3" down pipe help...

[ajluvsboost]

i just got a 3" dp for my car. its a gsx. the mods i have are, fmic, intake, bcs mod, and the dp. i just put it on today and im running with it open, but my stock exhaust rests in the dp so my 2nd o2 sensor will still get the exhaust. wen i go into boost, it seems to fall flat on its face. is this fuel cut possibly?. is that a lack of back pressure? could anything else be wrong? thank u soooo much for all your help!

 

[matthewdesigns]

How much boost are you running, and on what turbo...t25 still? The extra flow that the larger, open dp is giving you could be leading to a lean condition. You could be feeling timing being pulled to combat knock if you are overrunning your fuel supply and getting too lean. Fuel cut is very abrupt and harsh in comparison.

Do you have a logger? A boost gauge? You need both before you go any farther with your car mod-wise.

 

[Illmat1c]

For one who needs 2 o2 sensors and you just have the downpipe going right to the rest of the exhaust which is stock?

 

[95GSXCO]

I dont think it can be lean from the second o2. Thats the front o2's job. As for back pressure I would say no thats more on the bottom end (TQ). I would double check everything and you know you should have done a BLT before even posting did you?

 

[vanilla gorilla]

The open flowing dp isnt going to cause you to run lean, IMO. Sounds like another problem.

 

[ajluvsboost]

fuel cut from boost is what is was i think. i have a boost guage and i was running round 15-16 pounds with the mods i stated b4. i dont have a mbc so i ran the vacuum line from the turbo st8 to the wastegate and capped off where it goes to the bcs. now im running 11-12 pounds and its running fine now. but yea my stock exhaust is still on from 2 inches b4 the downstream o2 sensor and its just resting in the dp, not bolted on. im gonna get the rest of my exhaust put on within a week or so. should i run the 3" dp into 2.5" the rest way back and then the muffler? and i might need 2 get a new 2nd o2 ### i was trying to take it out and rounded the bolt a lil bit using a socket made to take the o2 out. any other way i can get it out? thanks!!

 

[se0nz]

sounds like another problem to me... but you still haven't given us one giant piece of key information and that would be what turbo you're running. that can say alot but i would say still try to do a BLT and see where you're at... while you're at it spend 30$ and get yourself a MBC.

 

[ajluvsboost]

sorry, stock t25. checked it for shaft play and the puppy is perfect! im getting a mbc in a few days. what size piping after the downpipe should i got with??

 

[viperlp01]

probaly like 1 in or so... just stay 3in after your 3in dp.

 

[GofaST4life]

stock t25, like everyone has said its probably over boosting, thus causing fuel cut. IMO when you get your MBC hooked up correctly, turn it all the way down, so you don't cause anymore damage.

Do you have a aftermarket boost gauge? - if not, that should be your next purchase.

 

[97GSTAUTO]

probaly like 1 in or so... just stay 3in after your 3in dp.

. But in all seriousness. All t25's fall flat one their faces. Get a real turbo. You are not really going to get any significant gains from a 3in exhaust with a t25.

 

[ajluvsboost]

ill go 3". will i gain power over stock even to its the t25? but down the road i do wanna upgrade.

 

[97GSTAUTO]

I would imagine so. I couldnt tell you first hand because I changed everything from the exhaust ports back all at once. So I went from bone stock to what I have now in one day. But I did try pushing my t25. I could not feel any real difference between 15ish and 17ish psi. Yea, turning up the boost an extra few psi did yield better midrange. But after that it wasnt worth it. You are just pumping alot of hot air into the engine. A turbo will deliver you the biggest single gain. Its like night and day. It will give you the biggest smile on your face after installing it. A nice BIG OILY SMILE. Oh and bleeding knuckles too. Maybe not bleeding knuckles. I just have a habit of cutting some part of my hand every time I get into the engine bay. But eventually if you continue to mod a 3in will serve you well.