Does premium gas make a big difference over regular?

[Deleted member 35644]

D.I. has a cooling effect on the combustion chamber that MPI doesn't. The cooling staves off pre-ignition.

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[Faceme]

I live in Japan and our high octane is around 93? i believe (100+RON)..
No differnce in terms of mileage, but there is a def. difference in terms of sheer power.

But again, quality here is top-knotch so even regular gas didnt cause any problems for my car even under WOT.

I think you should spend more time worrying about quality of gas and changing oil than octane..

 

[BlackandBlue]

Not sure I get why the type of injection affects knock. Knock is pre-ignition. How the air/fuel mixture arrives in the combustion chamber would seem irrelevant.

Well if you put it in .001 sec or before detonation takes place it does make a difference.

Has the world gone crazy to the fact 87 and 12:1 would get you laughed out of a speed shop twenty years ago.

The miracles to make 12:1 and 87 to work is incredible.

Fact 87 will knock at times.

 

[ChaoticFury09]

Everything I've seen says 91 octane is what Ford used to achieve their stated HP. Short of asking a Ford engineer, there is no way to tell if they also tried 93 and got better results, but chose not to state them. You'd need some dyno time to prove otherwise.

As far as I know it’s always been 93. You can look it up under specifications on their website and then the sub category engine.

Where did you see it say 91?

 

[ALLSTOCK]

Ugh I am I'm just asking if a higher grade premium does anything more than the lower grade premium (91).....

yes

 

[Deleted member 35644]

As far as I know it’s always been 93. You can look it up under specifications on their website and then the sub category engine.

Where did you see it say 91?

Interesting that they'd recommend an octane level that's not available everywhere. I guess the folks in CA don't get all 310 horses.

 

[Loki-GT]

Just to answer an unasked question. 87 will knock in a port 12:1 engine. It is science.

Ford gets around this with direct injection and cooling but the engine will knock when the port fuel system is in use.

12:1 is just beyond the maximum of 87s stability.

Imagine going back to the 60's and saying hey we run 12.1 compression with 87 octane! Technology is something!

 

[Qcman17]

As far as I know it’s always been 93. You can look it up under specifications on their website and then the sub category engine.

Where did you see it say 91?

Perfect thank you that helps as it seems the cars power was determined with higher octane than 91.

 

[ChaoticFury09]

Perfect thank you that helps as it seems the cars power was determined with higher octane than 91.

No problem, happy to help. I have no idea what kind of a different 93 to 91 has but I would assume less than 93 to 87.

 

[Qcman17]

No problem, happy to help. I have no idea what kind of a different 93 to 91 has but I would assume less than 93 to 87.

Yes I agree its likely fairly small. But at least this supports the idea that the ECM can ramp up some to utilize better fuel. In the Camaro SS I had GM said 91 minimum & 93 was recommended. It said the car could handle 87 but cautioned pretty strongly against it. More of a use it when you are stuck only kind of thing.

Ford seems to be more liberal about the use of 87.

 

[Qcman17]

.......... In some cases one or two octane points can mean the diff between a blown engine and a great run.

Okay then which pump is the "go pump" & which pump is the "blow pump"? LOL

 

[TexasRebel]

Imagine going back to the 60's and saying hey we run 12.1 compression with 87 octane! Technology is something!

Wouldn't be unheard of... Tetraethyl Lead was great.

 

[TorqueMan]

Speed limiters are due to tire ratings, AFAIK.

If you have concrete Ford based information concerning top speed limiters and radiators please share it.

I shared a link for you in my last response on this topic. Dave Pericak, the S550 chief engineer, has stated publicly the speed limiters (all of the S550 models at the time of the interview were electronically speed limited--I don't know if that applies to the GT-350/500, Bullit, etc.) are due to cooling concerns.

Not sure I get why the type of injection affects knock. Knock is pre-ignition. How the air/fuel mixture arrives in the combustion chamber would seem irrelevant.

Engine knock is not preignition, it's detonation. You can search on YouTube for a video explanation of the difference, but suffice it to say engines can run under light detonation pretty much indefinitely, while preignition can destroy your engine in just a few seconds.

With port injection the fuel and air are mixed in the intake port during the intake stroke. With direct injection the fuel is injected directly into the cylinder. Direct injection provides another means of controlling the combustion event (along with ignition timing) and is one of the reasons we can use lower octane fuel in a relatively high-compression, turbocharged engine.

 

[Decosse]

Just throwing a thought out there. The PP models have larger front brakes, and in the past I'd heard (not necessarily S550) that braking capability is also a factor in top speed cut-off. If you can accelerate to 168, you have to be able to stop- not just slow down, but STOP- and that's is a different ballpark than 124. My car came from the factory with W rated (168) Goodyear Eagle F1s, and it is limited to 124.

As far as octane ratings go, I will say my car is seems smoother accelerating-eager? on 91. Of course, when it is 108 outside with 8% humidity, every car I've owned had a little ping on 87. And to further confuse the issue, I have read a few posts and articles suggesting that many premium fuels use less ethanol in their highest octanes, therefore the fuel itself has...help me here, I'm half asleep- more specific energy? Is that right? per gallon. Engineer/ chemist types, please step in and tell me what I mean, lol.

I've done the 87-89-91 experiments a lot, and found that here, in the summer, Shell 91 gets better fuel mileage and smoother acceleration -even with A/C-than 89 gets in the cooler months without a/c. On a side note, the other day I noticed that a Maverik station on the outskirts advertised ethanol free premium.....

 

[millhouse]

Interesting that they'd recommend an octane level that's not available everywhere. I guess the folks in CA don't get all 310 horses.

That is not the recommended octane, just the octane the used to achieve max horsepower. Minimum octane requirements remain at 87.

As for horsepower on the 5.0, the 2015-2017 GT was down around 10HP on 87 vs 93 during. For anyone doing a SOTP test, 10hp really is negligible. My guess is the 2018+ 5.0 having both port an direct injection is going to be similar.

The full report can be seen here:
https://newsroom.aaa.com/wp-content...ium-Fuel-Phase-II-Research-Report-FINAL-2.pdf

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