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Realistic Injector Lag Times?

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Hi all

First post here apart from the introduction.

I have some deatschwerks 800cc injectors in my RB26 and the quoted lag times seem vastly different to any other brands. The spec sheet says 0.22miliseconds at 14v and 43psi. I guess what I'm asking is does this seem viable?

I'me awear they are "cheap" injectors and probably not up to the standards of Sard ect. But surely if it was easy to make injectors with such fast lag times then surely the more expensive items would be equally fast. Looking around on the net I can't find any others that are even half as fast.

Could the quoted figures be wrong do you think?

Chris

Yes that isn't that uncommon for large low impedence injectors.

Thanks for the reply.

If it's not uncommon do you have any examples of 800cc low impedance that are anywhere near 0.22ms? I can't find any under about 0.8ms.

I'm now wondering if a budget injector can achieve such a fast lag time why are expensive injectors so slow? Would the ideal injector not have as fast response time as possible in order to maximise the possible flow?

Cheap/expensive, anyway they are all Denso/Bosch/Siemens

Sorry, seems I eddited my post at the same time you responded...

So if I find out what base brand the DW injector is then the Lag time should be similar to others of the same brand?

Depends on what modifications DW have done with the base core

Anyway, they don`t work correct with lag time, indicated in the datasheet or what? ) You could try to discover the approximate lagtime with the scope yourself. You will need a scope, a ballast resistor serial connected to the injector with the resistance that will not dramaticaly change the injector driver-to-earth chain resistance and will limit the maximum current for the injector, a power source that can handle this current. Measuring the voltage drop on the resistor with the scope you will discover the time from the injector needle down to injector needle up state.

I think that this kind of lag time diversity occuring because of the fact that different manufacturers confront lag time with different events. First ones assuming that lag time is the time needed for the needle to fully open, the other ones that lag time is the time needed for the fuel to start flow out the injector, the third ones somwhere in the middle.

I'm only suspicious of the values as they seem at least 4 times faster than any others I've come across.

I didn't realise how important the lag time was until watching some of the videos on here.

I'm just paranoid about trying to tune an engine for the first time when the lag times could be throwing all of my and the ECUs calculations out.

I don't have access to any of the things you mention in order to test lag time myself.

Thanks for the info though.

You shouldn`t be afraid of wrong lag time numbers, the main thing that should be accurate is lag time curve, if it`s accurate but shifted up or down a bit then the error become static, and easily canceled by numbers in VE table during engine tuning. Who cares which number do you have there 50 VE or 55 VE, 90 VE or 92 VE anyway it`s far approach of the reality, because it sums all errors you have in calibration (of course if you have 100 VE on idle it`s a reason to find a way to minimise that error). If the shape of the curve is wrong then you will have a permanent headache with AFR floating every time the voltage changes. To stop being perfectionist you could watch Injector Charecterisation webinar and realise that there is a LOT another stuff happening with the flow, not only lag, you should have a really powerful ECU and a lot of engineering research in order to tune injectors perfectly.

I haven't had much to do with deatsch werks injectors so I can't comment on the latency values. As someone has already noted in this thread, the base or core injector is still coming out of a bosch or siemens or denso factory somewhere along the line. None of the mainstream injector suppliers in the aftermarket are actually 'making' their own injectors.

In the perfect world we would have absolutely accurate latency values and our tuning would improve in accuracy by a very small margin. Realise though before you beat yourself up too much that 10 years ago many ECUs didn't even include deadtime tables and there was no compensation for injector latency applied. Even with the ECUs that did account for deadtime, we had no access to accurate data so these tables were often ignored or incorrectly filled in. We still could achieve great results.

My point is that inaccurate deadtime values are not going to stop you producing good results from your tune. If you can get the right data then obviously we want to use it, but sometimes it's just not feasible to get this data.

DW are a large enough company you would expect their settings published to be reasonably accurate.

I would plug in their deadtime, fire it up and see how it reacts.

If its nice and crisp off the floor to very light throttle inputs, and quick to react mid rev range when free revving it, then I would leave it at that and continue tuning.

In my experience with injectors that provide poor/incomplete data, small changes to dead-time rarely affect the overall fuel flow enough to wildly throw out your target AFR's.

DW seem to quote their battery offset data a little usually. I think the actual offset is given by:

Actual Offset = Minimum Pulse Width + Battery Offset

I came to this conclusion when I was looking at the data for some 350cc mx5 injectors and noted that some of the value were negative. See http://www.deatschwerks.com/products/fuel-injectors/sport-compact/mazda/miata/1990-05-miata/22s-00-0350-4-detail

Plotting the flow rates versus pulse width data supplied with the injectors showed that zero flow was definitely on the positive side of zero.

You might want to confirm this conclusion with their technical support.

Dave

What ECU are you using?

The DW injector times never appear to be accurate and every time I've had to tune them I've generally had to adjust them

Thanks so much for the replies guys.

I guess the reason I was so worried about the lag times possibly being inaccurate was due to the G4+ auto tune function. As I understand it (probably wrong?) if the ecu thinks the injector is open longer than it is, the calculations will be wrong?

Dwlee: The lag times from that injector surely proves that the specs given for mine are not the values I should be entering. It's some pretty awesome design if they can open before the signal is sent.

The calculations will be wrong. If injector latency in lag time table is lower than in reality, then some part of injector pulse will not be effective and actually will be as an adder to injector latency, hence you should make a pulse a bit wider in order to achieve your target AFR. However usually it`s not a problem with the current calibration. But if you replace the injectors with those, which have proper characterisation data, then your calibration will be wrong. You will have to re-tune the base fuel table, or adapt lag time table/flow fate table of new injectors with IMPROPER data (not accurate that have been provided from manufacurer e.g Injector Dynamics)

But do not panic, the maximum influence on AFR improper latency applies on low injector pulses (idle). If the injector pulse = 10-15 ms on maximum load, then 0.3-0.4 ms of error doesn`t affect much