Has anyone experimented with this much? I've been playing around with it (cautiously, without a knock sensor) and I like my '88 GT auto best with 91 octane E10 ('premium' at this altitude, no E0 available) and about 14-15 degrees (difficult to tell precisely, timing mark appears to be exactly on the leading edge of the tab from above) base timing. I arrived at this through experimentation, and it feels noticeably better than 87 octane E10 ('midgrade') and factory-specified 10* BTDC. I've been driving it this way for about two years/10k miles. The engine is now at 160k miles and is stock, except for a K&N filter, modified air intake, Walker 15026 catalytic converter, and Ocelot Exhaust. With this combination, I easily passed the Colorado I/M 240 (dyno) emissions test three weeks ago with 50% or less than the allowable readings in all categories. Great, right?

But I feel like there may be more to this. My off-idle tip-ins are better cold than warm - I think open vs. closed loop - and under hard acceleration (closed loop), power comes up very noticeably, almost suddenly, at 2000-2500 rpm. Advancing the base timing further does not improve more. So I'm wondering if the timing curve in the chip may be a little late and/or lazy (chip is an '87 49-state stock chip, stock ECM). I'm thinking about playing around with the chip programming myself (never messed with an ECU chip but have comparable experience from my work). But has anyone been down this road already? No point in repeating what's already been done...

Without a knock sensor, you need to play it safe with ignition timing. I learned that the hard way, when I was younger. My first Fiero was an '86 with a Duke. I found that if I advanced the distributer, and put premium gas in it, the throttle response improved. A few months later, I was disassembling the engine to replace broken piston rings.

On my (somewhat modified) V6, I noticed acceleration enrichment having a greater effect on throttle response than ignition timing. The amount of additional fuel you dump into the engine on tip-in is subjective and up to you.

When my Fiero is fully warmed up, if the ECU tries to maintain a constant AFR during a throttle blip, it is OK. The engine is perfectly driveable that way.

However, when I use more acceleration enrichment fuel, the blip response becomes more lively. The AFR (after an initial lean spike) may dip down by 1 AFR or so like this. For free revs in neutral, I don't tune using the wideband as much as using my ears to evaluate the rev-happiness of the engine. In-gear, I don't want an excess amount of acceleration enrichment to flood the engine and temporarily reduce torque (I look at the wideband to check this).

The downside of too much acceleration enrichment is more CO and HC emissions on tip-in, but if the emissions tests you must pass are at constant RPM, acceleration enrichment won't be a factor.

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You can play with timing, but rotating the whole distributor is a sledgehammer approach.

By playing with the calibration, you can tweak the timing in areas that make the car feel more lively, without necessarily affecting the WOT timing curve, or other areas.

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Worst case scenario, you can always pull the old Volkswagen trick:
One calibration to pass the test that drives poorly, but is clean
Another calibration that is nice for everyday driving, but that is dirty

[This message has been edited by pmbrunelle (edited 09-06-2020).]