HELP! 2009 ZR1 / 416 LS9 — Calibration Review, Return-to-Idle Stalling, and Street Drivability

Hi everyone,

I’m looking for help reviewing and refining the calibration on my modified 2009 C6 ZR1.

I’m attaching my current tune file, two datalogs, and an updated build sheet. The car is already tuned, running, and driving, but there are issues I want to resolve and areas of the calibration I would like reviewed thoroughly.

My priority is drivability, reliability, and consistent, usable performance—not simply chasing a larger peak horsepower number. I’d appreciate help identifying what needs attention and developing a structured approach to correcting it.

Main issue: RPM drop and stalling when coming to a stop

At moderate and higher speeds, the car generally feels good. The most noticeable problem happens at low speeds when I quickly release the accelerator and coast to a stop:

RPM drops excessively, and the engine struggles to recover to idle.

Sometimes it stalls.

Occasionally, I have to apply throttle to bring the RPM back up and prevent it from dying.

This happens both with the clutch pedal depressed and after shifting into neutral.

The car has a Kong low-vacuum supercharger bypass valve installed. I want its operation and any interaction with the drivability issues considered during the review.

Fueling and airflow calibration concerns

There are also concerns about excessively rich fueling under boost and a volumetric efficiency calibration that appears abnormal or not properly configured for the combination.

I would like the tune and logs reviewed to establish what is actually happening, identify any incorrect settings, and determine what needs to be corrected. If the included logs don’t contain enough information to verify these concerns, please let me know what additional data is needed.

I’m not assuming every issue is calibration-related, and I’m willing to have necessary mechanical checks completed.

Vehicle and combination

Vehicle: 2009 C6 Corvette ZR1, manual transmission, with functioning A/C.

Location: California, near sea level.

Fuel: 91-octane gasoline, E85, and blends through a flex-fuel setup.

Engine: Darton-sleeved 416.3 cubic inch / 6.82-liter LS9, approximately 10.2:1 compression.

Heads: CNC-ported LS9 heads.

Camshaft: Cam Motion, 236/252 degrees at .050 inch, .620/.603 inch lift, 118-degree LSA; cam card specifies a 114-degree intake centerline.

Supercharger: Kong-ported OEM LS9 blower and snout, with a Kong low-vacuum bypass valve.

Upper pulley: Kong Performance 2.35-inch LS9 GripTec.

Harmonic balancer: Lingenfelter C6 ZR1 Corvette Overdrive Harmonic Balancer. The build sheet lists 14% supercharger overdrive from the balancer alone, excluding the additional effect of the smaller upper pulley.

Fuel system: ID1700X injectors, DSX 320 pump upgrade with updated controller/wiring and filter, and DSX flex-fuel conversion.

Charge cooling: C&R intercooler bricks and a ProSpeed D3 heat exchanger system.

Exhaust: Kooks 2-inch headers, off-road X-pipe, and BBE mufflers.

Driveline: RPM Level VI manual transmission, MGW shifter, and McLeod RXT1200-series twin-disc clutch.

The attached build sheet contains the remaining hardware details.

What I want reviewed and improved

Return-to-idle and stalling

Identify why RPM drops too far after throttle release and why the engine doesn’t consistently recover when coming to a stop, depressing the clutch, or shifting into neutral.

Startup and idle quality

Review startup behavior, idle stability, and idle recovery with A/C both on and off.

Airflow and VE calibration

Check whether the airflow/volumetric efficiency calibration is properly configured for the engine, camshaft, and supercharger combination, and identify any inconsistencies that need correction.

Fueling and flex-fuel operation

Evaluate the concerns about rich operation under boost, along with the injector configuration and fueling calibration for California 91, E85, and blends.

Light-throttle operation and transitions

Improve low-speed street manners, smoothness when applying or releasing the accelerator, and predictable throttle response.

Power delivery

Make the available power progressive and controllable rather than abrupt. I understand tires, suspension, and road conditions also affect traction; I’m looking for the best reasonable behavior from the calibration.

Mechanical verification

Identify anything that should be checked mechanically before making calibration changes, including bypass operation, possible air leaks, or other hardware concerns.

How I would appreciate help

Please review the attached calibration and logs and point out:

Anything clearly incorrect or inconsistent.

What the logs show around the drivability issues.

Which concerns are supported by the data and which still need verification.

What should be addressed first.

What additional channels or operating conditions need to be logged.

How to verify that each change improves the problem rather than masking it.

I want to understand the reasoning behind the changes and work through this methodically rather than adjusting tables without a clear direction.

Ultimately, I want to get the most out of this combination without sacrificing reliability or everyday usability. I understand a build like this has compromises, but a car that starts cleanly, idles reliably, drives smoothly, and delivers consistent performance matters more to me than the highest dyno number.

I’m willing to gather additional logs, complete mechanical checks, and work through revisions. I’d also be interested in paid remote calibration review or tuning assistance from someone experienced with modified LS9 combinations if this needs more focused attention than a forum discussion allows.

Attachments

Current calibration file

Datalog 1

Datalog 2

Updated build sheet

Thanks for taking the time to review everything and help me get this combination sorted out.

There is a lot that you're asking here that is beyond the scope of what I'm going to be able to solve from a couple of data logs and your existing calibrations sorry. Stalling problems are easily the most common issues with larger cams on the LS platform. The two tables I'd srat with are your base running airflow table and your throttle follower - torque table. These need to be adjusted along with setting a realistic idle speed (which in your case does seem appropriate). Driveability issues aren't always obvious in a log file and you'd need to be more specific about the nature of these issues and when in the log file you're seeing them.

In general I'd say your tune needs some work. The fuel trims are in general very negative (-15 to -20%) and the VVE tables don't represent what I'd expect from a thorough calibration. Since your ECM doesn't have wideband sensors I have no visibility on what the actual AFR is under WOT/full boost however it's targeting 11.3:1 which is probably a touch on the rich side but not wildly inappropriate.

In short, I'd say there's some work to do here on this tune and there isn't sufficient information for me to provide a complete and thorough account. Is this an engine that you are intending to take on the tuning work yourself? We at HPA don't provide remote tuning services so if you're not using our courses to tune the engine yourself then that's not something I'd be able to help with. There are a number of worked examples in the reflash tuning course as well as webinars that cover idle tuning that would help you out in the first instance. Regardless though, you'll need wideband AFR data to properly calibrate this.