What compression can be run safely in B18C5 on 92 octane without detination.Does anyone now how much I should shave the head to bring the compression up around .5 points.What type of whp will .5 points compression give me.Thanks

 

people have gotten away with 13.5:1 compression on 92 octane....I wouldn't go over 12:1 though.

 

Don't use high octane. I would say 89, make sure you only use copper plugs, you should be fine.

 

WHAT!?!

 

One point of compression is good for about 3% more torque, or that is the rule of thumb. As for milling the head, you cannot reverse that, and some cams will have too much lift to work with a milled head. I would use a 2 layer head gasket by Spoon or Mugen.
As for what you can run, I have run 12.0:1 with 92-93 and no problems. Tuning is the key for that...


Jason

 

As far as the octane question, use 92 or 94 if available. MY 91 rex runs stock compression of 9.2:1 and with a gude 2522 cam and 18 degrees of ignition timing, occasionally I get a slight knock when it is hot outside using 89 octane. My cooling system is efficient and with 198,000 miles on the beast, some carbon buildup may have increased compression by.1 or so. Spark plug heat is also optimal. You do the math on which octane to use.