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Hey Guys,
I have a gas station near me that doles out 100 octane pump gas. I'm wondering what ratios to run? I was going to run the tank down to pretty much empty then do 6 gallons of 91 and 3 gallons of 100 for about 100 miles of mountain driving out here in the wonderful Santa Cruz Mountains in the Bay Area, CA.
Cheers,
Matt
It's the 76 Station on Hwy 9/Big Basin Way in Saratoga right before you enter downtown. Yet another reason all the moto clubs meet there before driving like lunatics up the the top. Thanks for the reply!
2012 P31 C63 Coupe Trackrat, 2019 GLE63S Coupe Beast
I know it goes against what is commonly believed, but I picked up 3mph in the 1/4 on a stock tune just switching to race gas. No other changes. Same day, same conditions.
Was my pump gas bad? I don't know. But I do know these engines run noticeably better/smoother/stronger on 100 octane. With an 11.3:1 compression ratio, and how hot these things run, I like the overhead provided by the 100 octane anyway. I suspect that timing is pulled on the top end when really beating on it, even in stock form, when using regular old 93 pump...
it's not that pump gas is bad. It's that it isnt what i would call real 93. ethanol has a much higher octane rating and they are mixing in atleast 10% almost everywhere. so for example purposes lets say its 110octane. so mix 10% of that with some 90 octane and it averages out to 93. In most cars running premium is a waste of money as is race gas. The difference is our engines are 11.3:1 compression which is crazy for a street car. It is a performance car designed for good fuel. The stock ecu has the ability to both retard timing when the fuel is crappier than desired or advance it if it can take it without detonation. If you've never used race gas than dont go saying it's a waste. 3mph is no laughing matter for a few dollars more per gallon at the track.
I know it goes against what is commonly believed, but I picked up 3mph in the 1/4 on a stock tune just switching to race gas. No other changes. Same day, same conditions.
Was my pump gas bad? I don't know. But I do know these engines run noticeably better/smoother/stronger on 100 octane. With an 11.3:1 compression ratio, and how hot these things run, I like the overhead provided by the 100 octane anyway. I suspect that timing is pulled on the top end when really beating on it, even in stock form, when using regular old 93 pump...
Yep I agree. Heat and beating on it, ECUs gonna pull some timing. With the 100oct it should be running a good advance.
it's not that pump gas is bad. It's that it isnt what i would call real 93. ethanol has a much higher octane rating and they are mixing in atleast 10% almost everywhere. so for example purposes lets say its 110octane. so mix 10% of that with some 90 octane and it averages out to 93. In most cars running premium is a waste of money as is race gas. The difference is our engines are 11.3:1 compression which is crazy for a street car. It is a performance car designed for good fuel. The stock ecu has the ability to both retard timing when the fuel is crappier than desired or advance it if it can take it without detonation. If you've never used race gas than dont go saying it's a waste. 3mph is no laughing matter for a few dollars more per gallon at the track.
I think the discussions of higher octane fuel are often incomplete and misleading.
One aspect that is rarely mentioned is that high octane fuel burns less well and has lower energy content per unit. As a result your car will consume more gas for the same output, and at 100% output have directionally lower power that when driving lower octane gas.
Unless, that is, another effect comes in, like the ECU counteracting engine knocking due to premature combustion.
My take is, excessively high octane is detrimental to power and consumption compared to lower octane fuel, unless the engine starts knocking, in which case higher octane avoids that problem. So, the million Dollar question is, what is the min octane level at which the engine will not get early detonations given the conditions it is used in (street driving or track, summer/winter, etc.).
A related topic is compression ratio: Someone posted the NA M156 has an 11.3 CR. If that is so, then that is NOT a high CR when comparing globally. It is somewhat high within the context of the US, a country with a history of low CR, large displacement (low efficiency) engines. CRs of 12.5 are not uncommon in high efficiency, smaller engines as common in Europe and Asia. Recently some manufacturers (e.g. Ferrari, Mazda) have developed higher CR engines (in the 14-15 range) for fuel efficiency. If you google it, there is plenty of info available (e.g. Mazda Skyactive).
Last edited by Wobble64; Jun 27, 2015 at 07:38 PM.
2012 P31 C63 Coupe Trackrat, 2019 GLE63S Coupe Beast
Sorry, you guys are just wrong.
And anything over 11:1 is considered quite high for a production car.
There's quite a bit of research that shows fuel in Europe is of significantly higher quality than what you find here in the US. Ethanol content is also much less.
And anything over 11:1 is considered quite high for a production car.
There's quite a bit of research that shows fuel in Europe is of significantly higher quality than what you find here in the US. Ethanol content is also much less.
what the hell are you saying?
ok, the car has 11:1 compression (or whatever). Its tuned from the factory for 93 and will use knock sensors to pull timing on **** water 91. If there is no knock, the car cannot advance timing any further.
Running higher octane is generally just for extra safety in hot weather or track time because clearly higher engine temp/intake temp could result in detonation.
Blkrokt,
do you think so or do you know that our cars knock with 93? Did you monitor timing, for example, via an OBDII device?
I'd love to get some actual data.......
99 octane fuel is common in the UK. I run it all the time. I'm guessing the 63 engines in the U.S. Are somewhat detuned to run on crap fuel. My car recommends a minimum of 98 octane. No ethanol in our fuel here either. I tend to use Shell V Power which is 99 RON.
99 octane fuel is common in the UK. I run it all the time. I'm guessing the 63 engines in the U.S. Are somewhat detuned to run on crap fuel. My car recommends a minimum of 98 octane. No ethanol in our fuel here either. I tend to use Shell V Power which is 99 RON.
A photo from inside of my fuel cap.
no.
Your fuel is 98 RON. Fuel in US is 93 ron+mon/2.
They are roughly similar.
If the car pulls timing on 93 under normal conditions, then MB doesn't really know what they're doing.
Either way, I bet that any knock is well gone by 95 octane. Anything above that is useless.
Quadcammer is right, the way octane rating is used in Europe and the US is different. Europe used the RON, the US uses the average between RON and MON. Practically, the difference between the 2 in our octane range is about 4.5, i.e. a US 93 is about 97.5 according to how octane is quoted in Europe. Or a European 98 would be 93.5 in the US.
However, in some states in the US the highest usually available gasoline might be 91 octane.
Aah ok my apologies. However when I was out working in Wichita I did overhear a conversation from a group of guys saying to avoid the gas stations that used ethanol in the fuel. I just smiled politely as I didn't have a clue what they were talking about
I think you meant Mazda. Yes, I just checked e.g. the CX-5 has 2 engines, a 2 l and a 2.5 l. Both have 13:1 compression ratio and use Regular unleaded fuel.
The CX-9 is different, but that one uses a Ford engine.
2012 P31 C63 Coupe Trackrat, 2019 GLE63S Coupe Beast
Originally Posted by Mike450
Dumping 100octane into this car and claiming a performance advantage without any data logging is pure 100% speculation.
3mph in the 1/4. Same day, same conditions. Only difference was Sunocco 93 pump vs VP109 100 octane unleaded. That's better than any data logging. Can't dispute real-world results. I'll dig up the slips and post them.
And the car certainly "feels" smoother, stronger, faster to me when I have it loaded up with race gas. These engines love it.
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