what octane matches 11:1 comp

[REAPER]

Since I have been steered away from octane boosters....What octane of race fuel should I use for a 440 88.5mm piston with an 11:1 copression. I dont want to use something too high. Thanks Reaper:confused:

[TORO1968]

I believe you would be fine with plain-old 93 octane pump gas at 11:1... From what i've seen, that's the upper limit as far as avoiding pinging with premium pump gas...

Anyone else have suggestions?

-Jordan

[cals400ex]

from what i read those wiseco 440's are well below a true 11:1 ratio which means you should be fine on 93 octane.

[TC426EX]

Premium pump is what you need....

[fastforward400]

My buddy's runnin a stock bore 11:1 comp (fresh rebuild) with 110. Another friend has a stock 250X running 110. Theres seem to be doin ok

[Quadzilla]

I have a Ross 10.8:1 piston but am running custom Cometic gaskets that are 8 thousandths thinner than stock XR (not EX) gaskets so my compression is about 11.2:1 roughly. I run 110 mixed with pump premium. I have not tried just premium alone as of yet...

[sickmojave]

Originally posted by fastforward400
My buddy's runnin a stock bore 11:1 comp (fresh rebuild) with 110. Another friend has a stock 250X running 110. Theres seem to be doin ok

your friends are just wasting money. sure they will run fine but they would run fine on 93 so why pay twice as much for gas.:o

[wilkin250r]

A lot of it depends on your "true" compression. As stated earlier, Wiseco has had some problems meeting thier advertised compression numbers, although I've heard it's been taken care of.

You can try the 93, you might be ok. If not, get a leaded race gas and mix 1 gallon of race gas to 4 gallons of 93 octane pump gas. That will bump you to probably around 98, which should run fine with 11:1. If you STILL have problems, I'm sure 3 gallons of 93 mixed with 2 gallons of leaded race gas will work.

If your STILL having detonation issues after 3:2, then you are running higher than 11:1 for sure.

[REAPER]

The 440 kit I purchased was a I.M.S kit which includes a J.E. piston not a Wiseco. Do the "true" compression problems also associated with I.M.S. and J.E. as well?? Reaper

[Quadzilla]

I think that most of the confusion lies in the gaskets. The EX and XR piston, cylinder, head, valves are the same, it's the head gasket that makes the difference on the compression. The EX head gasket is thicker than the XR thus lowering the compression.

Here is where it gets confusion. Most piston manufactures (if any??) don't make a different piston for the XR vs an EX. They just use the compression ratio that the piston is rated for with XR gaskets. If you use EX gaskets, this will make the piston a lower compression than advertised.

I know that Ross works this way and I believe that JE does also. I know for a fact the Wisco was doing this, but some have said that this has been "corrected". I'm not sure if that means that they actually make a different piston for a EX or if they just tell you that it will run at a lower comp ratio with EX gaskets. Hopefully somebody will chime in who knows the deal with Wisco. Bottom line, it's all about the gaskets.