What's the reason for Torque dip in BRZ Dyno ?

[Element Tuning]

The correct answer was stated. When you fully maximize the intake and exhaust cam timing to deliver the most low end torque and the most midrange torque this is what you get, a big dip between the two points. This is what I had to do when developing base maps from scratch with the Hydra EMS and when swapping cams for built motors. Once you've maximized the total overlap you can then attempt to use conventional fuel and ignition tuning to minimize the dip. It's never enough so you have to take away a little of your low end gains and a touch of your midrange gains to smooth this out.

We should be up and running on the Hydra EMS over the weekend and I'll start working on maximizing tuning gains.

Now if you can time a turbocharger system to ramp boost there it will be non existent. A supercharger is just going to exacerbate this.

Thanks
Phil Grabow

[ravnos04]

^ yup...timing gets my vote...GL with the tuning

[jedibow]

I have an interestinmg thought...

Could they both be related, meaning the deactivation of the port injectors, and the increase in timing during the low point in the torque? Could they be attempting to smoothout the transitional period for the fuel flow once the port injectors are closed. I believe that arghx7's post on the D4-S system states that the port injectors are used at low speed, however we do not know what load values the port injectors stop at as of yet. This is just a theory, I can't imagine why they would increase timing in that area otherwise.

Increased timing (advanced) allows the engine to burn a richer AFR, it also decreases the cylinder temperatures, I believe that during the transitional phase there would be both conditions.

[icemang17]

So the "dip" is caused by ignition timing? Interesting....must be a MPG-emissions issue.... Having Direct injection really changes EVERYTHING in tuning...since you have the ability to add fuel when the intake valve is CLOSED.....detect a knock....add a bit of fuel.....that will cool the charge enough to remove the knock.....which is why the compression is SO high already...

[serialk11r]

Originally Posted by icemang17

So the "dip" is caused by ignition timing? Interesting....must be a MPG-emissions issue....

Previous posters were simply pointing out the difference in ignition timing, correlation != causation :P
I'd trust what arghx7 says, just saying.

[arghx7]

Originally Posted by icemang17

So the "dip" is caused by ignition timing? Interesting....must be a MPG-emissions issue.... Having Direct injection really changes EVERYTHING in tuning...since you have the ability to add fuel when the intake valve is CLOSED.....detect a knock....add a bit of fuel.....that will cool the charge enough to remove the knock.....which is why the compression is SO high already...

Just a reminder: there are NO wide open throttle pulls in any emissions certification test. None. Zero. Zip. The closest you will get is the US06 cycle, but that's still not going to have WOT in it during certification. Now, allowing the cat to run too hot in WOT will reduce its life, so fuel does play into that. The reason you get a richer mixture at high load and heavy throttle is to keep the cat from overheating, although knock suppression does play a role as well.

As I was pointing out in another thread, if somebody can log the estimated catalyst temperature off the CAN bus we can see if the torque dip corresponds to an area of high catalyst temperature. This might imply that the factory tune has countermeasures built into it. If we can log absolute load that will give us an idea of pumping efficiency in the torque dip area.

[jedibow]

Originally Posted by arghx7

Just a reminder: there are NO wide open throttle pulls in any emissions certification test. None. Zero. Zip. The closest you will get is the US06 cycle, but that's still not going to have WOT in it during certification. Now, allowing the cat to run too hot in WOT will reduce its life, so fuel does play into that. The reason you get a richer mixture at high load and heavy throttle is to keep the cat from overheating, although knock suppression does play a role as well.

As I was pointing out in another thread, if somebody can log the estimated catalyst temperature off the CAN bus we can see if the torque dip corresponds to an area of high catalyst temperature. This might imply that the factory tune has countermeasures built into it. If we can log absolute load that will give us an idea of pumping efficiency in the torque dip area.

Check my thread for the data,

George

[jedibow]

Okay, so no drastic change in the cat temp, however the pumping efficiency does decrease in the torque dip, this is interesting because timing increases, kind of counter intuitive? I will re-insert my original hypothesis that maybe the torque dip is located in the transition period between port and direct injection, changing to just direct injection? The increase in timing should cool off the EGT's, however because of the loss in efficency maybe they remain constant?

G

[johnbradley]

We only logged 1137* Catalyst temps, so EGTs arent too warm. I know I mentioned what I saw as a probably cause in the OpenECU thread but thought I'd throw the EGT data in.

[jedibow]

Originally Posted by johnbradley

We only logged 1137* Catalyst temps, so EGTs arent too warm. I know I mentioned what I saw as a probably cause in the OpenECU thread but thought I'd throw the EGT data in.

I was seeing about the same range, however mine where slightly lower, probably due to the altitude and the ECU running more advance.

George

[ahausheer]

Intake harmonics that cause a decrease in how efficiently a cylinder fills will lead to a decrease of power and torque as there is simply less air in the cylinder. You can combat this to a degree with timing and fueling which we are seeing but you cant fully resolve the issue. I am fairly certain this is the issue.

[mact]

Originally Posted by Boosted2.0

Sorry - pic to go with the above post:

In my Nissan Maxima days if I remember correctly people tried to get the A/F on NA motors to around 13:1. If that's the case for this engine then there's some nice power to be made in tuning.

[arghx7]

Originally Posted by johnbradley

We only logged 1137* Catalyst temps, so EGTs arent too warm. I know I mentioned what I saw as a probably cause in the OpenECU thread but thought I'd throw the EGT data in.

I'm not sure where you're putting your thermocouple or how you are logging the data...