swodo

I think the GT ECM can automatically adjust from 89 octane to 93 plus . So how is anything to be really gained from a 93 octane tune? Am thinking of getting a tune and leaving ONLY this feature untouched, rather than getting a 93 octane tune and changing it when travelling to areas where high octane is not readily available or carrying an octane booster. Does the engine part of a tune really do anything besides retarding the spark? Really more interested in the transmission and accelerator modifications.

Sorry if this a stupid question.

Derf00

The 2005-2009 Mustangs do not adjust to Octane, anything above 87 Octane is a waste of money unless you have a tune for it. Only the 2008-2009 Bullitt edition has this capability.

A tune alone will net you the most power gains without boltons. Typically 20-25 hp at the flywheel.

A tune for a specific octane is more than just a timing thing on these cars. You should contact one of the many forum sponsors that offer tuning and ask them what is different in the tunes for different octanes they offer so that you have all the information before assuming or guessing.

08'MustangDude

Turbocharged, Supercharged, and VVT engines are the only ones that highly benefit
with higher octane. This is how Dodge was able to have their V6 motors go from
250HP (3.5 V6) to 305 HP (Pentastar 3.6 V6). The 3.5s do not have VVT, but have
spark timing advance. The 3.6 has VVT and spark timing advance, thus the huge
gain from 250 to 305 HP in the 3.6 V6 Challengers. Chargers only got 289 HP,
but easily up'd.

I had a '07 Charger, got a tuner, and it only gave me +15 HP, and I had to use 91
octane else you could hear it knocking under load. The timing was farther advanced,
but the lower octane fuel was detonating prior to spark. Tuners help, but motors
that do not have VVT just don't get any REAL gains.

If the 05-09s were able to advance the timing, you'd have more than 210HP from
a 4.0 motor. Look at the Dodge 3.5 V6 I mentioned with 250HP, and here the Mustang's
4.0 is only netting 210? .5 more displacement, -40 horse power. I tried to find a Charger
before buying this '08 Mustang, but just could not find one in good condition, for the
same price. I had a 2010 lined up that needed a rear bumper cover, but the dude backed
out on me, then just marked it sold last week.

The advance in timing is why you need higher octane, so the fuel is ignited by the spark,
and not detonation. A tune for these cars, say, for 91 octane is a change in timing using
programming. It is set advanced, so you need the higher octane for the tune, and cannot
use 87 because now the timing is advanced and won't retard enough for 87. Valve timing
will never change, so you're limited on power gains.

You can squeeze ~330 HP from that 3.6 VVT Pentastar V6 with a tune and intake alone.

If you want more of the Mustang's power to get to the wheels, an Underdrive pulley is another
step. They DO NOT add horsepower, they just deliver more of the available HP to the
wheels by reducing parasitic HP loss at the accessory pulleys by reducing their RPMs,
thus reducing the load at the crank pulley.

If the chance should be bestowed upon me, where someone wants to trade their Charger for
my 'Stang, done deal... I just needed a spare vehicle... Charger gets better MPG too!!

Dino Dino Bambino

Only the 2008 Bullitt and the 2010 GT came with adaptive spark timing, so adding higher octane fuel to a 2005-2009 GT with a stock ECU tune confers no benefit.
If you want to gain a few HP without changing any hardware, get a custom ECU tune for your choice of fuel grade.