I've got quite the decision to make....

[stinkysGTI]

ok, I have a 2001 GTI VR6. I have an exhaust and cai. My O2 sensor took a dump and instead of replacing that [$190], i'm going to get a chip [$250 - 400] to bypass it anyway and run straight pipe. So either way, sensor's out of the equation.

My real problem lies in what diameter to make the pipe. I dont wanna just do it at somethin like 3.25 and be screwed with a major loss in torque, or make it too small and get a loss overall.

Remember, I'm planning on just going straight pipe so the only restriction will be the pipe itself.

I'm also going to be making a downpipe... probably before the removing of cats to ensure that all checks out. Since thats a much smaller piece which makes for less work.

So, what I'm getting at is what size should I run to keep the VR6's infamous torque, yet make gains on power??


Bonus Question!! :D
Any suggestions on a chip? I'm researching but of course they all say they're great, or the best.
All I've been told is Garrett is probably the best for VW

[stinkysGTI]

damn, it said html was ON [i] = italics [shoulda used BB]
and when am i not a newbie anymore :P

[Mr_Diesel]

Wait wait wait.... which chip is going to allow you to bypass the oxygen sensor??? Unless you use some form of stand alone, you definatly need your oxygen sensor... ESPECIALLY with your stock ecu. o2 sensor is crucial to air/fuel metering.

[stinkysGTI]

i thought most chips took over control of the o2
and yeah, i know its needed very much with a stock. mines messed up and runnin too much fuel.

i didnt plan on doin the pipes till i had a chip [since i thought it would bypass]

i figured, if im gonna cut it all out anyway to run straight, i could get rid of it..... i just dont know enough yet about the electronic side of engines, so sorry to sound like a total noob :)

so no matter what i'll have to replace it huh?


well then, what do you recommend for diameter of exhaust for a vr6?

[jettadude]

you need the front o2 sensor, the rear one just makes sure your cat is working.

[stinkysGTI]

yeah, i had read up on each of em so i'm all checked out on the o2 sensors now :wink:

So on my lunch break I went to a VW dealer... i know, its an evil place. All dealerships are.
I just walked in and went to the first mechanic i saw :) and started askin him questions.

My car only gives me a problem when it's been sitting for a while and fine once it warms up... or rather when the O2 sensor warms up.

I think my coolant temp sensor is what's doin it. Since when the car's started, the O2 sensor runs in open loop [or whatever its called], it listens to other components - such as the coolant temp sensor - to control the fuel to air. Once the O2 warms up [600F] it takes over and that's when my car runs fine.

I figure since it's doing what the coolant temp is tellin it, and the coolant temp sensor is stuck, it thinks the car's warm even though I just started it. So it's sending in too much fuel for the cold engine to handle.

coolant sensor = $50
o2 = $190


so i think thats it :)

hey, what about my straight pipe question. What diameter will allow for power gains, but not kill the vr6's infamous torque?
im doin downpipe n all

[burn_your_money]

Yeah, your O2 sensor is ignored when the engine is cold so it's probably fine.

[stinkysGTI]

yep yep :)

i ordered th ecoolant temp sensor from worldwide auto parts. $22 :D
autozone wanted $50

i'll let ya guys know after this weekend

[GoodDayForADrive]

Sounds like you got the sensor issue worked out. As for the straight pipe, Diesel probably knows what diameter would work best, I think he put straight pipe on his VR6.

[stinkysGTI]

thanks for reading

That's who I thought about and I sent Diesel a pm, but havent gotten a response yet. He seems pretty active on here though, but I dont wanna bug him.

I have plenty of time to figure it out though. So maybe I'll wait, and THEN bug em :)

A buddy of mine who has a WRX said I should buy the exhaust he's getting and modify it. His is 4" down to 3" I think. That'd be interesting eh? :D A WRX's piping on a GTI.
Seriously though, I'd rather make something that'll work perfectly rather than make one thing and find out I could've done it another way and gotten more out of it.

[Mr_Diesel]

Stock pipe size is optimal for torque... you just need to remove your inline restrictions (IE: crappy mufflers, resonator and add a free flowing cat). Leave the pipe the same size. Once you get your chip, cams, performance exhaust manifold, downpipe, free flowing cat and intake system then increase pipe diameter by 1/4 inch and you'll be pushing some impressive numbers.

BIGGER IS NOT ALWAYS BETTER! (unless you have a turbo, then go big... but you do not have a turbo so don't even think about it).

Also, don't try to bypass the o2 sensor... I don't know if you have already come to this decision, but it's crucial if you plan on running your vw ecu... ( no chip in the world will bypass your o2 sensor with the vw computer.)

It's also true you don't need the second o2 sensor, but if you want to pass obd 2 emissions next time, I suggest you leave it in there.

[Matty-O]

Or save yourself all the hassle and crazy ideas and get a set of these...

http://www.jegs.com/webapp/wcs/stores/servlet/CatalogSearchResultView?storeId=10001&catalogId=10002&langId=-1&resultsPerPage=25&pageIndex=1&searchTerm=Exhaust+Cutouts

[jettadude]

Stock pipe size is optimal for torque... you just need to remove your inline restrictions (IE: crappy mufflers, resonator and add a free flowing cat). Leave the pipe the same size. Once you get your chip, cams, performance exhaust manifold, downpipe, free flowing cat and intake system then increase pipe diameter by 1/4 inch and you'll be pushing some impressive numbers.

BIGGER IS NOT ALWAYS BETTER! (unless you have a turbo, then go big... but you do not have a turbo so don't even think about it).

Also, don't try to bypass the o2 sensor... I don't know if you have already come to this decision, but it's crucial if you plan on running your vw ecu... ( no chip in the world will bypass your o2 sensor with the vw computer.)

It's also true you don't need the second o2 sensor, but if you want to pass obd 2 emissions next time, I suggest you leave it in there.

according to this guy that runs a dyno, mainly for muscle cars and stuff, 2.5" pipe is good for up to 300HP/tq which is what a stock vr6 has out of the downtube, i think it drops down to 2.1/4 so i just put 2.5" all the way back but its up to you.