SNS does affect boost in open loop mode but not in closed loop mode. SNS is used to estimate the initial WG% required when going from low throttle to high throttle (open loop mode) but boost regulation (closed loop mode) is controlled by other parameters. Closed loop mode will never begin unless the open loop mode first gets the boost up fairly near the desired target. Too little SNS will prevent the boost from ever getting high enough for closed loop mode to start while too much SNS will cause the turbo's rpm to get too high while the boost is rising initially resulting in uncontrollable overshoot. Adjustments are easiest to estimate when they're based on log data collected in a high gear or while going up a substantial hill so that engine rpm isn't changing very fast. And don't get anal about preventing overshoot entirely because A) it isn't possible with this type of control system and B) brief overshoot to as high as 19-20 psi for less than 2 seconds produces no ill effects as long as fueling can keep up with it. When boost levels stay too high for more than about 2 seconds then the head temperature (specifically the surface of the combustion chamber) starts to rise and increases the likelihood of knock.
----- Original Message ----- From: "Rob Ebersol" <[EMAIL PROTECTED]> To: "Ray Ayala" <[EMAIL PROTECTED]> Cc: "Miata Power List" <[email protected]> Sent: Friday, June 20, 2008 11:41 AM Subject: Re: boost control >I was in the process of finding a proper WG SNS value. The manual actually >says to find WG SNS based on boost target (page 18): > > " A value of WG SNS needs to be found that allows the boost to rise up to > BOOST TGT without overshooting. If the boost fails to reach BOOST TGT, > raise WG SNS. If the boost pressure goes past BOOST TGT, stop > accelerating and lower WG SNS." > > Therefore since my first WG SNS value of 44 surpassed the target, I > dropped it to 42 and lost all boost control activity. Then I raised it to > 43 and no boost control, and then back to 44 and no boost control. Is > that not odd? And depower/repowering still shows the proper stored values > in the ecu. > > Or am I not understanding that properly? > > I have lots of logs- will get to them on the pc shortly. > > thanks, rob > > > On Jun 20, 2008, at 2:11 PM, Ray Ayala wrote: > >> And FWIW SNS should be based on your turbo, not on your boost target. >> The Link manual describes how to determine the SNS setting, and that >> needs to be done before the other adjustments are set up. > _______________________________________________ Miatapower mailing list [email protected] http://list.miatapower.net/cgi-bin/mailman/listinfo/miatapower
