Effect of timing on fuel economy?

[JQmile]

A while back I accidentally ran my Nova drag car at about 45 degrees of timing, locked out, from idle on up. It had race gas in it, and I was just cruising, so it didn't detonate, but a swear it got about 20mpg rather than the normal 8mpg. Don't know for sure, cause I don't have a gauge, just a fuel cell. Engine is a 355cid 12.5:1 compression small block chevy. Anybody else try running stupid amounts of off idle timing with any success?

[Southcross]

some engines just eat timing like its hashbrowns for breakfast... what really starts to hurt efficiency is at the top end of your RPM scale, the timing advances and becomes so early it actually tries to act as an engine brake by pushing down on the piston while its still on the compression stroke.

[ESmooth]

What about on eco-driven cars that rarely see anything north of 3500 RPM?

[SVOboy]

A lot of people will advance their timing just a hair to get one or two more free hp, but I'm not an expert and I'm not entirely sure it even works

[gone-ot]

...the 'original' Chrysler (Lee Iococca era) LEAN BURN systems actually used ignition "advance/retard" to accelerate/back-off the engine beyond idle.

...anybody remember this?

[silicon_toad2000]

I'd say the OEM's would have already tried that.
You won't know until you do some partial throttle dyno runs.
Supposedly the magic number is that the mixture should reach full combustion/maximum pressure at 14 degrees after TDC. So you need to ignite the mixture at a point early enough that the mixture is all combusting at that point.