17.5:1 compression ratio
Close
    
    
Page 1 of 2 12 LastLast
Results 1 to 10 of 11
Like Tree11Likes

Thread: 17.5:1 compression ratio

  1. #1
    Senior Member elime's Avatar
    Join Date
    Jul 2010
    Location
    San Jose, CA
    Posts
    6,984

    17.5:1 compression ratio

    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?
    Last edited by elime; 07-29-2019 at 05:47 PM.
    Long live the internal combustion engine!

  2. #2
    Senior Member TW-Brian's Avatar
    Join Date
    Dec 2010
    Location
    Pleasanton, CA
    Posts
    5,747
    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 !

    Good luck,

    Brian

  3. #3
    Senior Member MtnMan75's Avatar
    Join Date
    Jul 2019
    Location
    MD, USA
    Posts
    107
    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.
    Purple likes this.

  4. Remove Advertisements
    TW200Forum.com
    Advertisements
     

  5. #4
    Senior Member FIRE UP's Avatar
    Join Date
    Jun 2019
    Location
    Lake Havasu City AZ
    Posts
    188

    Smile

    Or diesel!
    Scott
    Purple likes this.
    Retired SDFD, 30 years,
    2004 Itasca Horizon 36GD CAT C-7 330HP
    2008 Honda GL1800 Goldwing Caliente red
    2007 TW 200 "Blue Noid"
    2115 Jeep JKUR Rubicon
    2011 GMC Sierra 1500 Extended Cab 4x4
    HAM, KI6OND
    Me, the wife and our killer Mini Schnauzer, "Sophie"

  6. #5
    Ken
    Ken is offline
    Senior Member Ken's Avatar
    Join Date
    Aug 2016
    Location
    Houston, Texas
    Posts
    1,932
    Quote Originally Posted by FIRE UP View Post
    Or diesel!
    Scott
    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.
    1993 TW200 just over 46,000 miles

  7. #6
    Senior Member RaZed1's Avatar
    Join Date
    Oct 2015
    Posts
    293
    Quote Originally Posted by Ken View Post
    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.
    Ken likes this.

  8. #7
    Senior Member elime's Avatar
    Join Date
    Jul 2010
    Location
    San Jose, CA
    Posts
    6,984
    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
    Ken and MtnMan75 like this.
    Long live the internal combustion engine!

  9. #8
    Ken
    Ken is offline
    Senior Member Ken's Avatar
    Join Date
    Aug 2016
    Location
    Houston, Texas
    Posts
    1,932
    [QUOTE=elime;1012878]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[/QUOTE

    You know your stuff. I have heard your bike runs really great.
    1993 TW200 just over 46,000 miles

  10. #9
    Ken
    Ken is offline
    Senior Member Ken's Avatar
    Join Date
    Aug 2016
    Location
    Houston, Texas
    Posts
    1,932
    Quote Originally Posted by RaZed1 View Post
    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.
    1993 TW200 just over 46,000 miles

  11. #10
    Senior Member MtnMan75's Avatar
    Join Date
    Jul 2019
    Location
    MD, USA
    Posts
    107
    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...

Page 1 of 2 12 LastLast

Sponosred Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •