Ford Mustang: Compression ratio at sea level vs Denver

Just as boost from a supercharger or turbo increases the effective
compression ratio of an engine less dense air does the opposite. At a
higher altitude there is less atmospheric pressure. Therefore less air
enters the cylinder on the intake stroke which in turn reduces overall
static and dynamic pressures. The drop is about one point at altitudes
above 4,500 feet. This is why 85 octane is sold in Colorado (and other
high elevation areas) because most of the cars driven there were
engineered to run on 87 octane at, or near, sea level.

Scott Williams wrote: 

"Michael Johnson, PE" <com> wrote in message > Scott Williams wrote: 


compression ratio is a calculated figure of total cylinder/chamber
volume to the compressed volume. the difference in volume from bottom
dead center to top dead center basically. it doesn't change!!
compression pressure on the other hand does. that's where the
difference is.
Chip

Chip Stein wrote: 

That's why I used the terms static and dynamic compression. The
calculated ratio using volumes does not change. Most refer to effective
CR to descibe how the engine responds under differing atmospheric
pressures due to high altitude or use of forced induction. At 4,500+
feet the effect is like lowing the CR 1 point at sea level.

So my 10:1 302 is effectively only a 9:1 here in Denver?
Scott

"Michael Johnson, PE" <com> wrote in message
news:com... 
Williams wrote: 
in 
85 
altitude. 
take 
air 
use 

I'm not sure how I managed to make the other post but you should be able
to tune the engine like it has a 9:1 CR. Keep in mind that you might
have to run higher octane gas at lower elevations. Using 87 octane
might be enough though.

Scott Williams wrote: