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4D Tuning and MAP source.

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I have a question about vacuum reference for the ECU. On a GTR with ITB's there is a balance port. If we were tuning the car purely off MAP as Y-axis on our fuel table, this would be the correct port to use for our vacuum reference.

But... If we are using the TPS as the Y-axis and MAP is a multiplier built in to the fuel equation would we not move our MAP sensor source to before the throttle blades? Other wise would we not get the same mid throttle instability in our tune? As if we were tuning it purely off manifold pressure before the throttle blades (not using TPS as Y-axis) where there is a difference between the pressure before and after the throttle blade at partial throttle angle.

Our MAP multiplier for our fuel equation needs to represent atmospheric pressure before the throttle blades (NA) or a multiplication there of (Turbo Charged) and represent manifold pressure before the throttle blades.


I have tuned one rb20det (4 throttle bodies and turbo) for racing engine just with - MAP for load and for ignition, and it goes quiet well.

i did took vaccum tubes after throttle bodies from each one cilinder and detached all together - to MAP sensor.

After watching this webinar, i would rather do with alpga-n tuning for fuel (+double pressure double fuel and + correction table) and MAP just for ignition.

But important to get good pressure signal too.

I atach picture, maybe You could understand how I did get good MAP signal.

Attached Files

With a multi throttle engine you want to take the manifold pressure signal from the factory balance pipe after the throttle bodies. This is important as what we need to know is the manifold pressure at the intake valve. Remember that even with a turbo engine you will still see vacuum at part throttle and if the manifold pressure signal was taken from before the throttle you will never register this vacuum. The vacuum or boost is a critical aspect of the fuel equation.

If you weren't seeing vacuum but were seeing boost, the fuel equation won't work correctly and you would end up trying to tune around what would equate to an overly rich mixture under vacuum.

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