Ford focus 91 octane question

[graver555]

I have heard some engines can get better mileage with 91 octane, because the knock sensor will advance (or Mayby it was retard, I'm not sure) the timing. Any truth to this? Would it be worth experimenting with?

[graver555]

It's at 2011 btw if that helps

[KrautBurner]

if the car isn't made to optomize premium
it won't help

if you can advance your timing, you may be able to squeeze more mpg out of premium

but the knock sensor is a safety feature, to retard timing if needed
this will lower your fuel economy


rule of thumb
do not run Premium fuel in a vehicle that is not designed for it

[Cobb]

For the cars that can take advantage of it, the cost isnt worth it from a mpg stand point. From a drive-ability point it does.

The 2nd gen insight behaviors like a completely different car on 93 octane, but you dont break even or save more. Its just more fun to drive.

[redpoint5]

My TSX is designed to run 91 PON, but I don't notice any difference in MPG running 87 (although there may be some small unmeasurable change).

I do notice less power and retarded timing when running 87 octane, but it doesn't appear to affect the MPG in any way that I can measure.

[Cobb]

red, I think your gearing is too low to benefit from it at highway speeds, maybe in the city. The higher octane fuel allows the engine to handle more load at a lower rpm and run higher tming. If its a turbo or super charged engine it can handle more boost at lower rpms too.

[graver555]

We'll I tried testing it today. I had gone on a work trip yesterday about 250 miles and gotten about 33 mpg. I put 91 in it on the way back, but I hit such a crosswind and headwind I stop even trying to be consistent with the driving style from the way there, and ended up just trying for max mpg at 45 once the wind died down

Actually hit 37ish with cruise on

[Thenorm]

your engine was designed for 87. it won't advance the timing. The car nornally runs full advance until it senses knock then retards it.

If Ford could easily get an MPG improvment by specifying 91 octane, they would just to help their CAFE fleet mileage.

also, do a quick match calculation to see how much MPG imrpovement you would need to see tust to break even on the more $$ gas.

summary: don't bother

[Cobb]

graver, higher octane loves more load. If you get a chance do a 0-60 run to see what other differences you see. For the insight for example the engine runs lower rpms under harder acceleration and seems to peak the tach at 4700. On the moose piss cheap stuff it bounces off the red limiter.

[graver555]

We'll it sounds like it won't help so I'm not going to do Aba tests as it is my gf's moms car anyway.

Thank you for all the replpies