Why premium fuel?

[Sweendog]

I always thought higher compression engines required premium, but I've been reading around and see that a CBR has about the same compression ratio as my R1100, yet only requires regular gas.

 

Just wondering if any of you mechanical engineer types could clue me into why the difference...

[David13]

I always use 91 as my bike is considered high compression at 12 to 1.

However, I have heard 'engineer types' what say it doesn't matter, etc.

On 87 I would only use it in someone else's car, or bike.

The Harleys supposedly use regular, but they would not be considered high compression at 10 to 1.

I saw a group of Harley rentals, and they said they were told by the rental agent that they must use 91.

I only use 89 or 91. My preference. I don't care what any expert says.

The only thing I wish I could remember, is, when I go to Mexico, should I use Magna, or Nova?

dc

[BailyD]

used regular, municipal gas in 2007 RT-P and found it knocked. now using premium and it never knocks?

[ragtoplvr]

Many years ago Mr. Honda discovered that detonation pretty much disappears above 10K RPM.

 

Small bore undersquare engines have much higher ratio of cylinder head wall area to combustion volume also reduces detonation.

 

Water cooling means more consistent temperatures, so tune can be very precise, less chance of detonation.

 

Little tiny pistons can be pretty strong, same for heads, so can resist detonation better

 

and a lot more little details.

[ShovelStrokeEd]

Combustion chamber shapa and size is the primary reason. Compare bore size on a CBR1000 to the bore size of the 1200RT.

 

Another factor is the swirl pattern ine chamber which, to a certain extent, is dictated by the port entrance angles. Other things are valve included angles and sizes. Swirl provides cooling of the combustion chamber, including the piston tops. Temperature of those pretty much determines when an engine will detonate.

 

A large bore means high surface area. Much harder to cool.

[Peter Parts]

It's ironic - low octane gas is more explosive and actually provides more ponies when it fires.

 

But high octane is more "forgiving" of poor head design (like the boxers) and allows greater flexibility for your rpm choice. I love to load up with Sunoco 94 and then drive lazy in the city, lugging to stops.

 

Ben

[Joe Frickin' Friday]

I always thought higher compression engines required premium, but I've been reading around and see that a CBR has about the same compression ratio as my R1100, yet only requires regular gas.

Just wondering if any of you mechanical engineer types could clue me into why the difference...

 

Octane buys you time. Testing with laboratory rapid-compression devices shows that when you quickly squeeze fuel-air mixtures up to a pressure/temperature high enough to cause autoignition (and then hold it at that final volume), there’s a short delay before combustion actually begins, and that delay is longer if you’re using higher octane fuel. That delay is also shorter if you’re dealing with higher pressures/temperatures.

 

So in an engine, your goal is to get all of the mixture to burn via “normal” combustion (deflagration) before the burn transitions to detonation. You can either shorten the burn time, or alleviate the conditions that cause detonation.

 

There are several parameters that affect the burn time:

• Bore size. For a given flame front speed, the smaller the combustion chamber, the less time it requires to burn all of the mixture there. A CBR1000 has a bore diameter of 76mm; an R1100RT, 99mm.
   
  
• RPM. The faster your engine is turning, the more turbulence is generated in-cylinder. Turbulence greatly accelerates combustion by stretching/distorting the flame front, creating more surface area for reaction. Turbulence is a huge factor in why a CBR1000 engine can run at 1000 RPM, and can also run (not just run, but actually make scads of power) at 12,000 RPM. At 12,000 RPM, the burn time is much, much shorter; detonation is much less likely than when lugging the engine.
   
  
• Multiple ignition points. If you’ve got a very large cylinder bore diameter, you can shorten the burn time by lighting the mixture at a couple of different spots. Multiple spark plugs will do this for you, and helps large-bore engines (e.g. the R1200RT) run with high compression and advanced spark timing without knocking.
   
  
• Intake port design. “Swirl” (rotation of the air around the bore axis) is usually employed in diesels to help mix the burning fuel spray with the charge air. In spark-ignited engines the intake ports are most commonly configured to generate “tumble” flow, or rotation of the mixture around an axis perpendicular to the bore (imagine a wheel rolling across the top of the piston). This flow structure gets distorted during compression, until somewhere near TDC it breaks down into fine-scale turbulence; as described earlier, this turbulence helps speed up combustion by a huge margin.

If you’ve got an engine that’s suffering from detonation, there are things you can do to alleviate the causative conditions:

• Reduce combustion chamber surface temps. Move more coolant, or redesign the coolant passages to mitigate hot spots. The CBR engine may have better cooling than the R1100RT.
   
  
• Reduce mixture end-gas temps. As the first part of the mixture burns, it expands. This compresses the unburned part of the mixture, raising its temperature and pressure and moving it closer to detonation conditions. If it is in fact detonating, then we need to reduce the starting pressures/temperatures. One way to do this is by retarding the spark timing so that the piston has moved farther down by the time the flame front reaches the end gas. Another way is to reduce compression ratio. The CBR may have the same compression ratio as the 1100RT, but we know nothing about its spark timing under the various operating conditions; likewise with the RT. The CBR may have significantly retarded spark timing under certain operating conditions to cope with detonation.
   
  
• Run higher octane fuel. This buys you more time to get the mixture burned.

 

It's ironic - low octane gas is more explosive and actually provides more ponies when it fires.

While this is often true, it’s not universally so. Alcohol is often used as an octane booster, and it does reduce the per-gallon energy content, but there are other ways to increase octane rating without compromising energy content.

 

[Lawman]

What Mitch said..

[4wheeldog]

As usual, Mitch has the answer with the facts to back it up.

 

Back to the practical, the real world........Try regular, listen closely, and if it doesn't knock, use it. If it does, up it a grade.

 

I live at high elevation (Read, 20% less air, so lower effective compression). We have 86 octane regular. It works great in my RT. Except when it is really hot out. Then I will put in some middle grade or premium, depending on how much gas is already in the tank.

Fuel changes by location/season/elevation. If I go down to sea level, and it is warm out, I might have to use middle grade. If I use premium in the colder months at elevation, starting is just a bit slower, and cold running is not as good.

 

I don't know if Mitch will agree with this, but I think that the less octane, the less additives that wind up as carbon deposits. Folks that use premium often are stuck using it because of the deposits.......Vicious cycle. Or maybe I am just a cheap bastard, justifying my actions. Good Luck!

[rabbibgr]

The new 1200's have a knock sensor. this means that if detonation is occuring, the timing is retarded. I guess this means that lower octane fuel can be used, but at the cost of some power

[Joe Frickin' Friday]

I live at high elevation (Read, 20% less air, so lower effective compression). We have 86 octane regular. It works great in my RT. Except when it is really hot out. Then I will put in some middle grade or premium, depending on how much gas is already in the tank.

Fuel changes by location/season/elevation. If I go down to sea level, and it is warm out, I might have to use middle grade. If I use premium in the colder months at elevation, starting is just a bit slower, and cold running is not as good.

 

Masako and I got married in Las Vegas. We rented a car there, and for our honeymoon, we went to Grand Canyon, Bryce Canyon, and Zion. We got gas in Bryce, and being a cheap bastard, I filled up with the lowest octane they had (86 or 87 I think), which is lower than the minimum octane you can get at lower elevations. The car had a knock sensor and could adjust spark timing to compensate for low octane, so I figured why waste money on gas?

 

Then we drove from Bryce, through Zion, back to Las Vegas.

 

Bryce Canyon (the rim) is at about 7600 feet, and was comfortably cool when we left.

 

Las Vegas is at about 2000 feet, and temps were around 100 when we pulled into town.

 

The low octane, low altitude, and high temps exceeded the ECU's ability to adjust the spark timing; during the last half of the trip from Zion to Vegas the car was knocking so bad I was scared it wasn't going to make it into town.

 

[EddyQ]

Then we drove from Bryce, through Zion, back to Las Vegas.

 

I'd driving my family down from North Rim to Vegas the first week in August. I'll have to remember this tip.

 

Thanks!

[4wheeldog]

I live at high elevation (Read, 20% less air, so lower effective compression). We have 86 octane regular. It works great in my RT. Except when it is really hot out. Then I will put in some middle grade or premium, depending on how much gas is already in the tank.

Fuel changes by location/season/elevation. If I go down to sea level, and it is warm out, I might have to use middle grade. If I use premium in the colder months at elevation, starting is just a bit slower, and cold running is not as good.

 

Masako and I got married in Las Vegas. We rented a car there, and for our honeymoon, we went to Grand Canyon, Bryce Canyon, and Zion. We got gas in Bryce, and being a cheap bastard, I filled up with the lowest octane they had (86 or 87 I think), which is lower than the minimum octane you can get at lower elevations. The car had a knock sensor and could adjust spark timing to compensate for low octane, so I figured why waste money on gas?

 

Then we drove from Bryce, through Zion, back to Las Vegas.

 

Bryce Canyon (the rim) is at about 7600 feet, and was comfortably cool when we left.

 

Las Vegas is at about 2000 feet, and temps were around 100 when we pulled into town.

 

The low octane, low altitude, and high temps exceeded the ECU's ability to adjust the spark timing; during the last half of the trip from Zion to Vegas the car was knocking so bad I was scared it wasn't going to make it into town.

 

My home is at 7220'. The lowest point in NM is around 2200', somewhere down near Las Cruces, which is damn near Tejas. ABQ is over 5000', and I consider that the "Low country" for purposes of carb jetting. So 86 octane works fine in everything I have. I adjust when I go elsewhere........But you gotta love EFI, when you live up here.

 

What I find amazing is how few folks that live up here realize that octane requirement is directly proportional to air available. Unless you own something with forced induction (Blower, turbo), it is pretty unlikely to need more than 86 octane.

[Rockrib]

I've asked myself this same question every time I pull up to the pump. All good info.

So, if I may Hijack for a moment; What about octane BOOSTER?

Will it give any better performance?

I use cetane booster in my pick-up and I'm absolutely certain (well, kinda certain...) that the truck runs better with than without.

Or is this apples and oranges?

[ragtoplvr]

Cetane booster (diesel) is the opposite of octane booster, it causes easier detonation. Yes, low cetane fuel does need help in diesels.

 

Some Octane boosters do work. Others are to get the consumer.

 

Stick with a Big name name brand. The best ever used was Bardhal Instead of Lead Gold, Sadly it is no longer available. The 104 works but the price!

 

That is all I have.

[Joe Frickin' Friday]

So, if I may Hijack for a moment; What about octane BOOSTER?

Will it give any better performance?

 

Depends what you mean by "better." It should increase the octane rating of the fuel, which will make it more resistant to detonation. If your engine knocks - or if the ECU has been retarding spark to avoid knock, costing you power/efficiency by doing so - then octane booster should cure that problem. But if your engine wasn't knocking (or if the ECU had not been retarding spark), then octane booster won't make any difference.

 

I use cetane booster in my pick-up and I'm absolutely certain (well, kinda certain...) that the truck runs better with than without.

Or is this apples and oranges?

 

Your truck owner's manual should specify a minimum cetane number for the fuel. If the engine is healthy, you shouldn't need a cetane improveer as long as the fuel you're using meets the spec in that manual. If there's something wrong with your engine, or you're using fuel with a cetane number lower than spec'd by the manual, you may end up with crappy fuel economy and low power output; a cetane improver can help under these circumstances.

[4wheeldog]

What about octane BOOSTER?

Will it give any better performance?

 

From a cheap bastard's point of view, higher octane fuel is less costly than octane booster.......Unless you need more than is available at the pump.

On a related subject, when mixing low and high octane fuels (You have a tank of 87, and you are filling with 91), the octane rating of the end mix is more than the sum of its parts.......Equal amounts of 87 and 91 wind up being a bit more than the 89 you might expect. So, if your motor is knocking, 1/3 of a tank of premium might be plenty to bring your octane up to acceptable levels.

[Mister Tee]

As a practical matter, I've noticed that 89 octane worked just as well as 91 octane in my RT, so I always ran that (they don't have 90 octane at the pumps in my area.) 87 performed ok, but the octane was low enough to engage the adaptive spark timing system and my mileage would fall off until I ran a couple tankfuls of 89 or 91 octane through it.

 

Both my GSXR 750 and my Concours C14 also require 90 octane as well, and I've ran 87 pump octane in both with no problems whatsoever (noticeable knocking) and neither are equipped with adaptive spark timing systems. I run mid grade 89 in both.

[SuperG]

When did they start putting knock sensors in rt1200?

[Boffin]

When did they start putting knock sensors in rt1200?

 

From day 1.

 

Andy

[OlGeezer]

As usual, Mitch has the answer with the facts to back it up.

 

Back to the practical, the real world........Try regular, listen closely, and if it doesn't knock, use it. If it does, up it a grade.

 

 

This has been my yardstick. My 1150 was happy new running on 89 octane, but as the engine aged, compression has dropped and is now quite happy with 87 octane. I think I'm about 8:1 (105 psi left, 115 psi right). Yeah, I know I will be needing a valve job soon.

[Sweendog]

Thanks for the explanation, Mitch!

 

I figured there are many parameters that have to be considered when designing an engine and choosing a fuel. I was really scratching my head as to why some twins (Like my Silverwing) run fine on regular, while other twins (Like my RT) require Premium. I was also hoping for a good summary, so I don't have to find a bunch of Mech. E. papers to read myself to sleep... ;^)

[Sweendog]

One other thing, I'm not sure I'll run mid-grade, as I'm really not sure if I would hear or recognize knocking when it occurs. It's painful to pay more for premium, but in the end it only amounts to a dollar or two more per tank, and I'd hate to have to fix something because I cheaped out on the gas.

 

(I'm finding these BMW parts are friggin' expensive!)

[SuperG]

A GS riding friend only fuels at one specific gas station, I asked him why.

There one Exxon station that still has three separate filling hoses, one for each grade. He gets premium from there, he states his GS was knocking on other stuff.

As you notice most gastations have a single filling hose and fuel grades gets switched in the metal fueling cabinet or where ever the selecting valve is.

 

His theory is that if the person before you filled with regular gas; there is nearly a gallon of regular sitting in the hose between he handle and the selecting valve (not sure how he got the gallon measurement). When you select premium by pushing a button you get regular first until it flushes out of the hose and premium fuel fills the line. So the person behind you get x amount of premium upgrade for free.

 

I have never thought about it before he mentioned it.

I figured I post it since we are talking about premium vs. regular.

 

PS: I have tested regular on my 05 RT, did not hear knock, this is the second thank of 87, (we also have 91 and 93 here in Texas depending on the station). Elevation is 900' where I am at. Still got 52mpg average on a mild 50/50 city/hwy mix riding solo.

[FlyingFinn]

...there is nearly a gallon of regular sitting in the hose between he handle and the selecting valve.

 

About 1/3 of a gallon according to "industry sources".

 

--

Mikko

[BerndM]

I use midgrade 89 octane with good results on my 05 R1200RT.

I tried regular 87 but rattled too much on takeoff.

My R1200GS ran great on 87 but the gearing was different.

[jaytee]

Really? BMW has designed their engine to produce the most power and best efficiency in premium fuel. Sure, they gave also protected the engine with an anti-knock sensor but retarding the timing robs power.

 

Why people are willing to pony up tens of thousands of dollars for an air cooled boxer but are unwilling to follow the manufacturers specs for gas is beyond me.

 

Really???

[OlGeezer]

A GS riding friend only fuels at one specific gas station, I asked him why.

There one Exxon station that still has three separate filling hoses, one for each grade. He gets premium from there, he states his GS was knocking on other stuff.

As you notice most gastations have a single filling hose and fuel grades gets switched in the metal fueling cabinet or where ever the selecting valve is.

 

His theory is that if the person before you filled with regular gas; there is nearly a gallon of regular sitting in the hose between he handle and the selecting valve (not sure how he got the gallon measurement). When you select premium by pushing a button you get regular first until it flushes out of the hose and premium fuel fills the line. So the person behind you get x amount of premium upgrade for free.

 

I have never thought about it before he mentioned it.

I figured I post it since we are talking about premium vs. regular.

 

PS: I have tested regular on my 05 RT, did not hear knock, this is the second thank of 87, (we also have 91 and 93 here in Texas depending on the station). Elevation is 900' where I am at. Still got 52mpg average on a mild 50/50 city/hwy mix riding solo.

 

Only fills up at one station? Your friend must not ride very far. I can't believe one GS has a knocking problem even if one gallon out of five is regular. That means the average octane rating is still 90.2.

[OlGeezer]

Really? BMW has designed their engine to produce the most power and best efficiency in premium fuel. Sure, they gave also protected the engine with an anti-knock sensor but retarding the timing robs power.

 

Why people are willing to pony up tens of thousands of dollars for an air cooled boxer but are unwilling to follow the manufacturers specs for gas is beyond me.

 

Really???

 

Because the cheapest thing on a BMW is.....THE RIDER!

 

What's even funnier is using the term "power" and "BMW" (particularly Boxer engines) in the same sentence. Very few of "us" riding Boxers are interested in power.

[jaytee]

Lol! Touche!

[Selden]

It's always difficult to get consistently accurate mpg measurements, but on a recent ride to Delaware and back, I decided to use almost exclusively premium, rather than midgrade, and I averaged just over 48 mpg, which is about 8%-10% better than I usually get on midgrade. Basically, if the price differential between grades is $0.10, I use premium; if it's ) $0.15, I may go one way or the other, and if it's more than $0.15, midgrade. ASSUMING my recent mpg figures are accurate, the added fuel efficiency cancels out the added cost.

 

Power has never been a concern; as Rolls Royce is reputed to have said about their cars, it's always been "sufficient" in my experience, even on a 12-year old R1100RT that I have detuned by using GS intake tubes.

[tallman]

Selden,

8% of $3.50 is over .25/gal.

10% is .35 so if the premium is w/in .35/gallon then it is a no brainer, IMO.

Of course lots of what I do is no brain errrs.

 

I run premium almost exclusively.

My choice and I'm happy to do it.

Best wishes.

[SuperG]

Really? BMW has designed their engine to produce the most power and best efficiency in premium fuel. Sure, they gave also protected the engine with an anti-knock sensor but retarding the timing robs power.

 

Why people are willing to pony up tens of thousands of dollars for an air cooled boxer but are unwilling to follow the manufacturers specs for gas is beyond me.

 

Really???

 

That's it... the above statement and "cheapest thing is the rider" just tickled some feather. ------ not really just kidding.

 

An even better question is: why does a $20K motorcycle owner does not follow manufacturer's instruction to the letter?

 

My answer is: curiosity! - the same--> that killed the cat

 

Manufacturer's will print certain things in the manual to cover their a$$ for all conditions in general.

and sometimes for profit making reasons as well. Such as use BMW part# 3$%67%$#6 final drive fluid, but my dealer want to sell me amsoil, because that is what they put in the bikes in the shop.

Or, I don't use GM part # 34%^$#@223 powersteering fluid in my suburban because it is same as powersteering fluid from walmart. I also exceed 50 mph on the installed mini spare tire after a flat.

You know the list could go on....Why KTM team puts rotella dyno 15-w40 diesel engine oil in the KTM engine at the GNCC, WORCS, Enduro or 24-Hour Race? why not KTM part # 3455^%%$$ engine oil? Those cheap bastards!

 

Why does a Harley owners (hundreds or thousands) replace a perfectly good fuel injection system with outdated old tech carburetor? Do they know better then the engineers?

 

If you follow manufacturers instruction to the letter, then you are a better man the I.

 

I love taking things apart (new things) and see if I can make it better( better for me!) I guess others are the same way, want to experiment or see what it is like to deviate from "normal".

 

 

 

 

 

 

 

[Mister Tee]

In our area, we have three grades available - 87, 89 and 91. Fuel spec calls for 90.

 

I noticed no difference in mileage whether I run 89 or 91, so I ran 89. If I ran 87, the adaptive spark timing system would kick in and my mileage would drop noticeably, until I ran a tank or two of mid grade.

[Selden]

Selden,

8% of $3.50 is over .25/gal.

10% is .35 so if the premium is w/in .35/gallon then it is a no brainer, IMO.

Of course lots of what I do is no brain errrs.

 

I run premium almost exclusively.

My choice and I'm happy to do it.

Best wishes.

That assumes that my 8% difference in gas mileage is accurate...

 

It's surprising that so many stations stick to a $0.10 pricing increment between grades, which is what was common when gas was $2.00 a gallon. A pretty good argument can be made that premium is a better relative choice now than then.

[tallman]

I'd never question your accuracy.

 

Having a happy bike is the goal.

Best wishes.

[Mister Tee]

It's surprising that so many stations stick to a $0.10 pricing increment between grades, which is what was common when gas was $2.00 a gallon. A pretty good argument can be made that premium is a better relative choice now than then.

 

I noticed that myself.

[Dan M]

The other advantage of using high quality, high octane fuel is the additive package. Better detergents will help keep injector and combustion chamber deposits in check.

 

I run premium in everything and if I have a choice, it is always BP, Shell or Mobil.

[BerndM]

Really? BMW has designed their engine to produce the most power and best efficiency in premium fuel. Sure, they gave also protected the engine with an anti-knock sensor but retarding the timing robs power.

 

Why people are willing to pony up tens of thousands of dollars for an air cooled boxer but are unwilling to follow the manufacturers specs for gas is beyond me.

 

Really???

 

Yeah, I'm cheap! No question there.

 

But I also figured I didn't need 110 HP for the way I ride

 

Last year, I rode a 1700 mile round trip to Yosemite and Tahoe from my home near Disneyland in SoCal.

We crossed the High Sierras 4 times reaching almost 10000 feet in elevation several times. Temps varied between about 28F degrees and 100F degrees. Mountain roads av speed about 35 mph, highway about 75-80 mph. Had 3 fully loaded cases.

My overall average miles per gallon per the on board computer as well as the old fashioned paper & pencil method indicated 50.3mpg.

I SERIOUSLY doubt that running 91 octane would have improved on that. The engine NEVER once pinged, even climbing at almost 10K feet.

So I figure, why give the damned gas companies one red cent extra.

Not me.

YMMV

regards

Bernd

 

[jaytee]

It's one thing to substitute a final drive oil with the same or better specifications- it's an entirely different (and dumb, IMHO) thing to deliberately substitute a LOWER specification fuel.

 

I'm equally astounded by those who run 91 in an engine specced for 87. No, detergents and whatnot make no difference whatsoever in fuels from the same maker at different octane ratings. I guess some people like to spend more money to have their engines run less efficiently.

 

It still blows me away the amount of superstition about fuels exist in otherwise technically inclined motorcycle (and automobile) enthusiasts.

 

For crissakes, people, go read a book on this or just ask an engine tuner!

 

 

[BerndM]

It's one thing to substitute a final drive oil with the same or better specifications- it's an entirely different (and dumb, IMHO) thing to deliberately substitute a LOWER specification fuel.

 

I'm equally astounded by those who run 91 in an engine specced for 87. No, detergents and whatnot make no difference whatsoever in fuels from the same maker at different octane ratings. I guess some people like to spend more money to have their engines run less efficiently.

 

It still blows me away the amount of superstition about fuels exist in otherwise technically inclined motorcycle (and automobile) enthusiasts.

 

For crissakes, people, go read a book on this or just ask an engine tuner!

 

 

You should hang out in front of a refinery sometime. We have lots of them here in SoCal. You have EVERY different name company trucks in there picking up fuel. So what you're saying is false, at least around here. Basically, you have no idea whose gas you're getting at any given station at any given time.

I've seen YouTube videos that show this very clearly.

Also, I'm pretty sure from articles I've read and TV programs I've seen that the detergent issue is a myth and has been for at least the past 20 years. Earlier than that, yess it may have been an issue, but apparently no longer. the different companies might have different types of chemical additives, but not so you notice.

I've got several hundreds of thousands of miles on my family's vehicles using virtually 100% ARCO fuel. There has NEVER been an issue of any sort with this "Cheap" gas.

Again

YMMV

Regards

Bernd

 

 

 

[jaytee]

I completely agree with you, bernd, so I have no idea how you can say what I said was completely false unless you just didn't understand me. Different brands do have different additive packages they add to the same fuels they pickup from the same refineries and storage tanks.

 

What I was taking about where cheap vs expensive was concerned was 87 vs 91. My entire point is that it is foolish to use a lower specification gasoline in an engine specced for 91 (regardless of brand) just as it is moronic to use an expensive 91 in an engine specced for 87.

 

The brand (unless truly formulated differently) makes very little difference compared to the octane specification of the fuel.

 

Hope that clears it up a bit for you.

 

JT

[BerndM]

Hey JT

OK we're good , I did misread your comment.

As far as not using what the bike maker recommends is somewhat subjective.

I did in fact try all three grades of gas in the bike (05 R1200RT) and ran thru a FULL tank of each. Like I said, the 87 octane caused pinging on takeoff IF I let the rpm drop a bit too low.

The 89 octane runs perfectly under ALL conditions (so far) for the last 5000 miles or so. The 91 octane provided ZERO benefit over the 89 that I could discern OTHER THAN provide more profit to the gas company.

The cost / benefit analysis is clear TO ME, for MY riding situation

on MY bike and the 89 seems perfect.

I understand that different bikes, even of the same model, might respond differently because of location, altitude humidity and riding style. That's understood. I'm only stating what MY personal experience is with MY particular bike.

I realize that that at only 10 cents a gallon difference between 89 and 91 gas, its only 70 cents per fillup if I was on fumes. No biggie, BUT imagine what a huge amount of money that could be for the gas companies if everyone in North America paid that extra dime per gallon for possibly no real necessity, other than that's what the manual says.

Regards

Bernd

 

[Peter Parts]

If you are simply scooting down the highway, regular gas is OK because the engine isn't trying too hard and so knocking isn't probable. On the other hand, you can't always hear knocking so the ear-test isn't trustworthy protection against harming your engine.

 

Better additive package is a good reason to go premium, assuming that is what the oil companies are doing.

 

The real difference is spark timing: using high octane is like adding retard. You get less power but more grunt and flexibility. The only way it would help MPG, I think, is if premium let you use lower gears. So I use premium around the city for sure (and elsewhere as well).

 

Basic problem is that the Oilhead cylinder heads are not SOTA so they use more gas (yet SEEM "lean") and need higher octane than they ought to.

 

Ben

[jaytee]

For me in an R1200S with higher compression than the other hexhead motors I feel there is no option but to use 91. I want the extra engine protection especially since I do wind out the motor most every day at least when I get on the freeways. I also expect to be able to run 87 if I have to and trust to the knock sensor to retard the timing and keep my engine safe if necessary (which it was on a recent trip to central California).

 

But day in and day out I definately want that safety margin.

 

Peter, I understand in a given engine designed for 87 that running 91 is less efficient, hence my comment about doing such a thing is counterproductive. However, you are completely incorrect where a higher compression engine designed for 91 is concerned. In the case of my S it is very clear that the engine produces more power on 91, especially at very low or very high RPMs under load due mainly to spark advance.

 

JT

[tallman]

Just following, not to you.

 

It takes some time and significant mileage, ususally, for issues to develop. So I'm glad those who choose to run nonspec gas post that they do so. Will avoid any bike purchases from them.

It would be interesting to compare a boxer run on regular to one run on premium after 75-100,000 miles.

Tear down after compression testing and look inside for any deleterious effects.

[OlGeezer]

Just following, not to you.

 

It takes some time and significant mileage, ususally, for issues to develop. So I'm glad those who choose to run nonspec gas post that they do so. Will avoid any bike purchases from them.

It would be interesting to compare a boxer run on regular to one run on premium after 75-100,000 miles.

Tear down after compression testing and look inside for any deleterious effects.

 

Still, I would be surprised if you could conclude that any differences between two engines, a very small data sample, was purely due to octane difference. Even if you could, a valve job at 100k is not an unreasonable expense regardless of the grade of gasoline.

[4wheeldog]

What, exactly, does the acronym "SOTA" refer to?

[SageRider]

What, exactly, does the acronym "SOTA" refer to?

State Of The Art

[tallman]

Could be.

But, if I sell a motorcycle that I've owned I want to be able to tell the prospective buyer that I did things in a certain way.

Fuel, services, etc.

 

Seems everyone wants to buy a preowned bike that had the oil changed at 3,000 miles, services done early, was never dropped and tires are new.

On the other hand, it seems some folks want to use nonspec fuel/oil/ ride tires to the cords and stretch service intervals.

That's fine as long as full disclosure accompanies the for sale ad.

Just my .02.

YMMV

Best wishes.