+4mpg now just by advancing IGN

[YeahPete]

Interesting. Does this mean If I run premium i will get more mpg?

[RobertISaar]

POSSIBLY.

it really depends on how your PCM reacts to it. i know with GM OBD2 stuff, there are multiple main spark tables, which one is used depends upon how much knock is detected.

try it for a tank or two.... the difference between 15 gallons of regular and 15 gallons of premium is $3....

[nbleak21]

Originally Posted by RobertISaar

because you've changed the conditions.

with a grille block in place, the engine is under less load since there is less aerodynamic drag to fight against. an engine at the same RPM, but with lower load can GENERALLY get away with running more advance without running into knock.

I agree with the changing conditions and aero load being slightly lower, but the bigger factor, at least in my Acura, seems to be the warmer intake air allowing a higher degree of timing advance.

[ever_green]

Originally Posted by nbleak21

I agree with the changing conditions and aero load being slightly lower, but the bigger factor, at least in my Acura, seems to be the warmer intake air allowing a higher degree of timing advance.

i have noticed that on warmer days ignition timing is higher. i had no clue higher temps means higher ignition timing.

[RobertISaar]

warmer air is less dense air. less dense air-charge means lower load.

[ECONORAM]

Originally Posted by RobertISaar

POSSIBLY.

it really depends on how your PCM reacts to it. i know with GM OBD2 stuff, there are multiple main spark tables, which one is used depends upon how much knock is detected.

try it for a tank or two.... the difference between 15 gallons of regular and 15 gallons of premium is $3....

Very true. My Jettas gained because the original timing was conservative. My 07 RAM gains 1.5mpg with premium, but ONLY when I run a 91 octane tune with my Superchips tuner. On the factory tune, changing octane has no effect.