AVCS - Intake and Exhaust Timing

[KoolBRZ]

It's how velocity is affected by restrictions, not injections. The injection angle is really about timing. When velocity is increased by reduced restriction, then fuel injection must be changed, otherwise part of the fuel goes out the exhaust, unburned. That throws off the oxygen sensor, and reduces the power output of the engine. But, changing the angle helps it burn more completely.

[Kodename47]

Originally Posted by KoolBRZ

It's how velocity is affected by restrictions, not injections. The injection angle is really about timing. When velocity is increased by reduced restriction, then fuel injection must be changed, otherwise part of the fuel goes out the exhaust, unburned. That throws off the oxygen sensor, and reduces the power output of the engine. But, changing the angle helps it burn more completely.

So why not change the PI angle then, seeing as that injects the whole 720 degree cycle?

It's fine throwing out theories, but you have yet to show me why changing the DI angles is beneficial or makes any improvement. So you'd inject later in the cycle? Does this not impact on fuel mixture within the cylinder, which could have a negative impact on performance? How does that impact charge cooling (one of the main reasons for DI)?
@Matt@Cosworth care to chime in seeing as you've done the most extensive testing?

FYI unburnt fuel doesn't throw off the O2 sensor, the lambda sensor measures oxygen gases.

[KoolBRZ]

Originally Posted by Kodename47

So why not change the PI angle then, seeing as that injects the whole 720 degree cycle?

It's fine throwing out theories, but you have yet to show me why changing the DI angles is beneficial or makes any improvement. So you'd inject later in the cycle? Does this not impact on fuel mixture within the cylinder, which could have a negative impact on performance? How does that impact charge cooling (one of the main reasons for DI)?
@Matt@Cosworth care to chime in seeing as you've done the most extensive testing?

FYI unburnt fuel doesn't throw off the O2 sensor, the lambda sensor measures oxygen gases.

FYI unburnt fuel DOES throw off O2 sensors, because the oxygen that would have been used to burn it would have been converted to CO2. Since the fuel is unburnt, the oxygen is also unconverted, so, there is more oxygen present along with the unburnt fuel. The fuel isn't unburnt because there isn't enough oxygen, it is unburnt because the conditions for complete burning were less than optimal.

The DI angle is changed to compensate for the increased scavenging caused by lower restrictions in the Intake and Exhaust. An optimal angle will burn more of the fuel, so the combustion is more complete before being swept out by the Intake air. Since I have less restrictive Intake and Exhaust than OEM, I have more scavenging than OEM. AVCS timing is also as much as 30 degrees different than OEM, to give the charge better conditions to burn completely.

PI is great under low-load conditions at low engine speeds. It burns cleaner and is more efficient. But it knocks, bad, under medium to high-load and medium to high-speed conditions. DI cools the charge, is much less prone to knocking, but is limited by the size of the injector. PI for cruising, DI for accelerating, and 80/20 DI to PI at high-speed/high-load. I'll have a DI/PI table to show soon. Just working to smooth out the transitions now.

[Kodename47]

Originally Posted by KoolBRZ

FYI unburnt fuel DOES throw off O2 sensors, because the oxygen that would have been used to burn it would have been converted to CO2. Since the fuel is unburnt, the oxygen is also unconverted, so, there is more oxygen present along with the unburnt fuel. The fuel isn't unburnt because there isn't enough oxygen, it is unburnt because the conditions for complete burning were less than optimal.

Unburnt fuel will be occur when injecting before the exhaust valve closes. CO2 has nothing to do with it. The O2 sensor will read lean and not register the unburnt fuel. This is not throwing off the O2 sensor, as you put it, just something to note. You don't tend to get unburnt fuel after the spark event, if it's not fully burnt in the cylinder it continues to burn in the exhaust. This is why you get hot EGTs due to retarded timing or too much fuel etc.

Originally Posted by KoolBRZ

The DI angle is changed to compensate for the increased scavenging caused by lower restrictions in the Intake and Exhaust. An optimal angle will burn more of the fuel, so the combustion is more complete before being swept out by the Intake air. Since I have less restrictive Intake and Exhaust than OEM, I have more scavenging than OEM. AVCS timing is also as much as 30 degrees different than OEM, to give the charge better conditions to burn completely.

DI is alot less prone to bypassing the cylinder than PI due to location and fuel pressure to the injectors. Again you haven't really stated specifically what's wrong with the OEM values, you're making broad statements (assumptions) but no valid data to back it up. What you're actually wanting to do with the DI angles is adjust the EOI to spark timing for adequate cooling. This is more relevant for changes in fuel quantity being delivered rather than cam timing. Go read papers about DI SOI/EOI, there is very little mention of cam timing

Originally Posted by KoolBRZ

DI cools the charge, is much less prone to knocking, but is limited by the size of the injector.

... yet you can supply far more fuel from the DIs than PIs.

[Matt@Cosworth]

Originally Posted by Kodename47

So why not change the PI angle then, seeing as that injects the whole 720 degree cycle?

It's fine throwing out theories, but you have yet to show me why changing the DI angles is beneficial or makes any improvement. So you'd inject later in the cycle? Does this not impact on fuel mixture within the cylinder, which could have a negative impact on performance? How does that impact charge cooling (one of the main reasons for DI)?
@Matt@Cosworth care to chime in seeing as you've done the most extensive testing?

if you change the inlet cam timing then the injection timing should travel with it, on very highly tuned engines ( F1) with pfi the injection timing map varies by 200 degrees
the gains are small however on the FA20 as its not that strongly tuned
I found about 3-4Bhp on our supercharger tune by varying the DI timing in conjunction with the altered cam timing and little extra by varying the PFi timing also

[Kodename47]

Originally Posted by Matt@Cosworth

if you change the inlet cam timing then the injection timing should travel with it, on very highly tuned engines ( F1) with pfi the injection timing map varies by 200 degrees
the gains are small however on the FA20 as its not that strongly tuned
I found about 3-4Bhp on our supercharger tune by varying the DI timing in conjunction with the altered cam timing and little extra by varying the PFi timing also

So how about on NA, equivalent to your 1.2/1.3?

[KoolBRZ]

Here is the PI/DI table I've been working on. On my car, with less restrictive Intake and Exhaust than OEM, it is responsive at the low end, accelerates well with very little knock, and gets >30 MPG at 2400 rpms. Using @shr133's AVCS tables as shown previously. I'm also using the OFT 93 Octane Base Timing B table with 91 Octane fuel. I also have the Phantom ESC, but for testing purposes, I left it turned off. It also works very well with the ESC turned on.

[Matt@Cosworth]

Originally Posted by Kodename47

So how about on NA, equivalent to your 1.2/1.3?

I tweaked the DI timing ever so slightly on the 1.3 tunes to match the revised cam timing - it was worth about 2 bhp at most

[R2]

Originally Posted by Matt@Cosworth

I tweaked the DI timing ever so slightly on the 1.3 tunes to match the revised cam timing - it was worth about 2 bhp at most

I'm starting to look at DI timing and I'm struggling to understand the theory behind advancing or retarding it. To me it makes sense to advance it so the fuel has the longest time to evaporate and cool the charge and minimize knock, but I understand there is the problem with impingement on the piston if it's too early. Secondly, where does the slight improvement in power come from? It doesn't seem like VE will change with DI angle, and assuming ignition timing is the same, how does one injection angle make more or less power than another?

[Matt@Cosworth]

there's a couple reasons
1) as the engine speed increases air velocity in the port also tends to increase, so where the air is entering the cylinder can change slightly and this leads to different mixing and combustion characteristics -hence you need to adjust DI timing with speed and load
2) as the cam timing changes, so the timing of the arrival of the inlet charge air also changes so again you need to alter the DI timing to meet the new arrival time to give you the best mixing

so assuming that subaru / toyota have done their job and if you were to stick with the stock cam timings then you could also leave the DI timing alone
however, move the cam timing and you need to at least check if you need to move the DI timing also

[Nah]

Originally Posted by KoolBRZ

Here is the PI/DI table I've been working on. On my car, with less restrictive Intake and Exhaust than OEM, it is responsive at the low end, accelerates well with very little knock, and gets >30 MPG at 2400 rpms. Using @shr133's AVCS tables as shown previously. I'm also using the OFT 93 Octane Base Timing B table with 91 Octane fuel. I also have the Phantom ESC, but for testing purposes, I left it turned off. It also works very well with the ESC turned on.

I'm currently using your ADVCS tables with an e85 tune... very very nice... I have done the recommended DI change at .2 to 0 you think I should try a custom DI/PI map. I've got jdl uel headers no cat.

[KoolBRZ]

Originally Posted by Nah

I'm currently using your AVCS tables with an e85 tune... very very nice... I have done the recommended DI change at .2 to 0 you think I should try a custom DI/PI map. I've got jdl uel headers no cat.

These are the AVCS and PI/DI tables from my latest tunes, called 40-20 because they get 40 mpg on the highway, but only 20 mpg city! But maybe it's just because city driving has more stoplights.

[Nah]

Lol nice... Wouldn't those tables cause me to lose power all around though? I mean theres almost a 20 degrees difference in certain areas? I'm looking for max power extraction. Lol but good to have for that drive to cocoa beach I'm planning to make soon.

[Nah]

Just outta curiosity, has anyone ever changed their base tables and achieved positive results?