High Performance Fuel Injectors
Thread Starter
Joined: Jan 2019
Posts: 322
From: Warren MI
Just wasnt sure what it was used for. Education for me.
Joined: Feb 2008
Posts: 6,465
Simple version is that the guts of an injector are machined to flow a specific amount of fuel, usually a small amount more than what the factory engine is capable of needing (so that the nozzle can be optimized for ideal spray pattern given that flow). Think of your shower head - you don't want to shower with a solid garden hose stream of 1/2" pipe water shooting at you, you want it forced through a bunch of smaller nozzles to evenly distribute the water over your body.
The problem is, for people that do a lot of engine modification, theres generally not much headroom for them to flow much above stock power because you can only force so much fuel through those tiny holes at a given pressure. However the engine absolutely must maintain a certain air-fuel ratio (or you risk destroying it), so people in that situation will tend to swap to a larger injector that flows more fuel (ie has slightly bigger or more holes). This can be a slippery slope depending how far you go - as you eventually run into a similar problem with the fuel pump - it can only flow so much at a given pressure, and must be upgraded to a higher flowing unit to ensure the injectors have enough flow to keep up with the engine.
In general, if you haven't added boost (or a significant amount of NA horsepower), you probably don't need higher flow injectors. You can tell if you need them or not by looking at the frequency/ IPW while tuning the pcm (and everyone making enough power to need bigger injectors would also need to be tuning the pcm).
For example - when I swapped in my L67, I removed the stock 36 lb injectors and replaced them with 65 lb (because I added heads / cam / headers / big pulley drop on the supercharger). Later I swapped to a larger supercharger and E85 (which has a different air:fuel ratio target and needs more fuel than gas) and swapped to 110 lb injectors.
The problem is, for people that do a lot of engine modification, theres generally not much headroom for them to flow much above stock power because you can only force so much fuel through those tiny holes at a given pressure. However the engine absolutely must maintain a certain air-fuel ratio (or you risk destroying it), so people in that situation will tend to swap to a larger injector that flows more fuel (ie has slightly bigger or more holes). This can be a slippery slope depending how far you go - as you eventually run into a similar problem with the fuel pump - it can only flow so much at a given pressure, and must be upgraded to a higher flowing unit to ensure the injectors have enough flow to keep up with the engine.
In general, if you haven't added boost (or a significant amount of NA horsepower), you probably don't need higher flow injectors. You can tell if you need them or not by looking at the frequency/ IPW while tuning the pcm (and everyone making enough power to need bigger injectors would also need to be tuning the pcm).
For example - when I swapped in my L67, I removed the stock 36 lb injectors and replaced them with 65 lb (because I added heads / cam / headers / big pulley drop on the supercharger). Later I swapped to a larger supercharger and E85 (which has a different air:fuel ratio target and needs more fuel than gas) and swapped to 110 lb injectors.
Last edited by bumpin96monte; Jun 19, 2022 at 10:45 PM.
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