Author Topic: crankcase vol. (no drilling involved)  (Read 464 times)

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Offline 1manband

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crankcase vol. (no drilling involved)
« on: June 04, 2015, 09:44:27 pm »
jonsereds 52

first 1/2 of photos.....crankcase volume at BDC.

2nd 1/2 of photos........crankcase volume at TDC.
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Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #1 on: June 04, 2015, 09:48:25 pm »
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Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #2 on: June 04, 2015, 09:51:36 pm »
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Offline aclarke

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Re: crankcase vol. (no drilling involved)
« Reply #3 on: June 04, 2015, 10:57:04 pm »
Super cool.  Thanks for sharing!

Offline aclarke

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Re: crankcase vol. (no drilling involved)
« Reply #4 on: June 04, 2015, 11:12:35 pm »
1.4 to 1.50 would be a common ratio on cr125 or other modern dirt bikes. The tz250 GP bike is around 1.4 as well. Interesting




Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #5 on: June 05, 2015, 05:32:22 am »
...looking at it again this morning.......made couple of errors..  at BDC, there is 5cc more volume of goop.  another error i found was forgetting to subtract out about an inch and a half of connecting rod volume....possibly a few cc's.

will correct this.  don't see the end result changing much at all, even if i fix these errors.

....thought it would be a lower ratio, too.
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Offline aclarke

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Re: crankcase vol. (no drilling involved)
« Reply #6 on: June 05, 2015, 09:49:08 am »
So the 1.85 ratio represents a smaller case volume vs the bike motors? (1.4 ratio)   

I'm assuming the  bigger ratio  would equate to higher crankcase pressure and result in moving more fuel/air per time unit than the larger case bike motors. 

I'm wondering how this plays into the bike T/A graphs and if they are co pletely skewed towards the bike motors with their different crankcase volume/ratio?

 End result COULD be equal if you have a small motor moving air faster for less duration vs. The large motor moving air a bit slower for LONGER duration but I'm not sure the Blair Jennings data works this way or there are losses from moving the fuel air at higher pressures. (Perhaps more short circuiting)

Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #7 on: June 05, 2015, 10:06:31 pm »
...and this would help to explain the 'time' element being off.

want to look at few other things that go along with this as well.
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Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #8 on: June 06, 2015, 06:12:42 am »
the two corrections up-thread:

Total BDC volume = 94 - 40 + 18 +21 = 93 cc

Total TDC volume = 21 + 48.4 + 94 - conn rod vol 1.2cc = 164.6 cc

ratio: 164.6/93 = 1.76

1.76:1
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Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #9 on: June 06, 2015, 08:18:31 am »
one of the things which i was looking for by doing this, was how much air/fuel mix volume was moving in per single rpm.

estimate (based on crankcase volume, ratio, and motor displacement):  approximately 14.6 cc total per rpm.

not much.  hahaha.

previously.....cc'd the transfers they were approx. 4cc each.

........not really within the scope of this discussion but interesting to me at least.

edit: adding reference.  blair page 392.  top of page.


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