| wstar |
11-07-2011 10:00 AM |
Quote:
Originally Posted by Jordo!
(Post 1394813)
As a precaution on a very hot day (again, in-cylinder temps increase the chance of knock), running the car at constant high load on the track, the extra octane might be a reasonable precaution, in that it will prevent power loss/damage from possible knock events, but it will not give you any additonal power than you were already capable of making given your tune.
Incidentially, that is also why tuners will find better power on boosted cars by running a bit richer a mixture -- the extra fuel is not fully burnt, rather it just cools the piston, reducing heat, and therefore quenching possible knock.
Anybody want to add to/amend that?
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I'll add a little to this: what I've seen tuning this car with UpRev (various internet posts from dyno tuners, mostly lines up with what I heard from mine) is that on N/A cars, there's not much point tuning the timing on our engine. Whatever you set the tune to is basically just a baseline, and the car adjusts on its own based on knock sensor feedback. To quote from UpRev's own Tuning Guide:
Quote:
On the newer vehicles equipped with VVEL, the ignition advance algorithms rely heavily on knock sensor feedback. In
many cases it is not possible to make the ECU run more advance because as soon as you increase the values it hears
something on the knock sensor and adjusts accordingly. For VVEL vehicles you WILL still have to pull timing for forced
induction applications so that it won’t ping before it has a chance to do any learning. However for NA applications about
all you can do is pull back the high spots and smooth the table out. The ECU will do the rest on it’s own. In our testing
we found that pulling LARGE values from the main ignition table caused a LARGE power drop on the first run, but after a
few consecutive runs the ECU would advance the ignition right back to where it was before based on knock sensor
feedback.
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Given the above, I think it's highly likely that if you reset the ECU and put in a little learn time on a higher-octane fuel, chances are the ECU will pick up a bit more timing advance on its own resulting in some small power gains. It might be difficult to manage switching back and forth between race gas and 93 octane this way though, without getting more knock than you want on the way back to 93 (hence it's better to have specific maps as decent starting points).
The track I was at this weekend sells an unleaded 98 (Sunoco 260 GTX. They also had a 110 but it was Leaded). I showed up with a full tank of my usual 93, and topped off with several gallons of the 98 as we went through the weekend, avoiding fuel starve issues. I figured as the heat went up it was good for a little detonation insurance policy, might help clean the engine out a little as well. I wouldn't have been surprised if a full tank of the stuff would net a slight power gain once the ECU adjusted, but IMHO it's really not worth worrying about. By the end of the weekend I was probably running about 40% 93 and 60% 98, and now I'll mix it back to all-93 over my next few gas station trips. |
