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Author Topic: Calculating volumetric efficiency  (Read 2846 times)

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Offline paulages

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Calculating volumetric efficiency
« on: July 02, 2013, 08:06:54 PM »
I realize that this figure is dependent on an actual CFM measurement through the head, but I'm wondering if anyone has calculated the volumetric efficiency of a CB? I'm playing with header lengths for an engine build...

Paul
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paul
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1974 CB550 (735cc)
1976 CB550 (590cc) road racer
1973 CB750K3
1972 NORTON Commando Combat
1996 KLX650 R

Offline Doctor_D

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Re: Calculating volumetric efficiency
« Reply #1 on: July 02, 2013, 10:33:26 PM »
I ran the numbers once.  It took a while to do, and lo and behold it wasn't a lot different than I'd been taught.  I think I came up with 104 point something.

The rule of thumb is that for well sorted street performance two-valve motors, 105% is a safe estimate for VE.
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Offline turboguzzi

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Re: Calculating volumetric efficiency
« Reply #2 on: July 03, 2013, 12:58:42 AM »
paul, is it you? wow :)

i found this ages ago, quite good, try to leverage some of the parameters i put in the table

things are going to be quite sensitive to flow coefficient / minimum inlet cross section if i rmemebr right

the fit with the 500/4 dyno results was quite good, the 750/810 kawi has ended up at 90- something rather than the 102 predicted,

but is a nice baseline calc

http://forums.sohc4.net/index.php?topic=81813.msg919313#msg919313

aahhh! scheisse! he went payment....it was free before!

http://www.schmidtmotorworks.com/engine_designer.html
« Last Edit: July 03, 2013, 03:06:45 AM by turboguzzi »
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Offline paulages

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Re: Calculating volumetric efficiency
« Reply #3 on: July 03, 2013, 10:49:36 AM »
Yossef-

Yeah, in the flesh! Finally finding time to work on the RC project that's been collecting parts on the shelf for a while now, and pipes are the big hangup at the moment. I'm building 4 megas, so length is mostly going to be controlled by the space itself, but I am curious about pipe diameter. I plugged the numbers into another online calculator playing with different VEs and they all suggested header I.D. in the neighborhood of 1.02".  :o I think I'll just stick with 1.5" O.D., using the stock flanges, but I can't help but wonder if they're too large?
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paul
SOHC4 member #1050

1974 CB550 (735cc)
1976 CB550 (590cc) road racer
1973 CB750K3
1972 NORTON Commando Combat
1996 KLX650 R

Offline HondaMan

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Re: Calculating volumetric efficiency
« Reply #4 on: July 03, 2013, 11:13:35 AM »
Quote from: paulages on July 03, 2013, 10:49:36 AM
Yossef-

Yeah, in the flesh! Finally finding time to work on the RC project that's been collecting parts on the shelf for a while now, and pipes are the big hangup at the moment. I'm building 4 megas, so length is mostly going to be controlled by the space itself, but I am curious about pipe diameter. I plugged the numbers into another online calculator playing with different VEs and they all suggested header I.D. in the neighborhood of 1.02".  :o I think I'll just stick with 1.5" O.D., using the stock flanges, but I can't help but wonder if they're too large?

Great to see ya back!
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Offline turboguzzi

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Re: Calculating volumetric efficiency
« Reply #5 on: July 03, 2013, 03:09:54 PM »
for what it's worth, rene was running pipes off a CBR600 in his 500/4 racer and it wasnt slow

would measure for you but sold my F2 some weeks ago...

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Offline paulages

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Re: Calculating volumetric efficiency
« Reply #6 on: July 04, 2013, 12:54:41 AM »
Quote from: turboguzzi on July 03, 2013, 03:09:54 PM
for what it's worth, rene was running pipes off a CBR600 in his 500/4 racer and it wasnt slow

would measure for you but sold my F2 some weeks ago...

CBR600 wasn't slow?  ::)  ;D
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paul
SOHC4 member #1050

1974 CB550 (735cc)
1976 CB550 (590cc) road racer
1973 CB750K3
1972 NORTON Commando Combat
1996 KLX650 R

Offline RAFster122s

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Re: Calculating volumetric efficiency
« Reply #7 on: July 04, 2013, 01:57:47 AM »
500/4 racer was faster, much more breathed on...
+1 on seeing you back paulages...
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Offline RAFster122s

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Re: Calculating volumetric efficiency
« Reply #8 on: July 04, 2013, 02:02:20 AM »
Paul, is that 1.5 the ID or OD on the header pipes? The stock pipes being a double wall design the ID being less of course.
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Offline turboguzzi

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Re: Calculating volumetric efficiency
« Reply #9 on: July 04, 2013, 11:31:36 AM »
Quote from: paulages on July 04, 2013, 12:54:41 AM
Quote from: turboguzzi on July 03, 2013, 03:09:54 PM
for what it's worth, rene was running pipes off a CBR600 in his 500/4 racer and it wasnt slow

would measure for you but sold my F2 some weeks ago...

CBR600 wasn't slow?  ::)  ;D

A CBR600F2 is one fine, sweet motorcycle, just bit of a fridge. didnt bond with it, a friend needed a good bike ASAP, so it went... went back to vintage with kz750E :) a bit of a CB750 with just another cam ;)
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Offline paulages

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Re: Calculating volumetric efficiency
« Reply #10 on: July 04, 2013, 12:28:54 PM »
Quote from: RAFster122S on July 04, 2013, 02:02:20 AM
Paul, is that 1.5 the ID or OD on the header pipes? The stock pipes being a double wall design the ID being less of course.

Good call... just looked up my previous measurements (I love combing through my own posts on here for information... ::) ) and the I.D. of the stock 650 pipes are in fact 1".

1.5" O.D. in 16 gauge is going to leave an I.D. of 1.38", still larger than stock/ suggested size.





I didn't go anywhere guys, I've just been too busy to work on bikes much at all. Finally catching up to this RC project, then I can get back to some of my own fun stuff.  ;)
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paul
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1974 CB550 (735cc)
1976 CB550 (590cc) road racer
1973 CB750K3
1972 NORTON Commando Combat
1996 KLX650 R
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