11SHELBYGT500

Well, you're only losing 10 peak horsepower, so you still have 410 hp and you're not throwing money away at the gas station.

dmichaels

For the extra ~$3/fillup, I'll be putting in 93. Whats $53 vs $50? Especially when I'm hitting Limerock or the Glen later this summer!

11SHELBYGT500

I don't know how many times this has been discussed, but it's because you might as well give me the 50.00 because you're not using it. As for the track time, that's when you fill it with high grade, not when you're going to the grocery store.

thegame

Well on top of the obvious hp differences, wouldn't you be happier knowing your mustang isn't going to knock or detonate using 91 or 93? I know the PCM is going to react to 87, but how do you think it does this? It pulls timing based on knock. Modern engines are designed to handle a small amount of knock, but I know I don't want any of that activity in my motor. Just my thoughts, whether they be wrong or right.

dmichaels

With stock tuning, I could be convinced 93 is not quite worth it... It's also a bit of a precautionary measure (if a knock sensor goes bad, 93 is far less likely to knock than 87).

I come from the turbo car world, and I am very used to a tuned car that absolutely needs 93. Habits die hard

11SHELBYGT500

If its peace of mind you're looking for, than 50.00 a year is probably worth it...but try not worry so much. Lol

Ltngdrvr

It will knock on 91 or 93 too because the pcm is always trying to run the most timing advance it can and this is regulated by the knock sensor response.

This is how the motor makes more HP on the higher octane gas, also how it gets better gas mileage on the higher octane.

dmichaels

Are there data logs of knock sensors and ignition timing/retarding to this is the case? I'd like to see knock sensor voltage and timing charts (will be doing this data logging once I get my car and start playing around as long as I can identify the right parameters!...) I'd be very curious to see if timing is being pulled with 93 octane

dmichaels

haha I'll work on that - blew up a turbo at a track day at 6500 RPM (liberated the turbine wheel - shot out the cat-less exhaust I had...) and I'm a tiny bit more cautious now Unrelated to fuel octane, but I have an overall sense of cautiousness with my car now!

I figure if I do everything I possibly can to treat the car right (best fluids, good parts, etc) it will do its best to treat me right (not breaking, not acting unexpectedly). A bit overkill perhaps, helps me sleep at night tho

V6 Driver

This has been very interesting reading. I enjoy the different opinions.

I have finally been able to bring my car out of storage from its winter nap, and I have recently switched to 93 octane in preparation for a tune. In Wisconsin we have to use bullc**p winter/summer blend of reformulated gas. I realized when I stored the car I put a tank of 87 octane summer blend into it, and was getting 24mpg combined which I was pretty pleased with. Granted the car only has 3500 miles on it. Currently it is getting 18mpg with its first tank of 93 octane winter blend. We aren't supposed to get our summer blend until June. I am considering this to be crappy mileage currently but it most certainly will get better once we get our summer blend. At that point I'll apply the tune.

thegame

Um, no it won't. You are way off. The PCM is trying to run the pre-programmed tune - IE 91 octane or 93 octane (very conservative.) There are set timing and A/F ratio maps that the PCM runs. It only pulls timing whenever knock is present with lower octane or major heat soak or track days. With what you said, there would be absolutley no increase with an aftermarket tune if the stock PCM is already trying to add as much timing as possible. Understand? If you still don't follow, add 100 octane to your car and see if it makes more power on the stock tune. It won't. I assure you.

dmichaels

That's where I was going with my data logging question... from a tuner perspective, it would make sense to optimize for >93 octane, but from a OEM factory perspective, no point in writing programming that is always pulling timing.

Related to this, I was searching around for any tuners that offer a high octane tune (100 octane) - didn't see anything. Not that I'd run it as 100 octane unleaded is $$$ and without significant modifications the benefits are minimal on a N/A car. But I'd be interested to see for potential future upgrades I may consider

thegame

Exactly, I agree. Especially on a high compression motor. Of course, the PCM is crazy complex and closed loop vs open loop play a large part. But when we refer to timing and power, we are talking WOT open loop. I'm sure knock could be present at times during closed loop.

This is a little old, but a good read. There are three parts.

http://www.musclemustangfastfords.co...g/viewall.html

http://www.musclemustangfastfords.co...m/viewall.html

http://www.musclemustangfastfords.co...e/viewall.html

thegame

Sorry OP, I know we kind of got way off track with you original question. I didn't mean to turn this into a tuning / octane debate. Back on topic. I'm still only getting 13 mpg at best. But its worth every penny!

wentw1tj

could not agree more. 93 for my motor.

WhiteBird00

Sorry, you're wrong. The programming you talk about is the standard used on most fuel injected cars. My LS1 Trans Am had exactly the setup you mention - it was factory tuned for 91 octane and would retard the timing if the knock sensors detected lower octane fuel. That timing change caused a significant loss of power and mileage - much more than the difference in cost could justify. But running higher than 91 octane would have no benefit at all because the PCM wasn't programmed to handle it. The majority of current Ford engines have that same type of programming.

However, the 5.0 Coyote and the EcoBoost engines have a new programming paradigm called "adaptive spark control" that actually works the other way around. The base timing is set for regular (87 octane) fuel and the PCM will constantly monitor the knock sensors in an effort to advance timing for better performance. When higher octane fuel is used, the PCM will advance the timing to take advantage of it. Of course, this only works up to a point - there is a point of diminishing returns with timing advance where further advance actually reduces performance. That's why you will see increases up to about 93-94 octane but nothing much beyond that. Octane beyond that would only be useful for higher compression - the other way to use octane for more performance.

thegame

What you just said is very similar to what I said. I was just trying to make the point that the car isn't going to keep adding timing to the point of knocking, even with 100 octane. And you seemed to add to that. What part were you disagreeing with? I obviously am aware that there are hundreds of other factors such as IAT, IPW, Load, etc. in the tune. All in all, it's still pre-programmed on how the PCM reacts. Add or remove timing within the hundreds of tables depending on hundreds of variables in the tune. But it's not open ended as someone had stated.

WhiteBird00

I was trying to point out that your description referred to the most common PCM configuration of having a static program for a selected upper octane level and then retarding timing if the fuel didn't meet those parameters (i.e. knocking was detected). That configuration is NOT used on the 5.0 or EcoBoost engines. In fact, they are the exact opposite. They start with a program for low octane fuel and add timing advance up to what the octane level can handle. The fact that there is no improvement for 100 octane is not related to a PCM programming shortcoming but due to the basic physics - you can only advance timing to a certain point before it becomes counterproductive. That would be when the spark fires so much before top dead center that the flame propagation works against the rising piston resulting in lost power.

So, contrary to your post, the PCM program does not start with a 91 or 93 octane program and "pull timing" for lower octane. And it does try to add more timing advance as much as possible - up to the point of diminishing returns. I know for a fact that it will do that up to 94 octane and I would bet that it will go higher, perhaps 96 or 97 octane although I don't know that for sure. It might even go as high as 100 octane but I doubt it.

The key word you used is "conservative"... what the factory considers "as much as possible" is very different from the view of an aftermarket tuner. Aftermarket tunes work because they are tuning for a particular result (more power/torque) whereas the factory tune is much more conservative and is designed to balance other factors such as fuel economy, smoothness, engine longevity, heat management, etc.

thegame

I understand what you're saying. But I still disagree. The tune is still static in a way, but with more tables. It may start with 87 and work its way up. That part I'm okay with. but there is still a set limit in the ford tune for timing advance. And it's not the point of max power. How would you explain the power increase shown from an aftermarket tuner? I know they are tuned with performance in mind. And the factory has other factors - longevity, fuel economy, etc... In other words, timing is still limited on the ford tune. It may retard and advance some degrees to compensate for 87 vs 94 octane. But that's it. It will never even come close to approaching the point of diminishing returns. It will knock well before this and ford knows that. They do not even try to approach the kind of timing aftermarket tuners use.

WhiteBird00

It doesn't matter whether you disagree. It's been discussed and documented numerous times in newspapers, trade magazines and forums including interviews with Ford engineers. I suggest you read this article: http://www.autoblog.com/2009/12/28/d...ll-new-5-0-v8/ or do your own search for ford coyote "adaptive spark" if you prefer. The relevant quote is about 2/3 down the page: "The adaptive spark control system keeps the engine running right on the knock sensor all the time, continuously adjusting the spark advance to avoid detonation regardless of the fuel used."

Also, the point where increased timing advance causes a decrease in power usually comes well before detonation occurs. Have you ever actually run an engine on a dyno? You keep adding a degree or two of timing advance until you see a decrease in output - without any knocking or damage to the engine. So the engineers have built an upper limit for total advance into the program so that the PCM doesn't keep advancing the timing beyond that limit regardless of what octane fuel is used. That's why you probably wouldn't see any more power using 100 octane.

Aftermarket tunes are not all about timing. There are several other factors that affect power and torque - most importantly air/fuel ratio. Ford tunes that ratio very lean for both economy and emissions. Aftermarket tuners are free to push more fuel into the cylinders to create more power at the expense of fuel economy and emission levels. And they can do that at different points in the RPM curve so that they can still have economy until the engine is pushed.