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Location:
Lost in the K hole
Registered:
May 2002
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pressure/volume curve = simple maths ?
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Mon, 28 July 2003 08:40
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ok, question:
2 engines; 7mge and 7mgte...
- they both have the same cam (esentially)
- they both have the same swept vol per cyl (492.3mls)
7mgte: 8.45:1 c/r = 142psi cranking pressure
7mge: 9.20:1 c/r = 156psi cranking pressure
using this data, is there anyway to extrapolate the cranking pressure for 10:1 and 11:1 respectively??
whats the curve look like?
anyone??
cheers
ed
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Location:
Rosanna, Melb
Registered:
June 2002
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Re: pressure/volume curve = simple maths ?
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Mon, 28 July 2003 11:25
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I have no practical experience with this, but it seems that:
Cranking pressure = atmospheric pressure * CR
thus making your problem simple. From the readings you've given, atmospheric pressure is 16.8-16.9psi for both, a bit higher than the 14.7 that's the standard. Maybe it was just a cold cold day.
So 10.0 CR = 168 psi cranking
11.0 CR = 184.8 psi cranking
Hope this makes some sense.
Hen
PS, and I think the curve will just be stretched slightly vertically.
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Location:
Newcastle
Registered:
May 2002
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Re: pressure/volume curve = simple maths ?
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Mon, 28 July 2003 12:06
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Hmm...
That's an interesing problem. There are alot of variables in cranking pressure and it rarely directly relates to a CR. But if those variables were removed (ie same cam, bore x stroke, etc. as you mentioned) you may be able to make a rough estimate. But I think you might need more than two points to extrapolate from since it will more than likely be a curve of some order. I might ask one of my lecturers about it (I doubt they will have any answers though, they have been pretty dissapointing so far!)
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Club Member
Location:
sydney
Registered:
May 2002
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Re: pressure/volume curve = simple maths ?
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Mon, 28 July 2003 22:35
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Ive got no idea 
but contact stuart at oldcorollas (i think thats his addy at toymods as well?) and he will most likely be able to give you an answer
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