105-160 #/Hr Low Impedance P&H Port Injectors

Walter Sherwin wsherwin at idirect.com
Sat Jan 29 01:33:55 GMT 2000


Large injectors, on a BBC engine,  are not quite as problematic as they are
often made to sound.  Lots of wive's tales, but you can ignore most of them,
if you take the right precautions.............

First, assuming that you intend port injection for your BBC project and that
your BBC is to be artificially aspirated, your 105 #/Hr injector benchmark
tells me that you are expecting roughly 1100'ish max HP on gasoline?   If
this is not the case, then please clearly state your assumptions and/or
intended fuel.

You will find that large'ish port style fuel injectors (typically beyond
50-70 #/Hr) are all of the low impedance variety regardless of
manufacturerer, meaning that they are typically less than 4 ohms impedance
each and that they will require an individual peak & hold current driver
(typically 4/1 amp) for proper dynamic operation.  This is pretty much a
universal statement, no matter whether you examine large injectors from
Bosch, Siemens, Rochester, etc.

"Low Impedance" and "Peak & Hold" really describe the same end result, and
are meant to denote that the injectors must be individually switched via a
current controlled driver as opposed to the more common (cheaper) saturated
voltage switch driver.  The combination of an ECU current driver, together
with the electromagnetics built into a typical low impedance injector/coil
assembly, attempts to drive the injector harder & faster than normal in
order to effectively extend both the low and high pulse width flow response
of the injector.  The result is a "wider" dynamic performance envelope for
the injector(s).  This translates into both a superior idle and more
effective top-end liquid flow (relatively speaking).  The DIY & GMECM
archives contain a lot of interesting reading on this topic, if you seek
more knowledge.

When you contemplate the injector flow ranges that you have described, there
are really only two manufacturers to consider  1) Rochester '96s [aka MSD,
Holley, and others], and of course    2) Bosch '160s.

Personally, I would select the Bosch injectors for the following reasons:
quality, cost, spray pattern, linearity, heat tolerance, batch tolerance,
and availability.  Remember, that the Bosch injectors (in particular the
160's that you have mentioned) have been, and still are, the mainstay of
racing venues from Indy down to NHRA & IHRA and even weekend bracketeers.
By virtue of production volumes, and popularity, the Bosch 160's are far
more prevalent and sometimes more cost effective.  The Rochester 96's are
slightly more difficult to source, and are not as precise.  Kinsler, and
others, can feed your cravings for either flavour of injector.

A bunch of Pro & Otherwise racers around here use the Bosch 160's, and are
able to produce clean/stable/reasonable idles with a variety of ECU hardware
and software packages.  The trick is to control each of the large injectors
via its own P&H driver and to use ECU software that intentionally
encompasses wide dynamic injector ranges and firing schemes.  You should
personally discuss your injector thoughts with Electromotive, in order to
determine the best software control strategy and selection (kinda surprised
they did not want to sell you an injector set to match your application at
the time of sale???).

If you are interested, I can forward you photo images of both the Bosch '160
and the Rochester '96 injector spray patterns as photographed on my flow
bench, during rated psig operation.  As you will note, each is different and
satisfies differing needs in terms of desired injector targeting and wall
wetting parameters.  In theory for multiport operation, you want to target
the injector spray directly toward the backside of the intake valve face
from 3-4 inches distance away.  However, the physical dimensions of a BBC
make this difficult/impossible.   Practical theory reveals that if a person
can somewhat incline the injector spray plume into the cylinder head runner
tract, then the resultant distribution and effect should be okay.

Good luck with your project, and remember that many of the injector and/or
ECU companies often have "1-800" numbers.   Don't feel bad about asking them
a zillion questions.  It's their dime..............


>Date: Thu, 27 Jan 2000 14:32:07 -0800 (PST)
>From: Anthony Buccellato <clayb at sonic.net>
>Subject: Peak and hold vs. Saturated injectors
>It's finally time to buy the injectors. Horsepower, boost, and RPM
>requirements (plus a bit of overhead) dictate 105 lbs/hr units. I believe
>these will be low impedance units. Does this correlate to peak and hold,
>or saturated style injectors?
>I'm using an electromotive driver, so low impedance isn't a problem. What
>I'm primarily concerned with is idle quality with the large injectors.
>I've heard that saturated style have a longer minimum pulse width,
>relative to peak and hold style. Anyone have info on this?
>Also, what is the best angle to weld the injector bosses into the manifold
>at? Within the mechanical limitations of a Chevy big block, should I be
>aiming as close to the back of the valve as possible?
>Are there any injector mfg's that do a better job than others at
>atomisation? I've located 160 lb/hr units, but would prefer to get closer
>to my actual requirements, so as not to compromise idle too badly.
>- - Clay

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