Does less back presure mean, there more air being taken in to the engine? I just got my 10.5 hotside and ebay o2 housing installed and I want to know if i'll need a reflash. Im trying to figure out if this messes up with the air/fuel raito? Just wondering what other people think about this subject.

Btw I really didnt feel any of a increse in power with these mods. Maybe a reflash is a must for me to see gains.

Hope to hear from you guys soon.

Thanks for your advice in advanced.

 

Back pressure usualy means resistance of exhaust gases to escape into the atmosphere caused by the turbo and the exhaust system. The purpose of o2 housing and a full 3" tbe is to decrease back pressure in order to give you better top end horse power. The problem with too little back pressure is that it decreases low end and a bit of mid range HP.
In spite of everybody on these forums telling you to go full 3" and cat-less for maximun hp, remember that you might lose some power on the other side of the dyno chart....particularly the place you spend 90% of your driving

 

On the Evo, lack of backpressure does NOT decrease low end and mid-range. Running no exhaust at all provdes the best spoolup and most overall power.

DP, a retune is not needed for those parts, but you don't get the full gains without a reflash, because they allow for increased timing due to being less knock-prone afterwards.

 

 

so with a tune I should see better gains with the 10.5 hotside and o2 housing?

 

dp2580: I guess you dynoed before the hotside and O2 hsg. Nice numbers at any rate! Are you running catless? Did your boost level change after the mods? What DV/BOV are you running? What is the full list of mods included in the AMS Stg. III?

 

I am running catless. My boost level went about 1 psi higher. Look on the ams webpage. I have everything up too stage 3 with 272 HKS and 680cc injectors.