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Octane Limit?

NoVaGT

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For both 5.0s and EBs, is there an octane rating past which the engines can't utilize it for more power?

I'd imagine the EBs should be able to utilize the increased octane better than the N/A 5.0, but that's also another question.

Anyone ever try 100 octane race gas in their tank? Or 93 octane and some octane booster? I know these ECMs can utilize higher octane, but what's the limit?
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Interseting question. I've wondered the same thing, but since i really don't have an option to get 100 octane, I haven't much thought bout it. But some octane boost on top of 93, might be worth it.
 

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One way to find that out is to get MBT (maximum brake torque) and see which octane will deliver that value. I imagine it's around 33-34* which seems to be doable on E85 so my guess is around 105-108 depending on engine and fuel.

There was an interesting video done by YOLO where he kept adding timing to a 2019 and by 33* there were negligible gains
 

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Octane booster is bad news typically, I'd definitely steer clear of that especially in these newer vehicles. Many of the most common boosters contain MMT which will leave a manganese oxide coating on everything that comes into contact with the exhaust. Many car companies including Ford advise against using anything that contains MMT right in the owners manuals because it can damage emissions equipment as well. If a vehicle comes in for performance modifications and dyno tuning with octane booster in the tank we normally drain the fuel and put in new spark plugs before running it on the dyno.

The 2.3L EcoBoost for example is able to take full advantage of premium fuel 91-93 even on the stock tune and the factory HP numbers are obtained using premium. But on 87 octane for example they typically lose anywhere from 12-15% of their advertised power numbers from lack of octane forcing the vehicle to basically pull out power. You can run 100+ octane race fuel in them so long as it's unleaded, but if the car is not tuned to take advantage of octane that high it's not always going to provide much benefit. The higher the octane the slower the burn so going too high of octane is not always beneficial. VP Racing Fuels MS 109 is common on the 2.3L with a race fuel tune since it's unleaded and around 104 octane R+M/2.

Here is some info from the newer 2018+ Mustang owners manual on octane suggestions and mentioning not to use octane booster with MMT.

For best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended. The performance gained by using premium fuel is most noticeable in hot weather as well as other conditions, for example when towing a trailer.
Do Not Use: Fuels containing the octane booster additive, methylcyclopentadienyl manganese tricarbonyl (MMT).
The use of fuels with metallic compounds such as methylcyclopentadienyl manganese tricarbonyl (commonly known as MMT), which is a manganese-based fuel additive, will impair engine performance and affect the emission control system.
 

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samd1351

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Well, 93 it is then.
 
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NoVaGT

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Also sounds like if you're gonna do octane booster, better make sure it ain't got no MMT in it.
 
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Stock calibration has ceilings on timing so there is a point where the timing strategy will quit adding timing no matter the lack of knock.
 

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Stock calibration has ceilings on timing so there is a point where the timing strategy will quit adding timing no matter the lack of knock.
True, but those ceilings are pretty high (albeit slow to get to). In fact, the ceilings for the stock calibration is actually no less than a few of the aftermarket tunes I saw. The only downside as mentioned is it's slower.

For example, stock tune calls for 21* max timing (in 1 specific table) but then the general advance/retard lookup table give the ability to go +10/-10 timing for a max total possible of 31*.

My PP2 tune and another aftermarket tuner who shall remain nameless in this example, calls for 27* in that same table but then the general advance/retard lookup table is limited to +4/-4 for a max total possible of 31*.

So in this example, all 3 tunes have a ceiling of 31* so theoretically running the same gas they could all make the same overall power. Now of course as mentioned, the stock tune is alot slower to get there and the fact that it starts at 21* and ramps up will be overall slower than starting at 27* and ramping up from there.
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