What Octane does your bike need?

[TopCatGr58]

Wiseco stated that it should be 10.5:1, but others have postulated that that value was possibly based on the earlier engines with the smaller head/dome area, and that with the later engines/heads that the actual CR would be a bit lower??

I know the manual states the later engines were 9.0:1 vs. the earlier ones at 9.2:1.
At 9.2:1 the comp values are supposed to be 142 psi +/- 10% at Sea level IIRC.

After my breakin period I found the Comp values to be 180+ across all 4, and I DO live at sea level! I know there isn't a direct correlation between CR and comp values, but ~180 is an approximate 25% increase?? And as previously stated, I put in just the smaller 1179cc kit, not the 1196cc kit, for fear of making the cylinder walls too thin=easily overheated/warped, and also wanted to leave room for further boring if needed in the years to come...I hadn't yet learned about swapping the cyl. sleeves for a possible reboring to the same 1179 size with new rings provided the pistons weren't too worn.

T.C.

[Bonz]

10.5:1 is a good bump up from 9.0/9.2:1. I got a 1 pt bump 10.0:1 up to 11.0:1 with the ZRX over the winter and can feel the extra "zing". The pistons especially woke up the ZZR1200 cams that I had been running with stock compression.

For the Wiseco kit, that would make sense it was based on the older design since the pistons need to work with any XS.

[MPittma100]

Lots of Numbers

Are needed to accurately predict a static compression ratio. These numbers can be difficult to obtain without special measuring tools.

T.C. mentions a 40 psi gain in cylinder pressure with a bigger bore kit. That is substantial.

10:1 or more compression ratio makes great horsepower but also demands more octane than is currently available at the pump.

One would be well advised to get the numbers together prior to a piston replacement and/or bore increase to determine a precise compression ratio.

[willem.deboer]

Hey Bonz,

This carboning up problem, and the discussion about running it "HARD" to burn/blow it out made me think a bit. Many times I have encountered XS11 owners and riders at the rallies, and they want to ride their bikes like they are H-D's and are AFRAID to run the rpms much over 5K, and they want to LUG the engines at 2K rpms. I know the engines have power and torque and can run at that speed, but it's detrimental to the bike both with regards to the tendency for carbon buildup as well as draining the charging system since doesn't reach it's full voltage/amp capacity until at least 2500 rpm or more.

After my big bore rebuild in 2000 I ran 93 Premium in it exclusively for some 15 years but never had carboned up or fouled spark plugs. I do run a HI POWER/OUTPUT set of coils that help to provide a strong spark. I also habitually run mine at 3500 rpm or more and have no problems running it at 5K+ on the highway for hours.

SO...I postulate that part of folks excessive carbon buildup comes from running their engines at too low of rpms when putting around town and such. JAT!

T.C.

Agree. I tend to run the engine one gear lower than it invites me to, for that reason.
I installed a dual USB-charger and it came with a digital voltmeter built in. I noticed that the charging system only starts charging above 13 volts when revving above 2500 rpm. Now I understand this is normal behaviour ......

[donebysunday]

Small

engine was just on the radio, I'll try and relate what they said.

In the tests they performed E10 started to grow mold at 15 days.
Red Stabil was nearly useless and may actually cause problems. While they were excepting calls a man called and told them he had been using RED Stabil for years without problem. They told him if it works then don't fix it Seafoam was the product of choice. They said these fuel extenders were just forming a skin on the surface of the fuel to protect the fuel from exposure to air.
I WISH THEY HAD TESTED OTHER PRODUCTS and BLUE Stabil that used to have marine treatment on the label and now has ETHANOL TREATMENT !

Fuel was discussed and they said any fuel, even 94 octane was better than any ethanol fuel and actually recommended ethanol free premium for the small engines.