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?
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does retarding ignition timing reduce cylinder head temprature
- Thread starter pickler
- Start date
Lou Scannon
Automotive
It depends a lot on the engine design. Peak combustion temperature will be lower, but this period is very short. Heat rejection to the entire power cylinder including head will be greater due to less extraction of mechanical energy from a given amount of heat release. Exhaust gas temperature will be higher also and assuming exhaust ports in the cylinder head, this will drive more heat into the head. I would say it would take an exceptional engine design to run cooler cylinder head temperature with retarded spark timing, everything else being equal. Yes, exhaust valves will "take a beating", at any rate.
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
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
X2 with hemi.
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.
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.
- Thread starter
- #5
This is for idle operation. I retarded timing by 10* to 5* BTDC and raised the idle RPM to 800 in order to get better stabability. Stock high timing and low rpm settings sometimes caused stalling and an instable idle. The only thing I notice now is quick rise of underhood tempratures when idling with this setting. Due to the boxer design of this engine the headgaskets fail much earlier than most other cars. The aluminum head also likes to warp. Just wanted to keep the head temperatures in control. I actually think the head temps on this car are hotter when idling say in traffic than with higher RPM operation/highway/canyon driving. I have also slightly enriched the mixture compared to stock as I read richer mixture keeps the heads cooler. I'm soon bolting on a turbo charger with mild boost and I'm doing whatever necessary to keep temperatures in control.
- Thread starter
- #7
in a boxer engine critical engine fluids such as coolant and oil will always be in touch with the gaskets as opposed to an inline or V engine where the fluids touch only the side. changes in acidity of coolant and engine oil can corrode the gaskets easily. Subaru introduced a coolant 'conditioner' which doesn't seem to be working. They also used a single layer gasket design that is not as durable as the MLS ones.
"Stock high timing and low rpm settings sometimes caused stalling and an instable idle. "
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 -
Some Subaru folks go to a lot of trouble to "close" the "open" deck.
Some folks say the 2.2 with closed deck has no HG problems
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
BMW - siamesed bores
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 -
Some Subaru folks go to a lot of trouble to "close" the "open" deck.
Some folks say the 2.2 with closed deck has no HG problems
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
BMW - siamesed bores
Panther140
Civil/Environmental
You want as much of the energy to be used to push the piston down as possible. Any energy not used for that will be absorbed by the engine's metal in the form of heat, or be sent out of the exhaust via hot gas.
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
- Thread starter
- #11
I settled on 700 RPM, 10* BTDC timing and 14.4 AFR. That is 50 RPM increase, 5* of retard and .2 ratios of enrichment for idle compared to stock. Engine is dead silent now even with catted straight pipe exhaust. However my underhood temps still climb rather quickly at idle despite larger radiator and fans too. I'm just interested in keeping the head tempratures as low as possible. I know fueling enrichment helps greatly in reducing temps and so I have enriched my mixture quite a bit specially at low-mid range RPMs where my engine spends a lot of TIME under load. However I was not sure about ignition timing. So far I have been running rich (compared to stock) for couple years now and my head gaskets are lasting well compared to other friend's subarus. Just wasnt sure if I should advance or retard to keep the heads cooler.
The heat transfer rate through the cylinder head deck is mostly a function of engine output. Thus you should not experience overheating or detonation at the minimal load condition of idle. If you are experiencing excessive underhood temps at idle, it's more likely a problem with the airflow produced by the fan/ducting.
- Thread starter
- #15
Im getting xontradicting answers here. One person says mbt (when engine produces best torque and hence power) reduces temps but one person says heat is in sync with power. So should i detune timing for more colling (by reducing power) ot should i increase timing to cool?
- Thread starter
- #17
"Heat is in sync with power."
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
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
140Airpower
Automotive
Optimal timing for peak pressure around 15* ATC should produce the least heat absorption into the engine structure and the least heat into the exhaust and lowest underhood temps for the fuel consumed AND it should require the least idle air and lowest fuel consumption at idle. If there is surging or other instability due to some problems, then decreasing the advance can smooth things out, but it should increase fuel use and raise temperatures.
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.
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.
Hi Pickler,
How are you measuring cylnder head temp again?
Here's a guy nursing a water cooled SAAB engine along the highway.
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.
How are you measuring cylnder head temp again?
Here's a guy nursing a water cooled SAAB engine along the highway.
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.
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