Date: Mon, 13 Jan 2003 18:18:58 GMT From: Paul Halliday <pjghnopsamyonder.co.uk> Subject: Re: 9-5 Aero Raves & Rants (mostly rants)
in article Xns9301A5B184052fritzfriicomnopsam17.128.40, Gary Fritz at fritzxxxnopsamrii.com wrote on 12/01/2003 23:17: > Paul Halliday wrote: >>> It does sound very laggy doesn't it? The C900 turbos I've owned have >>> been very responsive. The turbo spins up as the revs climb and boosts >>> when you want it. It could be controlled a little for better boost on >>> well timed manoeuvres by holding in the broken white zone on the >>> gauge briefly before letting it go. > > I haven't figured out any way to do that on the Aero. Any time I'm not > actively accelerating, the turbo gauge returns back to its "rest state." > > Johannes H Andersen <johsnopsamsizefitterzzzz.com> wrote: >> I think the wastegate is on the exhaust side, so it doesn't help >> keeping the turbo spinning. AFAIK, there is also a valve on the inlet >> side that bypass the turbo, that is more interesting as it lets the >> turbo spin when off power. I'm sure there is someone out there who >> knows a lot more than I do, so I'm not going to stick my neck out - >> very far. > > Supposedly the stock Bosch diverter valve is slow, and somewhat fragile, > and I've been told a better diverter valve (like that Hyperboost at > http://www.stratmosphere.com/hyperboost.htm) can really improve things. > I'm seriously considering it. For the classic 900 APC unit, the theory goes that if the F pot (top boost) is increased with the P pot (controlling the default wastegate cycle), the spool up will be more sharp with a potential for over-boost. I'm thinking that if the top boost is controlled with a down tune, the spool up will also be more controlled. You need to look at it on a graph with RPM vs PSI and it will make sense. The other way would be to screw in/out? the wastegate slightly, but I'm not sure what each turn represents in terms of PSI for the 9-5. If gate is wasting, say, 5% at low/no pressure (95% closed) and then open at full pressure, screwing it in/out? will make the default waste a little higher. If it wastes more at rest, the boost curve will no doubt be more comfortable since it will fully open more quickly, with less top pressure. Help - we need turbo actualists, rather than theorists :) With your car Gary (which I gather is the same on other 9-5s), it looks like Saab have adjusted the turbo to prevent it spinning up with gentle rev climbs and only really blows when aggressively driving. That'll be the reason for the lag. Do you get a boost gauge with the 9-5 Aero? I presume that's how you know when it returns to a "rest state" as you put it. The classic 900s (forgive me, I've not driven a GM 900) climbed up the white zone with the revs as default - I take it the 9-5 Aero doesn't; it just boosts when you're "trolleying" it. If the ECU is a totally closed unit with no tinkering possibilities, I think the wastegate tweak might be the only solution, but with a loss of top power. I'll "make like a Johannes" and bow out to the greater knowledge of our peers. Paul 1985 900i 16V 1989 900 Turbo S http://pjgh.go.dyndns.org/saab/index.html
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