Author Topic: Exhaust AVCS Delete & Timing  (Read 1346 times)

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Offline Tezzating

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  • Ride: STI powered '09 FXT
Exhaust AVCS Delete & Timing
« on: March 05, 2016, 07:50:25 AM »
OK so while there's info on the internet, its a bit of a mess.. and I didnt trust it 100% so I double checked everything myself and compiled it into this list.

First you need to deal with the AVCS oiling ports. I opted to tap & set screw, Loctite then seal with Fuji Bond. Others weld or JB Weld, up to you how you want to deal with it.

1. Wrap in a rag and hold it in a vise


2. These are the four ports to tap/fill


3. Use a cutting compound and start tapping


Screwing & setting has no photo's cos I think we can all do that. I believe I used 10/24th set screws. Make sure you clean the ports first, get rid of cutting compound & metal filings.


Second you need to keep the oil in! You need WRX exhaust cam seals. STI seals seal against the AVCS gear, WRX seals seal against the cam shalf.
Part # 806732160



Finally you need to deal with the timing. Per the FSM; D-AVCS exhaust cam sits at 32 degrees at rest, fixed cam sits at 55 degrees.

So here's an LH ex. cam with the AVCS gear & a degree wheel set for 32 degrees. I assure you its lined up for 32 degrees.


Now without touching anything else, swap the AVCS gear for a fixed one, its indicating 38 degrees (ignore the wonky angle of the shot)


Which confirms what I read online.. WRX cam gear adds 6 degrees retard to the AVCS exhaust cam.

Each gear has 48 teeth. 360 degrees / 48 teeth = 7.5 degrees
This confirms what I read online as well.

38 degrees retard measured minus the FSM spec. 55 = 17, so we're 17 degrees out still.
2 Teeth = 15 degrees (7.5 x 2)
17 - 15 = 2; leaving us at 53 degrees retard.

At which point the vernier gears make sense to get us back to the correct timing of 55 degrees. They also make sense as the stock gears are plastic and I have an objection to that.

FWIW if I did it again I'd buy WRX exhaust cams for the W25 STI heads.. the lift & duration is the same post '08 (In 240/9.6mm Ex 240/9.8)