****Warning for 2006-2009 owners (DBW cars)****
01-06-2017, 09:14 PM
#271
"AFR has a much more significant effect on EGT than exhaust cam timing."
Lol...I'm done....
Lol...I'm done....
01-06-2017, 10:15 PM
#272
Join Date: Aug 2012
Location: Foothills East of Sacramento
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Thanks Billman.
01-07-2017, 04:10 AM
#273
OK, now I'm more confused. 
Not about adjusting the valves which I did a month or so after buying my '06 in the summer of 2014 and seeing this alarming thread title.
Unless it's different in the piston aircraft I've flown (vs cars) high exhaust gas temperature (EGT) is the result of excess fuel going out the exhaust rather than being converted to power. Too rich a mixture. Lean fuel mixtures, which produce lower EGTs, are a source of burned valves hence the ECU control of the air-fuel mixture something we had to control manually in piston aircraft engines (and may still today, my license is dormant).
-- Chuck
Not about adjusting the valves which I did a month or so after buying my '06 in the summer of 2014 and seeing this alarming thread title.Unless it's different in the piston aircraft I've flown (vs cars) high exhaust gas temperature (EGT) is the result of excess fuel going out the exhaust rather than being converted to power. Too rich a mixture. Lean fuel mixtures, which produce lower EGTs, are a source of burned valves hence the ECU control of the air-fuel mixture something we had to control manually in piston aircraft engines (and may still today, my license is dormant).
-- Chuck
01-08-2017, 10:12 AM
#274
Join Date: Aug 2012
Location: Foothills East of Sacramento
Posts: 5,623
Received 1,568 Likes
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932 Posts
Unless it's different in the piston aircraft I've flown (vs cars) high exhaust gas temperature (EGT) is the result of excess fuel going out the exhaust rather than being converted to power. Too rich a mixture. Lean fuel mixtures, which produce lower EGTs, are a source of burned valves hence the ECU control of the air-fuel mixture something we had to control manually in piston aircraft engines (and may still today, my license is dormant).
-- Chuck
-- Chuck
FADECS are another story!
01-08-2017, 11:08 AM
#275
Registered User
Anything richer (more fuel than air) than stoich (14.7:1 gasoline AFR or Lambda of 1.00 for ANY fuel) is technically excess fuel to convert all available hydrocarbons into a usable chemical reaction. Though there is some need to enrich beyond the theoretical 'perfect' value since atomization and molecular interactions aren't perfectly homogeneous in an always highly transient state inside your engine. Depending on how bad/good the cylinder head design is, it generally requires an additional point of AFR (richer) to guarantee that all available oxygen molecules coming in through the throttle body have had a chance to interact with the available hydrocarbons during combustion.
Excess fuel is also used to cool down the exhaust charge and prevent hot spots inside the combustion chamber (to prevent detonation), etc. Too much fuel though and you start increasing the pumping losses due to the engine having to move excess fuel mass. Therefore there is generally a range of AFR that lies somewhere between 12.5 to 13.5 AFR for most NA engines where the pluses/minuses generally have an insignificant effect on measured cylinder power. For a turbo engine (effectively nothing more than significantly increased dynamic compression ratio relative to atmospheric induction), the combination of variables tends to drift this desired AFR range a bit richer.
It's all a balancing act and if you do get an engine to work at leaner and leaner AFRs you also need to make sure the heat generated has a chance to be evacuated. The goal is always to make everything as compact as possible and the smaller the valve/port, the more chance it will see localized overheating with respect to the current metallurgy being used. So excess fuel is used to absorb the extra heat during combustion to keep the valves (imagine sticking your hand out the window into a frigid winter wind at 60mph versus doing so at 0mph) from experiencing increased localized temperature differential relative to ambient. Contact with the valve seat engages conductive heat transfer which is a lot more efficient than any other form such as convective or radiative. So you can either put gloves on your hands (better mettalurgy) or retract your hands back into the car more often and for longer (more time spent at 0 lift).
Anyway, all of what I said is just touching the tip of the iceberg and there are a few more factors that theoretically affect things. I don't really think it is worth my time to go any deeper considering the vocal audience we have here such as this guy who sent me the following PM. I guess I must not be the first person to call him out on his BS.
Anyway, there is a huge problem with arguing strictly in terms of theory without magnitude. For example, one can say that XYZ effects cause a certain coefficient to either go positive or negative while someone else can say that ABC effects do the opposite. But without knowing the strength of each individual variable (A vs X or B vs Y, etc.) it just becomes a pointless exercise where he who yells the loudest generally wins on the internet.
Anyway, I saw a change in AFR of almost half a point leaner after removing the catconv in my exhaust. This is a specific problem that Speed Density based ECUs like the S2000 have. I've heard the AP1 ECUs run fairly rich to the point of even being able to run an additional 10% displacement without any detrimental effects. The DBW AP2 runs the leanest of all 3 types and is most likely to push the AFR just beyond the range needed to maintain adequate EGT relative to the mettalurgy currently in use.
Excess fuel is also used to cool down the exhaust charge and prevent hot spots inside the combustion chamber (to prevent detonation), etc. Too much fuel though and you start increasing the pumping losses due to the engine having to move excess fuel mass. Therefore there is generally a range of AFR that lies somewhere between 12.5 to 13.5 AFR for most NA engines where the pluses/minuses generally have an insignificant effect on measured cylinder power. For a turbo engine (effectively nothing more than significantly increased dynamic compression ratio relative to atmospheric induction), the combination of variables tends to drift this desired AFR range a bit richer.
It's all a balancing act and if you do get an engine to work at leaner and leaner AFRs you also need to make sure the heat generated has a chance to be evacuated. The goal is always to make everything as compact as possible and the smaller the valve/port, the more chance it will see localized overheating with respect to the current metallurgy being used. So excess fuel is used to absorb the extra heat during combustion to keep the valves (imagine sticking your hand out the window into a frigid winter wind at 60mph versus doing so at 0mph) from experiencing increased localized temperature differential relative to ambient. Contact with the valve seat engages conductive heat transfer which is a lot more efficient than any other form such as convective or radiative. So you can either put gloves on your hands (better mettalurgy) or retract your hands back into the car more often and for longer (more time spent at 0 lift).
Anyway, all of what I said is just touching the tip of the iceberg and there are a few more factors that theoretically affect things. I don't really think it is worth my time to go any deeper considering the vocal audience we have here such as this guy who sent me the following PM. I guess I must not be the first person to call him out on his BS.
Originally Posted by Slowcrash_101
Oh please reconsider, my life will lose all meaning if I lose my credibility to some random jerk off on the internet. How will I ever pay my bills now, I'm certainly headed to social and financial ruin now. Please! It means so much to me to be accepted by a toxic community of egotistical douchebags.
Anyway, I saw a change in AFR of almost half a point leaner after removing the catconv in my exhaust. This is a specific problem that Speed Density based ECUs like the S2000 have. I've heard the AP1 ECUs run fairly rich to the point of even being able to run an additional 10% displacement without any detrimental effects. The DBW AP2 runs the leanest of all 3 types and is most likely to push the AFR just beyond the range needed to maintain adequate EGT relative to the mettalurgy currently in use.
01-22-2017, 06:55 AM
#276
Did you ever consider the speed of combustion and the effect it has on heat loss(to the cylinder walls, and coolant etc), and by consequence it's effect on the metal bits in the engine? Faster combustion much like moving your hand quickly over a candle reduces heat loss to the cylinder walls and combustion chamber, despite high EGT's, if the flame front doesn't spend much time near the cylinder walls, valve seats, guides etc, there's no problem. Fast combustion means less heat gets radiated to the surroundings, less wall quenching, more BMEP to drive the piston.
Idle is hard on the valve seats, and the cylinder walls because combustion during idle is slow, it's slow because there is little air flow, it's slow because of EGR dilution(no EGR valve it's purely a function of cam timing and port design). Thus like moving your hand slowly over a candle it burns the metal bits because the combustion flame propagation is slow and has more time for heat to be transferred to the metal bits.
Altering cam timing alters the speed of combustion, combine with the returnless fuel system, tighter emissions controls, 06+ engines are a perfect storm for valve wear.
Idle is hard on the valve seats, and the cylinder walls because combustion during idle is slow, it's slow because there is little air flow, it's slow because of EGR dilution(no EGR valve it's purely a function of cam timing and port design). Thus like moving your hand slowly over a candle it burns the metal bits because the combustion flame propagation is slow and has more time for heat to be transferred to the metal bits.
Altering cam timing alters the speed of combustion, combine with the returnless fuel system, tighter emissions controls, 06+ engines are a perfect storm for valve wear.
01-22-2017, 07:59 AM
#277
I did this valve adjust 3 years ago when I was at 42K on my 2009. The exhaust were indeed tight; Billman said I would have had torched valves when I hit 65K miles. I am at 61K now and with all the inclement weather we are having in California, I think I might take another look at see how it is going.
Thanks Billman.
Thanks Billman.
Thanks!
01-22-2017, 10:03 PM
#278
Registered User
Did you ever consider the speed of combustion and the effect it has on heat loss(to the cylinder walls, and coolant etc), and by consequence it's effect on the metal bits in the engine? Faster combustion much like moving your hand quickly over a candle reduces heat loss to the cylinder walls and combustion chamber, despite high EGT's, if the flame front doesn't spend much time near the cylinder walls, valve seats, guides etc, there's no problem. Fast combustion means less heat gets radiated to the surroundings, less wall quenching, more BMEP to drive the piston.
Idle is hard on the valve seats, and the cylinder walls because combustion during idle is slow, it's slow because there is little air flow, it's slow because of EGR dilution(no EGR valve it's purely a function of cam timing and port design). Thus like moving your hand slowly over a candle it burns the metal bits because the combustion flame propagation is slow and has more time for heat to be transferred to the metal bits.
Altering cam timing alters the speed of combustion, combine with the returnless fuel system, tighter emissions controls, 06+ engines are a perfect storm for valve wear.
Idle is hard on the valve seats, and the cylinder walls because combustion during idle is slow, it's slow because there is little air flow, it's slow because of EGR dilution(no EGR valve it's purely a function of cam timing and port design). Thus like moving your hand slowly over a candle it burns the metal bits because the combustion flame propagation is slow and has more time for heat to be transferred to the metal bits.
Altering cam timing alters the speed of combustion, combine with the returnless fuel system, tighter emissions controls, 06+ engines are a perfect storm for valve wear.
02-10-2017, 01:07 PM
#279
"Engine coolant temperature rises MUCH quicker when idling at 2000RPM than at 1000RPM even with no additional load on the engine."
Think about this for a second. When the engine is cold the clearance between parts is greater, the oil is thicker and doesn't flow as well. In this scenario increasing engine speed increases friction and with it heat. Or is combustion temperature the only source of heat in a 32% thermally efficient engine that wastes most of the heat it generates?
Think about this for a second. When the engine is cold the clearance between parts is greater, the oil is thicker and doesn't flow as well. In this scenario increasing engine speed increases friction and with it heat. Or is combustion temperature the only source of heat in a 32% thermally efficient engine that wastes most of the heat it generates?
02-16-2017, 07:40 PM
#280
Registered User
"Engine coolant temperature rises MUCH quicker when idling at 2000RPM than at 1000RPM even with no additional load on the engine."
Think about this for a second. When the engine is cold the clearance between parts is greater, the oil is thicker and doesn't flow as well. In this scenario increasing engine speed increases friction and with it heat. Or is combustion temperature the only source of heat in a 32% thermally efficient engine that wastes most of the heat it generates?
Think about this for a second. When the engine is cold the clearance between parts is greater, the oil is thicker and doesn't flow as well. In this scenario increasing engine speed increases friction and with it heat. Or is combustion temperature the only source of heat in a 32% thermally efficient engine that wastes most of the heat it generates?