The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: apaiva on May 26, 2012, 05:46:48 PM
-
Gas. Petrol.
Which grade should I be putting in my 81 R65?
My mechanic guy said I should only use high grade, 93 octane or whatever the highest available is.
Another buddy told me I should use regular grade because that was all that was available when the bikes were new, and the engine will run hotter if I use high grade.
FWIW, I've been using regular so far and it seems to run fine. I haven't tried high octane yet to compare.
-
Only run the high grade stuff if you are running in hot temps and/or mountains and getting pinging with the lower octane stuff. The higher octane fuel will run hotter and you won't get much benefit from it if you aren't getting pinging. Though often the premium stuff has more cleaning agents in it, it isn't usually that much different. I run the regular or mid-grade stuff in my bike - I will run the high octane stuff once in a while if I'm going to be running under higher loads or higher temps to avoid pinging, though it is tuned up well enough that seldom happens.
-
Regular grade fuel, which is usually 87 octane here in the US, is fine for an R65 .
If you develop any pinging/pinking/detonation, whatever term you like for it, then go up to mid grade .
I run regular, until the 'hot season' rears it's 'ugly head' here in the northern Sonoran desert suburb of hell that I reside in, then mid or premium grade is necessary .
-
Just trying to get my head around what this means with European fuel and engines.
US fuel is rated using (Ron + Mon)/2
European fuel is rated using Ron
To compare with European fuel I have to add 5 to the US rating.
So US 87 is equivalent to Euro 93
I know this thread is about an 81 bike. ( is it an 8.2:1 compression engine ?) but I bet the US guys with 79 - 80 bikes which have the 9.2:1 compression engines aren't able to run Regular without some pinging.
-
It's really nice to hear others with my point of view. It's such a widespread idea that premium is a better, more powerful fuel, that most tend to think if regular is good, premium is better. ::)
I run regular in my bikes (unless there's pinging) and believe it gives better mileage.
-
A little off topic, but there are a few oilhead owners, plus other makes of bikes with fuel injection on this site .
I've noticed on my oilhead, that the fuel mileage goes up around 5 mpg when using premiuim grade fuel, as compared to regular grade fuel .
-
Both my R65s get regular gas year 'round without any issues.
I do make sure timing is set correctly; ie: not too danged advanced. Last really hot ride was heading back into Kerrville TX after a Three Sisters adventure. Ambient air temp gauge on the Vapor digi read 116[ch730]F. No pinging from the Airhead but I sure was.
-
Barry - the R65 engines are 9.5:1 up until 1985, I believe - in the US anyway. Not sure about the restricted Hp version that was sold in Europe for insurance purposes. I think that the compression ratio was dropped for the R65 version of the monolever bikes as part of its retuning for torque peak at lower RPMs in the 85-87 years.
-
I have run Regular in all of my '79/'80 engines, and it was never a problem - in Indiana.
-
That's interesting Bob!
I didn't run premium in my R11S - mostly ran regular and I recall getting 50 mpg or even a bit better a few times. Can't imagine getting better than that. What was your mileage on the oilhead?
I've noticed on my oilhead, that the fuel mileage goes up around 5 mpg when using premiuim grade fuel, as compared to regular grade fuel .
-
One conclusion I draw from the discussion is that when it comes to pinging you really can't make an accurate comparison between the US (Ron + Mon)/2 octane rating and the Euro Ron rating
Even with the correction factor it's suggesting a 9.2:1 compression engine that runs fine on 87 US regular would be OK on the equivalent Euro 93 Ron and it certainly isn't.
According to the original riders handbook our Euro engines were supposed to have a minimum of 98 Ron. They ping on our Regular 95 and I presume they would ping even more on 93.
Also it seems Haynes got it wrong when it says all US engines after 1980 were reduced from 9.2:1 to 8.2:1 compression. To be fair I've seen the same statement several times elsewhere in detailed engine specs so they are not alone.
What does a US riders handbooks say about compression ratio ?
-
That's interesting Bob!
I didn't run premium in my R11S - mostly ran regular and I recall getting 50 mpg or even a bit better a few times. Can't imagine getting better than that. What was your mileage on the oilhead?
I've noticed on my oilhead, that the fuel mileage goes up around 5 mpg when using premiuim grade fuel, as compared to regular grade fuel .
With premium fuel on rural interstate type highways, 75-80 mph, I get around 62 mpg, with regular, around 56-58 mpg .
With my normal commute to work, I get 172 miles to low fuel warning, that's around 43 mpg with regular, with premium, it's usually around 192 miles to low fuel warning, or around 48 mpg .
From full to low fuel warning is 4US gallons .
I realize it's a float switch type indication for low fuel warning, so there is room for error, as with filling the fuel tank as well .
I've got an '01 BMW Z3, and it has the same behavior as the bike, 4-5 mpg increase with premium, over regular .
-
Technically, you SHOULD get better fuel mileage with premium, because the higher octane rating does imply that the combustion process can yield more energy per unit volume. But, I find that my fuel mileage improvement, if any, is generally ~2 MPG at best. Over the course of a tankful of gas, the net 5% (best case I've experienced with carbureted bikes) improvement in mileage doesn't offset the usually 10% - 25% increase in cost per gallon for the premium fuel.
-
Octane rating isn't a measure of increased power available from the fuel. It means it's less volatile - less likely to detonate due to hot spots in the combustion chamber. So I don't understand getting better mileage from premium - there must be other factors involved.
That's pretty incredible mileage, Bob!
-
From what the service technicians at the car and bike dealers told me, is the fuel injection system uses oxygen sensor input to adjust for different grade fuel .
With regular grade fuel, the mixture is richened to prevent detonation, with premium, no adjustments are made, I don't know anymore than that .
I've got a Bentley manual for the Z3, when I have time, I'll try to see if it's explained in there .
I'm also pretty light on throttle usage, I've had the oilhead just under 10 years and I don't think I've ever come anywhere near full throttle .
-
Higher octane means the engine can be run more lean (.ie less fuel) without pinging, so with FI systems that can sense the difference and adjust the mixture accordingly, the fuel mileage is improved and, assuming that you require using the same amount of energy to travel a given distance at a given speed, you use less fuel. So, effectively, the usable energy content is higher per unit volume (gallon or litre) because you are using less - you are using it more efficiently. Now, for carbureted systems which cannot adjust the mixture on the fly, this benefit is mostly lost.
It isn't that the fuel itself has more caloric energy per unit volume (though it could be depending on chemical mixture), but that the fuel can be combusted more efficiently by running a leaner air/fuel. And, of course, with more antiknock properties, be more easily run in engines with higher compression ratios, which can produce more power through increase in thermodynamic efficiencies.
-
I too don't believe premium has a higher calorific value. In the UK it may even be a touch less as it more likely to have the maximum allowed ethanol content. (sounds bizarre that you pay more for the privilege of ethanol but true).
I didn't realise that modern engines could get more MPG out of premium by adjusting the mixture as that should be fixed at least in a steady cruise by lamda control.
Modern engines can get more power and MPG by increasing ignition advance but only if the car has high enough compression and has been mapped to take advantage of high octane fuel in the first place. Premium will not benefit engines that weren't designed to take advantage of it.
-
I noticed this article in the recent news - if it proves to be reliable and manufacturable, it could go a long way to making hybrid electric vehicles much more fuel efficient and lighter. Somehow, a combination of a Wankel engine and a diesel cycle engine come to mind..
http://tinyurl.com/6mrwetk
-
Edit - You guys beat me to it -.......................
My understanding is this:
On an oilhead or other computer controlled-engine - you have a knock sensor, Oxygen sensor and a computer that adjusts timing.
Assumption: the more you advance timing, the more powerful and efficiently an engine runs...up until the engine knocks/pings/pinks (?) and then you drastically lose power and efficiency.
Is computer-controlled engines (definitley everything made after 1997 - OBDII), the computer has a set timing advance curve that it starts and runs at, and then slowly advances the timing until it detects knocking/pinging/pinking (which it can do way before you'd hear it) then it backs off a bit, and hangs there for a while, and then sometime later tries again to advance the timing for better power and economy (just in case you put premium in the tank this time...) Since it has a decent 'baseline' timing to start from, you rarely notice it trying harder, but since it does occasionally advance timing to see if it can get away with it, you should get a little more HP or at least a few more MPG when running premium over the cheap stuff.
Of course, and on old R65 with no computers at all (thank you very much :) it has one timing curve, set and forget - it stays at one setting until you change it with wrenches and screwdrivers... ever resistant to software problems and EMP's :)
I would expect that a computer-controlled engine would gain power or efficiency when running premium fuel, and an old R65 would never know the difference (as long as it wasnt pinking...)
-John
-
Nice description John.
There's no benefit on an engine that wouldn't have pinged without premium whether that's and old fixed advance engine or a modern mapped one that didn't have enough advance scope to take advantage of premium.
One thing I can learn from the knock sensor approach is that my old airhead should be set so that it can just be made to ping under extreme, unreasonable provocation that wouldn't normally be used otherwise it means I don't have enough advance.
Having said all that old motorcycle engines have pretty crude timing anyway because they lack vacuum advance which means they tend to run much too retarded in part throttle steady cruise conditions. All the more reason then to use the maximum possible safe advance to minimise that deficiency. That the deficiency is not that noticeable tells us that power loss on less than optimum timing is not as critical to the nearest degree as we might think. It has to be quite a long way out to lose say 10% of maximum power.
-
Also, the fuel mixture can be set much too rich to keep away from pinging, and still appear to be running OK - which also means that it is at less than "optimum" power levels. But, given the variabilities in fuel, road grade, temperature, and elevation/atmospheric pressure with simple systems that cannot sense and adjust to these sorts of variables, getting things within a relatively broad band of "pretty good" is generally about all you can hope for.
Let's face it - "normal" 4 cycle engines are generally only about 20% energy efficient - with computer controlled FI systems, etc. this can usually be brought up to 25% or maybe even 30%. They have scads of room for improvement, and they generally have to be running pretty darn low on the efficiency scale for it to be noticeable.
-
The ole farm implements do NOT have a knock sensor (except the rider) so there is no automatic timing advance when 93 is used (with EFI timing, is advanced until knock is sensed) Without timing advance no more power will be produced. There MAY be an additive in 93 by a particular refiner which helps "drivability" in the old carb bikes, but when you're stuck with a particular compression ratio AND timing curve, higher octane produces nothing. In a vehicle optimized for 93 with EFI, timing is retarded when a lower rated fuel is introduced and knock is picked up by the sensor. So, when the driver goes back to 93, he/she often notices improvement. An interesting question is why 2 cycle low compression engine makers are now favoring 93. Carbon in the cylinder causing "pre ignition" perhaps? I know my weedwhacker screams on the stuff.
-
If you are running your weed wacker on premium fuel then you have more expendable income than I!
I suspect that the recommendation for premium is for the (often higher, but not always) level of detergent additives, which helps with cleaning their innards and the fuel path.
-
On very "computerized" systems the premium can often provide more usable power as the computer doesn't have to retard the timing any. These engines have a knock sensor or two and constantly monitor and back off timing until the pinging stops. This reduced timing will usually result in a bit less grunt and a decrease in fuel mileage.