Help Me Understand Timing
 

With the help of Dad (Brent) a couple of weeks ago, he helped me to put together the general pieces of the tuning puzzle for any car. I was very appreciative of this.

After running some more logs on a revised tune, my car is still pulling up to 3 degrees of timing from the knock sensors, ending up around 21-22° of final timing. The AFRs seem to be staying relatively spot on, however.

I know that air temp, fuel octane, and other factors influence the car pulling timing to protect itself, I just don't know the details on why/how.

I'm looking for help to further expend my understanding of this stuff, and to know whether I am still okay running my car hard in the colder weather now that it's hear, and that nothing will happen.

Your good as long as you are not getting any knock

Well it's hard to tell sound wise when I'm rolling the car up to 7k....

That's not very helpful.....

He is getting knock which is why his car is pulling timing.

There are a few things to consider when discussing timing:

1. Quality of fuel being used
2. Commanded timing
3. Detonation
4. Cylinder pressure

Certainly not the whole picture but most of it.

Basically what happens is you command a certain amount of spark advance in the tune which can be RPM based. There is also a global spark advance modifier that works towards overall timing. When you hear of someone taking a few degrees out running nitrous for example, they are doing so on a global scale generally.

The knock sensors work to detect detonation. If they detect it, spark advance will be reduced and then ramp back in when it is back under control. Knock sensors can also allow timing to be added in vs. just for reduction.

Using a fuel such as e85 will allow for a greater amount of timing to be used as it is highly resistant to pre-ignition causing detonation. There are much deeper conversations that can be had about e85 and it's ability to resist detonation.

Then comes the whole discussion on octane rating and fuel. IMO you want to use the lowest octane fuel possible before detonation occurs. This ensures a more complete burn.

Cylinder pressure and dynamic vs. static compression have a lot to do with the detonation, timing, fuel discussion as well.

Not a cookbook by any means but a high level overview of what is happening.

I've filled up with 93 octane from 2 different Shell station in 2 different cities, and both datalog sessions showed up to 2.5-3° of timing being pulled from the knock sensor. This was denoted by a positive value under the knock sensor category. All the AFR were in check with what was being commanded.

I sent the datalogs to me tuner, who is one of the best ones in the Coyote platform (not AED), and his email back to me said that everything looked good and made small tweaks.

Both of these logs have come in colder temperatures than what my car was datalogging in the beginning, 65-75° now versus 80-85° before. Can that possibly be causing the issues?

I just want to know that my car is safe to drive hard, and that I won't screw anything up.

I will gladly forward someone my datalogs to look into if you supply an email.

Sending you a PM with my email address. I make no promises or guarantees but will look over it.

I'd try a different brand gas.

I've seen some cases where 93 with additives doesn't act like 93 without. Try it and see what happens. Your car should not be pulling that much timing. Doesn't sound like you're trying to give it too much timing. Try QT gas. Very high quality, the turnover in the gas in the tanks is good.

Help Me Understand Timing
 

I've never had issues with shell before, but I will try another brand next tank and log what I find.

As far as I know, I should be commanding around 25° or so...

I ran QT gas a few times and it didn't go over well...

Chevron exxon/mobil. Wbt pretty much hit the nail on the head.

Stock plugs? Did you gap down?

And I don't know much about the correct timing for NA 5.0s but isn't 25 a bit high? I thought most were around 20-22 and the race tunes were 23-24. I'd either get another tune or back the timing off till it stops knocking. Some cars act different than others.

I worked with aviation fuel for 9 years. Shell was the bastard son of fuel in that industry as well. It's funny that folks that feel they may have a fuel issue.....buys from Shell.

I have used Shell fuel for years without issue.

Fuel from the local Exxon comes from the same refinery as the local Shell station. The differences are the additives used.

One thing to be on the lookout for is general age of said gas station. I don't buy gas from an older facility. Jobbers can mess up and put the wrong fuel in the wrong holding tanks as well. It happens more often than one might think.

Find a station of your choosing and monitor logs periodically to see how the car is doing.

DirtyD's problem isn't fuel. He has too much timing in his tune for the fuel he is using. My recommendations via PM were to reduce timing and richen it up a hair.

Shell is fine, QT is fine. Stay away from RaceTrac gas.

http://www.toptiergas.com/retailers.html

I've never so much as touch the COPs with my fingers, let alone taken the plugs out. LOL