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Please explain: EMAP sensor, Exhaust Manifold Pressure Sensor

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It says: a) Running an Exhaust Manifold Pressure Sensor or EMAP sensor gives a unique insight into the dynamics of a running engine, especially one that is turbocharged.

b) Monitoring exhaust backpressure is one of the most useful things you can do on a turbocharged engine.

I don't get it in relation to cam timing, hmm, i really don't understand the whole concept of IMAP / EMAP calibration.

1) In my understanding this is only usable for calibration when both inlet and outlet valves are open? How and when do I use it?

2) Allows you to see how well your turbine housing/wheel is sized. How do I see? What is happening?

3) Allows you to monitor when the turbo is maxed out. How do I do? What is happening?

4) Efficiency of the motor (IMAP/EMAP). How do I know? What should happen here?

Thank you for clarifying, Olaf

Hi Olaf - when you say "It says" - what are you referring to? A course? A webinar? I'm just not exactly sure what you're referring to here..



I was searching for the use of EMAP sensors and found the statements above in the product descriptions. There are engine management systems that allows for IMAP/EMAP calibration but as I said I don't get the whole thing!

IMAP/EMAP is a load axis input that is offered by a few ECU manufacturers. What it looks at essentially is the pressure difference across the engine and this ratio is then used as the load input for the VE table. The idea is that the volumetric efficiency of the engine is dependent on this pressure ratio and hence it is potentially a superior load axis input when compared to the likes of MAP. In particular this load input in theory will do a better job of accounting for changes in barometric pressure. It's important to understand that IMAP is still the input used in the ideal gas law calculation that occurs in the background though - We're just changing the load axis.

IMAP/EMAP however does give a slightly unusual path through the VE table when compared to IMAP alone, as it's common for the EMAP to exceed the IMAP at higher rpm where the EMAP begins to climb sharply.

Separately we can use the EMAP data to give us some indication as to how well the turbine side of the turbocharger is sized to our application. Higher EMAP ratios aid boost response but the downside is that the turbocharger becomes restrictive at high rpm. It's common for example in drag racing applications to see the EMAP less than IMAP.

Check this webinar for some more information -

Thank you Andre for explaining. I really would like to have some real data to see the different pressures and the IMAP/EMAP ratio. Olaf

Hi Olaf, here's a screen shot of some logging from our 86 on the dyno. You can see the relationship between IMAP and EMAP throughout the rev range. I hope this helps.

Attached Files

Hello to everyone, can someone give some detalis about emap pulse attenuator device? Thanks!

The damper we're using is made by T1 Race in the US. We have a universal setup which I can't find on their website but they do ahve their R35 GTR specific kit. Xenocron have a similar product here:

It`s all clear now, thanks!