Is there a relationship between cam timing and throttle?

[radz28]

Hello everyone,

I just noticed something with my throttle at WOT I was hoping someone wouldn't mind sharing something about. I'm farting around on my car, as usual, trying to polish it to the best of my ability and understanding.

I'm seeing small (you might say tiny) dips in the throttle at WOT (around 6200 RPMs in the attached file). Admittedly, they are less than a half percent when they happen, but I was scanning my Channels to see what seemed to trigger it. What I think I found was when cam timing reached about 5.9*, the throttle would start to close from 99.9 to 99.5%. After dipping for the moment, it would reopen to what it was before. Sometimes I've seen it do it twice per hit, but it's mostly once, and seems like it's always when the cam retards (I think) to 5.9*. I've gone back to really old scans and seem to notice it's done this all along, even with the canned Maggie tune. The current tune (and attached file) is based off a tune I got help with a couple years ago that I've been trying to polish. My calibrator ?retarded? the cam up to 4* from stock, but I'm seeing the same behavior from old Maggie canned tune files that ?retard? timing 1-2* from the stock tune, too. I don't have any stock files, so I don't have a baseline, and I'm just a guy who plays with only his own stuff.

Is this behavior related to the cam timing? I believe I have some of the basic understanding of how airflow is calculated and requested torque is calculated, filtered, rechecked and then the throttle moves to the desired position and then torque rechecked (maybe I'm missing a couple steps, but have read posts by H Tanner as much as I could), and am wondering if this is a result of that, or something else. I don't THINK by current tune is off that much, as my VVE/Dynamic/MAF airflow are pretty close in these areas, and my VTT (to me, anyways) seems like it's not intervening. I know this is a tiny thing, and likely doesn't affect torque much at all, but it bugs me to see. It's one thing if it's just a Channel/PID idiosyncrasy/limit (like VVE ending at 512 or MAF airflow ending at 655), but if it's some sort of conflict or something I've unknowingly done, I'd like to know.

I, as always, appreciate any and all of your help and time.

Thanks,
Chuck

[TriPinTaZ]

The cam timing/movement affects the calculated torque. So, moving the cam timing away from stock will change the torque value that the ECU calculates. This could have an effect on the throttle closing if the delivered torque is higher than the commanded torque. Or if it causes the calculated torque to run close to another limiter. The simplest fix would be to ask for more Driver Demand in the WOT area. If that doesn't help, then you have a more in depth issue.

[radz28]

It was doing the same thing with stock cam timing, too, which is why I'm not even sure if this is anything to worry about. Of course - I'm not arguing any of your point; just trying to be clear. I was thinking along the lines of what you posted, and because my DD is TWICE the request as stock (still modelling this), I can't see how it could be that. My Driver Pedal, Driver Final, and Actual Axle TQ don't touch each other at all. I would have thought it could be a TB issue, but it did it with the stock TB, too, and it was reduced the exact same percent (0.4%), so I'm starting to believe more and more that it's just the PID (I can't even recall if I used SAE or not). Maybe I'll delete those channels, re-add them, and try again.

Thank you for your time. I appreciate it.