Author Topic: crankcase vol. (no drilling involved)  (Read 465 times)

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Offline EHP

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Re: crankcase vol. (no drilling involved)
« Reply #20 on: July 28, 2015, 10:22:59 pm »
alot of it is BS mainly because its impossible to reach the amount that is claimed it can do , its all just theory but its a dam good place to start figuring . Biggest thing is the parts cannot stand that pressure if you can get enough fuel to it , bike engines are far better built to start with than a chainsaw so the crank can stand alot more pressure . One thing that had my mind working was at 1.20 to 1 ratio on the computer dyno in the TSR program it showed almost double the hp compared to 1.47 to 1 but was going to burn pretty much 2 -1/4 fuel lines of alcohol/ nitro to keep it running so way more fuel than what a single carb could produce

Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #21 on: July 29, 2015, 05:51:39 am »
i'm with you ehp.  the bike thread was based on reed block motors.  pipe has huge effect.

my program does not account for crankcase volumes as of yet, but it will in the future.  when i worked the numbers with the calculator, for a piston ported/box muff motors.....only saw about a 5% increase in fuel charge entering the crankcase when just the volume was changed, depending on rpm.   

have not estimated a pipe motor with numbers.  not really an interest of mine. 
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Offline EvilRoySlade

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Re: crankcase vol. (no drilling involved)
« Reply #23 on: January 08, 2016, 04:07:32 pm »
Please help me understand the putty. Is it the volume underneath the piston?  I believe you could get accurate volume at bdc without the putty but then there is no way to measure the underside of the piston at tdc correct?  Unless you did this with cylinder on which is the no drilling thing, drill the piston to let air out I assume?  I have so many questions.

Offline Chris-PA

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Re: crankcase vol. (no drilling involved)
« Reply #24 on: January 08, 2016, 07:16:12 pm »
Interesting thread that I had not seen and need to read more carefully.  I'm still confused as to the definition of crankcase volume and exactly what volume this includes.  Does it include the volume under the piston?  Everything under the piston at BDC?  Is transfer volume included?

Then there is the question of what volume is this being compared to - it makes sense to me to compare it to displacement, but ratios will of course be different if a different denominator is used. 

Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #25 on: February 06, 2016, 08:09:37 am »
Please help me understand the putty. Is it the volume underneath the piston?  I believe you could get accurate volume at bdc without the putty but then there is no way to measure the underside of the piston at tdc correct?  Unless you did this with cylinder on which is the no drilling thing, drill the piston to let air out I assume?  I have so many questions.

yes, the only reason for the putty is to help find the volume on the underside of the piston itself, when it is at BDC.

yes.

the last one, yes, kind of the idea....but it is not really just to let the air out.   maybe the following will help to picture it using the "drill the hole in the piston crown method."

to get BDC case volume:  with cylinder removed, piston at BDC.  seal the piston skirt to the case deck with heavy grease.  fill the case and underside of piston with a measured amount of oil via the drilled hole. done.

one could measure the oil being put in there with a syringe and a length of tubing.......(buret or graduated cylinder would work too).

the reason for the putty, is just to do all this without trashing a piston.  not really a big deal, but it you are using 'one off' custom stuff, this can get expensive in a hurry.

the volume of under the piston is an additional portion of the case volume.  like in the first photo shown in this thread, the entire piston does not disappear below the case deck at BDC, so the volume of the piston that is above the case deck has to be measured some way is all.

hope it helps.

i will clean up the thread a bit.

reducing the case volume, can gain some rpms.  hope to show just how many as well.


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Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #26 on: February 06, 2016, 09:52:32 am »
Interesting thread that I had not seen and need to read more carefully.  I'm still confused as to the definition of crankcase volume and exactly what volume this includes.  Does it include the volume under the piston?  Everything under the piston at BDC?  Is transfer volume included?

Then there is the question of what volume is this being compared to - it makes sense to me to compare it to displacement, but ratios will of course be different if a different denominator is used.

just volume at TDC divided by volume at BDC.  some don't include the transfer port volumes, some do.

the volume under the piston is included at BDC.  the volume under the piston is included at TDC as well.

without transfer ports volume included:
case volume @ TDC = 200 cc
case volume @ BDC = 100 cc

so, the case volume ratio = 200/100 = 2.00

--------------

with transfer ports volume included:

say, motor has only 2 trans ports, each trans port measured out at 5cc each. so, 10cc total trans volume.

case volume @ TDC = 200 cc + 10 cc = 210 cc
case volume @ BDC = 100 cc + 10 cc = 110 cc

then, case volume ratio becomes = 210/110 = 1.91

------------

the difference in ratios is 0.09

rounding it off = 0.10

up to you, to decide whether to include them or not.


.....the folks who got the ball rolling on this case volume thing as referenced by the article linked in the thread, calculated the ratio differently.


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Offline EvilRoySlade

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Re: crankcase vol. (no drilling involved)
« Reply #27 on: February 11, 2016, 03:04:13 pm »
Thanks for the reply. Life threw me a wild pitch that hit me, so my saw play time has dropped huge amounts. When I get back on my feet I'm going to check a few for fun.


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Offline 1manband

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Re: crankcase vol. (no drilling involved)
« Reply #28 on: February 13, 2016, 05:23:04 am »
Thanks for the reply. Life threw me a wild pitch that hit me, so my saw play time has dropped huge amounts. When I get back on my feet I'm going to check a few for fun.


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..sometimes life = dodge-ball game, with multiple hits to the cranium and testes.  eventually the swelling goes down.

vegetable oil leaves a sticky film that needs to be cleaned using a brush.  think that something like transmission fluid would be better thing to use instead.  easier to flush out, and better for the seals.

will you be drilling?
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Offline Chris-PA

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Re: crankcase vol. (no drilling involved)
« Reply #29 on: February 13, 2016, 12:58:06 pm »
This is a topic that interests me - I've been reading that people believe that the case volume can be too small and that this will hurt performance, but I do not see the logic in that.  The swept volume of the case will always be the same on both sides of the piston, so there must always be "enough" volume.  The only thing I can think of is that a full circle crank might block flow to the transfer entrances, but otherwise I can't see the problem with reducing case volume.  It seems like less should always be better.

When drawing mix into the case you can have at best one atmosphere of pressure to push it in, and any extra volume just reduces that pressure differential and makes for less efficient pumping.  When pushing mix up the transfers you can generate much more pressure, but initially must push against the residual combustion pressure in the cylinder. 

 

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