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  #1  
Old 12-12-2005, 04:52 PM
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Default Calculating Head Squish Measurements - (REP)

Just wondering if anyone has had any work done by these guys?
Particularly cylinder head milling for higher compression.

Here's an extract

" milled for higher compression, the motor was built by REP (Racers Edge Performance) there was a spacer ring under the spark plug, which is included."

I am after just the head.

Also, if my head was milled for higher compression like stated above, would BP Ultimate suffice? It's a 98 octane premium fuel for high-performance engines. It's not an overly expensive "race gas" like VP etc, just BP's best premium fuel that they now have out the local BP.

Thanks for your help boys and girls

Last edited by Aus_Rider_22; 12-13-2005 at 06:31 PM. Reason: Changed Name so easier to refer to.
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  #2  
Old 12-13-2005, 10:57 AM
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Default Re: Racer's Edge Performance (REP)

If you don’t mind donating a little time and being resourceful you can complete the steps necessary to know what is needed to set up your head, for your particular bike and your desired octane requirements. This is going to be more benificial then sending it to someone for a cookie cutter job on a "typical" bike.

First you’ll need to make a few measurements so that you can do the math and find out where you’re at, and eventually where you want to be. Production tolerances can leave quite a bit of untapped potential hiding in your engine especially in regards to the squish band. Taking the production tolerances out of the equation and fine tuning the squish and compression ratio(s) to suite your available fuel can make a difference.

If you choose to continue make sure to double check your measurements and once you’re confident be sure to record them.

I would first measure the squish clearance with the head on. To measure the squish clearance you need to first find yourself a roll of 0.125" diameter solder (look at an electronics store like Radio Shack). Next bend a small length of solder into and "L" shape with the leg being about as long as 1/2 the diameter of the bore. Insert the solder through the spark plug hole making sure that the end of the solder contacts the side of the cylinder bore, preferably the left or right side of the bore (as opposed to the front or rear of the bore which may give a false reading due to the piston rocking on the wrist pin). While holding the solder against the side of the bore slowly cycle the kick starter so that the piston rotates near TDC, crushes the solder and descends enough to get the solder out. Be careful to only cycle the piston once so that you don't pinch the solder multiple times which could skew measurements. Remove the solder and measure the crushed thickness. This will be your squish clearance! Accuracy does count so try to use a measuring tool that will read down to 0.001" (dial calipers).

Next I would remove the head to measure the squish band. The squish band has two physical dimensions, the height and the width. The height is the distance between the gasket surface of the head to the top of the squish band. Measure the height (actually it’s a recess) in the head and the head gasket thickness. Measuring the squish height and head gasket thickness in conjunction with your total squish measurement will help you determine what the deck clearance is (height from top of cylinder to top of piston, can be + or - or even 0). Total squish - (squish height + head gasket thickness) = deck clearance. This is only easily determined when working with flat topped pistons. Next I would measure the width of the squish band (the flat portion from the edge of combustion chamber to the opposing edge where it starts to recess into the combustion chamber). Be sure to record each measurement.

After these measurements I would then measure the volume of the head, otherwise known as "cc-ing" the head. Again, accuracy counts so being able to measure down to 0.1 cc is to your benefit. If you can beg, borrow or steal an accurate measuring device (like a burette, syringe, etc.) that will allow you to meter down to 0.1 cc and a small piece of Plexiglas with a hole in it then you can do it yourself. Yes, you will need to fully install a spark plug, turn the head upside down and seal the gasket area of the head to the Plexiglas with a small amount of grease. Use your measuring device to fill the head with the liquid of your choice (water works) until it's full and record the amount it took to fill the head.

This measurement will only be the volume of your head if you do not use a head gasket and run 0 deck clearance. If you have + or - deck clearance and/or a head gasket (and/or a domed piston!) this will have to be figured into the equation to come up with total head volume.

Since you have the head off I would take two more measurements on the cylinder. The first would be the distance between the top of the cylinder and the bottom of the exhaust valve (with the exhaust valve closed) and the second from the top of the cylinder to the top of the exhaust port (with the exhaust valve open).

Knowing your head volume along with the two exhaust port measurements you can figure your actual compression ratio and see how close you are to the manufacturers advertised compression ratio. This will also allow you to crunch numbers and figure compression ratios for different octane gas.

Last edited by Faded; 12-19-2005 at 08:54 AM.
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  #3  
Old 12-13-2005, 12:38 PM
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Default Re: Racer's Edge Performance (REP)

Wow, I'm not even sure I understood half of what you wrote... not that you weren't clear, I"m just not familiar with all these terms... You one smart cookie Faded.
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Old 12-13-2005, 01:11 PM
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Default Re: Racer's Edge Performance (REP)

Quote:
Originally Posted by Aus_Rider_22
I am after just the head.

Wouldn't it be easier to keep looking for the head you lost?
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  #5  
Old 12-13-2005, 01:13 PM
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Default Re: Racer's Edge Performance (REP)

Quote:
Originally Posted by Woody_CRF
Wow, I'm not even sure I understood half of what you wrote... not that you weren't clear, I"m just not familiar with all these terms...
W, no worries; it's a two stroke thing.
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  #6  
Old 12-13-2005, 01:19 PM
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Default Re: Racer's Edge Performance (REP)

Quote:
Originally Posted by Aus_Rider_22
"...the motor was built by REP (Racers Edge Performance) there was a spacer ring under the spark plug, which is included..."
FWIW, the "spacer ring" is more than likely an indexing washer used to index the spark plug. If you want one you should be able to get them at an auto parts store; they're just copper washers that come in a few different thicknesses.
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  #7  
Old 12-13-2005, 02:20 PM
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Default Re: Racer's Edge Performance (REP)

Quote:
Originally Posted by Faded
If you donít mind donating a little time and being resourceful you can complete the steps necessary to know what is needed to set up your head, for your particular bike and your desired octane requirements. This is going to be more benificial then sending it to someone for a cookie cutter job on a "typical" bike.

First youíll need to make a few measurements so that you can do the math and find out where youíre at, and eventually where you want to be. Production tolerances can leave quite a bit of untapped potential hiding in your engine especially in regards to the squish band. Taking the production tolerances out of the equation and fine tuning the squish and compression ratio(s) to suite your available fuel can make a difference.

If you choose to continue make sure to double check your measurements and once youíre confident be sure to record them.

I would first measure the squish clearance with the head on. To measure the squish clearance you need to first find yourself a roll of 0.125" diameter solder (look at an electronics store like Radio Shack). Next bend a small length of solder into and "L" shape with the leg being about as long as 1/2 the diameter of the bore. Insert the solder through the spark plug hole making sure that the end of the solder contacts the side of the cylinder bore, preferably the left or right side of the bore (as opposed to the front or rear of the bore which may give a false reading due to the piston rocking on the wrist pin). While holding the solder against the side of the bore slowly cycle the kick starter so that the piston rotates near TDC, crushes the solder and descends enough to get the solder out. Be careful to only cycle the piston once so that you don't pinch the solder multiple times which could skew measurements. Remove the solder and measure the crushed thickness. This will be your squish clearance! Accuracy does count so try to use a measuring tool that will read down to 0.001" (dial calipers).

Next I would remove the head to measure the squish band. The squish band has two physical dimensions, the height and the width. The height is the distance between the gasket surface of the head to the top of the squish band. Measure the height (actually itís a recess) in the head and the head gasket thickness. Measuring the squish height and head gasket thickness will help you determine what the deck height is (height from top of cylinder to top of piston, can be + or - or even 0). Next I would measure the width of the squish band (the flat portion from the edge of combustion chamber to the opposing edge where it starts to recess into the combustion chamber). Be sure to record each measurement.

After these measurements I would then measure the volume of the head, otherwise known as "cc-ing" the head. Again, accuracy counts so being able to measure down to 0.1 cc is to your benefit. If you can beg, borrow or steal an accurate measuring device (like a burette, syringe, etc.) that will allow you to meter down to 0.1 cc and a small piece of Plexiglas with a hole in it then you can do it yourself. Yes, you will need to fully install a spark plug, turn the head upside down and seal the gasket area of the head to the Plexiglas with a small amount of grease. Use your measuring device to fill the head with the liquid of your choice (water works) until it's full and record the amount it took to fill the head.

This measurement will only be the volume of your head if you do not use a head gasket and run 0 deck height. If you have + or - deck height and/or a head gasket (and/or a domed piston!) this will have to be figured into the equation to come up with total head volume.

Since you have the head off I would take two more measurements on the cylinder. The first would be the distance between the top of the cylinder and the bottom of the exhaust valve (with the exhaust valve closed) and the second from the top of the cylinder to the top of the exhaust port (with the exhaust valve open).

Knowing your head volume along with the two exhaust port measurements you can figure your actual compression ratio and see how close you are to the manufacturers advertised compression ratio. This will also allow you to crunch numbers and figure compression ratios for different octane gas.
Faded,
That's some awesome information there. Are you a self tought mechanic?or did you go to school, your are VERY knowledgeable
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  #8  
Old 12-13-2005, 04:13 PM
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Default Re: Racer's Edge Performance (REP)

What an awesome post Andrew! Thanks for the PM also.

I've actually understood and could follow what you've typed.
What equation are you talking about with the head volume? I am guessing I will be needing it as I run domed pistons with a diameter of 53.93mm.
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Old 12-13-2005, 04:40 PM
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Default Re: Racer's Edge Performance (REP)

Quote:
Originally Posted by Aus_Rider_22
What equation are you talking about with the head volume? I am guessing I will be needing it as I run domed pistons with a diameter of 53.93mm.
Okay, really only one way of doing it then, and that is to pull the head off and find absolute TDC. Use some grease and seal the piston crown to the cylinder bore so that nothing can leak past to the rings. Put the head/gasket back on and cc the combustion chamber through the spark plug hole. This will give you your total combustion chamber volume without having to worry about head gasket thickness, deck height, ect. but is a little less accurate.

Once you have the combustion chamber volume and the exhaust port measurements you can figure out your compression ratio(s).

The manufacturer’s list two compression ratios, a high speed CR (one with the exhaust valve open) and a low speed CR (one with the exhaust valve closed). You can determine both compression ratios once you find out your head/combustion chamber volume and your two effective stroke measurements (one with the exhaust valve open, one with the exhaust valve closed). The formula for finding a compression ratio is:

CR = (V1 + V2) / V2

CR = Compression Ratio
V1 = Cylinder Volume
V2 = Combustion Chamber Volume


The difference between high and low speed CRs will be the V1 measurement due to the difference in effective stroke (the piston covering the exhaust port with the exhaust valve open vs. with it closed). The formula for finding V1 is here:

V1 = [ 3.1416 * D2 (squared) * ES ] / 4000

D = Bore Diameter
ES = Effective Stroke
and V2 You'll have to find out.
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  #10  
Old 12-13-2005, 05:38 PM
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Default Re: Racer's Edge Performance (REP)

Andrew, you've outdone yourself!

Invaluable info in this thread!

I vote this to be put into the knowledge base forum. I could change the name to "Calculating Head Squish Measurements"
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