Joker
...chaos? Its Fair!
- Location
- La Porte, Indiana
1mm over would give me how many more cc's
650/X-2 650 bore
- Thread starter Joker
- Start date
- Location
- Loveland, Colorado
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Joker
...chaos? Its Fair!
- Location
- La Porte, Indiana
Of all the google searches I did, I never thought to look on wisecos site
- Location
- Loveland, Colorado
I dd the math and comes out to 653.68 cc's. So it's 18.68cc over stock. You might get a bit more power but most all you power is in your ports.
Vumad
Super Hero, with a cape!
- Location
- St. Pete, FL
Formula ---------- Pie / 4 x bore^2 x stroke x number of cylinders
Stroke is 70mm, bore is 76mm
so...
3.14 / 4 x 76^2 x 70 x 2 = 635
1mm over is...
3.14 / 4 x 77^2 x 70 x 2 = 651.5
Group K website http://www.groupk.com/restof650k.htm
OEM 635 stock, 1mm over is 651.5, increase of 15.5cc, and increase of 2.4%
Edit: I corrected the 1mm overbore math. I used 657 copied from Group K's website. Doing the math, the result is not 657, but rather 651.5.
Stroke is 70mm, bore is 76mm
so...
3.14 / 4 x 76^2 x 70 x 2 = 635
1mm over is...
3.14 / 4 x 77^2 x 70 x 2 = 651.5
Group K website http://www.groupk.com/restof650k.htm
OEM 635 stock, 1mm over is 651.5, increase of 15.5cc, and increase of 2.4%
Edit: I corrected the 1mm overbore math. I used 657 copied from Group K's website. Doing the math, the result is not 657, but rather 651.5.
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Joker
...chaos? Its Fair!
- Location
- La Porte, Indiana
Anyone know port dimensions that will give me the best bottom end?
- Location
- Redding CA
OEM Stroke | OEM displacement | 1mm over | 2mm over | 3mm over |
| 650 70mm | 76mm 635cc | 77mm 657cc | 78mm 668cc | Not available |
| 750 74mm | 80mm 743cc | 81mm 760cc | 82mm 779cc | 83mm 795cc |
i did some math using a totaly stock motor base HP and at 1mm over you would add 1.8 HP but that's bone stock if your head, pipe, FA,carb add 20 % more HP then whats 20% of 1.8 right so it raises even more with bolt ons or port work IMOP
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Fro Diesel
creative control
- Location
- Kzoo
Going to have a used 650 group k motor for sale here in a couple weeks...rips hard, comes with milled stock head.
Sent from Fro Diesel using Tapatalk
Sent from Fro Diesel using Tapatalk
- Location
- New Jersey
seems like everyone has a different way of calculating displacement... Is that 657 including something other than just a cylinder shape cause my calculator says a little under 652cc. If anyone wants to take a calculator and multiply out vumads 1mm over equation you should get something closer to this: 651,927.049
not that it really matters though cause you should bore as small as possible
not that it really matters though cause you should bore as small as possible
- Location
- Loveland, Colorado
Yeah same here every one I have checked is off. I calulate it just a little different but did vumads equation on all of the same ones and its exactly what I got on my equation.
Also its more accurate if you use pie not 3.14 but tried both an only like a .8 difference on the cc so thats not were we are going wrong. Any one know why they are all off??
Also its more accurate if you use pie not 3.14 but tried both an only like a .8 difference on the cc so thats not were we are going wrong. Any one know why they are all off??
The only way I have ever been able to get good response and power form a 650 is with compression, timing, and 112 octane gas. The ports cannot be lowered much without losing power, and theres not enough of that to begin with. The only good pump gas option is a 750 engine.
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- Location
- Loveland, Colorado
Try vumads equation ( I have checked it and I know its correct) it comes out different from what weiscos sight. My way got me to the same spot vumads did. does anyone know why weiscos site is different?
- Location
- Redding CA
that's 657 from a website that builds motors Group-k i don't know what all this complicated math you guys are doing is but i doubt they are wrong
Vumad
Super Hero, with a cape!
- Location
- St. Pete, FL
When I made my post, I only added in the numbers Group K provided. The math does not work out to 657, rather to 651.5. I know the forumal is correct. Considering the stock bore/stroke numbers in the formula yeild 635cc, it's safe to assume the forumula is correct, and group K's website is incorrect. I updated my post to show the correct numbers, unless I made an error, and by me I mean Excel.
Vumad
Super Hero, with a cape!
- Location
- St. Pete, FL
From Excel using the displacement formulas...
650sx
70x76-634.7824
70x77-651.5971
70x78-668.6316
750sx
74x80-743.552
74x81-762.25698
74x82-781.19432
74x83-800.36402
Odd how some of the numbers match and some do not. Obviously the formula is pretty accurate. I wonder how Group K got their numbers. Maybe the issue is I used 3.14 instead of Pie.
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- Location
- New Jersey
The sites are just wrong. It's a very simple formula... Volume of a cylinder. They are either bad at math or use a different formula. I don't know what else you could use to calculate displacement.
