PI : DI Ratio Discussion

[thambu19]

Originally Posted by 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...

I am surprised that this is making a difference in drive feel. Usually it is just down to the emissions and fuel economy. In theory PFI should give better and more consistent mixing compared to DI and hence has faster 0-10% burn at low speeds and loads.

[Illuminaughty]

Originally Posted by thambu19

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

I'm not 100% sure on the MAF. Came home to a broken A/C last night so didn't get a chance to look at the logs. Totally reasonable that it was 160g/s instead of 260g/s.

[shr133]

Originally Posted by thambu19

I am surprised that this is making a difference in drive feel. Usually it is just down to the emissions and fuel economy. In theory PFI should give better and more consistent mixing compared to DI and hence has faster 0-10% burn at low speeds and loads.

I went back to 20% Toyota had it right...
The more PI you add it feels richer but I don't think it is, it just just feels rich..
But too little feels lean... I'm sure if you readjust the fuel maps it will make the same HP... But for drive ability 20% seams to be the sweet spot......

I went to 35% below 2000 rpm and 20.3 above in all cells...
Turing the PI on and off and on was making the torque dip worse and too much PI made the dip worse... I have a slight 500 rpm dip, in 1st gear I can't feel any dip...

Computers have made tuning too detailed... If you are going to run PI you will have the best transition to run them all the time.. unless there is a good reason to turn them off why would you... and not in the middle of the torque dip... Both PI and DI have advantages and disadvantages and it seams a mix is best...

[ztan]

Originally Posted by shr133

I went back to 20% Toyota had it right...
The more PI you add it feels richer but I don't think it is, it just just feels rich..
But too little feels lean... I'm sure if you readjust the fuel maps it will make the same HP... But for drive ability 20% seams to be the sweet spot......

I went to 35% below 2000 rpm and 20.3 above in all cells...
Turing the PI on and off and on was making the torque dip worse and too much PI made the dip worse... I have a slight 500 rpm dip, in 1st gear I can't feel any dip...

Computers have made tuning too detailed... If you are going to run PI you will have the best transition to run them all the time.. unless there is a good reason to turn them off why would you... and not in the middle of the torque dip... Both PI and DI have advantages and disadvantages and it seams a mix is best...

Interesting.

I was about to try this on my car, as I was wondering if going from 0 to 20 or 50% PI and back across load/rpm cells was making some fueling erratic by putting the PI pulsewidths in the non-linear range like the problem switching PI on and off in low loads at idle.

[Kodename47]

@shr133 are you dyno testing this?

[JB86'd]

@Kodename47 That's what I want to know. All of these threads with people changing the PI/DI ratios and AVCS, etc. saying it "feels" a certain way. The butt dyno is not trustworthy people.

[shr133]

Originally Posted by ztan

Interesting.

I was about to try this on my car, as I was wondering if going from 0 to 20 or 50% PI and back across load/rpm cells was making some fueling erratic by putting the PI pulsewidths in the non-linear range like the problem switching PI on and off in low loads at idle.

1 of my goals was to get rid of the dip and the dip starts when they turn off PI and change the cam timing and a few other things....
I don't know why you would turn PI on, off and on again.... Running both will smooth it out... At mid load I have no dip in acceleration.... I think turning off PI and the exhaust cam timing is for emissions not performance...

This will never be a drag car so I'm tuning for drive ability and passing power... So I am currently running this on my butt dyno for now till I get the maps sorted out... It doesn't take a genius to know if something works or not...

I'm getting to the point I have to dyno it and start doing 0-60s to sort out the small details... But it runs way better than stock at all rpms...

I don't know if running PI all the time will help HP on a dyno but it will make the engine run better and eliminate 2 transitions that help to cause lag and hesitation...

Just flash it and drive for a day if you don't like it just flash back...

[sato]

I just can't seem to find the three or specific posts, but the switch to DI only on that range was due to some condition that required the DI cooling effect, too hot a combustion event during that range, something like that. Not sure if they were speculating or some data was provided on that subject... if it was emissions related, tactic to prevent the catalytic converters from spontaneously exploding, or preventing engine damage.

Either way, I'm subscribed to topic and will stay attentive towards everybody's feedback.

Sent using Tapatalk

[Illuminaughty]

Originally Posted by thambu19

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

I think I'm running my DI's a bit too hard for sure. Going to have to scale down a bit on the DI ratio at the top end.

Let me know what you guys think.

http://datazap.me/u/incognico/2ndgeare85?log=0&data=

[Kodename47]

Originally Posted by shr133

1 of my goals was to get rid of the dip and the dip starts when they turn off PI and change the cam timing and a few other things....
I don't know why you would turn PI on, off and on again.... Running both will smooth it out... At mid load I have no dip in acceleration.... I think turning off PI and the exhaust cam timing is for emissions not performance...

This will never be a drag car so I'm tuning for drive ability and passing power... So I am currently running this on my butt dyno for now till I get the maps sorted out... It doesn't take a genius to know if something works or not...

I'm getting to the point I have to dyno it and start doing 0-60s to sort out the small details... But it runs way better than stock at all rpms...

I don't know if running PI all the time will help HP on a dyno but it will make the engine run better and eliminate 2 transitions that help to cause lag and hesitation...

Just flash it and drive for a day if you don't like it just flash back...

Are you logging PI/DI injection volumes or PW at all? The only reason I ask is that I tested something the other day with 25% PI ratio through the whole of the table (SC car so more volume) and the PIs weren't actually used until quite late and mid/late load. I'm guessing down to minimum volume or PW parameters so something else. I've got more testing to do, I'm trialing an easy way to get PI/DI error minimised without having to run fully PI or fully DI.

I agree that there must be benefits to PI with regards to the mixture benefits, but if you're saying that you didn't feel the dip then you'd see that on a dyno. However I know someone who says that they tested various ratios on a dyno and found little to no benefit from changing them. You really need to test not just the different ratios but the extra ignition timing it allows you to put in as a result.

[Kodename47]

Originally Posted by Illuminaughty

I think I'm running my DI's a bit too hard for sure. Going to have to scale down a bit on the DI ratio at the top end.

Let me know what you guys think.

http://datazap.me/u/incognico/2ndgeare85?log=0&data=

Try using my DI calculator, it will allow you to set a limit to the PW and calculate it accordingly for you. Also allows you to mess with the tables and see the changes

[thambu19]

Originally Posted by Kodename47

Are you logging PI/DI injection volumes or PW at all? The only reason I ask is that I tested something the other day with 25% PI ratio through the whole of the table (SC car so more volume) and the PIs weren't actually used until quite late and mid/late load. I'm guessing down to minimum volume or PW parameters so something else. I've got more testing to do, I'm trialing an easy way to get PI/DI error minimised without having to run fully PI or fully DI.

I agree that there must be benefits to PI with regards to the mixture benefits, but if you're saying that you didn't feel the dip then you'd see that on a dyno. However I know someone who says that they tested various ratios on a dyno and found little to no benefit from changing them. You really need to test not just the different ratios but the extra ignition timing it allows you to put in as a result.

Calibrating engines day in and day out at work (both dyno and vehicle) I can say one thing. It is extremely hard to verify changes accurately on the road unless you have dynamic calibration where you can change on the fly and feel the difference right away.

If it was my car I would not bother so much about DI at loads that are not knock limited. There is not much to get out of DI other than VE improvement and some added spark. I have experimented with injection timing for PFI from 50deg before IVO to 150deg before IVO and found that the earlier I inject the better the 0-10percent burn and HC at the expense of NOX. Which says if I had gone DI my mixture preparation would have been weaker.

At WOT I would go 100% DI. There is no reason not to unless at the highest of speeds where the spark is almost close to MBT (maybe 10deg from MBT in most cases). Here you may want some PI to reduce the PW of DI since the injection time available is pretty short as the speed increases. 5.8ms in our engine. So here we trade some spark advance for better mixture preparation to eek out better burn.

At idle it is always debated. Companies go DI and it can help hot restart. With engines with high effective compression ratio will get into huge Pre Ignition during a hot restart. Going DI it allows companies to run lean mixture in the first few (1-5) cranking cycles to avoid pre-ignition during cranking. This fuel control is not possible with PFI during cranking.

In my opinion once engine is up and running PFI is better for mixture preparation but companies have to do tradeoffs all the time and stick with one method and in the case of FA20 it is DI I believe.

Did the car come with PI during first cal release and then later get changed to DI? Or was it always DI during start and idling?

[ztan]

Originally Posted by thambu19

Going DI it allows companies to run lean mixture in the first few (1-5) cranking cycles to avoid pre-ignition during cranking. This fuel control is not possible with PFI during cranking.

In my opinion once engine is up and running PFI is better for mixture preparation but companies have to do tradeoffs all the time and stick with one method and in the case of FA20 it is DI I believe.

Did the car come with PI during first cal release and then later get changed to DI? Or was it always DI during start and idling?

Interesting. My calibration is A01G. First second of cranking is full PI, then DI gets added, full DI after around 6-8 seconds. Are later calibrations starting up with DI?

[thambu19]

Originally Posted by ztan

Interesting. My calibration is A01G. First second of cranking is full PI, then DI gets added, full DI after around 6-8 seconds. Are later calibrations starting up with DI?

As I mentioned it will depend on the dynamic compression ratio of the engine during cranking. Almost all engines with VVT go to their end stop positions when no cam dutycycle is applied. Most have a pin to keep them in place. When the cams are at this position the Dynamic compression they create is important.

Most Intake cams are locked at their most retarded position and most exhaust cams are at their most advanced position. I believe this is the safe position for most OEMs. A compression ratio of 5:1 is safe for a hot restart (the incylinder air temperature gets extremely hot in a minute of not running). When the engine is re-started the throttle cannot keep the load under 0.3g/rev because the manifold is at ambient pressure with the engine not running. This means during the first few revolutions the engine is seeing 100% VE (not really because intake cams close late into intake stroke) causing pre-ignition.

Ways around it is to delay fueling by a couple of cranking rpm so allow the hot air to be passed through the cylinder or going lean on the first few pulses.

This is more important on stop start engines and less of an issue with key start since the start quality is less of an issue with normal key start. I mean people do not care of the rpm flare up during a normal key start but dont want their engine to roar into life on a stop start event.

If toyota uses the option to not fire fuel in the first couple of cranking pulses then PFI would work. It will also work if their ECR is 5 thereabouts.

OEMs with pure DI will go for two injections with the second injection just before ignition. This way they can retard spark and get a CAT light off during cold starts. During hot starts this isnt a problem anymore and no real need for DI in my opinion. The thing is we dont know how many levels of strategies exist in the Toyota code. If they just want one strategy across all operating conditions they would choose one option vs if they had a cold strategy vs a hot strategy option