Gas/Octane Question

[triggerman]

Hi
Another stupid question of mine. I've been reading about Octanes in gasoline, and according to around 90% of websites there is no real benefits from a higher octane. Is there any real benefits? Or difference?

[vwhobo]

Originally Posted by triggerman

Hi
Another stupid question of mine. I've been reading about Octanes in gasoline, and according to around 90% of websites there is no real benefits from a higher octane. Is there any real benefits? Or difference?

There is absolutely no benefit to using a higher octane gasoline than the engine requires. Using a higher octane than needed can actually reduce the efficiency of your engine, cause you to get worse gas mileage and put out less power.

[triggerman]

There is absolutely no benefit to using a higher octane gasoline than the engine requires. Using a higher octane than needed can actually reduce the efficiency of your engine, cause you to get worse gas mileage and put out less power.[/quote]

Alright thanks, well how do you get worse gas mileage? I've been told using a higher octane gas helps the engine if it's a "high performance engine" What exactly would or could be considered a high performance engine?

[triggerman]

Alright thanks, well how do you get worse gas mileage? I've been told using a higher octane gas helps the engine if it's a "high performance engine" What exactly would or could be considered a high performance engine?

[vwhobo]

Originally Posted by triggerman

Alright thanks, well how do you get worse gas mileage? I've been told using a higher octane gas helps the engine if it's a "high performance engine" What exactly would or could be considered a high performance engine?

1. As I said in the previous post, decreased efficiency.
2. More correctly you need higher octane in a higher compression engine. I can't give you a specific number because it depends on factors such as engine design, materials used (aluminum or cast iron) and the powertrain management system. Generally speaking the newer (technolgy wise) the engine, the higher compression it can run before an increase in octane is required.

[VrrmPshh]

Ok im a little confused, cause my car only requires 91 octane, but when i put 100 octane in there it re-adjusts the timing and runs faster smoother and i get better gas mileage, so when you say no gains do mean once you reach the optimal octane for your engine ( which in my case is way above pump gas ) or when you go above what your car manual says ( which in my case is 91 ).

[vwhobo]

Originally Posted by VrrmPshh

Ok im a little confused, cause my car only requires 91 octane, but when i put 100 octane in there it re-adjusts the timing and runs faster smoother and i get better gas mileage, so when you say no gains do mean once you reach the optimal octane for your engine ( which in my case is way above pump gas ) or when you go above what your car manual says ( which in my case is 91 ).

In your case what I'll say is you have a great imagination. If your car requires 91 octane, that means it is optimized for 91 octane. Running 100 octane is a waste of money.

[asa67_stang]

don't most vehicles have programming built into the 'puter that allows lower octane through various tricks?
ie: retarding timing
leaning out the AF mixture
(if Forced Induction) lowering boost

it's just that they get the optimum power curve at X octane, but they can survive on Y octane
right?

[vwhobo]

Originally Posted by asa67_stang

don't most vehicles have programming built into the 'puter that allows lower octane through various tricks?
ie: retarding timing
leaning out the AF mixture
(if Forced Induction) lowering boost

it's just that they get the optimum power curve at X octane, but they can survive on Y octane
right?

You're right, although it depends on how smart the PCM is. Most cars get by with a knock sensor which retards the timing when detonation is present, some are a little more advanced then that. However that's a short term solution, if you regularly run gas with too low an octane rating there will most certainly negative long term results.

[asa67_stang]

good thing i told my mom she's been runnin too low of an octane on her Passat then, eh?
i was suitably impressed by that 1.8T and how well the rest of the car worked together, very nice

[VrrmPshh]

I wish i had more then just my "butt dyno" to prove that running a higher octane in my car was increasing its efficiency and performance, but i dont so i wont even argue the point as it is all goin off my word. I did however look in my manual to see if there was anything on running a higher octane and only found that it said use "at least 91 octane" which leads me to believe that perhaps 91 is not my car's optimum octane rating its just what subaru feels is the lowest you can go without any negative side effects. Now im not sayin 100 octane is my car optimum rate either but im going to do a little more research ( gradually increasing octane until i can no longer feel a difference ) to figure it out...i guess i could also just call subaru and ask them..but wheres the fun in that

[SuperJew]

Originally Posted by VrrmPshh

Ok im a little confused, cause my car only requires 91 octane, but when i put 100 octane in there it re-adjusts the timing and runs faster smoother and i get better gas mileage, so when you say no gains do mean once you reach the optimal octane for your engine ( which in my case is way above pump gas ) or when you go above what your car manual says ( which in my case is 91 ).

where do you get 100 octane gas?

[BavarianWheels]

.
.
You can read some "official" data here:

http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm

...but who really trusts the government anyway...

[VrrmPshh]

some gas stations sell GT-100, but i use 91 octane then add toulene acorrdingly heres an article on it that pretty much explains it all

http://forums.audiworld.com/s4/msgs/95187.phtml


it also explains that newer cars (like mine) do benefit from higher octane gas

[asa67_stang]

toulene is very harsh on rubber, dunno what effects it has when dilluted through gasoline