# Octane and you. **URL:** \ **Category:** NYSpeed Automotive\ **Created:** [July 16, 2005, 4:46pm UTC](https://forums.speedlife.net/t/octane-and-you/861 "2005-07-16T16:46:54Z")\ **Posts on this page:** 10\ **Page:** 3
**Author:** ![jay\_g](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jay_g/32/111288_2.png) [@jay\_g](https://forums.speedlife.net/u/jay_g)\ **Post date:** [July 22, 2005, 9:06am UTC](https://forums.speedlife.net/t/octane-and-you/861/41 "2005-07-22T09:06:31Z")
my '98 gtp has two spark tables depending on knock record. If no knock or low knock is recorded the “better” spark table is used, if alot of knock is recored the “bad” spark table is used. ---
**Author:** ![RuBiCaNT](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/rubicant/32/7622_2.png) [@RuBiCaNT](https://forums.speedlife.net/u/RuBiCaNT)\ **Post date:** [July 22, 2005, 9:15am UTC](https://forums.speedlife.net/t/octane-and-you/861/42 "2005-07-22T09:15:56Z")
> [@Inn-Tune](#): > > Many newer vehicles run what are called spark difference maps. They give the computer a base timing map and run algorithms which increase timing off that base map based on current and historic readings from the knock sensor(s) and other sensors. > > The majority of newer imports do this. For example: VW, Audi, Subaru, Honda, Mitsubishi, etc. Perhaps some new US don’t do this, but I’d be surprised if the higher performance ones didn’t. > > I guess you’re saying that 91 octane fuels have extra cleansing agents that remove carbon deposits? Is that what you’re saying? > > -Mike I know the SRT4 does this big time… ---
**Author:** ![Inn-Tune](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/inn-tune/32/7588_2.png) [@Inn-Tune](https://forums.speedlife.net/u/Inn-Tune)\ **Post date:** [July 22, 2005, 9:24am UTC](https://forums.speedlife.net/t/octane-and-you/861/43 "2005-07-22T09:24:55Z")
> [@num482](#): > > my '98 gtp has two spark tables depending on knock record. If no knock or low knock is recorded the “better” spark table is used, if alot of knock is recored the “bad” spark table is used. This would be the old system, but as usual US manufacturers are slow to convert. The bad spark table is generally only used when something is really wrong. If your car operates off two fixed tables alone and doesn’t advance timing on top of the “better” spark table’s fixed advance values, you won’t see more timing advance if you run a higher octane fuel than specified…UNLESS you have modified the car in ways that cause it to use the “bad” spark table with the standard fuel. Sometimes something as simple as an intake can cause the car to lean out enough to push the car into the “bad” spark table when you run the minimum recommended octane for the stock car. Running a bad tank of gas or having non-octane related runability issues can also put the car into the “bad” table. -Mike ---
**Author:** ![jay\_g](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jay_g/32/111288_2.png) [@jay\_g](https://forums.speedlife.net/u/jay_g)\ **Post date:** [July 22, 2005, 11:33am UTC](https://forums.speedlife.net/t/octane-and-you/861/44 "2005-07-22T11:33:16Z")
> [@Inn-Tune](#): > > _snip_ While im not totaly firmiliar with the hole tunning/spark table aspect of my car I think I understand what your saying. You are correct that with a bad tank of gas it will go into the bad spark table to save the motor, fight KR. Stock timming was only aloud to go to 15degrees advaced. Now thats also saying that you need to have 0 kr to have the full timming advace work for you. If I was seeing 0KR with say 91 oct I would have full advace at WOT and would not gain by going to a higher octane. Now I have mine tunned and have new timming tables burned. For instance stock set up was roughly 25ish degrees advaced max at normal curise speeds and 15 degress at WOT. Now my new tables are 28ish at normal curise and for my max WOT have a knob that I use to select what I want. Normaly I have it set around 16-18 depending on how hot it is and how many psi im running but I have the option to turn it up to 25 degrees advaced at WOT. The pcm will take what I set my WOT at and depending on different readings it takes it will go from thier, either give me the full advaced or pull timming as it see’s fit. Sorry for going off topic. ---
**Author:** ![Inn-Tune](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/inn-tune/32/7588_2.png) [@Inn-Tune](https://forums.speedlife.net/u/Inn-Tune)\ **Post date:** [July 22, 2005, 8:18pm UTC](https://forums.speedlife.net/t/octane-and-you/861/45 "2005-07-22T20:18:32Z")
A bit off topic, but that’s an interesting setup. What exactly does the knob control? Are you tricking the computer into advancing the timing by trimming the IAT or something? Perhaps this could be another thread… ---
**Author:** ![Vile](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/vile/32/7595_2.png) [@Vile](https://forums.speedlife.net/u/Vile)\ **Post date:** [July 22, 2005, 10:15pm UTC](https://forums.speedlife.net/t/octane-and-you/861/46 "2005-07-22T22:15:03Z")
only 93 for me… but i’m tuned for it. 13gal tank just gave me 427miles on my last fill 🙂 ---
**Author:** ![Z24Challenge](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/z24challenge/32/7231_2.png) [@Z24Challenge](https://forums.speedlife.net/u/Z24Challenge)\ **Post date:** [July 23, 2005, 2:26am UTC](https://forums.speedlife.net/t/octane-and-you/861/47 "2005-07-23T02:26:34Z")
> [@Vile](#): > > only 93 for me… but i’m tuned for it. > 13gal tank just gave me 427miles on my last fill 🙂 Cool to see you got yourself a new car :tup: ---
**Author:** ![jay\_g](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jay_g/32/111288_2.png) [@jay\_g](https://forums.speedlife.net/u/jay_g)\ **Post date:** [July 25, 2005, 6:30am UTC](https://forums.speedlife.net/t/octane-and-you/861/48 "2005-07-25T06:30:39Z")
> [@Inn-Tune](#): > > Perhaps this could be another thread… [http://www.nyspeed.com/forums/showthread.php?p=15857#post15857](http://www.nyspeed.com/forums/showthread.php?p=15857#post15857) ---
**Author:** ![Mysterio](https://avatars.discourse-cdn.com/v4/letter/m/e56c9b/32.png) [@Mysterio](https://forums.speedlife.net/u/Mysterio)\ **Post date:** [July 25, 2005, 3:58pm UTC](https://forums.speedlife.net/t/octane-and-you/861/49 "2005-07-25T15:58:48Z")
> [@BaD AZz Z/28](#): > > Sunoco doesnt have 94 anymore. > > Just wait until you calculate your mpg for each kind of driving, fill up a bit each day and figure out how far you want to drive that day so that you end up with the right amount of gas that night…you arent there yet 😉 Sunoco sells 94 still, here in ohio 🙂 ---
**Author:** ![Jesse](https://avatars.discourse-cdn.com/v4/letter/j/c77e96/32.png) [@Jesse](https://forums.speedlife.net/u/Jesse)\ **Post date:** [July 30, 2005, 6:51pm UTC](https://forums.speedlife.net/t/octane-and-you/861/50 "2005-07-30T18:51:35Z")
if your engine is stock… you will not get any usefull hp by advancing the timing and running higher octane. if your engine is stock higher octane will not make your car faster. Its probably actually slower because the fuel is burning slower. on any forced induction vehicle run atleast 91 to avoid detonation, unless it is tuned on a lower octane. unless you have a high comp engine from the factory or you have a modified engine running 91 us useless. the butt dyno doesnt work unless the gains are atleast 10hp+. [Previous page](https://forums.speedlife.net/t/octane-and-you/861.md?page=2)