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Thread: 93 K75S - Premium RON 90 OCTANE Fuel

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    93 K75S - Premium RON 90 OCTANE Fuel

    The K75S has an 11.0 : 1 compression ratio, which is probably the reason why BMW indicated an unleaded fuel with a premium RON was required. I am just wondering if the initial premise is still valid considering the quality of fuel nowadays produced and considering the fact that many modern day engines have much higher compression ratios and operate knock-free without the pre-ignition problems BMW wanted to avoid in circa 1993.

    I am wondering if anyone out there has been refuelling and riding their late BMW with regular gasoline without glitches?

    Why do I ask? Up here in Canada, Super/Premium high octane fuel can easily be upwards of 10 - 15 cents per litre more than Regular which can add up to 60 cents on the gallon. Fuel in Montreal is bordering on $1.65 per litre for Premium/Super, that's $6.25 per US gallon.

    Any thoughts on whether the theory of Super for a late model BMW might be obsolete.
    Last edited by ghyber; 02-27-2013 at 05:46 PM.
    1993 K75S Mystic Red Pearl

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    Debbie's Servant Lee's Avatar
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    I didn't know the K75 required premium.
    I rode K75s for 15 years, and 135,000 miles between the two bikes, and always used regular. Same with my wife's K75s.
    We had 1987 K75Ts and 1991 K75Ss.
    Lee 2011 K1300S
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    Past BMW Bikes, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT

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    The compression ration on ALL K75 engines was lowered to 10.5:1 either in 1987 or 1988 (Build date not model year).

    Most K75s will run fine on regular, but it is more a function of ignition timing, altitude, temperature, carbon build up, and local gas formulation. Euro octane #s are calculated different than US octane #s.

    It wouldn't hurt to try it, just look for pinging. Probably the best test would be to find a hill that is fairly steep and put the bike in a high gear so that you are in the 2500 rpm range. Then hammer the throttle. If the octane is too low it will probably ping. If not, you are PROBABLY good. Just be aware that pinging is NOT GOOD.


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    Quote Originally Posted by ghyber View Post
    The K75S has an 11.0 : 1 compression ratio, which is probably the reason why BMW indicated an unleaded fuel with a premium RON was required. I am just wondering if the initial premise is still valid considering the quality of fuel nowadays produced and considering the fact that many modern day engines have much higher compression ratios and operate knock-free without the pre-ignition problems BMW wanted to avoid in circa 1993.

    I am wondering if anyone out there has been refuelling and riding their late BMW with regular gasoline without glitches?

    Why do I ask? Up here in Canada, Super/Premium high octane fuel can easily be upwards of 10 - 15 cents per litre more than Regular which can add up to 60 cents on the gallon. Fuel in Montreal is bordering on $1.65 per litre for Premium/Super, that's $6.25 per US gallon.

    Any thoughts on whether the theory of Super for a late model BMW might be obsolete.
    Hmm ... methinks, or rather me wonders, whether the difference is even material? Sure, $6.25/gal sounds high, but the real number is the $0.60 difference in price between the two grades. I ride 12k miles/year, at ~40mpg, so I put in about 300 gallons. At $0.60, that would be $180 extra per year, or $15/month. Sure, if the bike can't tell the difference, then save the $$. But this falls in the "cheap insurance" category to me, along with buying good oil rather than discount, etc.

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    Debbie's Servant Lee's Avatar
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    Does the manual tell you to run 91?
    I no longer have a manual to check.
    Last edited by Lee; 02-27-2013 at 09:32 PM.
    Lee 2011 K1300S
    MOA # 30878
    Past BMW Bikes, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT

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    Quote Originally Posted by JamesInCA View Post
    Hmm ... methinks, or rather me wonders, whether the difference is even material? Sure, $6.25/gal sounds high, but the real number is the $0.60 difference in price between the two grades. I ride 12k miles/year, at ~40mpg, so I put in about 300 gallons. At $0.60, that would be $180 extra per year, or $15/month. Sure, if the bike can't tell the difference, then save the $$. But this falls in the "cheap insurance" category to me, along with buying good oil rather than discount, etc.
    Is it really "cheap insurance" if it's not doing anything? Just because it is the higher priced nozzle at the pump does necessarily make it the most conservative or better choice.

    Every bit counts and $180 is far from a little pocket change for me. The reality is that many vehicle owners feed Super high octane unleaded gasoline in the vehicles and don't even realize that they are literally throwing the difference out the window.

    The K75S is not a high performance engine. My 2013 Toyota Prius C has two engines, one is a 1.5 litre aluminium gas engine with 13.4 : 1 compression ratio and it runs on regular unleaded as per the manufacturer's recommendation. I can also run it on Super.

    ghyber
    1993 K75S Mystic Red Pearl

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    For what it's worth I am running the Bosch Type II Injectors installed on my 1994 K75S. I always fill up with 91 Octane No Ethanol Gas and get 50-52 MPG average highway and in-town. After I installed the Type IIs the K ran rich. I posted on this forum and was guided through the procedures to adjust the air/fuel mix. Personally I would not run lower octane fuel to avoid damage and poor performance.
    Expect The Unexpected

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    Quote Originally Posted by ghyber View Post
    Is it really "cheap insurance" if it's not doing anything? Just because it is the higher priced nozzle at the pump does necessarily make it the most conservative or better choice.
    Agreed.

    Quote Originally Posted by JamesInCA View Post
    Sure, if the bike can't tell the difference, then save the $$.

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    The manual on my 87 K75s (bought Sept 86) says minimum 91 ROZ. ROZ runs higher than ROM, as explained here:


    The reason is that the octane numbers in Europe are not the same as in the US. In Europe they use "ROZ" (Research Oktan Zahl), whereas in the US the spec is for the average between ROZ and "MOZ" (Motor Oktan Zahl), which is approx. 10 lower than ROZ. Therefore, a 93 octane US premium is equivalent to 98 octane Super Plus in Germany, and the German 91 octane regular would be posted as 86 octane in the US, ie. very much the same as the regular unleaded here.

    Whatever, I've run regular for the last 26 years with no ill effects. Stay away from corn blends if possible.
    1987 K75S
    Original litter
    Original owner
    2012 Ural Gear Up

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    Quote Originally Posted by Slipster View Post
    Personally I would not run lower octane fuel to avoid damage and poor performance.
    you don't get "better performance" by running higher octane. all you do is avoid pre-detonation- "pinging" - IF the motor is prone to pinging using a lower octane fuel. beyond that... you're just throwoing money out the tialpipe, and getting NOTHING back in return.

    it makes the most sense to run the lowest octane that your bike will run cleanly on. pre-detonation tneds to show up in high heat (ambient temp)/high load (weight)/high demand (full throttle in a high gear) conditions. change the conditions (run higher rpms is easiest to do, or get a divorce or go on a weight loss program) and you reduce the likelihood of pre-ignition. if still pinging- then you've determined that your bike needs higher octance than you've been giving it.

    running higer octane than needed is the number 1 cash waster, too frequent oil changes is #2. (see, i made it an oil thread! go me!)
    oh yeah. chrome is #3.
    carbon fiber is never a waste of money- it's classy!
    Ride Safe, Ride Lots

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    Europe uses RON (Research Octane Number) sometimes referred to as ROZ.

    US and Canada use AKI which is RON + MON (runs about 8-10 points lower than RON) divided by 2. So AKI the number that is on the pump is 4-5 points lower than the RON.

    My '87 S (11:1 Compression) says to use minimum 91 ROZ which would equal 87 AKI (pump number).

    Regular in US and Canada (with 10% ethanol) averages 87 AKI (the specified minimum for our bikes)

    Premium averages 91-92 AKI which is 95-97 RON.

    Unless there are extenuating circumstances, a US or Canadian pump marked 87 octane SHOULD be sufficient for a K75 (any model, as the engines are for all intents, all the same).

    That being said, I use premium, as I consider myself to be an extenuating circumstance (the way I ride), plus I've slightly bumped the timing, I ride a lot at sea level (denser air), and have slightly leaned the mixture to optimize power. All of which leave less margin for low octane. I don't mind the extra cost.

    Bottom line, according to BMW, regular should be fine. Your bike, your choice. Just DON'T let it ping (detonate).



    LONG MAY YOUR BRICK FLY!

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    Lee Fulton Forum Moderator
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    Slipster Slipster's Avatar
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    hey Lee - with your current listed setup and riding conditions - what mpg do you average? Thanks for sharing how your K is dialed in.
    Expect The Unexpected

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    Debbie's Servant Lee's Avatar
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    Quote Originally Posted by 35634 View Post
    the German 91 octane regular would be posted as 86 octane in the US, ie. very much the same as the regular unleaded here.

    .
    Thanks, I thought I was running what the manual called for, but it has been too many years to remember for sure.
    Lee 2011 K1300S
    MOA # 30878
    Past BMW Bikes, 2003 K1200RS, 1991 K75S, 1987 K75T, 1984 R100RT

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    Quote Originally Posted by Slipster View Post
    hey Lee - with your current listed setup and riding conditions - what mpg do you average? Thanks for sharing how your K is dialed in.
    I don't ride for MILEAGE. I ride for SMILEAGE!

    Most days, I spend most of the time in second or third gear hard on the throttle. Canyon or mountain twisties are no fun in 5th. On those days I get around 35+ mpg. On the longer rides where I'm just traveling I get around 45.

    My bike is a first week 1987 (original litter) 11:1 K75S with 130,000 miles. Last summer it pulled 54.5 rear wheel hp on a Dynojet trailer mount on a 101 degree day at 2100 ft altitude. Dynojets have a reputation of not having the best accuracy and the owner can easily miscalibrate it, but the numbers on the half dozen other bikes that I saw run that day (most of them new) were all right where factory specs said they should be.


    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

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    Slipster Slipster's Avatar
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    [QUOTE=98lee;861321]I don't ride for MILEAGE. I ride for SMILEAGE!

    Expect The Unexpected

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