HomemadeTurbo - DIY Turbo Forum

AFRs under boost should be 12:1 minimum. If you are pushing more power, or you have high IATs, or the power uptop is fading because you are either maxing compressor ability or choking against a too-small turbine, etc, you will want richer for safety reasons. I ran Trav-ASS' Pigtegra at 10.5:1 at 18 psi. I cost him 1.5% less power than the 11-11.5:1 most tuenars would have given him, which is a -----all amount. You get a couple times more power off of 2 degrees of ignition timing.

Ignition timing is pretty easy on a dyno. Take your first pull, then discard it as the engine is going to make less power the second pull due to being warmed up. Use the second pull as a baseline. I'd suggest going from there with a pull with +2 and -2 degrees total timing to see how power is affected. The very general rule of thumb is that (when starting from very conservative ignition timing) as soon as you stop making good power gains from advancing timing you are 3-6 degrees away from where you'd start knocking. Between minimum timing/best power and detonation is a plateau of more-or-less the same power output.

For a timing tolerant engine like and LS, or a big power/low vehicle weight ride that really rips through the gears like it's nothing and doesn't spent enough time under boost to get really really heat soaked, I run that minimum best timing. For a D-series with small bores that have to produce a LOT more combustion pressure to move the smaller piston down the bore + make the same power as a B-series, I jack timing back from 2-5 degrees depending on power level. All this is for engine longevity, and subject to change one way or the other depending:

1) owner doesn't care and just wants best power, period.

2) small turbine, restrictive manifold, unexperienced kid who'll beat on a poorly put together setup and then blame me when it fails, high IATs due to small IC or other reason, etc.

For the usual streetcar, it's very expedient and less expensive to just set AFRs, let ignition timing fall in a safe + conservative region, and turn up the boost if more power is desired. Dynos are for ballers who care more about a piece of paper to flash around and impress people, for cars that are too dangerous to street tune, and for people who are curious about how the engine will respond and want to learn. If you're Broke Dick Motorsports like myself, you can do a credible job of logging VSS over time to figure out power gains and tune going by that.