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Discussion Starter #1 (Edited)
Speaking of pistons..........I finally got around to measuring the dome volume of this piston

P7210018a.jpg

and it came out to 11.3 cc. Given the compression ratio of the TW is 9.5:1 and assuming a stock flat top piston (it does have a very slight dome) I calculated the head volume to be 23.1 cc.

I used the formula: cyl. vol. + head vol / head vol = compression ratio.

Or more exactly: (cyl. vol. - dome vol.) + head vol. / (head vol. - dome vol.) = comp. ratio ::: Cyl=196cc ; Head = 23.1cc; Piston dome = 11.3cc

With numbers: (196 - 11.3) + 23.1 / (23.1-11.3) = 184.7 + 23.1 / 11.8 = 207.8 / 11.8 = 17.5

On the box it says compression ratio is 11:1 Clearly, either the box is way off or my calculations are. Ideas anyone?
 

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Tony,

I think that you should install this piston into one of your bikes and determine the following:

-Will you be able to get the head on and bolted down?
-With the spark plug out, will you be able to turn the engine over without bending a valve?
-With the spark plug in, will the starter motor crank the engine over?
-If the starter motor won't turn the engine over, can you kick it over without breaking your leg?
-If you are able to kick it over and start the engine, congratulations, and how does it run?
-If you made it to this point, I think your calculations must be off :eek:;):D!

Good luck,

Brian
 

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From the pin to the flat top portion of the piston, is it the same as the stock or slightly lower? In an engine that runs as hot as this and a compression ratio of 17.5:1 you may want to just consider switching fuels to Halon.
 

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Or diesel!
Scott
 

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I think Elime may be onto a diesel hybrid. Start it on gas and when it starts running at 17:1, switch to diesel and it should diesel and run without the sparkplug.
That was commonplace on heavy equipment through the 1970's or so. There would be a handle that opened a third valve which increased the head volume to lower compression to like 6:1, so the engine would crank easily and start on gasoline. Run it for like a minute to warm up, move the handle the other way, the third valve closes upping the compression to 20:1 or whatever the diesel ran at, the tiny carb's throttle is sealed off, spark plugs turned off, and the injection pump turned on. Good idea, you could start like a 15 liter diesel engine in the middle of winter without ether and a normal automotive battery. Less complex than having a pony motor as well.
 

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Discussion Starter #7
Ad nauseam...... a little recalculation and some more measuring. I measured the head vol and it equals 24cc. I took into account the head gasket and using a bore of 68mm and a thickness of 1mm came up with 3.7cc. Cyl vol still 196.4 and dome vol still 11.3cc

Vol max / Vol min: 196.4 - 11.3 + 24 + 3.7 / 24 + 3.7 - 11.3 = 212.8 / 16.4 = 12.9 which is a whole lot better to work with than 17.5! Maybe if I added in the base gasket thickness it would approach the claimed 11:1

Picture of wrist pin in stock piston and Venolia piston at the same time showing deck height equal, or very very close to equal.

P7210018.JPG
 

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Ad nauseam...... a little recalculation and some more measuring. I measured the head vol and it equals 24cc. I took into account the head gasket and using a bore of 68mm and a thickness of 1mm came up with 3.7cc. Cyl vol still 196.4 and dome vol still 11.3cc

Vol max / Vol min: 196.4 - 11.3 + 24 + 3.7 / 24 + 3.7 - 11.3 = 212.8 / 16.4 = 12.9 which is a whole lot better to work with than 17.5! Maybe if I added in the base gasket thickness it would approach the claimed 11:1

Picture of wrist pin in stock piston and Venolia piston at the same time showing deck height equal, or very very close to equal.

View attachment 195930 [/QUOTE

You know your stuff. I have heard your bike runs really great.
 

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That was commonplace on heavy equipment through the 1970's or so. There would be a handle that opened a third valve which increased the head volume to lower compression to like 6:1, so the engine would crank easily and start on gasoline. Run it for like a minute to warm up, move the handle the other way, the third valve closes upping the compression to 20:1 or whatever the diesel ran at, the tiny carb's throttle is sealed off, spark plugs turned off, and the injection pump turned on. Good idea, you could start like a 15 liter diesel engine in the middle of winter without ether and a normal automotive battery. Less complex than having a pony motor as well.
That's pretty cool that they had that. With the EPA I am surprised they don't still use something like that since it probably wouldn't pollute as much since it warms up so good before introducing the diesel.
 

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From the looks of it, it should also do a much better job of oiling vs. stock too. I'd have to agree about checking valve clearance first, the difference between the two is considerable. I wonder how many ponies you'll gain with this...
 

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That's pretty cool that they had that. With the EPA I am surprised they don't still use something like that since it probably wouldn't pollute as much since it warms up so good before introducing the diesel.
This is a pretty good explanation of it.
 
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