reduced valve lift and early inlet valve closure
reduced valve lift and early inlet valve closure
(OP)
I have been messing around with my Subarus ECU for quite a while now. i have made some improvements in ignition timing and AFR which has made it both responsive and slightly more fuel efficient. For example I advanced part throttle ignition timing by about 3-8*.
recently i learned about its VVL system (valve lift) and i started tinkering with that. this engine does not have VVT or variable valve timing. I learned that from factory the VVL activates once idle conditions are not met. meaning as soon as throttle is opened high lift cams are engaged even at very low engine speeds. I changed the parameters so high lift cams are only switched to above 3000 rpm which is around where i near my highway top speed of 77mph, though i barely go above 70, but i wanted some buffer. Now according to service manual the VVL only controls lift of half of the intake valves, the other half are always in high lift mode to promote swirl. Also the low lift cams have a much much earlier closure intake timing of 10BBDC or -10ABDC. the duration of the intake cams in low lift is also very short. I also realized that operating with low lift cams requires much less ignition timing unless you approach higher RPMs (3200+) compared to high lift cams.
now here is my queston; will a reduced intake valve lift, early inlet valve closure and short duration improve fuel economy at part throttle?
recently i learned about its VVL system (valve lift) and i started tinkering with that. this engine does not have VVT or variable valve timing. I learned that from factory the VVL activates once idle conditions are not met. meaning as soon as throttle is opened high lift cams are engaged even at very low engine speeds. I changed the parameters so high lift cams are only switched to above 3000 rpm which is around where i near my highway top speed of 77mph, though i barely go above 70, but i wanted some buffer. Now according to service manual the VVL only controls lift of half of the intake valves, the other half are always in high lift mode to promote swirl. Also the low lift cams have a much much earlier closure intake timing of 10BBDC or -10ABDC. the duration of the intake cams in low lift is also very short. I also realized that operating with low lift cams requires much less ignition timing unless you approach higher RPMs (3200+) compared to high lift cams.
now here is my queston; will a reduced intake valve lift, early inlet valve closure and short duration improve fuel economy at part throttle?





RE: reduced valve lift and early inlet valve closure
There may be some theoretical gain from moving the charge throttling from the intake manifold to the intake valve, but without knowing the overall OEM engine management strategy, if you dick around with one parameter, you might unknowingly adversely affect something else.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: reduced valve lift and early inlet valve closure
Bigger concern is the fact that you're running "low lift" mode past idle. I am not 100% sure of the mechanism they use to achieve low lift, but it may not be suitable for higher RPMs. You might get away with it, but might not be safe on a mass production basis.
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: reduced valve lift and early inlet valve closure
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: reduced valve lift and early inlet valve closure
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: reduced valve lift and early inlet valve closure
RE: reduced valve lift and early inlet valve closure
RE: reduced valve lift and early inlet valve closure
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: reduced valve lift and early inlet valve closure
That would be an unusual engine. Best economy is almost always somewhere between 17 and 19 (with lots of extra ignition advance).
je suis charlie
RE: reduced valve lift and early inlet valve closure
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: reduced valve lift and early inlet valve closure
RE: reduced valve lift and early inlet valve closure
RE: reduced valve lift and early inlet valve closure
For something less than full load, there probably is a theoretical tradeoff between slightly rich at lower revs (which theoretically can make a little more torque) and stoichiometric at higher revs, but emissions considerations likely dictate that it runs stoichiometric.
RE: reduced valve lift and early inlet valve closure
Since, by dint of having to provide the correct feedstock to the 3-way catalyst at all times excluding AECD operation, gasoline passenger car combustion systems are optimized mainly for stoichiometric operation. Consequently, I wouldn't expect these engines to exhibit a lot of potential for improved efficiency at leaner than stoichiometric air-fuel ratios.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: reduced valve lift and early inlet valve closure
je suis charlie
RE: reduced valve lift and early inlet valve closure
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: reduced valve lift and early inlet valve closure