I have been using the Pressure modeling equation:
P2 = P1(V1/V2)^y
Where P1 is 14.7 psi @ sea level,
(V1/V2) is the engines calculated dynamic compression,
and y = 1.2 - The 1.2 value is from the article in
http://victorylibrary.com/mopar/cam-tech-c.htm, so I am not sure how they arrived at that value? In an idea system with no heat losses y should be close to 1.4 for air.
Anyhow for Temperature, if I use this equation:
T2=T1(V1/V2)^(y-1)
with T1 being the initial air temperature (in Kelven),
what value of y would best model the air temperature increase from compression in a real engine?
When I did some modeling with an 8:1 dynamic compression ratio, using y=1.4 resulted in temperature increases about 8:1 also.
using y=1.2, the increase was closer to 4:1.
So if intake air is about 100 degrees should the compressed air be closer to 400 degrees or 800 degrees or maybe somewhere in between?

I am no help here, but just as a sanity check, IF you are using Kelvin in that equation, I seriously doubt your intake temp is 100 Kelvin, which is -179 degrees Fahrenheit...

there is noway you will reach between 400-700 using that system for your calculations,NO WAY!!!.

What you are concerned about is the isentropic expansion factor or the ratio of specific heats. I'd recommend going to Wikipedia and looking at "Heat Capacity Ratio" for more info. I would guess that the deviation from the theoretical 1.4 for air is due to compressing a mixture of air and gasoline, and not pure air. Obviously if this is the reason it would only apply to a spark ignited engine.

I seem to recall my professor from my Internal Combustion Engines class in college said to use k=1.3 for the ratio of specific heats (what you are calling, y). I've usually seen it listed as k in texts on IC engines, like Richardo and Obert, etc.

Room temp in Kelvin is around 300K (27 C). I'd start with that as a starting point. I never thought I'd see a post on such things on here.

Is it adiabatic or isentropic? I'll have to think about it. Everytime I start throwing out engineering terms I get bashed or ignored, so I was kind of surprised someone else was daring enough to bring up such things. I caught hell for my rich/lean comments relative to stoichiometric ratios. I can show you where it is in Sir Harry Ricardo's book, The Internal Combustion Engine defining it, but couldn't convince anyone on here that I was right. The first issue of that book that I read was from 1953. I consider books like that to be the authority on such issues. I have the 1967 reprint, but it's only half as thick as I remember the 1953 printing.

I was using some info I found on this wiki page:
http://en.wikipedia.org/wiki/Adiabatic_process

I'm an electrical engineer, not a mechanical engineer or physicist, so my knowledge of thermodynamics is limited.

I was just trying to get an idea of how changes in air and engine temp affect the compressed air/fuel temps prior to ignition, or pre-ignition if the temps are too high? I know the diesel engines rely on the heated air under compression to ignite the diesel when it is injected.

When I worked the Thermal equation using a 1.2 factor for y (or K?) I converted 100 degrees F = 310.93 Kelvin, with the V1/V2 (estimated dynamic compression) of 8:1, I got T2 = 471.28 Kelvin which converts back to 388.63 degrees F?
With a y factor of 1.3, T2 = 584.71 F,
and with a y factor of 1.4, T2 = 826.11 F.

I would the fuel and losses to the chamber would reduce the factor below the ideal 1.4 factor?
My guess is the 1.2 factor may be a closer estimate.

I think if I took the time, I might be able to model a "real gas" model, and chamber, piston, etc to get a more accurate model, but I thought one of the mechanical engineer, or automotive books may have an estimate or formula already worked out?

One of the technical books I have is "Internal Combustion Engines" by V. Ganesan. It is very technical, but does not always have values defined for variables.

Dang, when I grabbed the book to get the authors name, I flipped through it and found an estimate used in one of the examples (page 152, example 4.3.) In the example it says to assume the "index of compression" = 1.3?

You guys must be getting bored..