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  1. #1
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    Pump gas tuning fun

    I remember long ago mentioning this to Cobb or somebody and they thought I was nuts. But I still think I would prefer hacked firmware that resulted in the throttle just following my foot and boost target just being a set number rather than targeting load.

    So I get my low boost ACN91 working pretty well but I notice that even though I have the load/boost doing what I want when the air charge stays at a constant temp, the boost is climbing as I heat up the air more on a long pull. This makes sense when the system is working right because when you target load, the boost has to go up to increase the density to make up for the density decrease due to temperature increase. But with really picky pump gas you go from no knock when things are cold to lots of knock when things are hot because the boost keeps going up.

    Of course "there are tables for that". So if you do the obvious thing and pull load as the air charge gets hotter that helps...but then your timing is trying to go up and you still get knock. But wait, there's a table for that too :-). Anyway, it just starts to seem ridiculous when you could get much more consistent results in much less time with a ball and spring boost controller.

    I'll get it where I want it...but just wanted to complain for a minute. It does look like there are still a couple of things that don't yet have different options in the flex fuel section that would ideally have them in order to not have low boost changes affect the E85 tune at all. It's still nice having turbos that do what I tell them to do, though. The response of the GC Lites is impressive.

  2. #2
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    If you want to start playing with everything you'll want a Syvecs...
    Three sets of brand new 991.2 3.0 headers for sale: Kline, Fabspeed, and Vektor Ceramic Coated

    IPD plenum for Porsche 991.2 3.0 for sale: $650

  3. #3
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    I'm sure you're right, but I'm the kind of guy that likes to stop just short of that and keep things at a point where a dealer can still look at it and not refuse to work on it. I'm really loving the easy flex fuel and the wireless OBD2 connection. I've almost got ACN91 where I want it (ignoring that I thought I'd have more power than the 425ish peak crank horsepower that I'd guess I'm at at ~15psi or so) and will go to low boost straight E85 next as soon as I'm done getting the airbag recall done at the dealership and work on those maps a little before I go back to mix for max power.

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    You can use the Load Limit Factor table to reduce the load based on IAT. Besides that DME will compensate ambient air pressure (there is a table to adjust load accordingly) and there is a lot of other crazy calculations going on. Getting boost to your desired target in all conditions is more or less impossible, but you should be able to keep it on target most of the time.

  5. #5
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    Yeah, I'm using the "Load Target Limit Factor (Charge Air Temp)" table to avoid having the boost rise with heat. I'm also derating the timing pretty early as the temperatures rise as well to compensate for the timing rising as the load is reduced. But I still think it would be easier to just target boost instead of load.

    But I can see from this experimentation that with straight ACN91 I should consider a cold air intake. I start a long pull at 70F and end up at over 100F by 4th gear. With an ethanol mix I don't need to pull any timing and the hotter air is no big deal. But power falls off pretty fast on pump as I pull out boost AND timing. Summer is going to be bad.

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