Grev dropping suddenly at high rpm

[brn12345]

I was doing a full throttle log last night after the header install and noticed that the Grev falls suddenly at high RPM even though the throttle is fully depressed. I added Engine Load calculated and it holds at 100% until I take my foot off the pedal. This happened in most gears but not always. I managed to get a photo of the log for the 3rd and 4th gears and in 3rd Grev seems normal to the shift point and in 4th it drops at around 7000rpm.


I am running OFT Stage 2.

[arghx7]

So one of these is an ECU RAM value, and the other one is a calculated value by the logging?

[jamesm]

Are you talking about the big drop off when it appears that you are shifting or something? Or the slow tail down after peak torque? If so, that's pretty normal. Load will peak at peak torque and then should stay pretty constant to redline. It's a function of VE, so cam timing has an effect. Load tailing off means VE is tailing off, and you're dropping torque.

[brn12345]

Originally Posted by arghx7

So one of these is an ECU RAM value, and the other one is a calculated value by the logging?

I am not sure what "Engine Load Calculated %" is but as far as my understanding goes Engine Load (I have always assumed this was the one the ecu used for looking up tables) as displayed in G/Rev is a function of RPM and MAF. If this value plummets before the throttle is released from full then there is something wrong. The engine cant go from high load to extremely low load this fast.

Originally Posted by jamesm

Are you talking about the big drop off when it appears that you are shifting or something? Or the slow tail down after peak torque? If so, that's pretty normal. Load will peak at peak torque and then should stay pretty constant to redline. It's a function of VE, so cam timing has an effect. Load tailing off means VE is tailing off, and you're dropping torque.

I am talking about the area in the photo attached I circled in green. On the left circle Engine Load (G/Rev) continues at a high value until the throttle is released. The other figure Engine Load Calculated % also drops at the exact same time. If you look at the circle in the top right, you will see that Engine Load (G/Rev) drops before the throttle is released. RPM, Engine Load Calculated are still high at that point.


I am starting to think there could be something amiss with the mapping. I might try flashing to a stock rom to see if this issue exists.

[Kodename47]

Hit the limiter?

[trustyler]

Originally Posted by Kodename47

Hit the limiter?

What exactly happens to the car when you hit the limiter? I noticed my car loses power and seems like the clutch is slipping or something. Does this make sense?

[jamesm]

It looks like that log was running about 3 samples/sec. I wouldn't worry about any synchronization between different channels at that rate. Collect another log at 15+ samples/sec and you'll have much better data to go by.

[SkullWorks]

I think jamesm nailed it,

[ztan]

Originally Posted by brn12345

I am talking about the area in the photo attached I circled in green. On the left circle Engine Load (G/Rev) continues at a high value until the throttle is released. The other figure Engine Load Calculated % also drops at the exact same time. If you look at the circle in the top right, you will see that Engine Load (G/Rev) drops before the throttle is released. RPM, Engine Load Calculated are still high at that point.

I am starting to think there could be something amiss with the mapping. I might try flashing to a stock rom to see if this issue exists.

Agree with James. This is a logging sync issue - your logs are collected at around 400ms interval (2.5Hz).

The math : Load(g/rev) = 60*MAF(g/s)/RPM(rev/min)

In your logs above, the g/rev number drops faster, but also recovers faster indicating that RAM call is lagging behind all the other parameters or derived from extra MAF and RPM calls.

What logging platform were you using? You can probably speed up by logging less parameters (derive load from above formula). I pull 30 parameters with 5 extra calculated parameters with the Tactrix standalone at a 50ms interval (20Hz). Techstream is much slower, but could also pull VSC data alongside ECU data.

[jamesm]

with ecutek it matters a lot which params you're logging. some have no effect on speed and are pretty much free whereas others cost 2 or 3 hz by themselves.

[Grip Ronin]

that the most up to date stage 2? 1.42

[Kodename47]

I guess he's using OFT.

Originally Posted by jamesm

with ecutek it matters a lot which params you're logging. some have no effect on speed and are pretty much free whereas others cost 2 or 3 hz by themselves.

Out of interest, which ones James?

[brn12345]

Originally Posted by trustyler

What exactly happens to the car when you hit the limiter? I noticed my car loses power and seems like the clutch is slipping or something. Does this make sense?

Its the built in retard limiter Shiv built into the map. It does exactly what you feel. Easily removed if you don't like it. I removed it last night for dyno testing and found I like it better without the retard limiter.

Originally Posted by jamesm

It looks like that log was running about 3 samples/sec. I wouldn't worry about any synchronization between different channels at that rate. Collect another log at 15+ samples/sec and you'll have much better data to go by.

Will give it a try thanks! I set BRZedit to log at 20, was logging at 100 before but I guess I was logging a whole bunch of parameters. Reducing them now and will test.

Originally Posted by Kodename47

I guess he's using OFT.



Out of interest, which ones James?

Actually I use BRZedit to log, Romraider to modify the maps, and OFT to flash.

Originally Posted by Grip Ronin

that the most up to date stage 2? 1.42

Yes its the most up to date stage 2 1.42.

[trustyler]

Ahhh..thanks for your clarification. Does it also prevent the engine from over-revving when a misshift occurs? Because if yes, I'd just leave it on I guess no matter how irritating it is.