Cat will create some restriction in your exhaust, making you boost a little less. 1.5bar is much safer. That's about 22 psi.

I believe it should be be about 20-21, but I'm fairly certain you won't knock now or it'll be minimum. I'd leave the cat in place until you can get the boost turned down.

oh yes its better, 1.5 bar its overboosting...yes i leave cat in stock place, another reason is that now is abou -3C outside temperature, how will changes boost at about +20 C outside temperature? what is stock usdm 2005 evo boost and oveboost?

Colder air is denser, so when it warms up basically you'll have less boost. Most people with MBCs have to adjust it during the summer and winter seasons because of the difference in the density of air.

USDM Evos should have the same boost but we usually go by PSI. Normal in metric units is 1.3-1.4 bar. You're really alright in terms of boost, but you'll see better gains if you get tuned for your exhaust so you don't have to run the factory cat. The factory one really is a huge restriction. It is robbing you of power.

yes i know that cat is huge restrictor...but now i havent how to make less boost....there is very much info about boost but everybody speak about normal boost or overboost....? how i understand 1.3 in low rpms and 1.1 in high is normal, but before i get 1.3 its for few second 1.5 (overboost) is it bad or no with stock map?

thanks...

1.5bar boost spike (overboost) is kind of high for an untuned car, but there are plenty of people on the forums here who have installed an exhaust without a tune without any serious problems. The spike will be the highest when it is very cold, but during the summer boost should be closer to stock. I think you'll be fine.

what differences is between MBC and EBC? does it help to drop boost?

both just regulate it. i don't have either, i use a pill in my wategate vaccum line and adjust by changeing wastegate duty cycle. i run 25 psi on my stock evo 8 turbo with no knock cuase i have a good tune.

but you are remaped yes? can evo acu automaticaly regulate fuel air ratio ?

So I installed the intake and induction box. I'm taking it out for a drive, and 4th gear wot into fifth I hear a bang, like a misfire. The cel comes on and its a p0234 eng overboost. The only mods I have are turboback exhaust and invidia test pipe w cel fix. What could cause this issue? I searched and didn't really find anything. I know I'm gonna need a tune but is this normal? Maybe another issue?

I would go and get the car tuned man. I am having the same problem, but I got that code and the famous knock and pop at WOT when I changed back to the Stock IX DV. All I need to do is raise the boost cut. But in your case, your seeing high boost numbers on the factory tune I am assuming. I would just go and get a tune, and your problem will be solved.