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BMW m20 ms2 alpha N question

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I am currently building an bmw m20b20 engine for rallying (will eventually be forged, and high revving), currently have it running on some throttle bodies and an ms2pnp ecu. I’m running the itb mode, so a blend of map and throttle position. However, I’m about to throw a big cam in it, and I don’t really like the big mess of pipes needed to run the map sensor on itb mode and the idle control valve (one from each runner into a collector).

Can I bin all the map and idle pipe work, just run the map sensor and fuel pressure regulator to atmosphere and run on pure alpha n with the throttle blades sprightly cracked for idle?

or is the map signal from the engine needed for other parts of the ecu?

I don’t need to have particularly stable or low idle since it’s a rally car, and I would rather have a simpler, cleaner engine bay.

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Sure you can. But be aware when you set a trim table up for 10% more fuel. That will not always be the case as the fuel flow will be changing at idle vs WOT due to the changing differential pressure. Same with altitude variations, but to a lesser extent.

Personally, I would ditch the idle control plumbing (ignition idle control is sufficient for a race car), but keep the MAP plumbing -- and run that to the fuel pressure regulator. Hide the MAP plumbing on the bottom of the throttles.

Thanks for the reply David.

Surely I can just tune the fuel on a dyno using the wideband?

Obviously I can’t account for altitude, but since I live in the UK it’s not really a problem anyway.

however I can simulate part throttle, and full throttle conditions etc, and should therefore be able to tune out the differential pressure as such?

Anyone done this and managed without the MAP plumbing?

Yup, naturally aspirated ITB setups often do not have a MAP sensor and that can certainly work well.

I do require a baro sensor in these cases to account for atmospheric changes via compensation tables.

Would the now unused MAP sensor be able to cover this function then? Just referencing it to atmosphere.

It would be perfect for that use.


Great, thanks everyone.

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