Whats the best gasoline for a Rebel? - Page 3

**GearJammer** · 08-02-2010, 10:58 PM

Quote:

Originally Posted by hedwards

If it doesn't knock at 87, it shouldn't knock at 91.

I'm curious on what way does it run better?

AFAIK the main issue is that of timing and compression. I don't personally know of any reason why the suggestion of the manufacturer wouldn't be correct, unless there's been some adjustments made in terms of aftermarket customization to change that.

Thanx for at least asking in a courteous manner......Only performance mod is open pipes. Had been running 87 without complaint, but this change to 91 octane was on the same day (meaning same ambient temps, weather, elevation, etc.) The run out was "o.k.", like I said, no complaints, but topped off with 91 for the run back and it was noticeably smoother and stronger......"peppier" would be a good word for it. Earth shattering ? No. But noticeable ? Yes.

I've since checked both the Honda OEM Service Manual and the Clymer's and can find no recommended octane rating in either one. Have an Owner's Manual in storage, but haven't gotten to it yet. Not sure if this being a 450 makes any difference, all I know is that the bike ran better and will be sticking with the 91 octane again.

Have seen Japanese manuals for other bikes in the past that had recommended 87 "OR" 91 octane.........so as far as I can tell, it's a matter of personal choice based on the individual bike and the performance of that bike.

**twocoolgliders** · 08-02-2010, 11:39 PM

Quote:

Originally Posted by maxweljames

twocool, anti knocking is actually a byproduct of higher octane ratings. As the octane level goes up so does the auto ignition temperature. Auto ignition is bad in a spark ignition system style engine. We only want the spark plugs causing the fire, not the heat from the cylinder walls.

What does all this mean for getting more power. The higher the octane the slower the ignition. A lower octane has a much faster burn rate and uses up it's energy before the piston produces it's full potential. You are correct that even with 87 there is no knocking, meaning there is no pre-ignition of the fuel. But by stepping up the octane, slowing down the burn we create energy over a larger time frame, allowing more power to be developed.

Mind you all this is happening faster than you can blink. An internal combustion engine is a beautiful thing, and we're fine tuning how it operates simply by changing the hydrocarbon level we induce into it.

Well not really...........slower burning does not mean more power, gas has the same power........slower burning does allow for more timing advance, which WILL give more power, and slower burning allows for higher compression which WILL give more power.........

BUT........rebel is not high compression, and rebel does not have timing advance...........so there will be no difference when using high test vs regular....

High octane has its advantages when used in an engine designed for it..........not rebel however!

Cookie

**twocoolgliders** · 08-02-2010, 11:46 PM

Quote:

Originally Posted by Blueberry

I use high octane in my Royal Enfield. Its a 500 single with a 90 mm stroke. It burns slower pushing the piston for a longer time. Slower burning also cools the piston and cylinder walls longer. I can kick start it in 1 kick hot or cold with high octane. Not so with regular. It helps in an engine that fires every 720 degrees of crank spin. The Rebel and 90 get regular. It burns faster and on a short stroke engine high octane can still be burning past bottom dead center and result in a drop in power and mpg. When all is said and done, run what you feel is best for your motorcycle.

Right, engine designed for high octane = use high octane (more to it than just compression ratio and timing set.....also piston diameter and stroke..

Engine designed for regular, use regular......no damage using high octane (usually, but like aviation fuel has lots of lead which can caus lead fouling and valve problems)

Those who say it "runs better" on high test are basing the run better on what exactly? Dyno test? Mileage? acceleration? 0-60 speed? What?

Actually there are many factors that are in play as to how the engine runs, beside the fuel........like air density, humidity, temperature etc........condition of plugs, carb setting, etc....

All of these factors would have to be kept exactly that same in any meaningful tests of "improved performance"......you would also have to define "performance".

It is human nature to believe in magic, superstition, urban myths etc.......

Cookie

**GearJammer** · 08-02-2010, 11:47 PM

Quote:

Originally Posted by twocoolgliders

Well not really...........slower burning does not mean more power, gas has the same power........slower burning does allow for more timing advance, which WILL give more power, and slower burning allows for higher compression which WILL give more power.........

BUT........rebel is not high compression, and rebel does not have timing advance...........so there will be no difference when using high test vs regular....

High octane has its advantages when used in an engine designed for it..........not rebel however!

Cookie

"and rebel does not have timing advance.".......

O.K......please clarify this for me as I'll admit that I'm not sure......Is "timing advance" the same as "ignition advance" ? Because if it's the same, then the Rebel most certainly does have timing advance.....it's one of the functions of the CDI......

**twocoolgliders** · 08-02-2010, 11:48 PM

Quote:

Originally Posted by cagie

This is true for a longer stroke engine where the higher octane actually has time to burn. The Rebel is a short stroke engine, so higher octane is a was of money as the slower burn doesn't do anything for the engine.

You are correct sir!

Cookie

**twocoolgliders** · 08-02-2010, 11:51 PM

Quote:

Originally Posted by maxweljames

A very good point cagie. It's such a micro level we're talking about. And outside of the actual fuel we have air temperature, pressure, humidity, etc. to concider. Blueberry makes a good point too, higher octane generally burns cooler, this adds to the efficiency of the engine as well.

All in all there will be days when the Rebel just seems to run a bit better, enjoy those days my friends.

Similar to my comments in post above..before I read this post............but running cooler is not always better.........engine is designed to run at a certain temperature.....too cool means not good fuel atomization etc...

My old honda scooter always would "run better" in cool to cold weather, than in hot........simple....the carb was adjusted too rich.........denser cold air brought the mixture to about right........hot day too rich......
Cookie

**twocoolgliders** · 08-02-2010, 11:57 PM

Quote:

Originally Posted by GearJammer

Did I mention anything about "anti-knock" ? The 450 didn't knock on 87 octane and doesn't knock on 91 octane, but it DOES "run better" on 91 octane. Don't care how you slice it, I know my own bike and how it performs...........and whether you like it or not, or believe it or not, it RUNS BETTER on 91 octane......

No I mentioned anti knock, becaues that is what higher octane gas is for.....

If you didn't get knock on 87 you are wasting your money on higher octane....

If you think it runs better, well Ok..........that is what you think.....can you quantify this? what does "running better" mean?

Then I asked an open question to anyone, to explain how higer octane in an engine designed for regular would make it "run better"

If this was fact, my scooter and Rebel would have "run better" when I put in high octane, but I could tell no difference (except the cost)

If this was fact, EVERYBODY would be using high test in all vehicles.......

If this was fact, somebody could give us a reasonable explaination using chemistry and physics.........

Cookie

**twocoolgliders** · 08-02-2010, 11:59 PM

Quote:

Originally Posted by hedwards

If it doesn't knock at 87, it shouldn't knock at 91.

I'm curious on what way does it run better?

AFAIK the main issue is that of timing and compression. I don't personally know of any reason why the suggestion of the manufacturer wouldn't be correct, unless there's been some adjustments made in terms of aftermarket customization to change that.

You are corrrect sir!

BTW my 1994 Mercury Capri manual and gas cap said "Use only regular gas" "do not use other than 87 octane" Hmmmmmmmm....

Cookie

**twocoolgliders** · 08-03-2010, 12:01 AM

Quote:

Originally Posted by GearJammer

Did I mention anything about "anti-knock" ? The 450 didn't knock on 87 octane and doesn't knock on 91 octane, but it DOES "run better" on 91 octane. Don't care how you slice it, I know my own bike and how it performs...........and whether you like it or not, or believe it or not, it RUNS BETTER on 91 octane......

Might I interest you in "E3" spark plugs? Guys claim "14% increase in fuel economy" and "better starting" and "better power" and "better running"........

Along with high test gas..........that would be unbeatable!!!

Cookie

**cagie** · 08-03-2010, 12:11 AM

I consede, I had always thought the owners manual said 87, but I was wrong. Here is the page from my 87 owners manual...

fuel-tank-fuel-type.jpg

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