RomRaider

anybody have any tips for AVCS tuning? I know cobb made some big gains on the LGT platform by tweaking the AVCS settings.
has anybody really gotten into this?

I have on the WRX and STi but not the LGT yet.

It is something that really needs to be done on a dyno.

I'd be interested in whatever info you have on the STI particularly.

Thanks

Basically go full advance on load as early as you can and then gradually pull them out once you have max boost...

That's the idea..

Things to look out for...

Some cars don't like too much cam advance on cruise, light load, the car will feel like it has a miss....

Don't advance too far on late model cars, Subaru stuffed up on some of the late model cars and you can advance the cams past the point they are supposed to be able to go to.... you'll know when/if you do it, the top end of the engine will get very LOUD.....

Smaller turbos may need the cams in longer....

You really need to do this on a dyno so you can see how the cams effect the torque curve and tailor it to suit the car/turbo/cooler/etc...

thanks, I may just alter my VVT tables a little bit to see what kind of effects it has

Just be careful as when you alter the cam timing the A/F ratio may change also.

How do I know how far the cams can be advanced ? Is there a physical limitation to prevent the valve hitting the piston ? This is what I'm scared of. I don't want to damage my engine. My car is a 2001 jdm sti. When you say it will get very loud, do you mean it will be caused by the pistons hitting the valves or something else ?

My understanding is if you set the AFR initially, it is based on maf inputs and in open loop the ecu will know how much fuel to put in for the required afr to be reached. I realise it doesn't always hit the target in the table so the actual afr we see on the wideband may be different to that, but it is what we measure on the wideband that really matters and once we are happy with that then it should be fine, no matter what the value in the table is.

Then, if we go and modify the cam timing, the AFRs we see measured on the wideband may change. This is because the amount of overlap between exhaust valve closing and inlet valve opening changes and we can end up with some of the charge going straight out into the exhaust along with the exhaust gases. This may combust in the exhaust and cause some of the unburnt fuel in the exhaust gas to burn too, and depending on the completeness of this combustion we will get AFR that is either richer or leaner than the original setting.

However, given that the ecu has fuelled for the incoming air mass, we know the AFR of the mixture in the cylinder is what it was before we made changes to the cam timing because none of these settings have changed.

Similarly, egts may be affected, ie increased, by the combustion that takes place in the exhaust, and although this seems bad again it is an artificial increase and is not indicative of the temperatures within the cylinder.

Is all this correct ? I really want to be sure I know what all the implications are before going ahead and making changes.

Thanks

I don't think what you are talking about, more overlap, is going to happen with the current implementation of AVCS; it is only able to advance valve timing on the intake side (at least for USDM cars; I know little about JDM stuff)

My car only allows adjustment of the intake, I believe it is the same as US STI. What will happen by advancing the cam then ?

if you advance the cam, you will achieve cylinder filling earlier in the intake stroke, possibly resulting in more cylinder filling
because the port velocity is going to be similar throughout the RPM range, while time to fill cylinder isnt going to be the same.
this is a more theoretical idea, but perhaps the AVCS system allows subaru to run more overlap than a normal turbo cam setup uses? then use AVCS to trim off overlap at low RPM where it would hurt cylinder filling and torque?
anybody actually know?

stupid 2.4ghz cordless phone killing my wireless...

On some of the later model WRXS it is possible to advance the cams too far and yes, they start making a LOT of noise when that happens, not sure it is possible to actaully hit the pistons.

On an aftermarket ECU you have to adjust the A/F after altering the cam timing, not sure on the factory ECU, ask me again next week and I should have an answer for you.

But I would think it will still change as the ECU code that calculates the fuel will be assuming the cam timing is unaltered when it performs its calculation.

If the aftermarket ECU utilizes speed/density to determine injector pulse width, then changing intake cam advance will alter volumetric efficiency, an important variable used to calculate how much air is in the cylinder. A MAF sensor-based system like the OEM ECU is immune from changes to VE, so its injector pulse width calculations shouldn't be affected by changing the intake cam advance.