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Exhaust System Modifications

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Hey Andre,

How do you typically approach a simple exhaust upgrade? Since installing upgraded (higher flowing/less restrictive) exhaust system components increases the VE of the engine, would you approach tuning these modifications the same way you would with an intake system upgrade? Would you just measure Lambda, adjust the VE or MAF Curve to increase Fuel Flow to obtain you target AFR again = more HP? I understand that less restrictive exhaust path reduces pumping loses = more HP, but what is the typical affect this has with regards to Measured AFR vs Target? Thanks for any input!

This will be very car dependent a lot of cars won't need any real adjustments especially if it has a afm, could be different if ur exhaust is mega restrictive

A better flowing exhaust should improve the engine's VE and hence it should require more fuel, particularly under load. This does depend however on how you are tuning - For example if you're using an aftermarket ECU using a MAP sensor then you will need to add fuel. If you're using a factory ECU with a MAF that is calibrated accurately, the MAF will measure the increased airflow and a lot of the work is done for you.

I usually find that particularly on a knock limited engine that a larger exhaust will allow a little more ignition advance to be used too. It goes without saying that you need to check this carefully while tuning though.

That sounds right. Thanks for affirming that for me.

So with regards to MAF Calibration or Re-calibration, is it typically only done when altering the intake (MAF Sensor) housing i.e. aftermarket intake set-up?

Any changes to any part of the intake tract (air filter, air box, intake plumbing, MAF location, throttle body) can and most likely will affect the accuracy of the MAF sensor's calibration. If you are going to change these parts then one of the first jobs you need to do is adjust the calibration of the MAF otherwise you will be tuning around inaccuracies.

You can check on the MAF calibrations accuracy by watching the fuel trims during normal running or logging commanded AFR and comparing this to measured AFR. You're looking in both situations for the error to be as small as possible. Generally with STFT I'm happy as long as they are within a +/- 5% swing but the smaller the better.

So to make these adjustments based on your ECU's Learned Fuel Trims, wether it's intake or exhaust, its just a simple matter of adjusting the 2D MAF Airflow Table to correct the values (Airflow in G/S) at a specific Voltage reading correct? We shouldn't have to adjust the actual Voltage axis, just the airflow axis?