Why does the "Justa" demand premium gas when other comparable engines do not? In other words, what return are Base owners getting in exchange for the roughly $2 surcharge per tank?

Idle curiosity ...

 

There are several threads on this (Well two that I know of for sure). Some Justa owners use premium some don't. S and JCW owners have too as I understand it.

The benefits are up for debate and has been debated in those threads. I do because I talked a service tech at my dealer and he said that he thought it was best to use it. Thats it. I really recommend you search for the threads and read them. Lots of info. Happy motoring.

 

i would rather put the best fuel in my car anyways. I have an S though so i have too. Think of it like your feeding your car organic gas.

 

Because the base compression for the Justa engine is higher than the S. Both are high enough compression to warrant the use of premium gas.

 

Per Miniusa you can use 87 on up in the Justa without harming the engine. 91 is "required" to meet the published EPA mileage and emissions numbers because that is what it was tested with.

 

One simple reason it keep that little yellow check engine light from blinding you while you are trying to get somewhere.

http://www.toptiergas.com/

http://pure-gas.org/index.jsp

And here is a bonus URL for your motoring pleasure.

http://www.motorcycleroads.us/index.html

 

Well, that's just the thing...you can't apply the "It costs more so it must be superior" rule to fuel that applies to most other consumer goods.
Premium gas is in no way "better" than regular, it just has a higher ratio of octane in it. "Better" is only relative to what your car is tuned for. Putting premium in a car tuned for regular is not "better", in fact in a lot of cases, it's worse.

 

Remember, the fuel/octane requirement for mini's have changed from year to year based upon the motor/ compression ratio and induction method...
if you manual says premium fuel required, failure to use it may/can cause $$ problems...
If it says premium fuel recommened, but lists 87 as the min, you get a bit more hp csuse the computer will adjust for the fuel.

 

The manual for my R56 says that 91 octane is highly recommended. Considering how much I have invested in this car, $2 a tankful sounds like cheap insurance. My gut tells me that I get better gas mileage and better performance with 91 octane so I'm getting a little something for my $2.

 

Seriously, not too much to spend for peace of mind...IMO

 

That depends on the year of the car....for the 2003 Cooper premium gas is required.....

 

It allows the engine to run the valve and ignition timing it was meant to. Running lower octane gas means that the fuel has a lower ignition point, thus in order for the relatively high compression engine in the justa to avoid knock or premature detonation (yes, yes, that's what she said) it has to pull timing, this will reduce the power produced and hurt your mileage. When a car manufacturer recommends that you use a certain grade of fuel, it's for a reason, and that's not so that the "evil" oil corporations can make more money (they don't give a crap what Shell is making on the gas we put in our cars), it's because that's what the engine is tuned to run most efficiently on.

 

This subject has been beaten to death here......just sayin...

 

It's beaten to death on pretty much any automotive forum, usually along with threads like "will these wheels fit?" and "what intake should I get/exhaust sounds best?"

 

In short, the answer to your question is, "compression ratio".

Cars that run on 87 octane typically have compression ratios around 8.5:1 to 9.5:1. Your Just a has a compression ratio of 11:1. Higher octane is required to prevent knocking (detonation) of the fuel-air mixture under the higher combustion chamber pressure that compression ratio creates.

The Cooper-S has a compression ratio of 10.5:1. But it is also force inducted, which creates higher combustion chamber pressure than the Justa's 11:1. So it requires higher octane gas.

Our cars have "knock sensors". When the sensors detect detonation, they tell the engine computer to retard the ignition (fire the spark plugs later in the crankshaft rotation). This stops the detonation so we can safely run lower octane fuel, but at the cost of lower power and efficiency.

 

To clarify, my question isn't so much "should I or shouldn't I fill with premium" ... instead, I'm wondering what the Prince engine running on premium delivers performance-wise, that a Civic/Corolla (etc.) engine running on regular gas does not.

(Only in terms of engine performance - not other aspects of handling.)

 

Yup...
the moral of the story is "Use what your mini requires"(this thread is in the general forum, all makes, models of mini's, classics, gen1 and gen2. Failure to do so can result in major dammage...things like cracked heads, piston issues, and valve problems...so using anything other than the manufactures REQUIREMENTS is done at your own (and your wallets) own risk...you own your car, do what you want, use canola oil for engine oil if you want, but the results may be poor.
Engineers make choices when desging and building things....JUST BELIEVE that when they say use product x or else, that recommendation is grounded in pure science, facts and figures.

 

If your question hasn't been answered by us explaining why this engine requires premium, then I'm not entirely sure what you are trying to ask.

 

It is simply a desgin choice made by an engineer...
the motor you refer to is a "family" of engines, on gen2 mini's.
some REQUIRE premium fuel, some reccomend it...
your question seems simplistc in that you are trying to compre a granny smith apple and a machontosh apple...
both similar, but different....which is the better apple? Depends on your tastes. Just like cars. Similar, but different.
Going with higher octane fuels give engineers options in desgin...things like optimizing efficency or power due to running with higher compression ratios...
but as with any car, you are buying a package deal....take it or leave it. The sum of a carss parts must be more than any single compotent, or it would be a pretty bad car...think...car A has the best tranny ever, great stats, but is mated to a crap motor...not to over simplyfiy, but you need to ask, why do i care? When you determine how much a car will cost you to fuel, run, etc, fuel is such a tiny % of true ownership...if the $2 per tank is a deal breaker...you need to ride a bike and save up more $$, youare as Dave Ramsey says, broke and living beyond your means.

 

I use premium, and I get why this particular engine runs better on premium than it does on regular. But when you compare it to other engines that run on regular and deliver similar (or better) specs on paper, I start to wonder why BMW designed the Justa to use premium - that's all.

To illustrate:

2012 MINI Cooper base
121 hp, 114 lb-ft
28/36 mpg
Premium gas

2012 Honda Civic LX
140 hp, 128 lb-ft
28/39 mpg
Regular gas


Again, I'm talking about engine performance only. I know the Cooper blows similarly-spec'd cars away in terms of overall, non-engine-related handling (that's why I bought one, very happy with it).

 

Ah, basically it boils down to this, there are 3 ways to increase power in an engine, 1) increase displacement, 2) increase compression/more aggressive timing, 3) forced induction. The Civic LX has a 1.8L engine vs the 1.6L in the mini, this allows them to run lower compression/less aggressive timing to achieve the same or better power as the MINI, thus it can safely run lower octane gasoline than the engine in the MINI.

 

PS
You ever drive a MINI (a premium small car), then drive a civic/corolla? Two opposite ends of the markets, both price and performance wise. One is a sporty small car, the other is what is refered to as "cheap and cheerful".
From the cars you picked to compare the mini to, you picked two prettyrock solid ecno boxes....something the mini is not....take a look at a mini owners reapir bill....not saying a mini is not a relilable car (mine has been great), but different ends of the same spectrum...one for an accoutant, one for a lover. If you want an appliance, the above mentioned cars are good options....the mini is more about emotions, the joy of driving.. a typical car driver thinks of the car as a way to get from a to b....a Mini driver might invent a place to drive to, just so they can drive from a to b (group car ride to get ice cream, drive a nice twisty road, or simply cruisethe boulevard).

 

Pure hp numbers don't a story...
It is also about tourque...
The old saying, people buy hp, but drive tourque.
That is why a diesel car can be a blast to drive, but have pretty small numbers hp wise...by using higher compression, bmw engineers got more tourqe per liter on less co2 output...a very important euro spec when it comes to taxes, etc.

 

Thanks for the replies and for putting up with my poorly worded question. I totally agree about the fun factor of the MINI, but that fun does not seem to come from the engine. It has to do with suspension, steering, braking, etc. If Civic is not a good comparo, then look at the Fit. Similar engine specs and displacement as MINI, but again regular gas. Yes it's less fun, but again, not (seemingly) due to the engine.

Maybe I don't know enough about car mechanics; if so then sorry for my ignorance. Just got curious while filling up (with premium) the other day ...

 

PS
mpg #'s are largely about aerodynamics....the civic is pretty good, the mini ismore looks..the steep windshield comes at a price....put the same motors in cars having the same drag...weight, etc...and then you could compare.