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Old 03-11-2016, 11:06 PM   #1
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Is Port Injection more important when boosted?

I had already settled on a set PI to DI table for my tune, but I wanted to make a small change to reduce some excessive fuel trims. I made 2 tunes, one with more PI, and the other with less PI than the original tune. I wanted to try both to see which one would reduce my fuel trims. Turns out they made the engine run very differently.
My theory is that since I am slightly boosted with a Phantom SC, part of the DI charge is getting blown through without getting burned, while the PI charge is actually burning more completely, since it isn't getting blown out.
What I'd like to know is, have any other tuners out there altered their PI/DI tables to keep more charge in the cylinders under boost?
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Old 03-11-2016, 11:23 PM   #2
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You seem to have awesome theories.
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Old 03-12-2016, 12:10 AM   #3
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Try it yourself. Make 2 tunes with radically different PI/DI tables and drive it. It's the same amount of fuel, but it runs very different. It gets different MPG too!
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Old 03-12-2016, 05:27 AM   #4
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Originally Posted by KoolBRZ View Post
Turns out they made the engine run very differently.
Correct

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Originally Posted by KoolBRZ View Post
My theory is that since I am slightly boosted with a Phantom SC, part of the DI charge is getting blown through without getting burned, while the PI charge is actually burning more completely, since it isn't getting blown out.
Think about this for a second, you're saying fuel injected directly into the cylinder is more likely to be blown out the exhaust than that injected into the port charge?

The complex answer is that you need to consider AVCS and DI timing more so than just ratios. DI requires time to mix well in the cylinder, adding PI will help the mixing. You need to run more ignition advance to get DI to produce the same power apparently due to this. If the DI SOI is while the exhaust valve is open then you run risk of unused fuel being lost but the same is the case for PI for any overlap.
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Old 03-12-2016, 05:57 AM   #5
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Try it yourself. Make 2 tunes with radically different PI/DI tables and drive it. It's the same amount of fuel, but it runs very different. It gets different MPG too!
Yes, I know.
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Old 03-12-2016, 01:46 PM   #6
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Quote:
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Correct


Think about this for a second, you're saying fuel injected directly into the cylinder is more likely to be blown out the exhaust than that injected into the port charge?

The complex answer is that you need to consider AVCS and DI timing more so than just ratios. DI requires time to mix well in the cylinder, adding PI will help the mixing. You need to run more ignition advance to get DI to produce the same power apparently due to this. If the DI SOI is while the exhaust valve is open then you run risk of unused fuel being lost but the same is the case for PI for any overlap.
It also gets noticeably higher MPG with more PI than DI, but only under 3000 rpms. Over 3000 rpms mileage drops dramatically with more PI than DI, and this is all with an IAM of 1, so it isn't because it's pulling timing. I've developed a revised PI/DI table, with a higher percentage of PI in the engine load ranges where I spend most of my time driving. I also tried using less PI, but it was less powerful and less economical. I believe the AVCS tables have to be set first, then PI/DI, then MAF Comp, and then Base Timing B. As soon as I have this mastered I'll start all over with E85.
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Old 03-12-2016, 02:30 PM   #7
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I also tried using less PI, but it was less powerful and less economical.
Very possibly because you didn't change ignition timing to suit,you need to change the timing strategy to improve the burn. There's a reason there are DI only cars out there and they get great economy.

Don't forget the PI ratio thresholds in play.
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Old 03-12-2016, 09:24 PM   #8
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Quote:
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Very possibly because you didn't change ignition timing to suit,you need to change the timing strategy to improve the burn. There's a reason there are DI only cars out there and they get great economy.

Don't forget the PI ratio thresholds in play.
I still have the stock PI ratio thresholds. I'm trying several other PI/DI tables as well as this one, which I will test at low rpms with high loads. I may need to rescale the tables for higher load conditions, so it will have some PI all the way to 4.0 load. On the other PI/DI thread there is quite a lot of information by experienced tuners, but nothing recommending more PI under boost conditions. Since boost is usually above 3000 rpms, I'm trying to limit my PI to about 2400 rpms. The thresholds means that it will get 0% PI from 1.2 - 1.5 load, but from 1.5 on up to 4.0 load it will get 20% PI. I'm not sure how well it will run at 1.3 and 1.4 load without any PI, that's why I might need to rescale the table.
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Old 03-13-2016, 09:48 PM   #9
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I still have the stock PI ratio thresholds. I'm trying several other PI/DI tables as well as this one, which I will test at low rpms with high loads. I may need to rescale the tables for higher load conditions, so it will have some PI all the way to 4.0 load. On the other PI/DI thread there is quite a lot of information by experienced tuners, but nothing recommending more PI under boost conditions. Since boost is usually above 3000 rpms, I'm trying to limit my PI to about 2400 rpms. The thresholds means that it will get 0% PI from 1.2 - 1.5 load, but from 1.5 on up to 4.0 load it will get 20% PI. I'm not sure how well it will run at 1.3 and 1.4 load without any PI, that's why I might need to rescale the table.
From my understanding decreasing the 35% threshold to <=20% will give you exactly what you want without editing the axes.
20% PI from 1.20 load and up (since 0.203 > 0.20 it's above the threshold)
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Old 03-13-2016, 10:10 PM   #10
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Port Injection: The 20% solution

I'm going to quote @moto-mike from this post http://www.ft86club.com/forums/showp...2&postcount=17
where he says
" We've seen some tuners swear by DI only, and others use 50/50 split or even full on PI in really high HP applications. I don't think either one is a good solution.

Think of it this way: DI fuel delivery will always be the optimal method, UNTIL you make the mixture too unstable or wash the cylinders. Wash is unlikely, but once you approach 7ms injection times (250+whp with e85) you begin to lose some of that benefit. The mixture becomes less stable. Between about 300whp you cross over the threshold where 35% PI has no negative effect. 20% PI on OEM tunes? We have found absolutely no repeatable HP gains, as in 0, like none-what-so-ever. Despite changes in timing, leaner or richer, more or less aggressive cam timing, or different injection timings...I think one car actually made 1hp over 20% PI mix...which is within the margin of error between runs.

So in reality, there's just no reason to overstress the DI system with long IPWs. Take advantage of the dual injection, max out the DI to about 6 ms (this way in sub freezing temperatures you have headroom) and then run port at no more than 80% duty cycle, or about 15ms."

I'm trying to create the best table WITHOUT modifying the PI ratio thresholds, because I haven't got the code to make that change for any other CAL ID besides my own. That means I have to stay >=35% PI below 5000 rpms and 1.5 engine load. I made a table where PI should always be on, and I re-scaled it to go to 4.0 Engine Load, see below. I tried it and found the acceleration above 1.0 load to be really good. I'm going to try reducing the PI percentage in the areas below 2800 rpms, and below 1.0 load to get the best power and drive-ability. This has proven that 20% PI at heavy loads performs well, the only questions are; where do I want to exceed 20% for better torque at low rpms, and how much at what loads.
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Old 03-13-2016, 10:42 PM   #11
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New table trials

I'm going to try the following tables to see how they work. PI is always on in all of the tables, even with the stock PI ratio thresholds.
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Old 03-13-2016, 10:55 PM   #12
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AFAIK people going higher boost fi change only the port injectorsto larger flow rate, as that seems to be the only option available

hence they are forced to alter the pi\di tables so as not to max out the di injectors and rely more heavily on the port injection to supply the required fueling throughout the mid and upper rpm ranges.

hence they have no option to run large amounts or exclusivly on di, so while use pi a lot more its more out of necessity, rarther than the best option possibly.
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Old 03-14-2016, 04:23 AM   #13
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DI gives you charge cooling in cylinder and therefore better knock resistance if you have good mixture. I tend to run higher amounts of DI in transitional areas for this reason. I think this is more what you need to concentrate on than feel. Changing the ratios only and then feeling the difference is no different to just changing the fuel map with no changes to anything else.... it's part of a bigger system, you're being too short sighted. Why not run 100% PI and only use DI when you need, it'd probably feel awesome.

Also, I have posted the thresholds for most of the modern calibrations. It's quite easy to find them on other cals to.
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Old 03-14-2016, 05:38 AM   #14
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Um, if adjusting the PI to DI ratios is throwing off your fuel trims, then you have an injector scaling problem and your tune is not correct. Going from 100% DI to 100% DI in any particular cell will not throw off fuel trims on properly calibrated injectors, or anywhere in between.

We fit larger port injectors to supply the additional fuel needed for boost because we have no direct injector replacements. The car overall will run much more smooth in low load on 100% DI especially when using larger port injectors. Running either set full time should not throw off your fuel trims any more than the other. If they do, your fueling is not tuned properly.

Touching on the info above me, I set up my car to run 100% DI up to .6 load. This will help the car run a lot better in load load situations (city driving) and transitional throttle situations. If you run 100% PI on large port injectors you may get some sputtering or hesitation when getting on and off the throttle, This is just because it takes longer for larger port injectors to supply low amounts of fuel than the stock direct injectors. Tip in can be tweaked to help but you really have no reason to run the port injectors under low load. Running 100% DI keeps things more cool as well on e85.
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