Premium grade ?

[apaiva]

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.

[nhmaf]

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.

[Bob_Roller]

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 .

[Barry]

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.  

[tvrla]

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.

[Bob_Roller]

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 .

[montmil]

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.

[nhmaf]

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.

[Rob Valdez 79 R65]

I have run Regular in all of my '79/'80 engines, and it was never a problem - in Indiana.

[tvrla]

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 .

[Barry]

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 ?

[Bob_Roller]

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 .

[nhmaf]

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.

[tvrla]

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!

[Bob_Roller]

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 .