quote:I'm wondering if it is a waste of time to stage injectors on a 351?
If we’re talking V-8s and Panteras, staged injection really isn’t necessary in most normally aspirated street applications. For a single injector per cylinder, when horsepower demands get high and drive the flow rate of your injectors up, larger injectors don’t have much resolution for fine tuning at low rpms. -You can’t get them turned on and off fast enough for idle and low speed trim. So when the injector pulse widths get very small and start approaching the injector recovery time (time to effectively shut down and ready to pulse again) it can pose a problem at low speeds. Conversely, small injectors won't be able to deliver high flow and power. Staged injection can allow the use of a smaller injector to handle the low rpm duties and as the rpm, power, and fuel flow demands exceed the small injectors ability to deliver at a reasonable duty cycle, the additional set of injectors also kick in so you get the best of both worlds…..good low speed resolution and plenty of fuel delivery capability. Full sequential can also help smooth out idle and low rpm operation since full sequential fires only once per engine cycle instead of once per revolution as in phased sequential.
On eight cylinder street engines of reasonable displacement (say 400 CI or so, more the better), you should be able accommodate 600 HP at sub 7krpm with a single 45 lb/hr injector per cylinder. If you will only briefly see the peak power and fuel demand (street banging) then you can get by with the high duty cycle and you may get more. If you’re living at high power levels (racing) you need a bigger and properly sized injector. Guys that are running boosted engines on the street and putting down big numbers also often run staged injectors for this reason.
One exception to my remarks above is rotary engines. Because you only have a couple rotors that have quite a bit of displacement, they’ll need staged injectors even at modest power levels and this is common practice for rotaries.
Interestingly enough, a pair of smaller injectors can be significantly less expensive than one large one; big production quantities for small injectors typical in passenger cars provides economy I guess. If your ECU can drive multiple injectors it may be one of the rare instances where more costs less. It only applies to the injectors boys, you pay dearly everywhere else.
Very high rpm racing engines will also use staged/multiple injectors per cylinder since they can have a very small amount of time available to deliver the fuel due to the high engine frequency. Varying the injector placement in the induction stack can potentially take advantage of higher harmonics. Some racers even have an injector placed (out of) above the stack to optimize performance. -All this is way out of my league.
Hope that helped. Happy New Year gents.
Kelly