Head shaved .080" Octane? Compression?

[80overShee]

A friend of mine has a head from Banshee that is cut either .075" or .080" (squish recut also). He is going to give it to me if I want it but what will the octane I need to run be? What should the compression be?

 

I am running a 66mm bore (+.080") on a stock stroke.

 

Thanks in advance.

[ssanddemon]

Whew, that's gonna be a lot of compression- something like 180-190, But depending on the rechamber, that number goes out the window. Not too big a deal to install it and check compression; just going to take a head gasket, pretty cheap. Personally I like mine the way it is at .035- I can run 92 oct. for playriding with the kids or race gas and tear $hit up. Going big comp. like that is gonna work the hell out of the crank and bearings and you are gonna have to run half-and-half at a minimum.

[csrmel]

like it was already said, it depends on the squish. i bet you could shave a head 80 thou and recut the squish enough to have LESS compression than a stock head. so it really depends man.

 

one way of checking things out is to measure the volume of the head. grab a piece of 12x12 inch plexi from home depot and use an old headgasket as a template to drill head stud holes in the plexi. next drill 2 small holes in the middle of the plexi right in the middle of the stud holes. now smear a small ammount of grease on the plexi and bolt it up to the head and also dont forget to install a sparkplug of the proper heat range, as different heat range spark plugs effect compression. colder plugs slightly reduce volume. probably best to use a stock heat range plug.

 

now flip the head upside down and using a MEASURED ammount of water, oil anytying really., add fluid to the hole in the plexi which will slowly fill the head up. do this untill each combustion chamber is full and measure exactly how many cc's you used to fill it up. this will tell you how much they cut away from the squish and should give you a reasonable idea of what to expect from the altered head.

 

remember to measure EACH combustion chamber as some shops could be sloppy and not do both exactly the same.

[Machwon]

It will need approx. 100-104 octane depending on how it was done, 50/50 prem. pump/race should be close.