Supercharged & forced-induction tuning help

Roots and twin-screw superchargers (Eaton TVS in Roush/Magnuson kits, Lysholm-style screws in Whipple) build manifold pressure almost in lockstep with RPM, so you see 6-12 psi early and hold it across the whole pull. There is no spool window to hide behind. Every cylinder fill at every point in the curve is a chance to knock if your spark advance is too aggressive for the octane in the tank.

That changes the whole tuning priority list. On a naturally aspirated car you chase the last degree of timing for peak torque. On a blown motor you deliberately leave timing on the table, run the air-fuel ratio rich, and treat knock retard as a fire alarm, not a tuning aid. TuneVault's audit is built around that mindset: it flags the high-load, high-RPM cells where a screenshot shows you riding the edge, and it tells you how much margin a typical pump-gas combo wants there.

The three variables you actually control are boost, octane, and spark advance, and you only get to pick two. If you want more boost on the same 91-93 octane, timing has to come down. If you want to keep timing up for response, you either drop boost (bigger blower pulley swap) or raise octane with E85 or a race-gas blend.

In VCM Editor this lives in the high-octane spark tables under Spark > Spark Advance, and on forced-induction GM combos in the boost/airmass region of those maps. A common pump-gas starting point is pulling 1.0 to 1.5 degrees of total timing per pound of boost over the stock target, then datalogging to confirm zero knock retard. TuneVault won't invent a number for your exact combo, but when you upload the table it will tell you whether the advance you're showing at peak cylinder pressure is in the conservative band most pump-gas blower cars run, or out past it.

Positive-displacement blowers compress air, and compressing air heats it. Intake air temperature climbs hard under sustained boost, and a Roots blower sitting in the valley bakes between runs. The classic symptom is a great first dyno pull and a scary second one: same throttle, more knock, because IAT is 40-60 degrees higher and the effective octane requirement went up with it.

This is why intercooler health and an IAT-based timing retard table matter more than peak-number bragging. In VCM Scanner you want IAT (or the charge-temp PID) logged on every pull. TuneVault checks that your tune actually has IAT compensation pulling timing as charge temps rise, not a flat table that punishes you only after the engine is already detonating. If your screenshots show no heat-related timing pull, that's the first thing it'll call out.

Commanded AFR is not delivered AFR. VCM Editor lets you command 11.5:1 under boost, but a maxed injector, a lazy fuel pump, or a saturated MAF will quietly lean that out to 12.5:1 right where you can least afford it. A wideband O2 is not optional on a blown car — it is the only thing that tells you what's actually burning in the cylinder. TuneVault will always tell you to verify with a wideband before you lean on the tune.

The safe pump-gas playbook is boring on purpose: rich mixtures (high-10s to low-11s AFR under full boost), conservative timing, and a hard look at injector duty cycle so you're not running out of fuel at redline. TuneVault audits for all of that, but it does not replace a professional tuner and it never promises a horsepower figure. You are responsible for what you flash.