Which EFI injectors to use?

[stownsen914]

I'm considering putting EFI on a 911 engine for track use. I am still considering which EFI computer to use. The engine has individual throttle bodies and will have 1 injector per cylinder. I haven't calculated the flow rate that I'll need, but I assume that which injector I go with, will have various flow rates available. A couple questions:
1. Which brand of injector to use? I wouldn't cost is no object, but I want to make sure I use good ones.
2. I understand there are low impedance and high impedance injectors. What are the advantages/disadvantages of each?

Thanks.

Scott

[jpnovak]

Its a bit difficult to make specific recommendations without knowing the build details.

However here are some general thoughts.

1. It does not really matter what brand injectors you use. Most of the OE brands (Bosche, Siemens, etc) make a quality product.
2. Make sure the injectors you choose have the right flow rate. Calculate the flow rate to 85% duty cycle for maximum fuel delivery. Use the smallest injectors that meet this criteria.
3. Larger injectors than necessary do not make more power. They just limit the ability to tune at idle.
4. Match the injectors with respect to your EFI system. High/low impedence and electronic wiring connector are important.
5. Injector will have EV1 (Bosch style) or EV6 connectors. Make sure the wiring harness matches the injector plug. EV6 is a newer style and slightly smaller than EV1. Many new slim body injectors have EV6 style plugs.
6. High impedance injectors will typically measure 10-12 Ohms across the terminals. Most systems are built to run high-impedence injectors. Overall good performance but slower transient response compared to low-I.
7. Low impedence injectors typically measure 2-3 Ohms across the terminals. They require more current from the EMS to drive. Not all EFI-EMS systems are built to run low-impedance injectors. running Low-I injectors on a high-I ECU will burn our FET drivers. Low-I injectors are most commonly used on very high HP engines where a large dynamic range of fuel flow is needed from idle through WOT. Usually boosted engines require this. Sometimes Low-I injectors are substituted for a secondary injector system.
8. Low-I injectors have a much faster on-off time (transient response) can provide good idle control at high flow-rate requirements.


Which ever system you choose make sure all the components are matched.

[JohnJL]

What Jamie said.

FWIW 26 lb Accel injectors worked for my 3.0L with ~240hp.

55lb Accel injectors work for the blown 3.2 @ ~350hp.

Be sure your fuel rail is on there rock-solid. I've seen some dinky brackets holding the rails on in some DIY jobs, no better firestarter than fuel spraying the engine compartment at 45psi...

[Brad394]

Originally Posted by JohnJL

What Jamie said.

FWIW 26 lb Accel injectors worked for my 3.0L with ~240hp.

55lb Accel injectors work for the blown 3.2 @ ~350hp.

Be sure your fuel rail is on there rock-solid. I've seen some dinky brackets holding the rails on in some DIY jobs, no better firestarter than fuel spraying the engine compartment at 45psi...

Just to add alittle to the above - stock ford injectors at this flow rate (26 lb) can be had for a very reasonable price from a variety of aftermarket or rebuilders - and you can have 2 as spares.

[Raceboy]

I would not use ancient style injectors but instead prefer newer, "pencil" style injectors because these have much better atomization, faster respomse and they are better controlled.

[Spenny_b]

Don't know too much about the intricate specs, but the guy who's doing the mapping work for my EFI conversion using MBE management is a big fan of the latest Siemens Deka injectors...great spray pattern, easy to drive, can be driven to high duty cycles. Few pics attached below, and the p/n's on the body are: 107961 & B162A01675. Amongst other engines, IIRC, he's using these on race spec Suzuki Hayabusa engines (i.e. v high rpms) both n/a and supercharged (280fwhp, and upwards of 360fwhp respectively) fitted to hillclimb/sprint single seater Raynards/OMS/etc.

[Raceboy]

I agree, Siemens Deka's are great and I've used them on most of my cars plus many customer cars, mostly the 630cc @ 3bar variant or 880cc @ 3bar variant.

For example, 630cc versions on supercharged 993 Carrera (VEMS P'n'P ECU) and the same ones on my ~400 hp 931 race-engine.

[stownsen914]

Thanks guys for your opinions on this.

Any other thoughts (thanks jpnovak) on whether high impedance or low impedance injectors are the way to go? It seems like there are more options available on the market for high impedance injectors ...

Scott