home made down pipe.. possible?

**guimond47** · 08-02-2011

hey guys , wanted to know if a home made down pipe is possible . i was gonna cut the cat off and do 2.5 " all the way to the Y ppe that goes out to the mufflers. is that a good idea and then buy some magna flow mufflers.

but doing a o2 sensor delete im gonna have to endure a check engine light until i get a over kill pcm. am i correct? will it affect performance until then...? its a 99 grand prix gtp

**blueguy** · 08-02-2011

Ummm...from the cat to the "Y"...isn't a downpipe. The downpipe is from the manifold to the cat...really.

Just get a set of headers...to be honest.

**Colossus** · 08-02-2011

1) Obvioulsy it's possible....depending on YOUR skills.
2) everyone is going to tell you stay with stock mufflers
3) No res? gonna drone like a b*tch
4) correct

**Colossus** · 08-02-2011

(Not a DownPipe).....right, so your basically building an exhaust

**Explicit_Spade** · 08-02-2011

As said above, just get headers...

It sounds like you may be looking at your resonator instead of your downpipe..?

**guimond47** · 08-02-2011

well reason i said that is becasue the stock down pipe is already 2.5 " isent it? im not that much of an idiot to not know the difference between a down pipe and a resonator explicit_ spade i have my motor out now doing a top swap and putting on a new tranny. wat would be good headers to run a 3.3 pulley maximum. without much KR. i have other mods as well i just wanna be safe before i drop down pullleys....

**Explicit_Spade** · 08-02-2011

I wasn't trying to talk down to you, Your wording just confused me. If you want to do a downpipe, use the stock flanges, then bend the pipe you want to add to the shape of the old down pipe. Cut the cat pipe out, weld in the catless pipe and ream out the flanges to match.

You won't gain much besides a higer price tag by running bigger exhaust all the way back.

**boostedcompg** · 08-02-2011

^agreed

**guimond47** · 08-02-2011

alright soorrry for the mis understanding soo your telling me headers and a stock exhaust is a better way out?

**Explicit_Spade** · 08-02-2011

You've got it.

Stock piping is good until 450-500hp or something like that. Then 3" works fine.

If you want a deeper tone with no rasp a glasspack in place of the resonator sounds nice. If you don't mind some drone and want something louder thrush turbo mufflers along with the glasspack sound great.