scottmcphee Posted March 27, 2006 Share Posted March 27, 2006 Just want to know if the cam program on the 2.5i engines change mechanically, or under electronic control.. Either way.. are there two distinct programs, or a continuous range of VVT between the endpoints? Thanks! Scott Link to comment Share on other sites More sharing options...
ebpda9 Posted March 27, 2006 Share Posted March 27, 2006 do they even have "v-tec" ? in this day and age i doubt they are all mechanical. Link to comment Share on other sites More sharing options...
scottmcphee Posted March 27, 2006 Author Share Posted March 27, 2006 what I'm digging for here, is if the "i" in the 2.5i means electronically controlled valves then I want to tap the associated (speed?) sensor and find the motor actuator and put a data log on those points and see what the cams are doing under various driving conditions... Scott Link to comment Share on other sites More sharing options...
iyalla Posted March 27, 2006 Share Posted March 27, 2006 On the 2006 2.5i I believe the i-active is mechanical by oil pressure. Link to comment Share on other sites More sharing options...
scottmcphee Posted March 27, 2006 Author Share Posted March 27, 2006 let me correct myself.. it's not VVT, it's variable LIFT.. here's from the Subaru web site: "Outback 2.5i and 2.5i Limited models feature a new naturally aspirated, 2.5-litre SUBARU BOXER engine that features Subaru's i-Active Valve Lift System - which helps to provide better low-end torque, fuel efficiency and performance - for 2006" ..anyway, the questions are the same. Anybody KNOW about the mechanics of this.. when the lift is being modified under engine control and load? Thanks, Scott Link to comment Share on other sites More sharing options...
iyalla Posted March 29, 2006 Share Posted March 29, 2006 Ok let me correct myself... I said it is mechanical by oil pressure. If you don't believe me then here is a quote from Subaru In response to engine speed and load, VVL varies intake valve lift by hydraulically and mechanically locking the tappet into a higher position by means of a transverse pin. The effect is that of having two separate tappets to act on the camshaft lobe operating the intake valve. Subaru VVL uses three lifter profiles for each intake valve lifter. The low-mid profile boosts air induction speed for greater torque. The high-lift mode decreases induction resistance for higher output. Variable lift works on one of the two intake valves. At low engine speeds, the two intake valves open at different levels, causing a swirl of air and fuel. At higher speeds, both valves are opened by the same amount. Basically as engine load gets higher the oil pressure goes up and forces pins to lock-in the second valve profile. Very simple. Subaru has another system on the B9 called AVCS which is electronically controlled. We probably won't see it in the Legacy 2.5i for a few more model years. Its probably on the H6 and maybe the GT. Here is its description. AVCS optimizes the engine's volumetric efficiency throughout the rev band by adjusting intake camshaft timing to employ the ideal intake and exhaust valve overlap under all engine operating conditions. AVCS can rotate the intake camshafts through a range of 35 degrees relative to the crankshaft. The Engine Control Module (ECM) regulates this movement, based on input from various sensors - airflow, engine coolant temperature, throttle position and camshaft position. Actually both systems are on the B9. The reason people didn't respond to your post was probably the answer was already given. Mechanical by oil pressure. Hope this helps! Link to comment Share on other sites More sharing options...
scottmcphee Posted March 31, 2006 Author Share Posted March 31, 2006 Now, this is becoming an interesting thread. Thankyou. At what observable oil pressures does this feature activate? Does the function have any hysteresis once pressure is achieved (lag on, lag off) (http://en.wikipedia.org/wiki/Hysteresis if you must) Since VVT is an oil pressure activated system, oil pressure in the 2.5i is going to be an important maintenance aspect of the engine.. Correct filter, correct viscosity, correct oil.. for it to work as designed. Too thin.. no feature. Too thick or dirty.. fouled feature (VVT stuck on?) Etc.. I learned some lessons coming off a Volkswagen 1.8 turbo engine, even if you kept that thing maintained to specification with oils, filters, and changes.. the engine does not endure real driving conditions and VW has been forced to put a campaign out for "free engines". That's right... $4K a pop if you can show all oil receipts and have bunked main bearing and valve bearings, and I'm sure VW aint happy about it - they discontinued the 1.8T and have replaced it with a 2.0T FSI. I didn't buy it.. that's another story, eesh. Sorry. I bought a 2.5i in a Subaru instead because I'm hoping it lasts longer. I just want to know how it works! Thanks Scott Link to comment Share on other sites More sharing options...
iyalla Posted March 31, 2006 Share Posted March 31, 2006 I am sure it has some hysteresis but I don't knwo how detectable it would be. If the oil pressure is controlled by a soleniod then thats another part that could fail eventually. There really isn't a lot information about the system out there. Try the NASIOC forum. I believe the cut offs are. 2000rpm<2000-4000rpm<4000rpm for the valve lift. Don't know what pressure the oil values are? Sorry. But if you find out let us know. Link to comment Share on other sites More sharing options...
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