Calculating Injector Sizes
When it comes to fuel injection, figuringout the right size injectors to use is critical, but it is also one of the mostmisunderstood aspects of EFI. More than that, and the injectors tend to beoverworked, causing heat to build up and efficiency to rapidly tail off.
.55,while those using power adders, superchargers, turbochargers auto Cap machine Suppliers or nitrous arerated at .
Another aspect when choosing fuel injectionis to select the right camshaft. This well-used Lincoln Continental Mk IVwas found at a swap meet.e.com. For mostmild-street engines a BFSC of . Cams designed for fuel injection applicationsfeature higher lift profiles and wider lobe separation. Moreaggressively modified, but normally-aspirated, engines are rated around . This term refers to its efficiency, i.
Itís surprising how often this isoverlooked, but it is utterly crucial to make sure that you choose the correctwiring harness and computer designed to work for a specific vehicleapplication.
Bigger, heavier cars, like this custom 1950Mercury, often require torquier, larger-displacement engines to move them. Because huge amounts ofair arenít required to be drawn down from the top of the manifold, the headsand intakes on EFI engines are designed to promote greater airflow inside theintake runners and ports, and the low lift and wide separation on the camshaftallows greater promotion of power and torque.
One of the most important elements whenplanning your next hot rod project is the engine, and choosing the right fuelsystem for that engine.
When it comes to engines and fuel systems,donor cars are a good place to start.
Taking that into account, we can use thefollowing formula to work out our required injector size based on rear wheelhorsepower (H), BSFC, C (the number of cylinders) and D (injector efficiency):
H x BSFC / C x D
So, if our normally aspirated, mild street V-8 engine is rated at 300 horsepower,this will give us:
300 (hp) x .50 is the accepted rule of thumb.50 / 8 x .80 = 20.Multiple carb setups or, if youíre Crate Injection Moulds Manufacturers not too concerned about tradition, tunedport fuel injection, can really add benefits. In thiscase, it would be 24 lb/hrunits, as found on many OE performance applications and through aftermarketsuppliers. Its big 460 V-8 and four-barrel carb are the perfectfoundation for a custom sled. If you donít, youíll be forever chasing electrical gremlins andsuffering with a car that just wonít run properly.
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Based on that calculation, we would need aninjector thatís closest to this flow rate for optimal performance.
In order to determine the size (lb/hr orflow rate) required, you need to find out what your engineís Brake SpecificFuel Consumption (BFSC) actually is.65. Unless youíre lifting the entireengine and EFI system from the donor vehicle and are not too concerned aboutindividual performance, youíll want a custom ground camshaft designed to workspecifically with your engine and fuel injection system to achieve a balance ofgood drivability, as well as ample power and torque delivery across the rpmspectrum.
When calculating injector size, there aresome general terms that are widely accepted, one being that optimal injectorefficiency is around 80 percent