07-16-2014, 09:04 PM | #197 | |
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I essentially monitor Direct Injection Time Final and/or DI requested volume (the latter of which is only available in an unreleased RaceRom beta, so not much use to most folks). I'll then gradually bring down the PI ratio until i'm ~10-20% under what i consider to be a safe limit (1ml or 6.5ms depending on the param that i have access to). I used this technique on an NA tune last night and was able to make considerable horsepower up top in the most knock-proned area of the curve. With stock port ratios knock up there was an issue @ ~15-17whp over stock (can't remember the actual timing or AFR values, i'd have to look), and by the time i brought down the port ratio and added a couple other tricks we were at 29whp over stock with no knock in sight. something to consider trying if you're fighting knock above 6500rpm or so. On an NA car you'll never get close to any limitation, even with 0% port ratio across the board. Last edited by jamesm; 07-16-2014 at 09:15 PM. |
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07-17-2014, 03:46 AM | #198 |
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I'm sure I was once told that having more PI at the top end was beneficial as it allows for more aggressive timing, something to do with the DI firing angles/time being an issue.
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07-17-2014, 10:04 AM | #199 |
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DI gives WAY more charge cooling though, which also lets you run more timing. I imagine that in knock prone areas a colder charge is way more beneficial.
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07-17-2014, 11:15 AM | #200 |
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^ yep. i believe it's the charge cooling doing the trick, but it's definitely an observable phenomenon lol.
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07-17-2014, 11:46 AM | #201 | |
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07-17-2014, 12:03 PM | #202 |
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You won't reach MBT on pump gas... you'll always hit knock first. But yeah, you basically got the idea.
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07-17-2014, 12:14 PM | #203 | |
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07-17-2014, 12:35 PM | #204 |
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07-19-2014, 06:33 PM | #205 | |
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I'm still getting a bit of knock past 6300rpm with no modification to the Port to DI ratios. And my MAF scale with modified temp compensation runs really rich with cool IAT's and closer to 12.5:1 when IAT get hotter, in case you were wondering why it's so rich. I modified the MAF temp compensation to run with low amount of correction from 68f to 130+f IAT's in closed loop (1.1v ~ 2.8V maf volts). Open loop (2.8v ~ 4.2v)is not so ideal. http://datazap.me/u/solidone/maf68-1...-1036&mark=971 |
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07-19-2014, 07:11 PM | #206 |
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Well this thread answered my curiosity if Subaru still uses closed loop & open loop strategy. My last car was closed loop all the time.
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07-19-2014, 07:41 PM | #207 | |
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Temperature compensations are one of the many things that subaru engineers probably did better than we can. They just shouldn't need to be messed with IMHO, and i've never been in a situation where i had to. |
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07-19-2014, 08:06 PM | #208 | |
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Well, using the stock compensation table there was at least a +- 4~5% fuel trim variation in closed loop due to temperature in lower intake volume closed loop operation. I dialed in a maf scale at approximately 66~72f IAT's. When ran within that temp range fuel trim were below 2% in closed loop. Once the temperature gets higher the the fuel trim would change pretty proportionately to the amount of IAT increase leading me to believe the temp compensation needed to be adjusted. |
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07-19-2014, 08:30 PM | #209 | |
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As for the temperature comp, I suppose you could split hairs trying to adjust comps beyond their factory effectiveness at every possible temperature range, but it'd be a lot of work for little to no material benefit. I've never found a need to do any of that, and my customers don't have temperature-related drivability issues that I'm aware of. Principle of least intrusion is important. You'll save yourself a lot of trouble by minimizing the amount of opportunities you give it to arise. Only solve identifiable problems after they've been identified, in other words. The goal is better-than-stock drivability, not an arbitrary fueling error number. Just my .02. |
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07-21-2014, 09:29 AM | #210 |
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wondering does this maf scaling technique work for a blow thru FI like the JR kit?
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