cold weather effects! and more (long) - Saab NG900 & OG9-3 Bulletin Board - Saabnet.com
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cold weather effects! and more (long)
Posted by Dean (more from Dean) on Tue, 16 Oct 2001 09:55:22
In Reply to: you got plenty more..., jayz, Mon, 15 Oct 2001 20:20:33
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For those who don't know already...
With cold air the turbo is so responsive that the boost pressure will overshoot its set point and hit the fuel cut. So I think that everyone will need to be making seasonal adjustments to deal with this.
I have a couple of workarounds in mind. One to increase the rate of rise of the pressure applied to the wastegate actuator to try to make it as fast as the cold weather boost rate of rise. This may help. Not tried yet.
The other would be to fit a pop-off valve to vent the 'pressure spikes'. This would need to be inexpensive and easy to 'bolt on'.
The pressure tap at the compressor housing provides some reduction of the spiking but at the expense of having high rpm boost pressure droop. Other locations can provide better high rpm performance but this creates pressure overshoots that are a greater problem. When you tune the MBC to avoid the fuel cuts, you then are tuning to the spikes and the steady state boost is then lower. So there are some definate issues. Not a perfect solution but definately better than running stock.
Shorter hose lengths are always best to reduce pressure overshoots. But that is only consistant with the pressure tap at the compressor housing. Longer hose lengths with other locations are then adding two compounding effects that create overshoots. Shorter hoses also lead to more manifold burns! :)
posted by 207.43.19...
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