Isn't 6 Injectors Enough?

     Depending on your application, 6 injectors for a six cylinder would typically be plenty.  However, when you start exceeding you original injector capacity, there are a few options.

• Higher Fuel Pressure

• Larger Injectors

• Additional Injectors

     Now, all of these have benefits and compromises.  For example, just raising the fuel pressure sounds like a cheap and easy alternative.  It is, but you get what you pay for, limited capacity to increase the total fuel flow.  As you increase the pressure, the fuel capacity only increases by a factor of the square root of the actual increase itself, so to get twice the capacity, you'd have to increase the pressure four times.  So, why not?  Well,  Bosch (tm) tends to rate their products to 5 bar, and anything above that is typically marginal.  There are a few specific products that'll go way beyond that, but they're far in between.  Especially when you start talking about the later model 15 ohm stuff.  They're pretty bad about any kind of fuel pressure, they just don't have the hp behind them to pull the pintle up.  So, to go from the factory 3.8bar to 5bar gives you sqr(5/3.8) = 1.147, or almost a 15 percent increase.  In turbo territory, that's not much.
     Ok, so that's limited, how about Larger Fuel Injectors?   That also proves to be more of a compromise than most people care to admit.   It seems that anything over about 37lbs/hr per cylinder on a 911 style engine starts to seriously sacrifice low speed calibration and drivability.  So, emissions, fuel economy, idle quality, low speed drivability, etc. are all compromised, and the larger injector you get, the worse it gets.  Sure they'll make tons of hp on top, but don't ask them to be nice.
     Additional injectors can mean a few things.  Most of the older 930 CIS turbo owners know about adding one or two additional injectors just above the throttle body.  This is a great way to increase the top end power without sacrificing any low speed performance.  The controllers aren't that expensive, and the setup can add another 100hp or so.  But that's CIS turbo's.  We talking about serious hp here, and that takes a good digital fuel management.  Sure you could walk the 930 route and stick a few more injectors on top and go for it, but we want more than 100hp additional, we want to double our output.
     The ultimate setup:  Twin-injectors per cylinder.  You've probably seen it on race cars for years now, and just never thought of it as a viable alternative on the street.  Well, guess what.  It is.
     The particular setup shown is on a 3.8L twin-turbo based originally on a C2/C4 (964) style engine.  We used the Motronics (tm) off of a 84-89 Carrera 3.2 with our pressure sensing conversion, but the customer just wanted more than that.  He wanted everything, so we went to the drawing board, and came up with what we feel is the ultimate solution without compromise.  The feet of the original manifold are replaced with billet aluminum CNC milled bosses that accept the two Bosch (tm) style injectors.  The manifolds are also aluminum, but extruded and welded to CNC milled receptacles with AN style fittings on the ends.  We used the original channels of the Bosch Motronics (tm) fuel system for the primary set of injectors while turning on the second set as the fuel requirements increased, running them both can provide us with anywhere from 74-100lbs of fuel, or some more quick math 74 / .5 (hp/lb) = 148hp/cyl.  148hp/cyl. x 6 = 888hp capacity.  Starting to sound interesting?  And that's with a couple of 944T injectors that just happen to have about the best atomization going.
     So, there has to be a drawback.  In theory, no, but in practice, there always is.  It's fairly complex to control, but with proper coding that's taken care of by the ECU.  You do need an additional injector driver set and capability to control it.  You need to place the additional injectors somewhere in the stream, etc.  But we've taken care of that.  These aren't compromises, only installation difficulties, so just leave it to the experts, and let's make some more horsepower!