Thinking about it
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| posted on 13/8/11 at 10:35 PM |
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Is combustion pressure constant
Does combustion pressure vary with RPM or when under load or does it remain constant during operation?
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coozer
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| posted on 13/8/11 at 10:39 PM |
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Hard to tell, why do you ask?
Static compression is the indicator of a good engine??
1972 V8 Jago
1980 Z750
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coyoteboy
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| posted on 13/8/11 at 10:39 PM |
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in-cyl peak pressures will vary across the rev range and across the load range. Largely due to throttle opening (i.e. cylinder fill quantity and hence
charge quantity) and ignition point. If combustion pressure didn't change you'd have a flat torque curve from idle to redline.
[Edited on 13/8/11 by coyoteboy]
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Thinking about it
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| posted on 13/8/11 at 10:45 PM |
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quote:
Originally posted by coyoteboy
in-cyl peak pressures will vary across the rev range and across the load range. Largely due to throttle opening (i.e. cylinder fill quantity and hence
charge quantity) and ignition point. If combustion pressure didn't change you'd have a flat torque curve from idle to redline.
[Edited on 13/8/11 by coyoteboy]
I keep getting air in the coolant system on a K series engine. No problem at low revs but after a run at high revs there is air build up. Suspecting
head gasket. My theory that if its a small leak of combustion gas into the coolant it may not be happening at low load /speed but if pressure
increases maybe its the case.
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Thinking about it
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| posted on 13/8/11 at 10:46 PM |
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quote:
Originally posted by coozer
Hard to tell, why do you ask?
Static compression is the indicator of a good engine??
I keep getting air in the coolant system on a K series engine. No problem at low revs but after a run at high revs there is air build up. Suspecting
head gasket. My theory that if its a small leak of combustion gas into the coolant it may not be happening at low load /speed but if pressure
increases maybe its the case.
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zilspeed
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| posted on 13/8/11 at 11:09 PM |
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People like LJK Setright, who understood these things, used to always quote engine power in BMEP.
Brake Mean Effective Pressure.
Basically, the force exerted on the pistons by the combustion process.
Cylinder filling is the key really, and it's only really at its peak when the throttles are wide open.
Less air in the cylinder at closed or part throttle definitely affects pressure.
So does engine condition and cam profile after all, because it's all about getting as much air as possible in there and compressing it.
If it was constant, we wouldn't be able to control the engine the way we do and throttle it.
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wylliezx9r
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| posted on 13/8/11 at 11:35 PM |
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Sounds like a definate head gasket to me.
I spent a lot of money on booze, birds and fast cars. The rest I just squandered.
George Best
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mangogrooveworkshop
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| posted on 14/8/11 at 07:06 AM |
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Test the coolant for combustion gasses
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britishtrident
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| posted on 14/8/11 at 07:09 AM |
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If the engine is throwing water out when the rpm is raised above about 1200 then on the first thing is to very carefully check the cooling system
raddiator, the top hose and any plastic T pieces for cracks. This is quite a common problem on Rovers and is often misdiagnosed as a head gasket
because there is no obvious sign leakage and the leak only occurs when the rpm is raised and water pump generates a head of pressure against the
resistance of the system.
In fwd MG-Rover often this gives the symptoms of a puff of sweet smelling smoke as car is driven away from the traffic lights as the leak sprays
antifreeze on to the exhaust.
It would help to know what particular model the engine is fitted.
If it is a head gasket the symptoms don't fit the normal mode of failure on K engines where normally the first sign is very slow loss of
coolant followed by oil in the header tank. In any event a head gasket change on a k series is not that major a job at least in the FWD cars.
[Edited on 14/8/11 by britishtrident]
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jollygreengiant
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| posted on 14/8/11 at 08:21 AM |
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Answer to your question, YES, it (cylinder pressure) varies with engine speed and cylinder charge.
Secondly, this is the second time that you have asked this (or similar) question in a month.
last posting
So you asked a similar question before, you had your question answered, have you had a cylinder leak test completed, I doubt it very much, have you
taken the vehicle to a garage and asked them to check for hydro-carbons in the header tank, I doubt it. The likely-hood is that, come what may you
will now have a head gasket failure, rather than a simple air leak, as postulated in this latest posting. Yes that was a remote posibility, but, as I
said in my last post on this subject, these engine are notoriously delicate with regard to cooling operation. It is also very posible that the head
gasket could only fail to the coolant and not to the oil as well. My experience with them is that the longer this is left un-rectified the more likely
it is that you will end up changing the engine due to the disturbance of a cylinder liner. GET IT CHECKED.
[Edited on 14/8/11 by jollygreengiant]
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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