High v Low Impedence and Lag Time - Motec

[driftshop]

Hey Guys,

I'm in the market for some Sard 800cc Injectors to suit 1JZ/2JZ.

I am currently using USDM 550cc Supra Injectors which are Low Impedence, however at peak torque the duty cycle is 80% - hence the upgrade to larger injectors.

Sard make a High Imp and Low Imp injecotr with lag times as follows:

Low Imp - 0.75ms
High Imp - 1.6ms

The injectors are the exact same price for High or Low Imp. High imp injectors can have a better resell value due to their compatibility with the PowerFC and perhaps a stock ECU and piggyback setup such as e-manage ultimate.

Low imp injectors are what every one is raving on about for performance applications, however the new rage in the USA has been Bosch 1000cc high imp injectors - presumably for their better fuel control being high imp?

How important is a Low imp injector in a performance application and would there be any adverse effects in performance and drivability if I was to go for the High Imp version and reset / retune the motec to suit.

Cheers

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Costa Tsimiklis

[figgie]

It is not that the Bosch injectors are the rage, they have overcome ever shortcoming of the old high imp injectors with none of the cons of the low imp injectors

The bosch injectors are great because they are LINEAR and since they are not low imp, pintle bounce and thereby low load control is intact.

[MarkMc]

Hi Figgie,
The MoTeC ECUs can obviously control either and you would assume that a shorter dead time would be better but what I would be mostly concerned about is making sure you have the correct battery compensation to account for the dead time of any injector chosen, this should realistically remove the low/high impedance question. You also want to stay away from the non-linear range of the injector (just after it opens there is a range of pulse width where the injector is not so repeatable). You will see Bosch usually quote both dead time and nonlinear pulse widths.

I wonder if the whole "which injector is better" thing is based on ECUs where the dead time is fixed and may be way off for some injectors and nice and close for others.......?

[injectordynamics]

I wonder if the whole "which injector is better" thing is based on ECUs where the dead time is fixed and may be way off for some injectors and nice and close for others.......?

I'm sure that's convinced a few people, but for the most part "which injector is better" comes down to linearity, droplet size, and spray pattern.

I am the guy supplying the 1000cc high impedance injectors and the rave reviews you have been reading on the forums comes down to a few simple characteristics.

1. They have a very tight spray pattern which puts the fuel past the valve and not on the runner walls.

2. Being an impingement style injector, they have small droplet size even at low pressure, and the stream velocity is very low which helps the fuel follow the air stream.

3. They have an extremely broad linear operating range. They are very controllable at low pulsewidths. So controllable that we regularly run them on 1300cc Suzuki Hayabusa motors with a smooth idle and good drivability. At the upper end they have a very short recovery time and so they can run to quite high duty cycles while still maintaining linearity. About 90% at 9000rpm on a 4 stroke engine.

4. They are very tightly matched. We test in groups of 200 and match them based on dynamic flow across the pulsewidth range as opposed to matching based on static flow.

5. And finally, we provide proper battery compensation values from 8 to 16 volts, and 40 to 100 psi in 5 psi increments.

There's really no magic, it's just the latest technology from Bosch combined with careful testing. The old EV-1 style injectors from Bosch are based on a 30 year old design. They have come a long way since then.

As for dead time, as Mark pointed out what is critical is to have the proper values and account for them. The actual value, high or low is of little concern as long as we are within a reasonable range.