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What Octane of gas do you use in your Rebel?

17K views 50 replies 22 participants last post by  jdock 
#1 ·
After reading a post about a brand new Rebel 1100 having black smoke coming out from their exhaust and blamed it from low oil there was no comment on what grade of gas they were using. Some might think its a waste of money to use either 91-93 octane, however thats what I use in both the Rebel 500 & 1100. So far no issues. What octane of gas do you run in your Rebel?
 
#35 ·
My '72 Trail 90 runs on 87 octane E0 so I get 93 octane E10 and leach out the ethanol using water. Ends up at about 87 octane. The alternative is traveling 100 miles out of my way to get 93 octane E0. Every other bike I own can handle E10. No E15 around here.
 
#36 ·
If you want to take care of your ride, and don't ride that often then just avoid ethonanol. And/or avoid mom m pop gas that is Hella old or super cheap like Walmart some circle K where they have water in their gas. I worked for city hall and one truck always ran like crap whe we got gas from local circle K.
 
#37 ·
Ima little late to the convo but here’s my 2¢. I have been running 87 since new (2020) and today I added 1.5 gallons of 91 into my half full tank of 87 so a blend if you will of 89. The ride to my barbers after that down the 55 fwy in SoCal. My rebel 500 was way quicker and smoother on acceleration than it has ever been. Felt like I was going downhill. I’ve took this together to my barbers from work over a year now and even after that going back to work and home after was a whole new ride. Manual calls for repair gas and maybe 91 isn’t the answer but maybe in between at 89. That might just be it for me. I do gave have arrow heaters and a mussari gp muffler if that helps.
 
#38 ·
Ayedrien, it's not the higher octane that's increasing power. The chemistry being used to raise the octane rating is also oxygenating the fuel. If the octane rating was increased using something like toluene which contains no oxygen, there would be no performance gain without raising cylinder compression or advancing the ignition. An actual octane molecule has no oxygen atoms. Ethanol and other oxygenaters can increase performance but they also have an affinity for water. I wouldn't worry too much if you go thru it fast enough. I think MTBE can only absorb half the amount of water that ethanol can.
 
#40 ·
If it came from a station that sells E0 and mixed with what's already in the tank, it would yield an E5. I know Exxon uses a full 10% in their highest octane.

Another possibility or contributing factor could be a higher detergent content is used in the high octane which is something else Exxon does. It might run better on low octane after running a tank thru.
 
#42 ·
Actually ethanol does not increase HP. It allows for a higher compression which does increase power output of the engine. The compression is to low on engines running gasoline therefore there is less power output from having ethanol in the gasoline. See the wiki quote below.

"Ethanol contains approximately 34% less energy per unit volume than gasoline, and therefore in theory, burning pure ethanol in a vehicle reduces range per unit measure by 34%, given the same fuel economy, compared to burning pure gasoline. However, since ethanol has a higher octane rating, the engine can be made more efficient by raising its compression ratio."

 
#43 ·
Sonwon, you're talking about higher octane but that's not what jdock is referring to. Ethanol gives power to an unmodified engine because it adds oxygen. It only needs a richer AFR to make up for the lesser amount of pure hydrocarbons that it displaces. Same is true for any oxygenant. It looks like a stock Rebel does run rich enough up thru the mid range according the measured AFR. Most bikes are a little rich at full throttle and might see the same benefit. If fueling isn't rich enough, E0 would make more power.
 
#45 ·
Thank you for the clarification, in my defense nowhere was oxygenanted mentioned. And as you pointed out this relies on a rich fuel mixture which was also not mentioned. I suppose if it is rich enough it could work however modern engines are designed to run lean to reduce emissions. I doubt the Rebel 500 would be rich enough to benefit from E10. I admit I have never seen a fuel map for a stock Rebel 500. Do you have one?

In personal test in cars E0 tends to provide a little better fuel mileage. I run E5 in an 1100 since the E0 is more than double the price and is very hard to find. I know my Sportster runs better with E5 than E10. E10 gave it this odd stumble when really hot, likely a problem with air cooling over water cooling, the ECM didn't properly adjust to E10, just the fact E10 burns hotter, or all of the above. The E10 did meet the knock requirements of the Sportster. I also like having a little less corrosion water sucking fuel in the tank so I use E5 in all my bikes.
 
#47 ·
The O2 sensor is used to control AFR at idle and cruise automatically so that gets adjusted to around 14.2:1 for E10. As revs go up and loads increase, manufacturers tend to keep things pretty much on the increasingly too rich side. That's according to various dyno charts that show AFR. What I'd like to know is the ethanol content used. Here's one for the CB500:
Rectangle Slope Font Line Plot
 
#49 ·
The engineers who designed the engine and the EFI system know more bout engine design in general and your Honda Rebel engine in particular compared to we all in this forum. Not only they designed the system, but they had to test every parameter to make sure they'll have the least amount of warranty claims under normal operating conditions. I would listen to what they recommend.

In my Honda Rebel 1100, they recommend using a fuel with at least 86 octanes and maximum 10% ethanol. In the U.S., the cheapest unleaded gas is 87 E10. Any performance gains from using a higher octane or lower ethanol content will not offset the increased cost. I would recommend everyone to save some money and follow the manufacturer recommendations (unless you are tunning your engine to different parameters, but that's a different story).

The only exception is when the bike will sit unused for more than 30 days. Ethanol is hygroscopic. It adsorbs water (different from absorption) which means it attracts water. That water corrodes metal parts. Ethanol also increases the level of oxygen in the gas, which turns the paraffins and other gasoline molecules into a gel. That gums up the ejectors and other components. In summary, ethanol-containing gas sitting in the bike for more than 30 days is a big no-no. You should add stabilizers or use ethanol-free gas whenever you will not use all the gas in the tank within a 30-days period.
 
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