[David Gordon]

I now have a station by me that sells 104 Unleaded. My car is stock, save for a cold air intake. Would adding 5 gallons gain me any power? With no tuning. Will the cars computer reconize there might be no knock and add timing on its own?

[KingLT1]

No, the ECU will not add anymore timing then what is programmed in the high-octane spark table. That map is always the target then you have several other modifier tables that add/remove spark based on different thresholds...IAT, coolant temp, humidity. What higher octane fuel will do is help prevent timing from being pulled due to knock.

Now if you did a flex fuel sensor and tune then the ECU would add timing over pump gas based on the amount of ethanol content in the fuel.

[David Gordon]

So areas where they only sell say 90 octane, car runs exactly the same as areas where they sell 93 octane? Even if it is the same DA?
My area sells 90 and 93 both, as well as 91. Am I wasting money spending the extra .25 buying the 93?

[hawk02]

Adding a few gallons of 104 won't gain you any power but it might prevent you from losing power due to knock retard.

The spark timing on the stock tune is fairly aggressive. GM's LS and LT engines tend to produce a high degree of knock as a result. The GM engineers rely on the knock sensors to tell the ECU to pull timing based on the degree of knock in order to protect the engine from catastrophic failure.

Reduced timing means reduced power. You'll hear engine builders say these GM small block V8s love octane. And they do. It seems to me the sweet spot is around 95-96 octane. Above that and it's diminishing returns.

[NG329]

Originally Posted by David Gordon

I now have a station by me that sells 104 Unleaded. My car is stock, save for a cold air intake. Would adding 5 gallons gain me any power? With no tuning. Will the cars computer reconize there might be no knock and add timing on its own?

Typically, adding race gas does not add power. The higher octane is what prevents detonation in your combustion chamber when running an aggressive tune (timing advance). You're able to tune for more power with higher octane but it does not magically add horsepower.

Some things I've learned over the years regarding race fuels:

1) Leaded racing fuels are actually good for the engine as it provides a coating for the valves. Don't use with catalytic converters tho. They'll destroy them quickly. Also, they age your O2 sensors quite rapidly.

2) Race fuels with a lower spec gravity tend to keep the engine temps cooler. I ran VP Racing C12 in my supercharged motorcycle and never ran into heat issues even after prolonged use.

3) Oxygenates in Race fuels are what had horsepower. Ethanol is oxygenated which is why guys see jumps in power. Outside of E85, these fuels are typically not cheap. Also, they are highly corrosive including E85 if it sits for an extended period of time.

[KingLT1]

Originally Posted by David Gordon

So areas where they only sell say 90 octane, car runs exactly the same as areas where they sell 93 octane? Even if it is the same DA?
My area sells 90 and 93 both, as well as 91. Am I wasting money spending the extra .25 buying the 93?

93 octane is more knock resistant then 90 octane but it doesn't make more power on its own. If you are getting kr on 90 chances are 93 will reduce that. if you are getting kr on 93 chances are mixing race fuel will eliminate it. You are just getting back your factory rated horsepower not any extra was my point.

Your next hurdle would be timing retard from high inlet air temps. a stock ZL1 is pulling timing almost anytime you floor it in the summer because it's IAT vs spark retard table is set really conservative. GM has to factor in a large safety margin for error.

The only way around it is a flex sensor and run ethanol, mix race fuel, or run a concentrate additive like torco. Then you could raise the IAT temp threshold up so the ECU doesn't pull timing because the stock blower lives in the 130-140 range and that is where GM sets this table to start pulling timing.

[Vigilante375]

Originally Posted by David Gordon

So areas where they only sell say 90 octane, car runs exactly the same as areas where they sell 93 octane? Even if it is the same DA?
My area sells 90 and 93 both, as well as 91. Am I wasting money spending the extra .25 buying the 93?

The car is tuned, from the factory, to run on up to ~95 octane. Anything higher and it will not benefit from it.

The lower the octane you put in the car below that ~95 rating, the less power the car will make because the car will have to pull timing to compensate for the increase knocking from the lower octane fuel.

Always get the highest octane (up to ~95 octane) you can at the pump to ensure you're getting the correct power output.

[David Gordon]

Originally Posted by Vigilante375

The car is tuned, from the factory, to run on up to ~95 octane. Anything higher and it will not benefit from it.

The lower the octane you put in the car below that ~95 rating, the less power the car will make because the car will have to pull timing to compensate for the increase knocking from the lower octane fuel.

Always get the highest octane (up to ~95 octane) you can at the pump to ensure you're getting the correct power output.

So adding 4-5 gal 104 might help under full throttle.

How much does adding a flex sensor cost?

[NG329]

Originally Posted by David Gordon

So adding 4-5 gal 104 might help under full throttle.

How much does adding a flex sensor cost?

$300 for the sensor then you'll need to tune it with HP Tuners (device plus credits) to activate it. So factor in $700-$800 or so total.

[Grumpy1]

Unfortunately my area does not support e fuel so that's out
I assume the ecu be tuned for the higher octane like 100, 104, etc,

[LT4 650]

Adding 104 octane will not add power but like others said could help with knock or pulling timing toward the top end.

I used to own a stock Hellcat (please don't ban me...LOL) and I was running it at a 1/2 mile event and one of the racers suggested I throw 3-4 gallons of 100 octane in it to keep from pulling timing toward the end of the run. It gave me almost 3mph more speed which is a lot in the 1/2 mile.

[JSH]

Originally Posted by David Gordon

I now have a station by me that sells 104 Unleaded. My car is stock, save for a cold air intake. Would adding 5 gallons gain me any power? With no tuning. Will the cars computer reconize there might be no knock and add timing on its own?

No. It wouldn't help you.

[Vigilante375]

Originally Posted by David Gordon

So adding 4-5 gal 104 might help under full throttle.

How much does adding a flex sensor cost?

Use this to figure out how much of what you want to add to get what octane rating you want.

http://www.bazellracefuels.com/Calcs/OC1.htm

[Snowwolfe]

You guys should try to find an episode on Engine Masters where they did dyno runs on the same motor but using different octane fuel. 87-93 made no difference in power. Same for 104. It was an education for sure.