is about 11:1 to high on pump gas.

[TrikerR]

hi just found out this piston im getting makes the compression ratio about 11:1, would i have to run pure race gas with that.

[Blown 331]

What kind of bike? Air cooled I think is border line, liquid cool you will be fine. I'm wanting to see what others have to say about this too.
If it's in the ATC110. I think you should be ok with 93 octane since it's a smaller piston. If you get a cam with more overlap it will lower your dynamic compression as well.

[RideRed250R]

run the atc110 with sythetic motor oil, and 93 octane * wil lbe fine, i know of a guy who runs a 350x with a 12:1 piston on 92
adam

[OldSchoolin86]

On an air cooled you'll be lucky to run 93 with 11:1. Any higher you'll need race gas for sure if everything is working right.

[Blown 331]

I could be wrong but a 350X with 12 to 1 on 92 octane seems really questionable to me.

[MO350X]

What I live by with regards to high compression:
1. You have to be religious about keeping FRESH premium (keep Sta-Bil in there if you insist on "storing" fuel in your trike's tank, come hell or high water) in the tank. Yes, fuel does go bad! And faster than you think.
2. Jetting is critical (lean is no longer mean it becomes a recipe for disaster).
3. Timing is also critical (make SURE it's spot-on).
4. Make sure the decompression cable adjustment (350X, for example) is spot-on or you'll beat your leg to death.
5. You're not going to hear detonation (pinging) over that "bad boy" pipe and/or your friend's ride until it's WAY too late and you've done BIG $$ damage.

Higher compression on pump gas?
Check out the old Cannondale (now ATK) quads:
They are 12.5:1 on premium pump gas BUT...they have computer controlled timing and fuel injection...thus no quirky fueling/ignition problems.
They're always perfect.

Don't worry, it CAN be done but don't cheap out on parts or tuning or you'll regret it.

[OldSchoolin86]

Higher compression on pump gas?
Check out the old Cannondale (now ATK) quads:
They are 12.5:1 on premium pump gas BUT...they have computer controlled timing and fuel injection...thus no quirky fueling/ignition problems.
They're always perfect.

Don't worry, it CAN be done but don't cheap out on parts or tuning or you'll regret it.

The Cannondale quads should be no where near this thread. Those are liquid cooled motors that keep the temps down a lot more then an air cooled. Of course you will be able to run higher compression ratios without as many problems. Now 12:1 in an air cooled on pump gas just isn't gonna happen unless something is wrong.

[Wickedfinger]

My Scrambler 400 has a 12:1 cool head and it runs on 92 octane just fine. Also, compression should not effect jetting - you are just compressing the same amount of fuel charge into a smaller area. If your jetting was correct before the piston or head modification, it will in theory be correct after it. However, you should always plug check after any motor, carb or intake modification. (TimSr will tell you to check it even if you've changed fenders, tires or even applied a new decal ..... lol)

[OldSchoolin86]

My Scrambler 400 has a 12:1 cool head and it runs on 92 octane just fine. Also, compression should not effect jetting - you are just compressing the same amount of fuel charge into a smaller area. If your jetting was correct before the piston or head modification, it will in theory be correct after it. However, you should always plug check after any motor, carb or intake modification. (TimSr will tell you to check it even if you've changed fenders, tires or even applied a new decal ..... lol)

Isn't the scambler liquid cooled?

[Wickedfinger]

Yes, yes ....... I don't think it would matter air or liquid cooled. If anything, the tolerences on an A/C motor are, of course, much less allowing for more flexability ... yada yada .... anyway, its the incoming fuel charge thats responsible for over 80% of the cooling on any A/C motor - I think 91 - 93 pump gas should burn slower and cooler enough to work fine. Worse case - you have to buy octane booster if it pings.

[Wickedfinger]

hi just found out this piston im getting makes the compression ratio about 11:1, would i have to run pure race gas with that.

11:1 dosent sound right. A 10.5:1 Wiseco medium compression runs fine on pump gas.

[83185s]

i just put 92 in my 200x with a 12:1 wiseco bored to the max and it runs really good...it ran fine on 87 too...but i can definetly tell a difference between them

[OldSchoolin86]

Yes, yes ....... I don't think it would matter air or liquid cooled.

Ouch, my heart aches from words like this. 11:1 in a liquid cooled could get by with almost 87, an air cooled would need 93 to handle it.

[TrikerR]

thats the piston there.

(email from seller)
This piston is 6.3mm Dome with Valve Reliefs. Compression Ratio is unknown but I estimate it to be around 11 to 1. If you have any further questions please let me know

im just going by what they say. if i cant get 93 octane here, will i have to run octane boosters.

thanks guys for your help

[Wickedfinger]

That looks like a 12:1 to me.