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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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Old 02-27-2016, 07:04 AM   #2 (permalink)
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IF I remember correctly.

Low lift long duration is good for fuel economy/low end power. (more torque down low)

High lift long duration loses low end torque, but better power up top.

It's much more complicated than that, but that's a basic thing I was told long ago.
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Old 02-27-2016, 12:10 PM   #3 (permalink)
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The intake valve close has the greatest effect of any valve event. Opening and closing earlier will increase low end torque and help fuel economy
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Old 02-27-2016, 01:12 PM   #4 (permalink)
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Fyi, late intake valve closing is a popular strategy to reduce effective displacement for highway driving.

I'll seach the web, but how exactly is subaru controlling lift? Is it continuously variable or are there specific settings?
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Old 02-27-2016, 01:48 PM   #5 (permalink)
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Quote:
Originally Posted by ksa8907 View Post
Fyi, late intake valve closing is a popular strategy to reduce effective displacement for highway driving.

I'll seach the web, but how exactly is subaru controlling lift? Is it continuously variable or are there specific settings?
link for: Subaru: i-Active Valve Lift System (AVLS)

The camshafts on an AVLS-equipped engine have specially designed lobes for intake valves. They feature two different cam profiles:
1. A low/mid-lift profile
2. A high-lift profile
Which cam profile is utilized is regulated by the Engine Control Module (ECM) computer. The AVLS-equipped Subaru engines use oil pressure generated by the engine to activate the different valve lift settings.

The intake valve timings from service manual are as follows:
Low speed Open BTDC 0 Close ABDC –10
High speed Open BTDC 14 Close ABDC 62

from a calculator:
Your low cam has an Overlap of 14.00 degrees and has in Intake Duration of 170.00 degrees. The Exhaust Duration is 224.00 degrees. Your Lobe Separation Angle is 91.50 degrees.

Your high cam has an Overlap of 28.00 degrees and has in Intake Duration of 256.00 degrees. The Exhaust Duration is 224.00 degrees. Your Lobe Separation Angle is 106.00 degrees.

Last edited by ever_green; 02-27-2016 at 02:01 PM..
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Old 02-28-2016, 12:44 AM   #6 (permalink)
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256 on the intake is still kind of light.

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