Why did my tuner do this? DT correction of VE map

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Why did my tuner do this? DT correction of VE map

Postby BCs300z » Fri Mar 08, 2019 2:43 pm

*This post is in reference to RB26DETT tuning*

Ok... so I am posing this question here to get educated... not to knock my tuner.

Lately, I have been very interested in learning more about VE tuning and trying to remove all the magic and mystery behind the process. That said, I have read several articles here and around the internet that have truly helped to shape my understanding thus far, so thank you. After reading through a response that Scott left here: viewtopic.php?t=5463 (reference VE tuning basics) I have a couple questions specific to my current setup.

So, my tuner is really big on dead times and how dialing in the proper dead times is key to everything. I have been comparing his map (and assoc. settings) to the Haltech base map for the RB26. I noticed that he has the cell value for idle (1000 x 0.0) in the base map set to 42. And he has corrected the dead times on the injectors by +0.204.

After reading Scott's post, I decided to tinker around with just the idle cell in the base map, raising it to 50. In doing so, the car got super rich. Expected. But, I was then able to lower the dead time value back to the manufacture recommended value, and the RB went back to running AMAZING!

The Haltech base map for RB26 has 48 in the idle cell. This value allows me to set the injector dead time at OEM (or very, very close). So why would a tuner lower the value in the idle cell, just to make the compensation in the dead time value? What is the benefit to this across the whole map? And is this type of practice actually wasting additional fuel? It is my understanding that a larger dead time equates to an injector being open longer (essentially), so is it not better to have a larger value in the map and a dead time closer to the manufacture setting?

Again, just trying to understand and be educated on why my tuner approaches tuning in this way. Please fire away with as much technical info as you like.

Thanks in advance,

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Re: Why did my tuner do this? DT correction of VE map

Postby HaltechMatthew » Mon Mar 11, 2019 3:44 pm

I would say you are over-thinking it. But then again most of the internet tuners do too so don't go too deep into it.

Dead times have very little impact on the actual running of the engine. If they are set a little too low, the VE will be artificially high at light load. Conversely if they are set too high the VE will need to be set low at light load. Basically the less fuel you are commanding the more of an impact you will see. End result is that if the AFR is correct it makes little difference.

What does make a difference is if the shape of the dead time curve is off, you will get different AFRs at different system voltages. Also, it impacts only at light load and virtually nothing at full load.

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Re: Why did my tuner do this? DT correction of VE map

Postby BCs300z » Sat Apr 06, 2019 8:58 am

Thanks Matt. This is informative and just what I was looking for. I appreciate the time you took to respond

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