Is there a formula for determining the need octane for a given cr. If there is does it take into account the dynamic compression ratio or only the static? Is there a quick table somewhere that shows the relationships like a spreadsheet?

 

My engine comes up with it's own formula, unfortunately it usually wants more octane... It also will depend on load and altitude and things like that. If you are running around 9.5:1, you should be safe with regular fuel. Other than that, your engine will tell you what it needs.

--Mike

 

Here's a list of things that affect octane requirement
load
carbon deposit levels
manual or automatic tranny
air temperature
water temperature
iron or aluminum heads
bore diameter
spark timing
boost level
EGR level
humidity
squish
swirl/tumble
number and location of spark plugs
sharp edges/hot spots
and I've probably forgotten some

Here's a good link:
http://www.chevron.com/prodserv/fuel...rgas/ch5.shtml
look under "Octane Number Requirement and Octane Requirement Increase"

Look at the table in Figure 5-9.