Project GD STI – Improving the Fuel System with Injector Dynamics and Other Details


Because for the fear we developed of typical low cost aftermarket injectors when researching this article,  we bit the bullet, spent more and upgraded our sidefeed Subaru injectors to Injector Dynamics 1000cc/min top feed injectors.  These will have more than enough fuel for whatever plans we may concoct in the future.  We chose Injector Dynamics injectors because we feel that they are some of the best units on the market.

Injector Dynamics starts with brand new properly sized OEM quality injectors which are matched in batched sets using Injector Dynamics measuring benches and methodology.  First, new injectors are dynamically broken in on a bench for about an hour.  Injector Dynamics has found that it takes about this long for new injectors to settle down and produce consistent flow results. The injectors are then flowed thought their dynamic range using the proper fuel pressure and using fuel as the test fluid, not test solvent.  The temperatures are carefully controlled during the test for consistent results.

After break in and flowing the injectors are sorted into matched sets. Within each set the dynamic flow rate (slope) will vary no more than +/- 1%, and the dead time (offset) will vary no more than +/- 20 microseconds which is equivalent to +/- 1% at a pulsewidth of 2 milliseconds.  To our knowledge only Injector Dynamics offers complete operating range matched injector sets. 

It is this dynamic flow matching across the pulsewidth range that separates Injector Dynamics from the others.  Other companies that claim to sell matched sets typically only match the injectors for flow when they are held wide open.  Although this is better than nothing, wide open flow is probably the least critical attribute that should be matched. The dynamic flow at low pulse widths and deadtime is very critical for achieving good idle quality and driveability at low rpm and throttle openings with big injectors.  It is also the hardest to match injectors under these conditions and Injector Dynamics injectors are matched from the low to the high range of pulsewidths.

Tight matching at low pulsewidths will allow us to use big injectors without sacrificing idle, off idle, and cruise quality while the matched offsets ensure that the individual injectors respond properly to atmospheric and voltage compensation built in to the ECU.

The data for our matched ID1000 injectors can be found here.  With precise matching, ID1000 injectors will provide smooth idle and good part throttle driveabilty in engines with cylinders as small as 325cc! Cobb has utilized this data to develop excellent base maps for the Access Port.  The ID1000 injectors have a stainless steel metering needle and seat so they are E85 compatible.  They come with the proper impedance for the Subaru ECU and the conversion pins and plugs so you can modify your harness for a sano plug in.  Other applications have a top hat feed adaptor so the injector can be an easy plug and play for many different cars.
Since the ID injectors are top feed instead of side feed like the stock Subaru injectors, we had to get new fuel rails.  Injector Dynamics supplied these nice billets parts.  All of the hardware is stainless, a nice touch.
Our kit also came with quality Earl’s AN fitting and pre terminated Pro-Lite hose.  This made working on the fuel system as easy as possible.  The Injector Dynamics kit is a nice piece!
Although they would not allow us to show you their dynamic flow systems, Injector Dynamics allowed us to show you their injector break in flow bench.
To feed our big injectors we obtained a high flow in tank fuel pump from AEM to replace the stock fuel pump.  The AEM unit flows an amazing 320 liters per hour at 43 psi.  The pump is 39mm in diameter and will directly replace many OEM pumps.  The AEM pump comes with several sleeves and spacers to help adapt it to many different cars.

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