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Old 02-27-2016, 02:36 AM   #1 (permalink)
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reduced valve lift and early inlet valve closure

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?

Last edited by ever_green; 02-27-2016 at 10:18 AM..
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