Re: about a/f ratio - Saab Performance Bulletin Board - Saabnet.com
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Re: about a/f ratio
Posted by Vigge [Email] (more from Vigge) on Sun, 29 Feb 2004 09:12:55
In Reply to: about a/f ratio, Steve88SiS, Sun, 29 Feb 2004 08:31:38
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I'am not sure what exactly causes this but this was the case with my viggen right after IC swap last week.
I dynoed the car with std IC and right after with the new IC (link below).
Mixtures went leaner with the new IC.
If we look at the situation under WOT with before and after.
ECU request a airmass of quntity X, turbo control makes sure that the boost is so high that this quantity is achieved.
After std IC we have boost b and temp t
with new IC (assumed to be better) boost b-something temp t-something
As the engine rotates same quantity of airmass should be drawn into the engine regardless of temp/boost ratio in the intake manifold.
I think here is what causes the problem, new IC will flow much much better.
Std viggen ic will flow 100 or so Cfm (10psi 1psi drop) and a good aftermarket over 400.
This will cause a situation where boost with the new IC is closer to that of what's in turbine. I let my self know that there is no way for the ECU to predict this. The only way is to adjust the boost level slightly lower based on MAP and intake temp values. This happens with delay.
If this is the mechanism you should be able to see it with TECH.
There is a ratio that can be read, actual airmass/calculated airmass. Usually the calculated should follow the actual in slight delay.
Now there should be a bigger deviation at first.
I would also be interested of hearing if this is how it happens or not. I only know for sure what a wideband lambda showed for my car.
posted by 195.237.1...
http://195.237.18.37/viggen/IC
Posts in this Thread:
- Installed spearco IC on Viggen today, Steve88SiS, Sat, 28 Feb 2004 21:41:29
- Total cost?, Jeff in ATL, Sun, 29 Feb 2004 08:30:35
- Don't understand this...., zeke, Sun, 29 Feb 2004 06:06:52
- yep, you're right, Steve88SiS, Sun, 29 Feb 2004 08:33:53
- Re: Don't understand this...., Vigge, Sun, 29 Feb 2004 06:56:46
- I reset ecu, results, pics, Steve88SiS, Sun, 29 Feb 2004 11:15:35
- Re: Don't understand this...., Dean, Sun, 29 Feb 2004 09:30:09
- about a/f ratio, Steve88SiS, Sun, 29 Feb 2004 08:31:38
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