ever since i got my 94 855 turbo ive had a rough idle issue, cant boost past 9psi, and im starting to believe this 17 year old car has a clogged cat. I just got my ard white tune and really want to feel 14 psi i believe that my evap purge valve is bad since i have the evap code. i believe the bad valve in conjunction with clogged cat may be my misfire problem??. so my question is would it help my performance (and possibly help fix misfire prob) by just welding a 3" straight pipe? i live in iowa so there is no emissions tests or anything like that. i have my own welder and know how to weld. would a magnaflow work well? ive heard of some guys on here using them. i would like to get the 3 inch downpipe but im pretty sure i have the conical flange so i just wanna wait. my exhaust sounds kinda restrictive and when i punch it... also on another thread of mine i couldnt get past 110... i know i know misfire problem doing a top speed dumb of me but i couldnt help it. Cant boost past 9si even with mbc turned all the way up cant get past 110, rear 02 sensor code, exhaust sounds restrictive specially after cold start. so tell me what you guys think about all this and what i should please and thanks!!!!

 

It is certainly possible that it could cause the problems you describe. You can check for a restricted cat by installing a low pressure gauge (0-15 PSI) in the upstream O2 sensor bung. Pressure at idle should be very low - 1.75-2 PSI I think.

 

if its bad it should be that low?? i hate taking out o2 sensor because usually you have to use a torch and you can strip out the threads that way...ill try getting it out without a torch tomorrow and check the pressure.

 

No that is normal pressure at idle, a restricted exhaust would be higher. You could drill a small hole in the exhaust and rig a gauge, just tack it back together when you're finished.

 

What I found:

"Remove the oxygen sensor and take your reading at its hole in the manifold or headpipe. Refer to the backpressure specs for the application. Generally speaking, more than 1.25 psi of backpressure at idle, or more than 3 psi at 2,000 rpm tells you there's an exhaust restriction".

 

Well I got the 02 sensor out with a little bit of elbow grease and got the fitting hooked up at idle it was at about 4psi... So I think I figured out my problem so now my question is will a single univ. Magnaflow sound good with a 3 in. Straight?

 

You might want to try youtube so you can hear some of the 850s posted with different types of setups. The sound usually isn't the greatest but it gives you an idea.