More Exhaust=less boost??!

Hi, i just came back from the Muffler shop after taking off the resinator and replacing it with a Y-pipe and taking off the stock mufflers and installing 2 new "Magnaflow" mufflers. The cats. were left alone so far. Now instead of the p.s.i. boost maxing at 12 p.s.i. it maxes at 9 1/2 p.s.i.. It sounds ok but its noticably slower. I read all the questions and feedback regarding exhaust here at SCCOA before i went to the shop and i was certain i would get more power but instead im dissapointed. The rest of the car is stock including the supercharger pulley which is what im going to do next. (10%?) Will i get atleast all my power back and more with the 10% or 5% pulley. And which pulley should i use? Also i assume removing the air silencer would be a good idea? HELP ME!!!

What size pipes did you have put on?

heres what i learned from some vets in the sc forum... its called back pressure... when the exhaust fumes have somewhere to go fast (like a bigger exhaust or straight pipe) then its less pressure from the engine to feed the sc... more back pressure = more p.s.i. ... less back pressure (nice exhaust or a straight pipe) less p.s.i. BUT still gives you more horses... try and keep your exhaust and maybe raising your p.s.i... its possible

boost is created by back pressure, the more backpressure you have the more boost you car is gonna put out. freeing up the exhaust reduces back pressure, therefore, causing less boost. you dont go into a muffler to free up the exhaust in hopes of getting more boost. what a free exhaust will do for you is allow better airflow and permit you to put on a 5 or 10% pulley without blowing headgaskets (which can be caused by too much boost). a car with a 10% pulley with free exhuast that pushes 12 psi, is gonnna have more airflow (although the same boost) as a stock car that pushes 12 psi. obviosly the one with more air flow will have more power.
its kinda like how your not supposed to base the purchase of your pressure washer on psi, you also want it to have a high gpm (gallons per minute) rating as well.

haha thanx livn... that was an easier way of explaining what i was wanting to say...

happened to me, my exhuast is extremely free flowing...i went from 12, to 8. now i gotta get that boost back.

Back pressure

thanks guys i understand the concept of to much flow=less boost but i really didnt expect the car to be any slower. Do you guys think with the 10% pulley overdrive it will be back to atleast the same speed (and faster then originally)? Thats all the car has done to it. Now im not sure if i should remove the air silencer. All i am doing to the car is the Y-pipe and mufflers of course, remove the air silencer, add new performance cats. and the pulley. what do you guys think? Thanks Bill

I have open exhaust, but I still see 14

improved exhause/less power

I would REALLY look for something else that was mis-adjusted or damaged. Loosing power with improved exhause does not make sense. When I did my exhause I was pegging 15 psi, removed cats, magnaflow resinator, flowmaster, took my psi down to 11 but had noticably more power. Look real hard for problems before doing any other mods, especially a pulley.

WHAT TO DO ???????????????

I HAVE HI FLOW CATS ONLY.................ADDED 10% pulley hits 16+...............ALSO A RAISED TOP& DOUBLE I/C........FAST FREDDIE

Remeber that your sc is still pumping out x amunt of volume of air. Free up pressure on the back side of the sc = less psi of boost but same volume it is just escaping easier. Open up the intake side now the SC can draw more air therfore more volume going into the same space and you will see an increase in boost even though you did not change pullies. What we really are intrested in is how much air (volume) is being pushed in to the cylinders
Hopes this helps