93 octane to 87

[RitzGT]

Peak, yes. There's a 10-15 hp hit in the mid range.

It's a small enough change that you wouldn't even notice. 15hp loss is only 3.5% of the GT's peak power. The ecu simply retards the timing if it detects any knocking. Totally safe and nothing to worry about on the stock programming. I normally run 93 "just because," but I've put 87 in a couple of times when I was running low and hit a gas station that was out of premium.

Best,

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[18psi]

I have a question I think might be worth discussing rather than keep the stupid back and forth between money and octane ratings and performance:

If I understand the OEM knock control strategy on modern OEM ecu's, the engine pulls timing on low octane due to knock. That means the knock already took place. So it's not proactive, it's reactive. Meaning you're causing damage to your engine. Now, say it retards the timing due to knock, from everything I'm seeing this car is similar to other modern cars, and it constantly tries to advance timing back, and if it runs into knock again, it pulls timing again. That means It's constantly playing with the knock/det threshold and there are multiple knock events happening inside the engine that keep pulling power.

Is this correct?
Or is the ecu logic such that the timing gets pulled until ecu is reset?

IMO, saving a couple bucks is pretty stupid if it's at the expense of knock/detonation happening in your engine frequently.

 

[RitzGT]

I have a question I think might be worth discussing rather than keep the stupid back and forth between money and octane ratings and performance:

So the engine pulls timing on low octane due to knock. That means the knock already took place. So it's not proactive, it's reactive. Meaning you're causing damage to your engine. Now, say it retards the timing due to knock, from everything I'm seeing, it constantly tries to advance timing back, and if it runs into knock again, it pulls timing again. That means It's constantly playing with the knock/det threshold and there are multiple knock events happening inside the engine that keep pulling power.

Is this correct?
Or is the ecu logic such that the timing gets pulled until ecu is reset?

IMO, saving a couple bucks is pretty stupid if it's at the expense of knock/detonation happening in your engine frequently.

Back in the stone age when cars had no fancy ecu or knock sensors, engines would occasionally knock under load, or if the timing was excessively advanced, you simply got a bad tank of gas, etc. Engines weren't flying apart as a result. The knock sensors today are pretty sensitive and the manufacturer SAYS that 87 is ok. What more do you want? Personally, I'm the type of person that puts the higher octane in because I specifically bought the GT to get the additional ponies. But using 87 isn't going to cause any harm to a stock engine.

Best,

 

[18psi]

Back in the stone age when cars had no fancy ecu or knock sensors, engines would occasionally knock under load, or if the timing was excessively advanced, you simply got a bad tank of gas, etc. Engines weren't flying apart as a result. The knock sensors today are pretty sensitive and the manufacturer SAYS that 87 is ok. What more do you want? Personally, I'm the type of person that puts the higher octane in because I specifically bought the GT to get the additional ponies. But using 87 isn't going to cause any harm to a stock engine.

Best,

maybe I should specify, I'm talking about 03-15 cars here. just tuned a few 2014's STi's last week. I'm a noob to mustangs, but not a n00b to very powerful modern cars and their very powerful modern ecu's/knock control strategies

I appreciate your feedback, but it seems like you're just talking out of your rear.
A knock sensor only detects knock after knock happens.

If these cars have an octane sensor that lowers timing before knock happens, then you have a leg to stand on.

 

[RitzGT]

I've been tinkering/tuning Subaru's and Evo's for the past 10 years and know for a fact many of those cars' tuning was set up/done exclusively for 93+ oct.

All of them say in their manuals that 91 octane is the minimum. most of them knock on 91, right out of the factory. years and years of proof/discussions

Same here with my hot rodded Audis (had my 2.7L twin turbo A6 up around 500hp). But that's a custom tune without all the factory safeguards on a forced induction motor, not a normally aspirated Mustang.

Best,

 

[18psi]

Same here with my hot rodded Audis (had my 2.7L twin turbo A6 up around 500hp). But that's a custom tune without all the factory safeguards on a forced induction motor, not a normally aspirated Mustang.

Best,

Nope, I'm talking about the OEM tune, logged and showing clear knock happening, and the timing retard that follows, then timing fed back in, and the cycle repeats multiple times over to keep the car from blowing up on bad gasoline.

Many well known companies like Cobb Tuning even have special maps for people in states with terrible gasoline. They run much less base timing and boost and make less power, because having the car constantly pulling dynamic advance due to low octane is a terrible reactive strategy and destructive to your engine.

 

[RitzGT]

Nope, I'm talking about the OEM tune, logged and showing clear knock happening, and the timing retard that follows, then timing fed back in, and the cycle repeats multiple times over to keep the car from blowing up on bad gasoline.

Whelp....if the manufacturer says 91 is the minimum, then that's another story. Ford is saying 87 is the minimum.

Best,

 

[69mach1-395]

I think where peeps get confused is the advertised power ratings use premium octane even though it will run just fine on regular octane. What is probably more important is to use top tier gasoline regardless.

 

[Emt1581]

I think where peeps get confused is the advertised power ratings use premium octane even though it will run just fine on regular octane. What is probably more important is to use top tier gasoline regardless.

Just curious but what is top tier gas? Is Shell better than Mobil which is better than Speedway?

Thanks

-Emt1581

 

[RitzGT]

Just curious but what is top tier gas? Is Shell better than Mobil which is better than Speedway?

Thanks

-Emt1581

Perhaps I can be of some assistance here:

http://lmgtfy.com/?q=top+tier+gasoline+retailers

 

[Emt1581]

Perhaps I can be of some assistance here:

http://lmgtfy.com/?q=top+tier+gasoline+retailers

addle:

-Emt1581

 

[69mach1-395]

That list has grown since I last saw it.
I like how the link shows one how to google something.;)

 

[Enzo]

The higher octane is always worth it. Lower octane will just help detonate before piston reaches top dead center. Which results in power loss and lower mpg. $4 is not going to make or break you, and if it is you shouldn't be driving a v8 to begin with. When I bought my car from the dealer I told them not to fill it up. I want 93 in it and I filled it myself. It's a great car and has an amazing power plant. Fill it with good gas and don't cheap out.

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[ponie1992]

So you are telling me going from 87 to 91 on a 11:1 compression ratio engine I am only gaining 4HP? I call BS.
Just found this graph. Yes the peak is only 5HP but look at the rest of the graph see how much difference there is.
Look how unsmooth the line is when on 87? That's your engine pulling timing.
Looks like the factory tune was limiting something closer to the redline. This is a 2011 5.0L.

Look at that torque increase!

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