Is it ok to mix 87 and 91 octane gas in a two stroke?


43 replies to this topic
  • Premixer112

Posted 13 November 2010 - 05:18 PM

#1

My brother and I are racing tomorrow and we are almost out of fuel so I went to the gas station to get some more. I usually get 87 unleaded, but I've read that it's better to get a higher octane gas, so I got 91. Well, I have a full tank in my bike right now and my brother has about a half to 3/4 full tank. My question is: at the races tomorrow, when it's time to put some gas in, is it all right to mix the 91 with my usual 87 that goes in there? Or should I just dump the gas that's in our tanks tonight? If it matters, I have a yz 250 and he has a kx 65.

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  • SubTexel

Posted 13 November 2010 - 05:22 PM

#2

My brother and I are racing tomorrow and we are almost out of fuel so I went to the gas station to get some more. I usually get 87 unleaded, but I've read that it's better to get a higher octane gas, so I got 91. Well, I have a full tank in my bike right now and my brother has about a half to 3/4 full tank. My question is: at the races tomorrow, when it's time to put some gas in, is it all right to mix the 91 with my usual 87 that goes in there? Or should I just dump the gas that's in our tanks tonight? If it matters, I have a yz 250 and he has a kx 65.


And you don't get pinging with the 87 on either bike? You can mix them yes, but you really should be running 91.

  • trailmeisterjoe

Posted 13 November 2010 - 05:37 PM

#3

yep....91 and NEVER the 87.

Joe

  • Premixer112

Posted 13 November 2010 - 06:00 PM

#4

Well damn, I've been using 87 since we got our bikes! Which was about 4 months ago.

  • brentn

Posted 13 November 2010 - 06:03 PM

#5

What elevation are you at?

Some elevations will let you get away with running lower than 91 than others. The engine was designed to run on 91 (don't use anything higher, performance will drop), and will usually start to ping if you use anything lower.

  • Premixer112

Posted 13 November 2010 - 06:09 PM

#6

What elevation are you at?

Some elevations will let you get away with running lower than 91 than others. The engine was designed to run on 91 (don't use anything higher, performance will drop), and will usually start to ping if you use anything lower.


I think it's around 500 ft.

  • OLHILLBILLY

Posted 13 November 2010 - 06:47 PM

#7

YZ250, I'd be running 91 in it no matter the elevation. I even use 91 in my KDX. Cheap insurance IMO.

  • rotordawg

Posted 13 November 2010 - 06:54 PM

#8

When you buy mid grade it is just a combination of low octane and high. So if you mixed a gallon of 87 with a gallon of 93 you would end up with about 90. Most modern gas stations have a mixer before it comes out of the nozzle. No harm in mixing it at all. Here in New England its all unleaded. All of the MX bikes today have high compression engines that prefer higher octane. But in a pinch I would use lower octane, especially if it meant pushing or riding, LOL

  • SubTexel

Posted 13 November 2010 - 07:11 PM

#9

What elevation are you at?

Some elevations will let you get away with running lower than 91 than others. The engine was designed to run on 91 (don't use anything higher, performance will drop), and will usually start to ping if you use anything lower.


Geez, not this higher octane causing a loss of performance.

Using a higher octane will not decrease performance. It will also NOT increase performance unless you are jetted for it and running modified motor (increased compression, etc...). All you will do is lose money, but not performance.

(I've dyno'd quite a bit of my cars with 110, 100, 100LL, 93, etc... Guess what? Same numbers until I tune for the higher octane. Same principles follow with dirt bikes).

Anyhow OP, yeah run 91 / 93 (whatever is available to you) and nothing less.

  • Northwoodslivin

Posted 13 November 2010 - 07:19 PM

#10

Interesting. I dont think high test should matter in a non high comp engine? I know that my YZ250F NEEDED high test due to it's high compression... But to answer your question, yes no problems mixing the two.

  • ekulb14

Posted 13 November 2010 - 07:24 PM

#11

What elevation are you at?

shoudnt make a difference i ran a a 125 at 5000 feet using 87 for years with no problems

  • SubTexel

Posted 13 November 2010 - 07:25 PM

#12

Interesting. I dont think high test should matter in a non high comp engine? I know that my YZ250F NEEDED high test due to it's high compression... But to answer your question, yes no problems mixing the two.


All MX bikes require 91 or higher, 2 and 4 stroke, as do a lot of the off road models.

  • Northwoodslivin

Posted 13 November 2010 - 07:25 PM

#13

shoudnt make a difference i ran a a 125 at 5000 feet using 87 for years with no problems


ditto.

  • motomatt16

Posted 13 November 2010 - 08:08 PM

#14

how many years ago were these years? way back when they werent all that high performance? or riding them like a old lady in trails?

  • ekulb14

Posted 13 November 2010 - 08:32 PM

#15

All MX bikes require 91 or higher, 2 and 4 stroke, as do a lot of the off road models.

humm not trying to bash you here but... idk about that

how many years ago were these years? way back when they werent all that high performance? or riding them like a old lady in trails?

it was a 2000 yz, no mods and riding the piss out of it on motocross tracks.

  • downonmonday

Posted 13 November 2010 - 08:37 PM

#16

Simple answer...yes, you'll be fine.

  • SubTexel

Posted 13 November 2010 - 08:39 PM

#17

humm not trying to bash you here but... idk about that

it was a 2000 yz, no mods and riding the piss out of it on motocross tracks.


Umm not to point out the obvious, but look in your manual.

Also, look at your head and piston... Anyone I've known who's run 87 (usually when trying to save money) has damaged those two in very short order (buddy was a tight wad, ran 87 on his 06 KX250... guess what happened? Yup..). I've known guys who put around on their bikes with 87 but you can hear the bike pinging under any type of load. Not the brightest thing to do.

  • Chokey

Posted 13 November 2010 - 08:49 PM

#18

Geez, not this higher octane causing a loss of performance.

Using a higher octane will not decrease performance. It will also NOT increase performance unless you are jetted for it and running modified motor (increased compression, etc...). All you will do is lose money, but not performance.

(I've dyno'd quite a bit of my cars with 110, 100, 100LL, 93, etc... Guess what? Same numbers until I tune for the higher octane. Same principles follow with dirt bikes).

Anyhow OP, yeah run 91 / 93 (whatever is available to you) and nothing less.

You're fighting a losing battle there, Texel, trying to convince people that using a higher octane fuel than necessary won't affect performance in any way. I've been trying to dispel that myth on here for years to no avail. It's such a widely believed myth that no amount of evidence or hard data will change most people's minds. People just don't seem to grasp the idea that octane rating has absolutely nothing to do with combustion temperatures, burn rate, or power production, it means nothing more than a fuel's resistance to detonation. But you can keep trying, maybe you'll have better luck than me. :p

  • Premixer112

Posted 13 November 2010 - 09:25 PM

#19

Well, I ended up draining both our tanks and replaced them with the 91 because you guys got me all paranoid lol. I remember using 87 in my 04 CR85 all the time and never had any problems.. I never new this was such a big deal.

  • Grassman100

Posted 13 November 2010 - 09:35 PM

#20

I use diesel in my YZ400F. Bitch to start though....:p:p





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