correct a detonation problem in an engine that has already been built. Why did those holes keep appearing in the pistons of certain CMB engines? Did this happen because they were pushed to hard or was there something else wrong?

Jim Allen

Jim

I was able to look at quite a few of these engines with holes in the pistons, these were the pistons that were dished, after taking out the dish there was only .061 thosands of material left right in the center of the bowl, just not enough material to survive very long before the material became to soft.

JM2CW

I would agree with this analysis because the thickness of the piston crowns in my .90 size engines is never less than .120". Many people think it is the material used that caused these failures. A piston made of A-390 would survive when the engine was pushed to it's limit, if the piston crown was of sufficient thickness.

When I refer to the correct transfer geometry in any two cycle engine there are two components to examine. The axial angles of the transfer windows when looking at the liner from a side view & the radial angles when looking at the transfers from a top view. Both angles must be correct to remove burnt gases from the combustion chamber without mixing with the burnt gases present & both angles are necessary to effectively cool the piston crown. Failure to accomplish both results in an engine that will easily go into detonation because the pistons heat, that is not removed, will be raised with each cycle. This heat cannot be removed with the piston's contact with the walls of the liner or excess amounts of water cooling to the head.

If you want high HP without risk of detonation, the squish clearance must be closed up. A squish band that does not work properly is much worse than having no squish band at all because it wastes a good amount of the fuel-air charge. Squish bands that are to large in area & ones that are not working always result in less HP.

CUT & TRY!!!

Jim Allen

 

[Jim Allen]

Here is a photo of a piston which has the metal in it's center melted out from detonation. When this happened the glow plugs center post began to glow cherry red. The red lines indicate the vapor trails that were left. The engine's size was .80 cu in with a 1.060" bore & it was developed from a .70 cu in engine that could make 6.5 HP at 24,000 RPM on 65% nitro. All the axial & radial angles of the transfers were cut the same in both motors. Bill Wiesneski, who bench tested more engines than any one in the world, gave me the answer over the telephone without ever seeing the engine. The radial angles on the transfers closest to the exhaust window were cut at 30 deg. He told me to cut them as much as possible, without causing short circuiting out of the exhaust window. The final angle was 43 deg 30 min. I set my first straight away record with this engine. Bill also taught me that the direction of transfer streams can be greatly influenced with a simple change in the thickness of the liners wall.

Final testing showed that the engine could be over leaned without burning the glow plug. In fact it would only begin to sag slightly when over leaned.

 

[Charles Perdue]

Mr. Jim, could you show us an illustration of the radial and axial angles of the ports that you are talking about. :wacko:

Thanks, Charles

 

[Jim Allen]

Mr. Jim, could you show us an illustration of the radial and axial angles of the ports that you are talking about. :wacko:

Thanks, Charles

Mr Charles,

The photo shows one of the actual prints used to make the .80 cu in liner. The print is drawn at a 1:5 ratio. All angles are measured from the center line passing through the exhaust window & the rear boost port. Also on the print is the "T" top exhaust window & the cutter diameters used. The original 33 deg 30 minute radial angle can be seen as well as the modified 47 deg 30 minute radial angle. A special 36 hole dividing plate was made which allows indexing to 1/4 of a deg or 15 minutes is used to make liners. No axial view is shown because the main transfers were flat on the top & bottom. Does any one still think that a Dremel tool could be used to do this type of work?

Jim Allen

 

[Charles Perdue]

Thanks Mr. Jim. I understand it better now.

Charles

 

[Andy Brown]

I am not sure about this at all (the assumption that nitro content makes little difference)..... I am curently testing 3 different head buttons with the exact same volume, just different percentage squish band percentage. I am POSITIVE that squish velocity is the controlling factor in excess detonation. It is especially bad in the small engines with no excess horsepower. You have to ask them to put out more than they want and the result is detonation. The controls of squish velocity are in 2 classifications: The first are those items that affect SV tremendously with only a very small change and those that change the SV only a little bit with changes.

The first group is Squish Width, Squish Angle, Peak RPM, Head Clearance.

Those that fit into the second group are Compression Ratio, Exhaust Duration

It is really a balancing act with SV. If you get it too high, the engine will detonate, too low and the engine will not have good low end power.

" It is especially bad in the small engines with no excess horsepower. You have to ask them to put out more than they want and the result is detonation."

Marty,

For years I have been hearing you say that the small engines do not have any excees horsepower. I just wonder why you say that? Does any racing engine have "excess horsepower"? As you know, a good .21 will put out over 2.5 HP. That's nearly 12 HP per cubic inch. Does a CMB 101 put out 12 HP? I don't think so. Maybe what you are really saying is that our .21 boats are SLUGS....too heavy for the 2.5 HP engine. Lets see. A 4 pound .21. That's 1.6 pounds/HP.

Extrapolating from Jim's 6.5 HP .70 on 65% nitro, That's 9.3 HP/ CI. A single 90/101 boat would come in about 10 pounds. That's about 1.1 pounds/HP.

A 16 pound twin 101 comes in at a skinny .86 pounds per HP. Yet the 101 engine is putting out only 9.2 HP/CI, about 20% less HP/ci than the .21

So I guess that is what you are really saying is that the .21 boats are too heavy, because certainly the .21 engine are among the most powerful engines on earth. I have even heard of some 3 HP .21'S. Maybe you have too? That would ba a whopping 14HP/CI. If it was a 500CI Top Fuel engine that would be 7000 HP. Hmmmm sounds like a number I've heard from the Top Fuel guys.

Well looking at all of that, while I don't think any race engine has "excees horsepower", I do think the .21's produce the "most Excessive horsepower" for their size.

Guess we need to get to work on those 101'S. Those 18 horsepower twins should be 28 Horsepower twins! Yeah Baby!

Even with a 3 HP .21 engine the boat could only weigh 1.7 pounds to accelerate like that 28 HP TWIN BADBOY!!!

 

[Jim Allen]

What is causing this apparent drop in the HP/CI as the size of the engine keeps getting larger. Is it friction losses, fluid dynamic losses, poor induction design, poor carburetor design, poor tuned pipe design, poor transfer design, poor metallurgy, etc., etc. If a .90 size engine made the same HP/CI as a .21 size engine, you would think that 9.5 HP would be easily obtainable.

None of the .90 size engines I built ever exceeded 7.5 HP. To achieve this 80% nitro was required & the engine had to turn 30,000 RPM. A good .45 engine can make 4.5 HP which means there is something really wrong with the design of larger size engines, mine included.

Jim Allen