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I belive all the things you are saying but dissagree with some of your terminology. Compression Ratio dose not change with the addtion of super chargers ect. It is the mathmatical diffrance between cylinder volume at BDC and TDC. The only way that C/R can change is, change in: bore, stoke, head gasket thikness, and combustion chamber size. I belive you are looking for Cranking Pressure or Cylinder Pressure. C/P is the pressure in PSI created during the compression stoke of the engine. It is by no means affected by C/R. It is directly affected by the cam shaft and valve timeing or a power adder like a super charger ect.

I have done my far share of reading on this topic. Some where in my many issues of Car Craft they talk about this.

Like I said before you know what you are talking about. Not very many people understand that highter octane ratings burn slower, try telling my buddys this.

 

It seems you are talking about the same things; but I too have heard it referred to as static and dynamic compression ratio. Static being the the calculation using only cylinder volume, combustion chamber etc..

 

Good post, tnelsmn.
You are correct in that what you're describing is static compression ratio, which is derived from the sweep volume of the cylinder using the full crank stroke from BDC to TDC. This is indeed a fixed number.
However, what you may not be aware of is that there are other methods of measuring an engine's compression ratio that are just as important as static C/R, two of which are dynamic compression ratio (DCR) which can be affected by something like variable valve timing, and (as mentioned previous) the Final C/R when dealing with aspiration assisted engines.
An important thing to keep in mind is that enthusiasts magazines (such as Car Craft, Hot Rod, et.al.) generalize much of the terminology and engineering principles in their articles for the understanding of the greater audience. So while the layman understands that a blower increases cylinder pressure, which results in more engine power, this alone doesn't tell the engine builder or engineer what kind of components to build the engine with, the octane rating of the fuel the engine will require, the cooling system required to deal with the heat generated, etc. Hence the need to determine the FCR, which is a completely different animal that the SCR, DCR, or cylinder pressure.

 

Yep, we're all on the same sheet of music, we're just singing in different keys...

 

wow, can you learn stuff here!
Now, knowingthat the term "compression ratio" I used for a long damn time is really "static compression ratio", I still think that is a fixed number in the engine without adding a supercharger or turbo. So , with no mods wouldn't the static be the same as the "final" (also commonly called "effective compression ratio)- see what happens when you tell someone to do a little studying?
I was on the way to getting a better grip on all this then you through in that chit about "dynamic ratios" and I realize that, while I possibly could learn all that stuff, then youthrow in the fact that timing can have an effect also and it's making me freaking crazy!
I will stick to oil changes, normal service and accessory adding on my scoot and leave the rest to those who have a real handle on it.
By the way, I'm going to try 91 octane instead of 96 as it will burn faster- right? Please let me live in ignorace -I'm comfortable with myselves!

 

Precisely why the cam you use needs to be matched up with the rest of the build. Port flow, static compression, and valve timing all should be matched for the 'complete package' to work its best.

 

Dude, you're killin' me!!! [sm=icon_rofl.gif]

 

Have a 05 883L and I have used 93, 89 and 87 octain with really no difference in performance. You save more fuel and wear on the bike by make sure it's properly serviced and maintained and getting good quality clean fuel