Author Topic: crankcase vol. (no drilling involved)  (Read 2135 times)

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Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #50 on: March 07, 2016, 07:53:30 am »
Oh - I'm not sure Crankcase Compression Ratio is the same as the Vc/Vs ratio they used.  It's still not clear what all is included anyway.  If it is supposed to be the same, then it's probably because their setup could only add volume. 

EDIT:  I think CCR is the ratio of the swept volume plus the case volume to the case volume, or:  CCR = (VC +VS)/VC

That is different from VC/VS

If you calculate it out, VC/VS = 2.44 works out to a CCR of 1.41, which is what Engine A is listed as.

So for the red line of Figure 5, the VC/VS = 2.44 is getting pretty close to the practical limit of what you could achieve, and it still is at almost full delivery ratio by 2,500rpm.  That scales to about 7,000rpm for an engine with a 10,000rpm power peak, so practically it would be very hard to reduce the case volume down so far that you push the peak delivery ratio up above your power band.

I'd still like to know if the transfer volume is included - it should be.

imo, think that the difference in the numbers is not that big a deal.  does sound silly i know.  for the following reason......

both results are interchangeable when using them just to scale a graph.  thinking that you will not buy into this.  hahahaha.

ok, put another way,  the end purpose of figuring any of this out is not to see just how much beer you can drink while juggling numbers in a calculator.
for any of this to be useful for anyone, the end goal is to find the estimated case volume needed for a certain rpm.
both CCR methods, while different, give the same result when a rpm point is equated to it.  the shape of the graph does not change.
so, the CCR is just along for the ride.  think you will find that the author's use this interchangeably, if you stick to the way they set the graph up in the relationship using sqrtVc/rpm, that i quoted.

trans volume....up to you.  if 0.1 or so CCR makes a difference?  wouldn't think it would change anything as far as the graphing is concerned.  10cc looks to only have an impact when you are way way up in the rpm range, possibly well beyond physical limitations anyway.
 
as you have already found, achieving the proper case volume runs into physical limitations very quickly, and it's doubtful that they can be met.

i deserve a good kick in my backside.  ignore my ramblings above.  did not see this before i plugged in numbers from motor A.  using a chainsaw motor the difference was slight, with motor A is is quite large.

will post up some motor A stuff today.
hiatus

 

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