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Webinar 92 AEM sensor

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At the start of your talked about the AEM exhaust pressure transducer did you ever do any logging with it if so is it possible to see the data, I am interested to see if it can pick up the pressure pulses as the exhaust valve opens. Trying to see if there is a vacuum before it closes.

Yes I've got some data however not with me unfortunately. I'll post when I can but to answer your question - No unfortunately.

These sensors are a relatively low cost sensor that at best wouldn't offer the kind of speed or precision you'd need to accurately track the changes in exhaust pressure pulses that you're interested in. Even if the sensor was up to the task I can't log it fast enough to be useful. I'm limited to 500 Hz through the CDL3 which sounds like a lot, however at 7000 rpm that would only be one sample every 84 degrees of crankshaft rotation (assuming the sensor could even operate at this sort of speed). For that sort of work you'd most likely need to invest in the high end in-cylinder pressure transducers which are designed for this sort of purpose and can log at appropriate speed to register the sort of detail you're interested in.

That being said the exhaust pressure signal is inherently very noisy and to get a useable trace for my purposes we've had to mechanically dampen the sensor.

Hi Andre,

You would be surprised what you can get, I have got data from a Link MAF sensor at 25 hz and it sort of followed the same profile as the data I got from a Pressure transducer logged at 1,000 hz.

My personal opinion is that the thing we see as noise is the highs and lows of the reading or that is what happened with the MAP. You can also hold a constant speed then estimate were TDC is overlay a couple of firing events and you end up with a pressure curve.

My work on intakes has surprised me as to how much the peak vacuum is. The attachment with most red is the 1,000 hz and the other is the Link Map Sensor.

Thanks Keep well, love the courses.


Attached Files
  • Manifold-pressure-against-Long-acceleration2.jpg
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  • MAP-Sensor-plugged-into-manifold-at-pressure-reg-location.jpg
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

There's a range of sensors we commonly use in the aftermarket for pressure sensing and for me the honeywell range is my sensor of choice. As an example the honeywell data sheet lists their response time as 2ms which suggests that they are able to provide accurate data 500 times per second. I don't doubt that the sensors produce data when logged at 1000 Hz, and yes I'd agree that most likely the data may approximate what's actually happening. I've logged a 150 psi honeywell fuel pressure sensor at 1000 Hz through our M150 and I've seen what it produces however I wouldn't stake my reputation on the data being 100% accurate at that rate. The bigger problem though as stated is that even 1000 Hz really isn't high enough to see how the pressure changes through the engine cycle - You're only getting a glimpse every 40 odd degrees of crank rotation. As a comparison the Plex combustion monitor (just to give one relevant example) provides resolution of 1 crankshaft degree up to 11,500 rpm which requires a logging rate of 70 kHz.

Obviously it all depends what you want to do with the data and in turn this will define what accuracy and frequency of data you require.

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