Yes, another squish question

[32:1]

I'm tearing down my just purchased ec250r 12 to fit a piston kit, I will check my squish and adjust if needed, so whats the ballpark to run 95ron fuel, also what taper should it be from outside in, as I have cut them flat (to piston crown) and had detonation before. A buddy has a exc300 and that has a taper I'm guessing to force fuel away from egde and to aid chamber fill. Or am I shooting in the dark ?

Anyhow, any tips with this machine much appreciated

 

[stian]

I'm tearing down my just purchased ec250r 12 to fit a piston kit, I will check my squish and adjust if needed, so whats the ballpark to run 95ron fuel, also what taper should it be from outside in, as I have cut them flat (to piston crown) and had detonation before. A buddy has a exc300 and that has a taper I'm guessing to force fuel away from egde and to aid chamber fill. Or am I shooting in the dark ?

Anyhow, any tips with this machine much appreciated

Needless to say, since the post is named "another squish post", I dont need say that there is numerous posts about squish.. but i am saying it anyway.

Std squish is induvidual, but in the ballpark of 2,5mm. I once saw a table of recomended squish in a book, cant remember, but guessing it was Jennings or E.Goor or something. For a 300ccm its in the ballpark of 1.6mm.

Regarding the taper of the dome, I dont know. I think RB mills the head down to, say 1.6mm and cuts out the lost dome-volume in the milling. I do not think he alters the taper.

If you have more heads, you could read some on the subject, but people have good experiences with leaving it untouched. Taper that is.

Sorry for my english, not my first language.

 

[(F5)]

Your written English is better than most of the internet.

There should be no fuel in there only gas hopefully. But changing taper relative to piston to zero works well if petrol available is not complete swill.

1mm should be safe and ideal. But that would, make the compression away too high. Bowl machining required.

 

[Jakobi]

I've had one of my heads cut and corrected only, and the other with the band angle matched to the piston. I think stock is about +3 degrees. Both run well.

 

[motopsycho87]

According the the Jennings and Bell books, match the piston taper. I've got mine at 1mm and had to take a lot out of the head (you will be VERY surprised how much), including using 1.5mm base gaskets for lining the piston to the bottom of the ports.