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Old 08-17-2020, 09:18 PM   #3
Scooby Guru
Member#: 140444
Join Date: Feb 2007
Chapter/Region: NWIC
Location: Near Seattle, WA
05 Stage Free LGT


The 08 STI exhaust cam pulleys have springs on them which pull the cams into max advance, which is also max piston-to-valve clearance and zero overlap (best idle). With no power to the AVCS solenoid, the cam angle stays put.

The intake cam pulleys are sprung to go full retard, which also gives best clearance, no overlap, and best idle. In other words, all four cams are mechanically configured to move to the position that gives full safety and best low-RPM performance. Probably because after a cold start, the ECU leaves the solenoids unpowered for a couple/few minutes. In other words, the system was designed to be safe with no power to the solenoids.

I don't know about the 20X, but I'd be very surprised if they were different in this regard. AVCS needs oil pressure to work properly and there isn't any right after startup.

I ran the 08 STI heads in my 05 LGT disconnected for months while I worked on an exhaust cam controller, and there was no harm.

Someone else had a similar setup dyno'd that way, and found it to be down 40whp if I remember right. If I remember right, you'd want to adjust the cams by two teeth in the timing belt to get them back to single-AVCS cam timing. Or at least that was the case for the 272 cams that I used - that was my 'plan B' in case the AVCS controller turned out to be too hard.

For your stock cams you should get the specs to see how much they need to be adjusted.
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