davepl

If you go to the 1/4 mile drags and add half a tank of 110 octane, how long does it take the PCM to figure out that you're running decent octane?

I don't know if knock and advance are something it tries to optimize constantly or if you'd have to pull the power to the PCM and force it to start fresh.

I'm really not a fan of resetting the PCM, so I'm hoping it figures it out quickly... but don't know it's strategy.

Pro-Hunt

Good question! Interested in this as well.

fleming23

Timing is not going to increase due to the 110, knock retard should only be reduced. I don't remember if this is a return style fuel system but if so (and depending on where the return routes from), it should be pretty instantaneous as the fuel is burned through the injectors and the new mixed fuel is replenished.

If a returnless system, you would need to burn the fuel through the injectors, rails, and line to the tank before it could make a difference.

Knock is monitored in real-time so as soon as the higher octane fuel is burned, it should maintain maximum commanded timing.

Bill Dearborn

That assumes there was a knock issue before the higher octane fuel was put in the tank. If there wasn't there wouldn't be any difference in performance.

Bill

Slow Poke

With a stock car you will go much slower on 110 leaded octane and destroy your cats and degrade the 02 sensors at the same time. Even on 100 unleaded fuel and stock timing, you will go slower due to a slower burn rate. Stick with a 93/100 50/50 mix and it should be all you need for anti-knock. There will always be a little false knock.

The stock ecm timing is more sensitive to air and water temperatures and will take out timing due to weather conditions. You best bet is to try and keep the car cool and wait an hour or so between passes.

Clearing the ecm memory by disconnecting the battery post is easy. It resets the previous long term fuel trims, spark octane maps to Hi, and also relearns the A8 shift patterns. I use to see 6200 1st gear shifts before disconnecting the battery and then see 6500 1st gear shifts after a reset, but it relearns shift patterns over time and goes back to 6200 eventually. You really need a scanner like HPT to see all the changes.

dar02081961

Correct Bill, but if I may we need to explain.

There is always "knock" with 93 octane or lower in the Z06.
The Z06's PCM is designed to continuously probe for knock then set the timing just below the threshold of knock. So under most conditions the Z06 can and will take advantage of the extra octane. This is because the stock Z06 tune is "optimistic" and thus positioned to take advantage of better fuel by pulling less timing (actually allowing access to portions of the timing table that are not reached when running 93 octane because of the knock threshold).

The simple way to look at it is to say the Z06 is tuned for 95-96 octane. But the best most of us normally get at the local station is 93 octane. So your Z06 is always "pulling timing" slightly due to the "poor" 93 octane we have to run. But the day we get hold of some 95+ octane the PCM will be able to run all of the timing in the table without knock and pulled timing. Which should result in a few extra hp.

(Speaking strictly timing due to knock, timing is also pulled by the PCM for reasons other than knock and in a basic data log you cant see the difference.)