PI : DI Ratio Discussion

[Kodename47]

I'm sure you could go 100% DI earlier and I'm certain some tuners do. However I would put money that at lower loads there might be some benefits to PI as well as the cleaning properties. However it could be beneficial to start using DI earlier in mid to high load over 2k.

[shr133]

Hi guys,

I just got my FRS and a ECUTEK tuner but I have been tuning engines for years, started with holley carbs...

I think that it's more about drive ability...
I'm going to run both at all times to eliminate the transition point from DI to both...

Turing PI on and off and on again makes no sense to me. either on or off or a mix..

I have to do some tweaking, I filled in some gaps with 10% PI and it seams too low but it still runs better, so I'll go to a min of 20% PI at all times....

The 35% - 20% PI part of the map run better to me than either 0 or 10%...

[sato]

Originally Posted by shr133

Hi guys,

I just got my FRS and a ECUTEK tuner but I have been tuning engines for years, started with holley carbs...

I think that it's more about drive ability...
I'm going to run both at all times to eliminate the transition point from DI to both...

Turing PI on and off and on again makes no sense to me. either on or off or a mix..

I have to do some tweaking, I filled in some gaps with 10% PI and it seams too low but it still runs better, so I'll go to a min of 20% PI at all times....

The 35% - 20% PI part of the map run better to me than either 0 or 10%...

Keep us posted with more information and progress. Any data is greatly appreciated.

Sent using Tapatalk

[thambu19]

Originally Posted by shr133

Hi guys,

I just got my FRS and a ECUTEK tuner but I have been tuning engines for years, started with holley carbs...

I think that it's more about drive ability...
I'm going to run both at all times to eliminate the transition point from DI to both...

Turing PI on and off and on again makes no sense to me. either on or off or a mix..

I have to do some tweaking, I filled in some gaps with 10% PI and it seams too low but it still runs better, so I'll go to a min of 20% PI at all times....

The 35% - 20% PI part of the map run better to me than either 0 or 10%...

Running too low PI could lead to running at regions lower than the Min Pulsewidth. Every injector has a minimum pulsewidth which is usually 1ms for the type of injectors used in the FRS. I would advise using completely no PFI or partial (like 30-40% PFI) but never too low. As we go towards higher speeds and loads this is no longer a problem since a low 10% still results in a decent pulsewidth at peak power etc

[thambu19]

Originally Posted by ztan

I haven't looked at SOI parameter, but it does make sense that the injection window would be (SOI - spark timing). We'd have to assume that SOI and spark would be referenced off BTDC in the ROM.

Does anyone have the RAM address for SOI?

Kodename47 has had up to 5.8ms on the DI injector - anyone else gone higher?

Great thread!
Usually the SOI is about 40deg after TDC during the Intake stroke to avoid piston wetting. Normally the injection should end atleast 60deg before TDC firing for good mixture preparation (thumb rule). Essentially we have about 360-40-60 = 260deg. At peak engine speed of 7500rpm we have 8ms per 360deg. This reduces to 5.77ms for 260deg. So the number @Kodename47 is referring to is the absolute max PW that should be used before running into issues. At this time it is beneficial to start relying on some PFI for better mixture preparation (improves flame speed) instead of relying heavily on DI for knock relief. Saying this because at those high speeds we have seen combustion only a few degrees away from MBT considering this was calibrated on premium fuel.

From what I can see there will be more benefit from reducing enrichment for thermal protection than anything else. This is exactly what @shiv@vishnu has done. OEMS go crazy on thermal protection and sometimes run ridiculously high FAR (closer to 0.10) From my experience a FAR of 0.088 to 0.09 is enough to protect CAT and Exhaust at peak power. I think the OFT tune puts the engine just there.

For those running CATless headers they probably can push the AFR even a touch leaner. For those with OEM header I would not recommend any leaner than 0.085 at peak power.

There are certain engine speeds where engine is more knock limited than others. You can see this by looking at the stock spark timing. If at certain engine speed the spark advance is less than the adjacent speeds it indicates that this speed is more knock limited in normal setting. At these speeds you need a tad more enrichment since the spark is more retarded. In general the more spark you add the less enrichment you need.

[Kodename47]

@thambu19 did you look at my DI calculator I posted earlier? The DI injection timing is in the Romraider definitions.

[thambu19]

Originally Posted by Kodename47

@thambu19 did you look at my DI calculator I posted earlier? The DI injection timing is in the Romraider definitions.

I saw your linearization curve of pulsewidth to injector mass. For engines running constant rail pressure that goes out of the equation. From your analysis I think this engine has varying rail pressure.

This table is what gets used when engine is running open loop fuelling combined with airflow estimation. Usually this table is not messed with unless for E85 conversion. One easy way to make an engine accept E85 without messing with MAF scaling is to adjust this pulsewidth to mass curve and move it up by roughly 40% so the engine commands larger pulsewidth for the same requested fuel mass which is indeed calculated from airflow prediction/measurement.

Adjusting the MAF scaling isnt really the appropriate way to adjust for E85. If you think about it the airflow doesnt really change just because we are running E85 and as a matter of fact it actually drops due to the higher Fuel to Air ratio

[shr133]

Originally Posted by thambu19

Running too low PI could lead to running at regions lower than the Min Pulsewidth. Every injector has a minimum pulsewidth which is usually 1ms for the type of injectors used in the FRS. I would advise using completely no PFI or partial (like 30-40% PFI) but never too low. As we go towards higher speeds and loads this is no longer a problem since a low 10% still results in a decent pulsewidth at peak power etc

Thanks for the info...
I'm going to raise up PI in those areas to smooth out the power curve some more...

[Kodename47]

Originally Posted by thambu19

I saw your linearization curve of pulsewidth to injector mass. For engines running constant rail pressure that goes out of the equation. From your analysis I think this engine has varying rail pressure.

I meant this:
DI Calculator

I'm very much aware that the ratio/injection timing is only part of the picture as the IPW changes, I log both volume and PW for both PI and DI all the time

[thambu19]

Originally Posted by Kodename47

I meant this:
DI Calculator

I'm very much aware that the ratio/injection timing is only part of the picture as the IPW changes, I log both volume and PW for both PI and DI all the time

Nice sheet. Are you planning to use this to calculate the time available for injection and hence max PW?

[Kodename47]

Originally Posted by thambu19

Nice sheet. Are you planning to use this to calculate the time available for injection and hence max PW?

Pretty much why I did it. Have a look and play, you can copy your own tables into it.

[Illuminaughty]

Originally Posted by Kodename47

Pretty much why I did it. Have a look and play, you can copy your own tables into it.

Very excited to get home and look at this. I swear I've seen low 6ms DI PW on my logs, but I think they were somewhere in the low 6k RPM range. 7psi E85 fully stock fueling. I'd wager somewhere around 260 g/s MAF. Wonder how much fueling headroom I have if I tweak the PI/DI ratios.

[thambu19]

Originally Posted by Illuminaughty

Very excited to get home and look at this. I swear I've seen low 6ms DI PW on my logs, but I think they were somewhere in the low 6k RPM range. 7psi E85 fully stock fueling. I'd wager somewhere around 260 g/s MAF. Wonder how much fueling headroom I have if I tweak the PI/DI ratios.

6ms at 6K rpm wont be a problem but 6ms at 7.5K might be at the edge.

Are you sure about 260g/s?

I expect them to be in the 150-170 g/s range

With 220g/s air one could make close to 300hp

[shr133]

So I ran a few changes today and seams like ( seat of the pants) the sweet spot is 20% to 25 % PI for best drive ability and acceleration..
It will still pull good at 35% but seams to lag then pull...
DI seams to respond quicker more instant but pulls harder with some PI mixed in...
And the sweet spot seams to be 20% to 25 %, Toyota may have been right on that one.

I'm currently at 35% below 2000 rpm and either 20% or 25% above 2000 rpm in all cells but .100 column...
So I'm running 35% to 20% PI at all times and it's running great...

I will probably go to 20% above 2000...
I have to get out and do some more runs and data log...