EFI 8 Stack injector build process

[eschaider]

My engine uses two IAT (Intake Air Temperature) sensors because it is supercharged. One is located in the intake manifold and is called IAT2 and the other is located in the plumbing from the air cleaner to the throttle body and is called IAT1.

IAT1 is used to measure the incoming air charge temperature. IAT2 is used to measure the post intercooler intake charge tmeperature. The IAT2 sensor is used to pull timing if the pressurized intake air charge goes over a fixed temperature that I have arbitrarily set at 125˚F. This is used for detonation suppression in a supercharged application.

IAT1 along with my mass air flow (MAF) sensor is used to calculate the weight of air that the engine is consuming to properly adjust the injector pulse width to provide the correct amount of fuel to meet my commanded A/F ratio in the tune.

The 8-Stack style systems while not impossible to build as a MAF based system is quite challenging to do so with. As a result they are typically built as speed density which is one of three typical fueling strategies that are commonly available.

The speed density fueling model uses ambient air temp settings and manifold pressure (vacuum) measurements to calculate air mass moving into the engine. By using a volumetric efficiency table similar to the AFR table in a MAF based system the tuner can build a V(e) MAP with sufficient accuracy the injection system can properly fuel the engine.

In your build you will be using a Speed Density system. Your IAT1 sensor for ambient air charge temperature can be located anywhere in the incoming air path. I would not attempt to locate it in the intake throttle body not only because of the obstruction it provides to the incoming air charge for that cylinder but also because it will get heat soaked by the engine heated intake manifold and provide a false reading. Did I mention it takes an absolutely gorgeous (and stunningly expensive) intake system and garbages up the appearance department with sensors.

Because all you need is the temp of the incoming air charge you can place that sensor in the air stream closer to the air inlet for the engine, just like the IAT1 sensor in my twin screw blown engine. The only thing you want to be attentive to is keeping the sensor inside and slightly down stream from the air intake point so you are actually measuring the temperature of the incoming air charge and not the temperature of the ambient air (which is going to be close but not the same).

Positioning your IAT1 sensor closer to the air intake point makes placement easier without needing to hack up an air horn. Your installation will look much cleaner — it's already way over the top sexy!


Ed