AVCS - Intake and Exhaust Timing

[thambu19]

The ESC AVCS tables are running ton of Intake and Exhaust overlap. This isn't really needed when running a supercharger but is needed for NA + Headers.
If I were you id try a few setups to get an idea which direction to move
1. Id definitely try stock cams (I mean real stock). This is because most other cals I have seen seem to run a ton of overlap.
2. Try Stage1 (not 2)
3. Stage 2 but with 4deg pulled out from Intake and Exhaust at WOT. This would be my last choice.

Monitor knock while you do this. Use the best possible gas you can get hold of. The spark can be later adjusted to the final cams you pick

[KoolBRZ]

Originally Posted by thambu19

@KoolBRZ Are you running headers in yours?

I am running the PLM/Nameless long tube header completely catless front to rear. It is also coated inside and out, with a 3" to 2.5" reducer at the overpipe, resonated 2.5" midpipe, stock rear pipe, and axleback muffler.

Should I just reduce from 1.0 load on up, or should I reduce overlap all over the load range at peak overlap? I totally agree about the 3 degree steps. When I was working on AVCS before I could feel a difference with as little as 1 degree. (my ultra-sensitive butt-dyno, you know) I just finished working on it before I got my ESC. They seemed to work better than the OFT tables, so I kept them in. There are times when it is better to have the intake or exhaust advanced or retarded past TDC for better cylinder fill or performance reasons. So whenever the SC is on, or PI is 100%, there shouldn't be any overlap, or it will push the fuel right out before it is completely burned.
I'll run the overlap calculator on my AVCS tables and go from there. Send you pics later.

[Kodename47]

@thambu19 interested in a couple of thoughts....

Changes for a OEM style manifold but with no cat. As the runner design hasn't changed I'd assume that the AVCS will be similar to optimal stock?

What would you be looking for on said manifold for a PD supercharger?

Is there any way to determine if you've improved VE with a SC without a dyno? You have a valid point regarding overlap so is there a good way to indicate if the airflow isn't bypassing the cylinder. Most info I read suggests looking at MAF flow or engine load,, but I guess calculating overlap (or st least cam relationship) is the only way.

[thambu19]

Will give a detailed one when I get to hotel room. In general you want some scavenging to get rid of exhaust gases but beyond a point scavenging will not help. So the idea is to find the right amount. Oem cam timing is usually limited due to emissions more than anything. Regarding looking for improvements only trustable source is dyno. But you can look at maf too but maf can get good when you start scavenging. At that point the o 2 sensor will record lean indicating too much scavenging. Idea is to limit scavenging to 3%or so max

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[thambu19]

Originally Posted by Kodename47

@thambu19 interested in a couple of thoughts....

Changes for a OEM style manifold but with no cat. As the runner design hasn't changed I'd assume that the AVCS will be similar to optimal stock?

What would you be looking for on said manifold for a PD supercharger?

Is there any way to determine if you've improved VE with a SC without a dyno? You have a valid point regarding overlap so is there a good way to indicate if the airflow isn't bypassing the cylinder. Most info I read suggests looking at MAF flow or engine load,, but I guess calculating overlap (or st least cam relationship) is the only way.

So how much boost are you running? Like 10 PSI? First I have to throw in a nice disclaimer that I am still running stock and don't have an OFT (yet) so everything that I say in my posts is simply from my 5-6 yrs of engine modeling (GT-Power) and 2yrs of engine development/calibration experience at an OEM. But as a result of that I have seen how OEMS calibrate.

I am going to assume that you are running 10PSI boost. Since you are CAT less your exhaust in an NA world will scavenge harder or better than one with CAT. In general as the back pressure drops the scavenging picks up. Instead of starting with stock AVCS id start with Stg1 or Stg2 of OFT cal only reason for saying this is with no CATs your exhaust is similar to an aftermarket header? Mr.Pathak @Shiv@Openflash has done a great job on the cam timing using a Dyno so lets say we trust that more than anything else.

Now since you are running a SC you do not want the same levels of overlap as an NA engine runs. You can but that is a waste. If it was a turbo scavenging helps a ton at low speeds to keep the mass flow through turbine high but since this is a SC we don't want all the scavenging we can get instead we just need enough to reduce incylinder residual gases. As I said before some 2-3% O2 in exhaust must be fine or more than enough scavenging. As per this site http://wbo2.com/sw/percent-o2.htm 2% O2 in exhaust will show up as a AFR = 16.2 roughly. I you are running 100% DI and when you see an AFR of 16.2 when you are running overlap I guess that is the right amount of overlap where engine is running stoich incylinder. If you are targeting 12.0 AFR then you are looking for an AFR of 13.3 ish I guess? Not sure if I am making sense much.

Do we have control over injection timing of DI?

You would want to advance exhaust timing (subtract from OFT stage2) since you have more exh gas to get rid off. How much to advance depends on how much boost you are running.

Regarding intake you would want to run later intake opening or retarded intake (less overlap) once again the more boost you are running the more you can retard intake and still get good VE.

[thambu19]

Originally Posted by KoolBRZ

I am running the PLM/Nameless long tube header completely catless front to rear. It is also coated inside and out, with a 3" to 2.5" reducer at the overpipe, resonated 2.5" midpipe, stock rear pipe, and axleback muffler.

Should I just reduce from 1.0 load on up, or should I reduce overlap all over the load range at peak overlap? I totally agree about the 3 degree steps. When I was working on AVCS before I could feel a difference with as little as 1 degree. (my ultra-sensitive butt-dyno, you know) I just finished working on it before I got my ESC. They seemed to work better than the OFT tables, so I kept them in. There are times when it is better to have the intake or exhaust advanced or retarded past TDC for better cylinder fill or performance reasons. So whenever the SC is on, or PI is 100%, there shouldn't be any overlap, or it will push the fuel right out before it is completely burned.
I'll run the overlap calculator on my AVCS tables and go from there. Send you pics later.

I just looked up that header online... Man looks really slick... Perfect for scavenging.
You should reduce overlap where you start boosting and below that you should blend it into what ever surface works for you at the lower loads. Surfaces should always blend nicely because if you look at it that is how engines work. A good cam surf should be smooth and so is a good spark and a good FAR surface. When OEM go away from the smoothness it is because they had some issue or they went after some FE improvement locally etc.

Don't take away all overlap. You need some just enough to scavenge. But since you are boosted you don't need to rely on pressure waves to do the job for you like NA engines. See my comment above. Its all about getting just enough overlap. Too much and it will give diminishing returns unless you have a Turbo.

[ztan]

Originally Posted by thambu19

I just looked up that header online... Man looks really slick... Perfect for scavenging.
You should reduce overlap where you start boosting and below that you should blend it into what ever surface works for you at the lower loads. Surfaces should always blend nicely because if you look at it that is how engines work. A good cam surf should be smooth and so is a good spark and a good FAR surface. When OEM go away from the smoothness it is because they had some issue or they went after some FE improvement locally etc.

Don't take away all overlap. You need some just enough to scavenge. But since you are boosted you don't need to rely on pressure waves to do the job for you like NA engines. See my comment above. Its all about getting just enough overlap. Too much and it will give diminishing returns unless you have a Turbo.

How would you set up a turbo in comparison to NA or supercharger? Have sent you a file to look at for comments.

[KoolBRZ]

Well I don't have the Nameless one. I have the PLM imitation. Half the welds and it doesn't have the gradual increases in pipe sizes. So it has all the high-speed horsepower, without as much low-end torque. It was on ebay, make an offer, asking $400, offered $300, and now it's mine. I would recommend it as the best header for the lowest cost. Install is a bitch though. Had to remove the dipstick completely, and the bottom bolts of the center core support. It also requires a 3" overpipe or a 3" to 2.5" adapter. It doesn't leak and the angles are correct to clear the overpipe without rattling, even with the added .5" flange of the adapter.

[thambu19]

Originally Posted by ztan

How would you set up a turbo in comparison to NA or supercharger? Have sent you a file to look at for comments.

Hey budd... I just brought my work laptop for my vacation so no rom raider on this one. Generally for Turbo applications at the lowest engine speeds people use lots of intake advance (like 40 in our maps?) This introduces scavenging and also increases mass flow through turbine and helps to keep it away from surge line of turbo (this may or may not be needed depending on the size of the turbo with respect to engine). At this low speed the exhaust can be opened late to gain max torque and also because the net mass flow rate is rather small due to lower speeds.

In the mid speeds you don't need as much overlap and the exhaust will need to be opened earlier than at the lowest speeds because as speeds rise the mass flow rate through engines rise. This is also where you build max boost so the intake cam can be retarded

At peak speeds open the exhaust as early as possible depending on how much boost you are running. There will be a point where opening it early will help reduce exh gases from engine but going beyond that you lose torque. So finding the right balance is important so ofcourse without saying dynos are a must, sorry.

I have not looked at your bin file (can do when I go home next week) but I envision a turbo tune to have retarded exh and advanced intake at low speeds and they both gradually start moving towards an advanced exh and retarded intake at higher speeds. Do I make sense? English isn't my native tongue so bear with me. I come from the same land as @Shiv@Openflash although his English is a lot better than mine

Without a dyno we need to start looking for MAF improvements and keep an eye on exhaust O2 concentration. Too much exhaust O2 like 4-5% is not needed. Any cam setting that improves MAF without increasing O2 is a good setting.

Once we get into serious boost there is another factor and this is Effective compression ratio.
The idea is to get the air compressed by the compressor and cooled down by intercooler rather than having the engine compress it. So if we can trade some compressing by the engine and give it to compressor the gases at Top Dead Center during firing stroke is cooler. In other words if possible to retard intake cam to have a late intake closing without dropping the volumetric efficiency then that is a better strategy because the air is cooler by the time piston reaches TDC and as a result you can run more ignition timing. Using the piston to compress creates more heat than using compressor because of the presence of intercooler. So the more boost the more the intake needs to be retarded to make use of the compressor work effectively as long as VE (volumetric efficiency or MAF reading) does not drop.

[thambu19]

Sorry if anyone feels most of my comments are vague without giving away any numbers as to what timing to run when. That is because unlike the PI DI ratio where we can cell specifically that we want 100% DI at WOT it is very difficult to say I want this cam timing a this speed etc. Having worked on these things on a dyno I understand that cam timings is all about gas dynamics. Even a small change in pipe diameter of the exhaust will make it tune differently causing it to need a different timing. So all I can do here is give you guys the understanding of how things should be generally setup so folks can go try things out.

One thing to always remember is that many things go hand in hand. For example a change in cam timing will almost certainly want a change in ignition timing. Changing those two will definitely change your exhaust gas temperature and this means you will need a bit more or less enrichment (Air to Fuel ratio) or else you will smoke your CAT in no time if you have one. Blown CATs are not good my friend. Last thing you need is to melt your CAT and ingest it back into the engine. This sounds crazy but with the level of scavenging these engines run the CAT material can be sucked back into the engine and maybe even into the intake manifold/runners
If you are running CATless this is one less thing to worry althought I will always have a CAT on mine because emissions
Make sure you buy headers made with good quality steel that can take high temps. I am sure the OFH sold by @Shiv@Openflash is a pretty good one simply because I trust that one Mr.Shiv Pathak. If you are running CATless we only have to worry about keeping Exh temps below 1000C in most cases.
No one uses exhaust thermocouples to make sure this isn't happening. I haven't seen cases of burnt up exhaust valves either so we are good I have to guess. Either way it is good to keep your AFR at peak power in the region of 11.75 to 11.8 and not leaner than that. At lower speeds you can go 12.0 or 12.5 depending on which ratio gives better torque. As a general rule engines with high comp ratio can go from normal combustion to pre-ignition usually at their peak torque rpm. Seen that happen in real time so be careful. So be careful with your spark around 4500rpm to 4800rpm.

[solidONE]

Originally Posted by thambu19

Sorry if anyone feels most of my comments are vague without giving away any numbers as to what timing to run when. That is because unlike the PI DI ratio where we can cell specifically that we want 100% DI at WOT it is very difficult to say I want this cam timing a this speed etc. Having worked on these things on a dyno I understand that cam timings is all about gas dynamics. Even a small change in pipe diameter of the exhaust will make it tune differently causing it to need a different timing. So all I can do here is give you guys the understanding of how things should be generally setup so folks can go try things out.

One thing to always remember is that many things go hand in hand. For example a change in cam timing will almost certainly want a change in ignition timing. Changing those two will definitely change your exhaust gas temperature and this means you will need a bit more or less enrichment (Air to Fuel ratio) or else you will smoke your CAT in no time if you have one. Blown CATs are not good my friend. Last thing you need is to melt your CAT and ingest it back into the engine. This sounds crazy but with the level of scavenging these engines run the CAT material can be sucked back into the engine and maybe even into the intake manifold/runners
If you are running CATless this is one less thing to worry althought I will always have a CAT on mine because emissions
Make sure you buy headers made with good quality steel that can take high temps. I am sure the OFH sold by @Shiv@Openflash is a pretty good one simply because I trust that one Mr.Shiv Pathak. If you are running CATless we only have to worry about keeping Exh temps below 1000C in most cases.
No one uses exhaust thermocouples to make sure this isn't happening. I haven't seen cases of burnt up exhaust valves either so we are good I have to guess. Either way it is good to keep your AFR at peak power in the region of 11.75 to 11.8 and not leaner than that. At lower speeds you can go 12.0 or 12.5 depending on which ratio gives better torque. As a general rule engines with high comp ratio can go from normal combustion to pre-ignition usually at their peak torque rpm. Seen that happen in real time so be careful. So be careful with your spark around 4500rpm to 4800rpm.

So this applies to a non-catted NA setup? 11.75~11.8 AFRs? I always thought that was a bit too rich.

[KoolBRZ]

@thambu19, since these things go hand-in-hand, which ones should we do first? I've been using your PFI-to-DI table as a given, then changing my AVCS to get only 2-3% scavenging. Without getting into logs, I can say that backing off my AVCS has resulted in a richer AFR than requested, rather than a leaner AFR. I've also bumped up my Base Timing B by 2 degrees in the 100% DI areas. So far IAM stays at a solid 1, and FLKC at 0.

[thambu19]

Originally Posted by solidONE

So this applies to a non-catted NA setup? 11.75~11.8 AFRs? I always thought that was a bit too rich.

At peak power? Not really. At lower speeds yes it's rich. There the target will be 12.5

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[thambu19]

Originally Posted by KoolBRZ

@thambu19, since these things go hand-in-hand, which ones should we do first? I've been using your PFI-to-DI table as a given, then changing my AVCS to get only 2-3% scavenging. Without getting into logs, I can say that backing off my AVCS has resulted in a richer AFR than requested, rather than a leaner AFR. I've also bumped up my Base Timing B by 2 degrees in the 100% DI areas. So far IAM stays at a solid 1, and FLKC at 0.

When you say richer what's really happening is earlier with lots of scavenging the o2 sensor was reading lean due to excess oxygen. You may have to dial back on fuel now.

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