To paraphrase the immensely knowledgable RealStreet..."It is a question of heat more than boost pressure. Boost pressure is simply a measure of what's not getting into the engine. At a given horsepower level (amount of air the turbo is moving), a turbo with a less efficient compressor wheel for the given scenario is going to create more heat while moving that amount of air, that means for the same power this turbo will need 'more boost' to achieve it since the air is less dense and takes up more space".


That being said, cylinder pressure is a big factor as well. Can someone explain cylinder pressures and what is considered safe and best for endurance(longer life of motor) and how can you figure out what the max efficiency of a turbo/manifold before it is piping hot or hotter air than is optimal? Notice i say optimal as i realize its possible with tuning and higher octane to quail hotter AIT's and the subsequent detonation. But what is "optimal" or maybe better said as perfect in a perfect world? What are optimal AIT's. How do you measure cylinder pressure? I think that's enough to start.
Thanks guys! Have at It!

 

I used to have a cylinder pressure calculator link. I think there was a post on HT forums years ago about it. I'll let you know if I come cross it again.

 

You cant directly measure cylinder pressure without some extremely expensive equipment like in cylinder pressure transducers. Torque can give you a good idea though of what the cylinder pressure is doing. For instance...a car making 500whp at 9k rpm is likely going to have less peak cylinder pressures than a car with the same engine making 500whp at 8k rpms. You have to make more torque to reach the same power numbers at a lower engine speed. It is generally safer (as far as detonation risk is concerned)to make a certain power with a good flowing turbo setup that can make the power at higher engine speeds than to make the same power with a log manifold and tiny turbo at a lower engine speed. Also the more restrictive setup is likely going to be generating much higher intake temps. Also the restrictive setup will generate higher exhaust pressures creating reversion that can cause detonation as well.

 

I understand the general consensus of what a turbo with this or that will do or wont do. So are you saying that a log(more restrictive?) with a GT30 is going to produce higher AIT's in comparison to a tubular(less restrictive) with a GT30 with all other things equal? I understand that my smaller turbo is only so efficient before it is creating less than optimal intake temps at a given boost level. What is this efficiency... what is optimal AIT's? Is that efficiency effected by my log.... how? A log in theory should spool a turbo faster than say a sidewinder or ramhorn etc etc but explain how that has an impact on what amount of air a specific turbo can push before it is pumping less than optimal intake air temps. These questions are sincere and are not "loaded" at all. I'm just spicing it up to get a good solid broken down explanation.`
Thanks

 

At the same power level yes the log setup will have higher intank temps because you will surely be running at a higher pressure ratio than with the less restrictive setup.

 

I think that is not exactly right... here is why..... If the target hp was say 300whp the smaller turbo could still be efficient at whatever pressure level that took to create said 300whp and therefore wouldnt necessarily be creating a hotter AIT's. That's why i would like to know what optimal AIT's are and what efficient actually is considered to be....
with that said... what about the other questions? What is considered to be optimal AIT's. What about a healthy pressure ratio?