Nozzle Designs
Fuel injectors use a variety of
nozzle designs which affect the spray pattern. Pintle style nozzles use an
annular orifice to produce a conical spray pattern. Multi-hole designs use
precisely spaced and aligned orifices to deliver a cone shaped spray pattern
also.
Pencil or single hole nozzle styles are used to shoot a narrow stream of fuel
at a targeted area. Disc style injectors use a drilled disc that moves with a
spray pattern similar to pencil injectors.
While each design has its own advantages, it's generally accepted that disc
metering is quicker to respond and more resistant to clogging. Some multiple
hole designs use a ball and seat design to seal the orifice. This design tends
to offer longer service life with a wider spray pattern and increased fuel
delivery at the price of a slightly slower response time. Pintle designs tend to
react slower and have a shorter service life. When upgrading to larger
injectors, most industry experts recommend a ball and seat design as offering
the best combination of features and benefits.
Spray Patterns
There are several basic spray
patterns used in automotive fuel injectors. Pencil streams use a constant flow
with a narrow angle of distribution. Split pencil designs use multiple streams
and are commonly found in multi-valve applications. Bent or oblong spray
patterns are used when the spray target is not in direct line with the injector
nozzle tip. Conical spray patterns are more typical with performance injectors
and use a cone shaped geometrical pattern.
There are many theories about what kind of spray pattern is better and why.
While much of that depends on whether throttle body, port or direct fuel
injection is utilized, there is much research still going on in this field of
study. Spray patterns can be easily viewed on a test stand, but those patterns
are often distorted under actual operating conditions especially in the case of
forced induction engine applications. Some of the nation's leading universities
and research labs are using Phase Doppler Particle Analyzers, electron
microscopy and synchrotron X-ray beams in order to gain greater insight into
spray distribution, atomization and burn efficiency within the combustion
chamber to increase performance and reduce emissions. Even so, spray patterns
aren't as critical in many race applications since meeting emissions is not
an issue.
Sizing Injectors
While there are many different
types and styles of injectors on the market today, it's important to note that
all manufacturers use the same basic method of sizing, regardless of country of
origin. Domestic injectors usually measure fuel flow in terms of pounds per hour
(lbs/hr) while international applications measure in cubic centimeter (cc's).
A simple way to figure what size injector you need is to divide an engine's
peak horsepower at the flywheel by the number of injectors. That number should
then be multiplied by the Brake Specific Fuel Consumption (BSFC). For a
naturally aspirated engine, this number is typically. 50 After you've finished
multiplying, divide that by a Duty Cycle of .80. The formula looks like
this:
HP / Number of Injectors x BSFC / Duty
Cycle
Here's an example for an eight cylinder engine that we found would need a 24
lb/hr injector:
300 HP / 8 = 37.5 --> 37.5 X .50
BSFC = 18.75 --> 18.75 / .80 Duty Cycle = 23.43
To convert lbs/hr to cc's, multiply by 10.2. To convert cc's to lbs/hr,
divide by 10.2.
Readers should note, however, what Brake Specific Fuel Consumption
factor is in order to use the above formula correctly. A BSFC of .50 means
an engine will use .50lbs of fuel per hour for each horsepower it produces.
Competition engines with high volumetric efficiency should use a BSFC of .45
while forced induction engines should use a figure of .65.
For our readers ease, we have done all the math for you and determined a
horsepower rating per injector as shown on the tables below. Simply multiply the
listed rating by the number of injectors to determine if these will support the
peak horsepower for your engine.
| Domestic
Injectors |
|
>Each
Inj. |
| P/N |
Size
lb/hr |
Impedance |
Nozzle |
Supports |
| DMI24 |
24 |
High |
Pintle |
43 HP |
| DMI30 |
30 |
High |
Disc |
54 HP |
| DMI37 |
37 |
High |
Ball |
67 HP |
| DMI38 |
38 |
High |
Disc |
68 HP |
| DMI42 |
42.5 |
High |
Disc |
77 HP |
| DMI50 |
52 |
High |
Ball |
94 HP |
| DMI55 |
55 |
Low |
Ball |
99 HP |
| DMI65 |
65 |
Low |
Ball |
117 HP |
| DMI75 |
75 |
Low |
Ball |
135 HP |
| DMI84 |
84 |
Low |
Ball |
151 HP |
| DMI95 |
95 |
Low |
Ball |
171 HP |
| DMI165 |
165 |
Low |
Pintle |
297 HP |
| Sport
Compact Injectors |
|
Each
Inj. |
|
Size |
|
Nozzle |
>Supports |
| P/N |
CC |
Impedance |
Type |
90%
D.C.) |
| SCIO310 |
310 |
High |
Disc |
52 HP |
| SCIO400 |
400 |
High |
Ball & Seat |
68 HP |
| SCIO440 |
440 |
High |
Disc |
77 HP |
| SCIO525 |
525 |
High |
Ball & Seat |
90 HP |
| SCIO580 |
580 |
Low |
Ball & Seat |
100 HP |
| SCIO680 |
680 |
Low |
Ball & Seat |
117 HP |
| SCIO780 |
780 |
Low |
Ball & Seat |
135 HP |
| SCIO880 |
880 |
Low |
Ball & Seat |
151 HP |
| SCIO1000 |
1000 |
Low |
Ball & Seat |
171 HP |
| SCIO1600 |
1600 |
Low |
Ball & Seat |
275 HP |
Injector Connections
Injectors can mounted to the
fuel rail in any number of different ways. Top feed injectors use a rigid fuel
rail to press the injector into the injector bung on the manifold and seal the
O-rings. All Precision brand injectors for domestic applications are a top feed
style and use a 14mm round O-ring to seal against fuel leaks.
Precision also manufactures top feed replacement injectors for popular Sport
Compact applications such as Honda and Mitsubishi. While these may not fit every
application, stock fuel rails are typically replaced in favor of high flow rails
which will work with these upgraded injectors.
Electrical connections can be broken down into two basic types. The most
common today is the L-Jet connector which provides a weatherproof seal. Older
applications use a D-Jet style connector. Some manufacturers such as Subaru and
Toyota use their own style of electrical connector which is not compatible with
either of the above.
Wrap-Up
While most performance injectors are
designed for a universal fit, Precision offers a wide variety range of injectors
specially machined for most Honda and Mitsubishi applications. Developmental
work is also being done on new applications, so don't hesitate to call for the
latest information on what's available.
Call Us For All Your Fuel Injector & Fuel System
Needs!
Precision Turbo & Engine
Sales/Tech (219) 996-7832
24-hr. Fax (219)
996-7749
E-mail: Sales@PrecisionTurbo.net
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