Trob

ive used the search couldnt find the answer. so i always run the 93 octane tune on my car. but i dont always run 93 octane in it, sometimes 87 oct. sometimes 89 oct. and sometimes 93 oct. is this a bad idea? ive had the tuner for about 7 months always running the 93 tune but switching up the octanes and havent had any problems. just need some advice to possibly prevent a problem in the future.

boduke0220

i would always run 93 or atleast midgrade if you have it set for that

BOSTANG

You most likely can get away with lower oct. in winter but when it gets hot again you will have to go up in oct. Especially under hard acceleration and wot.

cliffyk

Most tuners in the $400 price range, including Sniper Special Forces, do not do much if anything differently when either the 87, 91, or 93 octane tunes are selected--this is one of those "little secrets" the people selling them don't tell you*, as they do not want to be responsible for blowing up your engine. They will all bump the Global Spark Adder scalar by 2° or so, and allow another 1° to 2° advance at various higher load settings in the Spark Borderline table.

There are also a number of "usual suspect" things done to make the switch from closed to open loop happen faster, etc.

As to fueling, the AFR at higher rpms and TPS values (in the Stabilised Open Loop Fuel table) will be leaned a bit (from 12.6:1 to 13.0:1-13.2:1). This latter change is because the OEM tune is rich at WOT, typically 11.0:1 to 11.5:1, despite the SOLF table values being 12.6:1 Setting the values leaner will get the actual mix closer to 12.0:1--still a bit too rich but better.

As I said in opening it doesn't matter what octane you select, these are the settings you will get--this is why it doesn't matter what fuel you use. They are the basic "clean-ups" for the OEM tune which is a very "safe" tune.

To take advantage of the higher octane fuel you will need to use the tool to add further spark advance. With Sniper SF you use the fine tuning dialog to add 2.0° to 2.5° to the Global Spark Adder (on top of the 2.0° the base tune adds), and 1.5° to 2.0° in each of the rpm range spark modifiers.

-------------------------------
* - Sniper actually does tell you this, indirectly, by telling those that ask to use the fine tuning settings described just above.

Trob

Thanks for all the replies and cliffyk for going in to more detail and explaining that to me.