Ok I was re-reading some books lately, and with some basic revelations people helped me understand on this forum, I have some ideas I wanted to bounce off you guys. The general concept is a sort of proof, as to estimating what type of boost you can safely run. Not to say such a proof is needed, as time and again it's proven by strong pump gas cars. But just a sort of theoretical or empirical exercise if you will.

Let me start with a few basics which I'm working with...

1. I believe I read that as boost pressure rises, peak cylinder pressure does not increase the same amount relatively. For example, doubling boost pressure does not double peak cylinder pressure. I believe this is because the cylinder pressure peak is only generated from a small percentage of the total air/fuel mix present in the cylinder.

2. The more air you can "pump" into the cylinders on the intake stroke, the more _AVERAGE_ work you can have done against the pistons. It is this average work and the work after peak cylinder pressure which is where turbo cars show their performance over NA cars.

3. Less back pressure will help control heat and help aid in preventing detonation. IE a larger turbine housing is better than a smaller turbine housing.

4. Larger compressors are generally more efficient and can produce the same boost pressure without heating up the intake charge as much as a small turbo. Less heat means less chance of det.

Now given the above 4 factors, and knowing that on 93 octane a mostly stock Evo can run 22-23 psi fine, is it not reasonable to conclude that a fully built Evo with a big turbo can probably run significantly more boost than that mostly stock Evo?

 

"Low" (relative to stock) compression, low timing, high boost, 100%+ VE, low IDC (plenty of fuel), standalone EMS, allows for it.

 

1- when you double the boost, you are not doubling the quatity of air. First reason, 15 psi of boost means an absolute pressure of 15 + atmospheric pressure (say 15 psi), which is 30 psi. If you double the boost, say 30 psi, your absolute pressure will be 30 + atmospheric pressure, which is 45 psi. Now although you doubled the turbo boost, absolute pressure went from 30 to 45 psi. It didn't double. Second, there is a loss in efficiency from the increased boost, so the 45 psi DO NOT contain 1.5 times air qtty more than the 30 psi, due to the loss of efficiency (more pressure is coming from heat)

2- I have no iea

3 & 4 are spot on, also note that less back pressure means less exst gas in the combustion chamber and more fresh air, mich means more oxygene and lower temperature. Larger compressor also means more air and lower temp.


Now as far as running more boost on fully built bigger turbo evo's, that is true. That is due to the efficiency of the system, which leads to two things: more air (oxygene) and lower temps