Hmmm, this is all very interesting. As I mentioned before, I have never noticed a seasonal difference in my peak boost before. From my understanding of the S4 ECU, there should indeed be no difference because it uses the MAP sensor in closed loop control. That's why I am always saying that upgrading the air filter should make no difference.
However I am interested in how everyone is reading their boost. Mine is with an electronic sensor mounted in the 'mid-bulkhead' area to the right of the battery. So my air pipe is 25cm long at the most.
If other people are using mechanical guages mounted on or near the dash, then their air pipes could be 1m long or even longer. If so then I would expect that ambient air temperature would have an effect on the reading???
Just a thought.
Anyway, I logged my MAF on the way home. Trouble is there were a lot of cars getting in the way so I didn't get the runs that I needed. So when I got home I found that my peak MAF was only 237.39 g/s, because my max. engine revs only reached 4920!
I decided to check my previous logs. Indeed I found my previous peak of 280.83 g/s was at 6640 rpm.
Here's a wierd thing: On that same previous plot I found a reading of 237.39 g/s at 4920 rpm...
Slight loss of peak boost
Dippy,
Quite good values.
220-230 ish is std car, 260-280 chipped.
280 G/S is a good figure. I think all MAFs top out around 290 G/S. Guestimate is max "MAF x 1.2" =@ 336 Bhp BHP. Quite high RPMs but with good exhaust quite possible. On k03s mine peaked at 5800 RPM @ 270 G/S with Hitachi MAF.
At WOT, uses throttle postion, MAF, IAT, Ambient temp and O2 values, in an "adjusted" MAP mode (approx 12.5:1 fuel ratio).
When MAF isn't available car runs in MAP mode. This is why after unplugging MAF car still runs OK, sometimes better as MAF values are discarded.
Quite good values.
220-230 ish is std car, 260-280 chipped.
280 G/S is a good figure. I think all MAFs top out around 290 G/S. Guestimate is max "MAF x 1.2" =@ 336 Bhp BHP. Quite high RPMs but with good exhaust quite possible. On k03s mine peaked at 5800 RPM @ 270 G/S with Hitachi MAF.
S4 uses O2 and MAF values in closed loop, attempting stoich or 14.7:1 fuel ratio, when cruising.RE: there should indeed be no difference because it uses the MAP sensor in closed loop control.
At WOT, uses throttle postion, MAF, IAT, Ambient temp and O2 values, in an "adjusted" MAP mode (approx 12.5:1 fuel ratio).
When MAF isn't available car runs in MAP mode. This is why after unplugging MAF car still runs OK, sometimes better as MAF values are discarded.
99 Ming Saloon, Tanoga S/S, De-cat APR D/Ps, Miltek catback, Forge DVs, RS4 suspension, K04s, I/Cs, MAF, Clutch, injectors, oil cooler, airbox, Y pipe, spark plugs, front brakes, Vast EFK, Walbro fuel pump, MRC custom tune, 18" B7 RS4 reps, Kumho tyres
KayGee,
Your signature implies that you're still running OEM cats, or maybe you have no cats?
Anyway it was clear that the Miltek full system made the car breathe so much better at the top end, so indeed that must be why I got 280.
What I was referring to about MAP was that the ECU knows what the boost is, so in UKS4APR1's winter case, if demanded boost was around 1.4bar (assuming that's the case with his map) but measured was only 1.0 bar then as a minimum the ECU would raise a DTC, but may even initiate limp mode!
Anyway, as I noted, I have never before noticed a cold/hot variation in my peak boost. I do regular peak boost checks just to monitor the 'health' of the engine, so I'm sure I would have noticed!
Your signature implies that you're still running OEM cats, or maybe you have no cats?
Anyway it was clear that the Miltek full system made the car breathe so much better at the top end, so indeed that must be why I got 280.
What I was referring to about MAP was that the ECU knows what the boost is, so in UKS4APR1's winter case, if demanded boost was around 1.4bar (assuming that's the case with his map) but measured was only 1.0 bar then as a minimum the ECU would raise a DTC, but may even initiate limp mode!
Anyway, as I noted, I have never before noticed a cold/hot variation in my peak boost. I do regular peak boost checks just to monitor the 'health' of the engine, so I'm sure I would have noticed!
2001 Silver S4 Avant
AmD remap, APR R1 DVs, APR bipipe, Full Miltek exhaust
H&R coilovers, AWE DTS, Porsche front brakes, Short-shifter, 18" RS4 replicas
Defi-HUD boost gauge / turbo-timer (with afterrun pump modification), Phatbox
AmD remap, APR R1 DVs, APR bipipe, Full Miltek exhaust
H&R coilovers, AWE DTS, Porsche front brakes, Short-shifter, 18" RS4 replicas
Defi-HUD boost gauge / turbo-timer (with afterrun pump modification), Phatbox
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