Boost question: I've seen 22-24 as a decent max, but is that a fueling or turbo wear limit?
07-20-2007, 07:59 AM
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Boost question: I've seen 22-24 as a decent max, but is that a fueling or turbo wear limit?
My question is, working on a homebrew setup here in Colorado (6000' elevation) and even with smallish 37# injectors at 23/24 psi we're logging about 50% duty cycle. (and I'm getting rich codes) There just isn't much air up here.
I'm happy with the performance, but the question I have is more boost considered bad mostly from a turbo longevity standpoint? Is the base engine under too much strain with more pressure? Or for most places is it a case of getting adaquate fueling?
I'm happy with the performance, but the question I have is more boost considered bad mostly from a turbo longevity standpoint? Is the base engine under too much strain with more pressure? Or for most places is it a case of getting adaquate fueling?
07-20-2007, 09:14 AM
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On my Mini CS there was only so much boost the SC would run before temp/resistance would cancel gain
Is it something like that? Would it generate so much heat at 30 psi that you would loose more HP than you would gain?
07-20-2007, 09:39 AM
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Using that as an extreme example, but 23 is about the magic number I guess. One more...
Keep in mind this is all hypothetical for the purposes of helping educate myself.
If the efficency is mostly temp based, would the "optimal" number change depending on ambient temps. Say 20psi on a 100 degree day and 25psi on a day in the 20's?
If the efficency is mostly temp based, would the "optimal" number change depending on ambient temps. Say 20psi on a 100 degree day and 25psi on a day in the 20's?
07-20-2007, 09:52 AM
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well, here's your car on the efficiency map running 20psi.
<img src="http://pictureposter.audiworld.com/77913/chuckk04map.jpg">
Do a little math, and you can make your own calculations. I suck at math, so am not even going to try and do it.
Do a little math, and you can make your own calculations. I suck at math, so am not even going to try and do it.
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07-20-2007, 10:03 AM
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OK, I'm not even close to ready for that! Any more tips? Is gp/s & PSI all you need...
to calculate the point at which more pressure fails to make more power? That would be cool to know how to calculate, but I wouldn't know where to start.
If there IS an obvious point where you've maxed power with boost then it would be great to know. Then when you make a change (like a monster DUH IC) you could increase presure and recheck calculations.
It sounds like I've pretty much just described custom tuning, but is that efficiency calculation (whatever it is!) the key to the whole thing for our cars? Obviously you would need to dial in fuel trims and adjust timing but figuring out optimal boost settings seems like a big part of the puzzle.
If there IS an obvious point where you've maxed power with boost then it would be great to know. Then when you make a change (like a monster DUH IC) you could increase presure and recheck calculations.
It sounds like I've pretty much just described custom tuning, but is that efficiency calculation (whatever it is!) the key to the whole thing for our cars? Obviously you would need to dial in fuel trims and adjust timing but figuring out optimal boost settings seems like a big part of the puzzle.
07-20-2007, 10:16 AM
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The equations underlying that chart are a swag, and the volumetric
airflow value is highly suspect, since it is taking the MAF at face value.
I've tried taking the stock MAF reading and comparing it to what it should be based on MAP, IAT, RPM, engine displacement, and VE inputs. The only way I could get them the same was to assume that at near peak TQ the VE was ~50%, which seems exceptionally unlikely.
I've tried taking the stock MAF reading and comparing it to what it should be based on MAP, IAT, RPM, engine displacement, and VE inputs. The only way I could get them the same was to assume that at near peak TQ the VE was ~50%, which seems exceptionally unlikely.