AVCS - Intake and Exhaust Timing

[D-VO]

On another note; what is the highest intake AVCS anyone has registered? Mine is 42.6499 and being that I have mine set to 49 - 52 in the area it occurs it makes me wonder if the oil pressure will never get high enough to achieve those angles.

[steve99]

Originally Posted by D-VO

On another note; what is the highest intake AVCS anyone has registered? Mine is 42.6499 and being that I have mine set to 49 - 52 in the area it occurs it makes me wonder if the oil pressure will never get high enough to achieve those angles.

or its the limit of the cam phaser ?

[D-VO]

I guess we would need to know what the available oil pressure is at 5000 rpm as opposed to lets say 7000 rpm. I may be able to test the theory in that case.

Good read and vid about it: http://www.ft86club.com/forums/showp...&postcount=305

[KoolBRZ]

@D-VO, do you get about 20 MPG average? Your tables have way too much overlap below 3000 RPMs. I tried your AVCS tables today and they would work good for a MT, but not nearly the low-end torque needed for an AT. I took the AVCS guide and followed it literally when it came to light load settings, in my opinion anything up to .7 load, The guide shows overlapping semi-circles for intake and exhaust, and for light loads, the exhaust closes at 0 degrees, and the intake opens at 20 degrees ATDC. There are only two areas shown that are certain, low rpm/light load, and high rpm/heavy load. For high rpm/heavy load exhaust closes at 10 degrees ATDC, and the intake opens at 5 degrees BTDC. Those two corners are where I start with my AVCS tables.
Here are your AVCS tables, except for the upper left and lower right corners. Try them and tell me what you think. I blended them in as best I could, but at least you can try these and understand what I'm trying to describe in terms of low-end power.

[D-VO]

Sure I'll give them a shot. My average is 28mpg. When I had to take the highway to work everyday I was at 30mpg. Keep in mind we have very different forced induction units. I'm using a c38 from KW. I also tuned the DBW and fueling to make the engine peppy in the low end. It easily breaks the 235's loose when turning onto perpendicular streets from a stop.

[KoolBRZ]

Originally Posted by D-VO

Sure I'll give them a shot. My average is 28mpg. When I had to take the highway to work everyday I was at 30mpg. Keep in mind we have very different forced induction units. I'm using a c38 from KW. I also tuned the DBW and fueling to make the engine peppy in the low end. It easily breaks the 235's loose when turning onto perpendicular streets from a stop.

But you don't have a turbo, so you can still be blowing unburnt fuel out the exhaust. You must have more restriction in your exhaust than I do, or you wouldn't be getting over 25 mpg. I have no cats, 2.5" all the way back, with a high-flow muffler. The DBW and fueling mods would hide the loss of power from too much overlap. Do you run PI and DI with the usual tables, or have you modded those too? I've found PI to be the cause of more problems than it is supposed to cure. Try using DI 100% up to 1.5 load. You may not feel much of a difference in the lower gears, but in 6th you should feel a difference. You can also run more timing advance with DI than with PI.

[Kodename47]

@D-VO AVCS settings for a centri charger will be different to those of a PD blower or one that gives boost like the ESC, especially at high load and RPM.

A certain amount of overlap at lower load will help fill the cylinder, don't think that overlap is bad. If you're getting good economy then I would suggest not changing anything.

As for the angles you're actually logging, it could just be the cam phasers as Steve said. At the end of the day the table values are targets.

[D-VO]

Originally Posted by KoolBRZ

You must have more restriction in your exhaust than I do, or you wouldn't be getting over 25 mpg.

I have a perrin cat-back with both cats in place. Good catch.

Originally Posted by KoolBRZ

Do you run PI and DI with the usual tables, or have you modded those too? I've found PI to be the cause of more problems than it is supposed to cure. Try using DI 100% up to 1.5 load. You may not feel much of a difference in the lower gears, but in 6th you should feel a difference. You can also run more timing advance with DI than with PI.

I'm using slightly less than stock PI in cruise areas, and I'd rather not use 100%DI in cruising areas as it causes more carbon build up on the valves.

[D-VO]

Originally Posted by Kodename47

@D-VO AVCS settings for a centri charger will be different to those of a PD blower or one that gives boost like the ESC, especially at high load and RPM.

A certain amount of overlap at lower load will help fill the cylinder, don't think that overlap is bad. If you're getting good economy then I would suggest not changing anything.

As for the angles you're actually logging, it could just be the cam phasers as Steve said. At the end of the day the table values are targets.

I was following the factory AVCS tables as a reference for better fuel economy. I tried advancing the intake AVCS as one of the images on the first page suggested last year, but ended up with more like 24 - 25 mpg. So far this is the best cruising economy I've achieved. I'm going to try @KoolBRZ 's AVCS tables today on the way to work to note any difference in performance.

[KoolBRZ]

The factory AVCS is way different because the engine has to work to pull the charge in. It also uses overlap for cooling and economy, which uses higher vacuum in the intake than we have because we are both supercharged. My SC isn't the standard switched ESC, but uses a controller tied into the throttle and runs the SC all the time on my current map, so the manifold pressure is different than stock. With higher pressure in the Intake, and lower pressure in the Exhaust, it's all too easy to just blow the charge right through during overlap.

[Kodename47]

Originally Posted by KoolBRZ

The factory AVCS is way different because the engine has to work to pull the charge in. It also uses overlap for cooling and economy, which uses higher vacuum in the intake than we have because we are both supercharged. My SC isn't the standard switched ESC, but uses a controller tied into the throttle and runs the SC all the time on my current map, so the manifold pressure is different than stock. With higher pressure in the Intake, and lower pressure in the Exhaust, it's all too easy to just blow the charge right through during overlap.

But how much time are you actually running positive pressure in the intake? This is taken from my latest log, average manifold pressure is in each cell.

[D-VO]

Originally Posted by KoolBRZ

@D-VO, do you get about 20 MPG average? Your tables have way too much overlap below 3000 RPMs. I tried your AVCS tables today and they would work good for a MT, but not nearly the low-end torque needed for an AT. I took the AVCS guide and followed it literally when it came to light load settings, in my opinion anything up to .7 load, The guide shows overlapping semi-circles for intake and exhaust, and for light loads, the exhaust closes at 0 degrees, and the intake opens at 20 degrees ATDC. There are only two areas shown that are certain, low rpm/light load, and high rpm/heavy load. For high rpm/heavy load exhaust closes at 10 degrees ATDC, and the intake opens at 5 degrees BTDC. Those two corners are where I start with my AVCS tables.

Okay I tried your settings today but fuel economy dropped off so far that I had to pull over at the nearest gas station and change it right away. (Yes I waited for calibration) I saw an average loss of about 7mpg maximum loss was 10MPG at 55 mph. Also, low end power dropped off quite a bit. FRS was not happy. I could have fussed with the DBW for sure, but my current set up is what works. So I'll just keep it as is. I'll post up the log when I get home later.
@Kodename47 I'm still trying to smooth out the Intake AVCS so I won't get such large errors in 1st - 3rd gears, but I don't want to loose my airflow. Have you or anyone else messed with the 'intake/exhaust duty correction' tables? I was thinking about giving those a shot, but I'm confused about its operation. In one of the columns it looks like if the error is +6.25 then it adds +3.00 to the AVCS which really doesn't make any sense.

[Kodename47]

No, not touched the OCV duty tables. TBH, I probably would leave them. This is just something that you might need to expect. Can you use VGIs tool to show the difference in logged AVCS over a couple of pulls and see if it really is consistent?

[D-VO]

NP. Do the pulls have to be in the same gear?