Octane requirements

[CMP]

I hope this has not already been discussed already, but has anyone done any testing on the performance differences when using 91 octane or 93 octane (or higher) on the '13 Shelbys with the stock tune? I know us CA owners have been told that 91 was the only option, but I know of one place (I use it to fill the jugs for my track bikes) that has 100, 98, 94, and 87 at the pump:rockon:. If ford recommends 93, I assume our cars will perform better with that level of octane resistance.

 

[railroad]

You are lucky, not everyone has access to those octanes at the pump. I buy VP and add to my toys to keep the average a little above 93.

 

[Ray Lucca]

Where is the "place" that has 94 Octane?? I'm in S. OC. We used to have 100 Octane Unleaded available locally, but the station quit carrying it..

 

[CMP]

It is probably out of your range. The gas station is located in Sunol, CA (northern California) off of highway 680 (at most 10 minutes away from me).

 

[CMP]

Well sort of a followup on a old post by me. Now that I have my car and have read over the manuals I noticed that on page 8 of the "2013 Mustang Shelby GT 500 Supplement" that both listings for 662hp and 631tq for the Shelby are listed as "on 93 octane fuel". This leads me to believe that the Shelby will be able to reach those figures on 93 octane fuel (at the motor) and that anyone that does not have access to at least 93 will be down a bit on power. Just a theory of mine and it has not been proven, but just going by what the documentation says.

This is mostly for Shelby owners that are limited to 91 octane (CA..me) unless there is a gas station in the area that might carry something better (not the norm, but there are some).:rolling:

 

[farmboy90]

Yup, that is expected. I just dump half a can of Torco in with each tank (since we only have 91 octane here as well).

 

[cluscher]

You won't gain performance with more octane. The point is that the car is tuned to a particular octane level. The stock tune will perform the same on either 91 or 93. When you add timing/boost beyond the stock calibration you will see more performance, but you also need more octane to prevent detonation. That is a scenario where you could be "safer" running 93 octane over 91 octane if you got a "93 octane" tune from a tuner.

 

[CMP]

You won't gain performance with more octane. The point is that the car is tuned to a particular octane level. The stock tune will perform the same on either 91 or 93. When you add timing/boost beyond the stock calibration you will see more performance, but you also need more octane to prevent detonation. That is a scenario where you could be "safer" running 93 octane over 91 octane if you got a "93 octane" tune from a tuner.

Will the stock tune pull those numbers on 91 octane? I know the octane level in the fuel will not give you any more power as it is basically a detonation resistance number, but is the stock Shelby tune setup for 93 or is it 91? From the documentation Ford is saying 93 is the level of octane required to reach their advertised hp/tq numbers. If that is the case it seems to me that the stock Shelby tune is a "93 octane" tune in itself (stock)..with 91 acceptable, but not recommended for ultimate performance.

 

[Iceman5000]

You won't gain performance with more octane. The point is that the car is tuned to a particular octane level. The stock tune will perform the same on either 91 or 93. When you add timing/boost beyond the stock calibration you will see more performance, but you also need more octane to prevent detonation. That is a scenario where you could be "safer" running 93 octane over 91 octane if you got a "93 octane" tune from a tuner.

I disagree. I have done dyno pulls on my KR a couple years ago, trying to prove this exact point. The 93 octane consistently pulled on average 13 more HP over 91 octane with a stock tune. We did three pulls on 91, and three on 93 after draining the tank. The next day we did 3 pulls on 93, drained the tank again and then 3 pulls on 91. The results were consistent.

 

[farmboy90]

I disagree. I have done dyno pulls on my KR a couple years ago, trying to prove this exact point. The 93 octane consistently pulled on average 13 more HP over 91 octane with a stock tune. We did three pulls on 91, and three on 93 after draining the tank. The next day we did 3 pulls on 93, drained the tank again and then 3 pulls on 91. The results were consistent.

Yup, agree with Iceman. He is correct. Of course there is a different result with different octane--the computer pulls timing to accommodate. That translates to lost horsepower.

 

[Planeswalker]

I disagree. I have done dyno pulls on my KR a couple years ago, trying to prove this exact point. The 93 octane consistently pulled on average 13 more HP over 91 octane with a stock tune. We did three pulls on 91, and three on 93 after draining the tank. The next day we did 3 pulls on 93, drained the tank again and then 3 pulls on 91. The results were consistent.

It's the same way with the coyote engine, lower octane = less HP.

 

[san6279]

We generally have 87, 89, and 92 here in WA. Wish we had 93, but I guess it is better than 91. Just don't hear many other members talking about 92, in this or other forums.

 

[cluscher]

It's the same way with the coyote engine, lower octane = less HP.

Because of knock sensors retarding spark advance, not because 93 octane itself performs better than 91 octane. My point is that if you put 91 or 93 in an 07-09 GT500 with a stock tune, which doesn't have knock sensors, the car will perform the same. The question becomes does the stock tune in the 13 rely on knock sensors to the extent that the knock sensors would retard spark advance with a difference of 2 octane in the tank. It seems this is what OP is trying to clarify.

The question for me is how far can the knock sensors go in altering performance and protecting the engine. Could you put 87 in the car and still be safe while in boost? Somebody here knows.

 

[Franz]

Yup, agree with Iceman. He is correct. Of course there is a different result with different octane--the computer pulls timing to accommodate. That translates to lost horsepower.

+1

My understanding is that Ford set the tune on the 2013s at 93 octane. While 91 won't damage the car, they have precautions in the computer to retard timing/decrease performance to compensate.

On the other end of spectrum (running a full tank of 100 oct race gas), running over 93 octane would not net a higher performance number because the computer does not advance timing upon detecting the higher-than-93 octane fuel. (Unless of course you have an aftermarket tune that recognizes race gas).

I also run a half can of Torco per tank to raise my octane closer to a 93/94 mix.

 

[kcobra]

Torco fuel accelerator. Cheaper than race fuel and a great octane booster. I run some in all my modded cars for a safety factor. I've blown way to many motors and since torco, not an issue anymore.

 

[Farmer-Ted]

Altitude also comes into play. At higher altitudes you don't need as high a octane rating because there is less air so less chance of detonation at a given timing advance. Car will not pull timing running 91 octane. I live at 4200 feet, we only have 91 octane because of the lower air pressure. We are down about 15% power compared to you guys at sea level. So using 93 octane or an octane booster here will have no affect on HP because the timing advance is already at the maximum.