+4mpg now just by advancing IGN

[ever_green]

i have been monitoring ignition timing on my impreza and cruising on the highway i recorded between 32-34 degrees IGN. i have heard modern knock sensors in new cars are pretty advanced and sometimes you don't actually even need an ecu tune to advance/retard timing. So I decided to run 91 octane and see if the car will 'advance' the ignition automatically and voila. My ignition timing according to scangauge now is 45 deg at highway speeds. i do have a before and after video.

this before video is from a while back but you can kind of make out the 35 ignition timing and ~33mpg

Subaru Impreza Scangauge II - YouTube

this one is from today and you can make out a whopping 45 deg IGN and ~37mpg on same stretch of road at same speed:

scangauge 2 ignition timing advance - YouTube

the thing that amazed me was how quickly the car adjusted the ignition timing and how much difference timing advance made. just after a few minutes cruising on the highway the ignition timing went as far as it could without knocking for ~4 more MPG. i remember playing with A/F by leaning out the ECU map, but that made not much difference and it made my engine run at unsafe temperatures. So this is much better. however i don't do any highway driving so it's good old 87 octane for me. but it is obvious to me now that my car CAN take advantage of higher anti-knocking index gas. the only downside is extra cost of 91 octane and increased engine braking. anyone else experienced this?

[mcrews]

my infiniti 2002 Q45 got lower mpg on lower octane, and the timing dropped to 29 at cruise.

[radioranger]

Great info, My Ranger has a distributor , the last year for them was 88 , anyway the ignition modules that plug in can go bad and one of the symptoms is a loss of advance, one day i started the truck and all it would do was idle, even grabbing the throttle linkage wouldnt rev it up just stall, so something for the late 80's early 90's Ford guys to think about, they make aftermarket modules with different specs, but havent tried any ,

[Cobb]

Might want to try some BP gas. The newer insight runs at almost 11 to 1 compression with its dual spark plug iDsi ignition. Myself and a few owners notice with BP or mid grade gas it will pull more timing and not vary the rpm or cvt ratio that often under a light load vs regular or the cheap stuff. Ive been buying my gas at sheetz as its 3 cents off with a membership card, but I like the behavior better on BP fuel.

[mechman600]

I would say that the 4 mpg difference is because of the lower ethanol content in the 91 octane gas, not the advanced ignition timing.

Your engine is smart enough to advance the timing when it sees high octane gas because higher octane gas has a slower flame front and requires more advance for the same power output.

[arcosine]

My saturn gets much better mpg with premium. With regular the timing retards to -5 degrees when hot at low rpm full throttle.

[Cobb]

Ive notice with the grill block when the temp gets above 185 the i2 starts to retard timing and upping the cvt ratio.

[ECONORAM]

When I had my 84 and 90 Jettas, each with a 1.8L, I saw a similar FE increase. The 84 I was able to set the timing up a few degrees at the distributor--no knock sensor. The 90 did have a knock sensor, and from the factory it had only 4*BTDC at idle. With 91 octane, I was able to bump it to 8* and I recall getting about 2 mpg.

[ever_green]

Originally Posted by Cobb

Ive notice with the grill block when the temp gets above 185 the i2 starts to retard timing and upping the cvt ratio.

that's strange on days that i use grille block my timings usually advance furthest and overall MPG improves. sometimes if i don't use a grille block my timing would not hit 44-46 deg the whole day...not sure why.

Originally Posted by mechman600

I would say that the 4 mpg difference is because of the lower ethanol content in the 91 octane gas, not the advanced ignition timing.

87 octane and 91 octane petro canada gas are both 10% ethanol. only shell v-power 91 here is 0% ethanol. i used 91 petro canada.

[RobertISaar]

Originally Posted by ever_green

that's strange on days that i use grille block my timings usually advance furthest and overall MPG improves. sometimes if i don't use a grille block my timing would not hit 44-46 deg the whole day...not sure why.

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.