Moonshine

You've accomplished overwhelming me with information. I don't really know what you're trying to prove. I still remain my answer to the OP's question. You obviously know quite a bit about fuel and using it to make something go. Do you work in this field or are you just a serious combustion enthusiast?

tbirdscwd

He's a thug when it comes to tuning......He's right in this matter also. If your car was tuned for 93 octane then you would almost certainly get pinging by dropping the fuel you are running down to 91. The whole point of having a car tuned for a higher octane is to run more timing and thus get more power out of your engine. If you add the timing but don't increase the octane......ping, ping, ping. Simple as that. Most pre-loaded tunes on heandhelds aren't nearly as aggressive as you can actually run on 93 octane. Yours is probably one of these tunes.

SeanAndKate

damn i didnt know i was going to class when I opened this thread.

cliffyk

I have designed and overseen production of OBD2 hardware and software, and tuning tools; and have been turning wrenches and tuning my own vehicles for nearly 50 years. I have also taught engineering at times in my life, which I hope explains my need to attempt to educate...

So, getting back to the OP's question, the real answer is:

No one in this forum can give you a definitive answer, because we don't know anything about your particular "93 octane" tune.

Try running 91 and listen for pinging, if you hear none then your tune is safe for running 91 octane gasoline. However if you experience pinging then either run 93 octane/octane booster--or avoid throttle positions and loads that make it ping.

As tBird' said, generic pre-loaded, so-called "custom" mail-order, and any other tune supplied by someone who has not had hand's on experience with YOUR car, will be very conservative "safe" tunes.

The last thing the supplier of these wants is to get a letter from an attorney representing the customer that ran 91 octane, at the track, with a true, aggressive, "93 octane tune".

I run 93 octane with +4.5° Global Spark Adder and 1.5° to 2.5° added in the "high" cells of Spark Borderline table. If I was to run 91 octane I doubt the engine would last through 3rd gear at the track...

Moonshine

Maybe I should buy a bottle of octane booster and play with my timing a tad? Maybe I'll let out a few more horsepower...?

cliffyk

Canned/mail-order tunes are starting points, if you know what pinging sounds like--and your tuner allows global tining changes--then bump the global timing 0.5° at a time and listening for it--when you hear the engine pinging back off 0.5°.

If your tuner allows (or only allows) rpm range timing changes then bump the timing 0.5° in each range and listen for pinging--back off the ranges in which you hear pinging.

While testing each change, do not just go out and "floor-it". Do a few initial runs with moderate load and 1/2 to 3/4 throttle, then increase the load and throttle bit bu bit. When you hear and detonation back off.

A little bit of mild pinging during these sorts of tests will not hurt anything, prolonged detonation under heavy load and WOT will.

One other thing, intake air temperatures make a lot of difference in an optimised tunes tendency to ping. I have three optimised tunes, one for each of the three seasons we have here in NE Florida--Fall, Spring, and F-in' HOT; there is no winter.

As IATs go up you need to be less aggressive with the spark advance.

Moonshine

I'll check it out next week. Car's locked up in storage and the programmer's at home. Be expecting a PM. =)

tator152

very impressive stuff in all the posts you've made in this thread... i'll go ahead and try out the 91 and take it easy and if i hear any ping then i'll try to add some octane booster and see if that helps. Thanks for all your info, its good to hear someone who knows their ****

stangit9090

I don't know why this thread is even on here.

If you can only get 91, tune it for 91.

You dont tune a car for a supercharger then not put one on it.

Moonshine

Some programmers simply don't have a 91 program. Read the thread if you'd like to participate in the discussion. =)