When building an engine, everyone knows that the right head and cam combinations and/or boost can equal big power. With so much focus on the big things, it is easy to over look the basics. The root concepts that make up an internal combustion engine, like air, spark, and fuel. Although, everyone wants to make big power, no-one wants an engine that falls flat due to fuel flow limitations.
Electronic fuel injection systems include three major components – the pump, regulator, and injectors. The pump supplies fuel pressure, the amount of which is determined by the regulator, and the injectors spray the fuel into the intake runners. While it is possible to tweak the fuel pressure and flow electronically, this has its limitations and the best way to ensure your engine gets enough fuel is with appropriately sized injectors. To discuss the importance of utilizing properly sized injectors and what exactly is properly sized, Richard Holdener with Speed Secrets and the guys from FAST team up to give us all a closer look.
When the factory designs stock fuel systems, they design it to flow enough fuel for the factory power output plus a little more just to be safe. However, when you make major modifications to an engine like heads, cam, or even boost, the factory fuel injection system is not going to cut it. This lack of fuel flow can not only put a damper on power output, but can also lead to lean conditions that can be dangerous for your engine. The good news is that this problem can easily be solved by an injector upgrade, but you have know what your fuel flow needs are to fix them.
The math to figure this out can be a bit confusing and involves brake specific fuel consumption. The easier way to go about picking the right size injector is to figure out how much power an injector will support by multiplying flow rate by 16 ( for a typical V8 only) and compare that number to your engines output. For example, a set of 50 Lb injectors will support 800 HP on a V8, but this equation only works on naturally aspirated engines because boost adds another variable and requires even more fuel.
Using a 5.3L that included a healthy COMP camshaft, a FAST manifold, and a centrifugal supercharger as a test engine, Richard demonstrates the importance of proper injector sizing. First, equipped with a set of factory LS3 injectors, that proved to be too small, the engine was ran on the Dyno. Not only was it obvious that the 5.3Ls peak horsepower output suffered but while looking at the air/fuel curve, it was easy to see that the engine leaned out, and dangerously so.
However, the same engine Equipped with a set of 75 Lb injectors from FAST, produced 665 HP @ just 8 PSI of boost. More importantly it produce a nice, steady, and safe air/fuel curve, proving the importance of supplying the right amount of fuel for the intended power output.
FAST, the industry leader in aftermarket EFI systems, is known for their LXSR intake manifolds, big mouth throttle bodies, and XFI management systems, but they also offer an assortment of fuel injectors in a wide variety of flow rates and sizes that would be suitable for many different applications.
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