NA LT1 Big Cam idle tuning questions and tune review

[turabo87]

Tuning a big cam (GPI Stage 3 226/246 .639/.639/112 +2 ICL) LT1 C7. My first big cam LT1 tuning experience too, so big learning curve. I've researched the forums for common GenV idle tuning principles, and I got it to at least idle with zero pedal, but it's still idling too low (currently 650 vs my target of 850) and stalling easily when "returning to idle" during a clutch in.

I've already:
Lowered VVE to about 80% of stock, got it ballpark on fueling with wideband on OL.
Switched over to MAF only, and rescaled the MAF, got it ballpark stoich with wideband on OL.
Cleaned up virtual torque tables multiple times (Airmass and MAP) to be closer to 50-100ft lbs in idle areas of around 0.20-0.30g air mass and 60-70kpa manifold vacuum pressure.
External Load, Torque reserve, all revised...
Driver demand revised (only for over 60-70% pedal areas though)
32% fuel lobe accounted in leading angle y axis scaling (not that it matters that much for idle I think anyway)

Because the cam is so jumpy, at this point I'm not sure what direction I should be going with the Idle Torque tables and Virtual Torque to continue moving in the right direction to get the idle closer to 850 instead of 650 and get it not stall after a "return to idle" clutch in. Looking for some pointers on what to log and look for to get closer. Tune and logs attached.

2014 Jonathan C7 HCI Calvo Tune.hpt

Jonathan C7 HCI idle log.hpl
Jonathan C7 HCI cruise and some WOTs.hpl

PS: O2 readings might look wonky at parts of the drive logs, because we found a spark plug that had a cracked insulator. Spark plug has been replaced since.

[Ben Charles]

Calvo needs to stick to vipers ha…

virtual Tq will fix it

[turabo87]

Calvo needs to stick to vipers ha?

virtual Tq will fix it

Haha, good one Ben. Not related to Antonio Calvo (that I know of, but who knows maybe we share deep Spanish lineage). Ok, Virtual Torque but you think I should continue to move VT even more towards lower values? Is it because my zero pedal engine torque is still lower than delivered and predicted engine torque? More interested in learning the why than the what, more the correct thought process than the answer itself.

Also, what are your thoughts on negative torque values for the lower air mass values (lower than 0.20) and vacuum lower than 60kpa at idle RPMs? I was hoping to decrease the negatives even further (meaning move them closer to zero) to promote more airflow/throttle cracking if the RPMs dive bomb.

[Ben Charles]

Some factory cars idle around -5 to 25 tq, I don’t have a problem with negative Tq at idle actually, doesn’t need to be too negative though or you’ll get higher then desired idle and throttle hang…

Get VVE and MAF right First, then play with VT, log commanded vs actual Idle speed and play with the VT to get right.

[turabo87]

"Sending out an SOS!" Well, last few days I've definitely been inching closer to the goal. Finally got actual idle RPM match target idle RPM with zero pedal, and engine is not stalling when I blip the throttle in neutral/parked. However, my RPMs still divebomb and stall when I clutch in during speeds.

I also noticed that during clutch-in decel (or just decel after a rev in neutral) AFRs lean out to like 20's despite having turned of DFCO settings for both clutch in and normal decel.

I'm just lost now, not sure if the answer to not stalling/RPMs dive bombing if it is because:
1. I still more work on the Virtual Torque?
2. Or maybe I need to up Driver Demand so it's not in the negatives for 0% accelerator pedal position?
3. Or perhaps it's not enough fuel in Decel Areas of the VVE map for idle or near idle RPMs?

I'm lost and need some further pointers please. Attached latest tune and 2 logs:

1. Driving around the block (speed bumps, stops, etc..) where you'll see I have to blip throttle as it nears idle to avoid divebombing and stalling.
2. Idle log with a rock solid idle in neutral and no stalling, where I'm reving engine and letting it settle to idle.

[turabo87]

Solved idle!!! It was a combination of VVE still a bit off during decel, but really mostly all of it was Virtual Torque!!! Ben you hit it on the money. I still had to go much more in the negatives for idle area and make smooth transitions. Over an hour of driving and no stalls, although a couple of dives below idle RPM to about 500RPM but never stalled.

Now I just have to see where my WOT timing is going sometimes. I suspect answer is Virtual Torque again, probably not high enough? Throttle stays open over 91% full pulls, but timing is being pulled somewhere, sometimes. Attached my latest tune and my latest logs.

[Ben Charles]

Log tq Management spark…. You’ll see it being pulled there.. main reasons for that is there trans (usually on the hit, if auto) or tq model if it’s closer to redline most likely

[turabo87]

Log tq Management spark?. You?ll see it being pulled there.. main reasons for that is there trans (usually on the hit, if auto) or tq model if it?s closer to redline most likely

Thanks Ben, I'll make sure to log Tq Management spark. It's an M7 trans though.

Anyway, about the idle, I jumped to conclusions too early. Still randomly stalls during clutch in (doesn't catch/blip idle quick enough, late to blip), and when it does catch it it tends to be pretty aggressive on the throttle blip and tends to overshoot it sometimes, tending to some minor hunting. I feel this Virtual Torque tuning for return to idle is an art form. I feel close, but man that last 5% of idle tuning is taking 95% of the time.


PS: Just found out from customer that the clutch assembly has a lightweight flywheel & clutch assembly from Tilton. 40 lbs for the entire assembly!! No wonder RPMS drop like a bomb.....Regardless keeps getting better and better with small adjustments in Virtual Torque (more negative numbers near idle airmass and even higher negative values for airmass of vacuum/decel, and smooth transitions), but wow what a long process...

[turabo87]

Finished the tune and delivered the car....just thought I'd provide some closing thoughts that could help another person going thru this. Virtual Torque had to be even further in the negatives for the airmass area of idle. It also helped to slightly raise my external load table, to hover over 55ftlbs instead of 50ftlbs for idle area, and interpolated up and down the range. Final result in idling was a delivered torque bouncing around 0 ftlbs. No idle hang whatsoever, although not a fan of how it returns to idle after a full pull and clutch in (sometimes on the verge of divebombing past idle RPMs and stalling if a full WOT pull is done with AC and clutched in afterwards to idle); the 50lb Tilton clutch and flywheel surely don't help.

As far as WOT TQ management in 1st gear, I got rid of it all by reducing Airmass Tq in Virtual TQ for 0.90 air mass into more "reasonable numbers" and interpolating smoothly into cruising areas, peaking at about 590-600ftlbs at 0.90g airmass and smoothing it out based on expected torque delivery of a WOT pull.

Final results: 503WHP/463 ftlbs TQ on 93 gas. Was hoping for more but airflow is seriously choked after 5kRPM, with MAP values starting to lower from 101kpa slowly down to about 97kpa thru the pull.

Now, if I can solve that occasional RPM dip/near stall conditions with AC without creating idle RPM hang, then I think I'll be completely happy with the tune.

Jonathan C7 HCI Dyno.pdf

[TriPinTaZ]

Now, if I can solve that occasional RPM dip/near stall conditions with AC without creating idle RPM hang, then I think I'll be completely happy with the tune.

Have you tried lowering the VVE table in this area? You can also lower the VT for MAP like you did for the Airmass.

[turabo87]

Have you tried lowering the VVE table in this area? You can also lower the VT for MAP like you did for the Airmass.

Yep, VVE was lowered and cleaned up after a lot of rinse and repeat, including decel areas. VT for MAP was also lowered. I personally think, feels like, I'm at a point close to start generating idle hang if I keep lowering VT by idle. Maybe that's the compromise needed for such a light flywheel and big cam, but i'd rather have the occasional stall after clutch in that idle rpm hang. I think the AC torque % load tables could use work, but I ran out of time with the car.