Hi Faylur,

Your choice of whether to run SCR 10:1 or 13:1 will depend upon two things I can think of and they are both related to each other:

a) octane of the fuel you'll be using
b) cam profile or more generally dynamic compression ratio

The idea is to create maximum cylinder pressure without causing detonation...

on ~92-93 octane pump premium you want to run DCR in the 8-8.5:1 range while you can run higher (9.0-9.5:1+) with high octane race gas (100-110-116 octane etc)...

Richard (techinspector1) is definitely the expert on this stuff and I'm just parroting what I've learned from him in the past...

-Chris