Compression vs Boost

[ISX]

I have been digging and digging and everything I read contradicts itself so I want to get a discussion going on this. There is a formula for efficiency that states that a higher compression ratio equates to a higher efficiency percentage. However, we all know the truck pull guys are running no compression and enough boost to top your air compressor at home. Then we have nascar guys running 14:1 gassers. Now the main point of discussion is 4 core things. Effective pressure and density/temperature/pressure at TDC compression. Effective pressure is the theoretical compression ratio you would have when running a turbo. Meaning an engine with 18:1---0psi boost has the same TDC compression pressure as an engine with 15:1----4.3psi boost, so the latter engine has an effective CR of 18:1. So using those 2 engines, here is what I get with everything being equal other than boost and CR. These are all figures at TDC Compression before any fuel or anything comes into play (I haven't got that complex with formulas, yet). [TABLE=width: 500][TR][TD]Parameter[/TD][TD]Engine A[/TD][TD]Engine B[/TD][/TR][TR][TD]Compression Ratio[/TD][TD]18[/TD][TD]15[/TD][/TR][TR][TD]Boost[/TD][TD]0[/TD][TD]4.3[/TD][/TR][TR][TD]Pressure (psi)[/TD][TD]841[/TD][TD]841[/TD][/TR][TR][TD]Temperature (F)[/TD][TD]1318[/TD][TD]1193[/TD][/TR][TR][TD]Moles of air (Density)[/TD][TD]0.0406[/TD][TD]0.0531[/TD][/TR][/TABLE]As you can see there is a 10.5% temperature difference and a 23.4% density difference. Now all the gasser forums I go to say these 2 engines would have the same power as they go by pressure for some reason and diesel guys go by density. I have no idea why but ok. So to me, because there is more density in engine B, you could throw more fuel in it so you could get more power. However, the counterattack of engine A is that the higher compression gives it a big edge on efficiency which I think is what the gasser guys are going by. Now I did run across one guy who said CR wins at low RPM but as you increase RPM, you need flow, so a low CR high boost engine would start to take the lead on power. There is also the difference in temperature which would make the fuel ignite faster. My books say igniting the fuel and having it burn as fast as possible is another trick to efficiency, which is why common rails are in production because they inject all of the fuel in an instant. The preinjection seems to just be there to make it marketable (quiet). I have searched for a long time, posted to forums about the actual physics of it so they could possibly enlighten me, but they told me they dont seem to know either. So does anyone have anything to add to this that I haven't already said concerning engine A vs engine B or just more info on the principles behind each scenario?

[CSM]

Tag for later. Let me grab my IC engines book this weekend...

[AH64ID]

So, how do you know how much airflow each psi of boost is? It's not universal and can be changed with turbo/intake/cam/exhaust changes. 30 psi of boost on my motor now is a lot more air than 30 psi was on my stock motor, and thus there is more to compress and higher pressure at TDC. So... why boost and not airflow?What is the effective CR of my motor, 17.2:1, and 60 lb/min of airflow?

[ISX]

So, how do you know how much airflow each psi of boost is? It's not universal and can be changed with turbo/intake/cam/exhaust changes. 30 psi of boost on my motor now is a lot more air than 30 psi was on my stock motor, and thus there is more to compress and higher pressure at TDC. So... why boost and not airflow? What is the effective CR of my motor, 17.2:1, and 60 lb/min of airflow?

This was mainly to show how compression ratio and boost can manipulate different variables. Me and this other guy are tackling the flow variable you are talking about and will get something up eventually. Waiting on resources to show up in the mail... Guess I need to stop posting just parts of equations and get the entire picture into view. To be continued..