Success with AEM O2 feedback?
06-26-2010, 05:12 AM
#11
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Originally Posted by maluch,Jun 25 2010, 10:15 PM
AT 8000 rpms the aem unit reads the AFR every 8 revolutions, which to me seems sufficient enough to use at wot...why do you think they are too slow.
06-26-2010, 10:19 AM
#12
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time to process is not an issue...if the computer is fast enough to control the engine at high rpms then it is fast enough for this operation.
the determining variables here are the rate of change of the engine speed and the time that it takes exhaust gases to make it from the cylinder to the 02 sensor.
if considering the first two gears on an engine with a redline of 8400 and a zero to 60 of 6 seconds. the average time passed for rpms to increase by 1 is 0.00037 seconds. this is the average so of course the maximums will be higher. 3rd, 4th and so on gears will be slower.
as for gas velocity, at ambient temperature of 20 C, exhaust temp of 700 C and pipe diameter of 50 mm, the velocity of the gases will be 98676 cm/sec @ 8000 rpms
using these numbers this is how the operation would go at 8k rpms wot:
time 0: combustion event
time 0.0010 s: exhaust gas makes it to the o2 sensor and afr reading occurs, computer is ready to make a correction for next revolution
time 0.0010 + 0.00037s: the engine makes correction, the rpms have increased by 2.668=8002.66rpms
looking at the numbers o2 fb should work at WOT
event if you are making crazy power and your rpms increase from 8000 to 8050(what i think is unlikely) it should still work.
empirically it has worked for me, but my engine is not yet fully tapped. i will see how it responds to o2 feedback when i am running 13.4 or higher at WOT.
the determining variables here are the rate of change of the engine speed and the time that it takes exhaust gases to make it from the cylinder to the 02 sensor.
if considering the first two gears on an engine with a redline of 8400 and a zero to 60 of 6 seconds. the average time passed for rpms to increase by 1 is 0.00037 seconds. this is the average so of course the maximums will be higher. 3rd, 4th and so on gears will be slower.
as for gas velocity, at ambient temperature of 20 C, exhaust temp of 700 C and pipe diameter of 50 mm, the velocity of the gases will be 98676 cm/sec @ 8000 rpms
using these numbers this is how the operation would go at 8k rpms wot:
time 0: combustion event
time 0.0010 s: exhaust gas makes it to the o2 sensor and afr reading occurs, computer is ready to make a correction for next revolution
time 0.0010 + 0.00037s: the engine makes correction, the rpms have increased by 2.668=8002.66rpms
looking at the numbers o2 fb should work at WOT
event if you are making crazy power and your rpms increase from 8000 to 8050(what i think is unlikely) it should still work.
empirically it has worked for me, but my engine is not yet fully tapped. i will see how it responds to o2 feedback when i am running 13.4 or higher at WOT.
06-28-2010, 06:34 PM
#14
Absolutely. It's easy to see a delay on logs between the fuel map and the O2 reading in lower gears or with fast acceleration. In higher gears or with slower ramp rates, the AFR and RPM tend to line up. The thing to remember is that it takes time for the O2 sensor to actually sense the change in the exhaust gasses. It does not react as quickly as the electronics it is connected with.
Tim
Tim
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