does retarding ignition timing reduce cylinder head temprature
does retarding ignition timing reduce cylinder head temprature
(OP)
Was just wondering if one retards timing from 15* btdc to 4* does this increase cylinder head temps? I know exhaust gas temps go up but I think that's because of part of the combustion escaping the chamber due to lack of burn duration? Not necessarily because the engine is running hotter. I have a feeling that in fact lowering timing will have a cooling effect on the heads but the exhaust valves will take a beating. Any thoughts?





RE: does retarding ignition timing reduce cylinder head temprature
Now if there is detonation occuring with the reference spark timing, retarding timing away from detonation could reduce head temperature, due to the effect of detonation on heat transfer to the chamber surface.
I suppose you could retard the timing to the point of making the cylinder more-or-less a gas generator, with the majority of the heat energy going into the exhaust, but this would be an unrealistic operating point, except in certain racing applications where such a mode may be useful for goosing the turbo very briefly, prior to acceleration. Still, with so much heat in the exhaust port, it's not clear that cylinder head temperature would go down; and as mentioned, this would only make sense as a very transient condition, where there would be little time for bulk temperature change in the head anyway.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: does retarding ignition timing reduce cylinder head temprature
So why do you wish to waste energy? Most internal combustion engines waste enough heat when running in good tune.
And again remember where the exhaust valves are and how they cool, the seats and the seats are in the head and if the exhaust manifolds are either integral or cast iron that will help dump some more heat back to the heads.
RE: does retarding ignition timing reduce cylinder head temprature
Is this your Subaru?
What don't you like about the cylinder head temp? What are the operating conditions?
Is 10 degrees the idle setting?
regards,
Dan T
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
I'd be suspicous of an intake leak or maybe even leaky fuel injectors.
What are the chances the high underhood temps are a result of blazing high Exhaust gas temperatures and no road speed draft?
Of course the poor exhaust valves may be suffering too, although they are bathed in vastly more fire under high loads
RE Subaru's head gaskets -
Their reappearing HG problems ( for the last 42 years ) have long puzzled me.
Subaru siamesed -
http://image.superstreetonline.com/f/30265235+w660...
Some Subaru folks go to a lot of trouble to "close" the "open" deck.
http://www.cgperformance.com/images/cg%20closed%20...
Some folks say the 2.2 with closed deck has no HG problems
http://i.imgur.com/QU6v3.jpg
Plenty of other aluminum engines have "open deck" designs and have to handle 4, 5 or even 6 cylinders worth of end-to-end thermal expansion.
Volvo 850 - separated bores - 200 kmiles easy without head gasket issues
http://www.tracystruesoaps.com/tutorials/850hg/coo...
BMW - siamesed bores
http://www.e90post.com/forums/attachment.php?attac...
RE: does retarding ignition timing reduce cylinder head temprature
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: does retarding ignition timing reduce cylinder head temprature
I guess your talking open vs closed deck? Any problems are likely how the engine is used and maintained. The ones I have dealt with are proof.
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
Underhood temp at idle might not reflect head temp especially in operation and under load.
RE: does retarding ignition timing reduce cylinder head temprature
je suis charlie
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
RE: does retarding ignition timing reduce cylinder head temprature
Yes - as the throttle is opened. Increasing power by optimising timing does not increase the total heat input (fuel flow) into the engine, it is merely converting more of the heat into work and less into waste heat to the cylinder and exhaust gas.
je suis charlie
RE: does retarding ignition timing reduce cylinder head temprature
A prime factor in heat absorption by the engine is the temperature-time product (T x t). The burn is exponentially quickest under the highest temperatures and pressures close to TDC and the expansion ratio is best soon after TDC so the reduction in burn temperature is fastest for a peak close to TDC. Then for the rest of the power stroke temps are lowest and heat absorption is least also with lowest heat into the exhaust.
RE: does retarding ignition timing reduce cylinder head temprature
How are you measuring cylnder head temp again?
Here's a guy nursing a water cooled SAAB engine along the highway.
https://www.youtube.com/watch?v=DKKudxE1wGA
He seems hung up on exhaust gas temperature.
When his EGT climbs as the throttle is eased off I believe it MAYbe caused by less than properly advanced part throttle ignition advance. I wonder if he is one of the guys who eschew vac advance on those 2 stroke SAABs.
Not so many shots of his cylinde head temp gage ( I'm guessing of the spark lug washe type). But sounds like CHT does not move much.
At idle an engine with a mechanically driven cetnrifugal pump has pretty poor coolant flow, which would hinder dissipating even the minimal heat rejected into the cooling system by the minimal heat generated by combustion at idle.