I have a turbo that has a 2.5" turine oulet and I want a 3" downpipe. What is the best approach to take:

a) weld 2.5 to 3 inch reducer to turbo exhaust flange and 3" downpipe

http://cgi.ebay.com/ebaymotors/Pipin...ts_Accessories

or

b) V-band 2.5 to 3 adaptor. Looks like alot more money and possibilities for leaks. How are you guys coming off of your turbos into 3" downpipes?

http://cgi.ebay.com/ebaymotors/2-5-4...ts_Accessories

 

Either one... Vband is more spendy and gives you some more wiggle room which is well worth it IMO.

I got a spoolin 3" DP that has a 2.5"-3" reducer flipped around and welded to the downpipe/Flange.

 

AFI has a downpipe that starts up 2.5" and then grows to 3" I believe

 

Is there anything wrong with bolting 3" downpipe w/ flange directly onto the hot side exit (2.5 Dia). I know there will be a 1/4" lip (stepped up) all the way around, but wont obstruct the air flow (but may cause some kind of turbulent effect). thoughts???

 

that will be fine and the best way.

 

You can make 3" downpipes on T3 4 bolt/5 bolt flanges without the step reducer.

 

it would cause turbulence but probably not the end of the world.

 

I just had my friend weld the 3" pipe right to the 2.5" flange no big deal, I used stainless "cap" bolts (type that use an allen key) because there was no room to get a socket on the flange bolts and it was all good.... make sure whoever welds it doesnt cake it up with filler rod or you will be doing a bit of grinding, we just fused mine with no filler at all.

 

holy crap dont bolt a 3 inch dp to a 2.5 outlet.

look at garrett's GT style exhaust housings, its a gradual reduction, thats the best way to go.

 

Now we're getting somewhere...

What GT style housings are you talking about? The turbo I have is a GT3271, so it is a GT style turbo.

 

For best flow do not bolt a 3" to a 2.5" outlet. The science behind it is boring but you will not get the best flow. That being said the difference is probably minimal, and unless your racing hardcore then you would probably not ever know the difference.

I would go to a 2.5" and gradually increase it to a 3".

 

A 2.5" collector bolted directly to a 3" exhaust WILL interrupt the laminar flow of exhaust up to that point AND if you are hoping to maintain exhaust scavenging for performance, the interruption of this laminar flow by turbulence will diminish, if not negate entirely, the benefits that are achieved by exhaust scavenging. So, yes, bad for flow. It is best to increase diameter slowly over duration. I'm not sure if their is such a product available, but it would be optimal.

 

http://www.sfxperformance.com/parts/VIB2630.htm

Check that link out. See if it works.

 

http://www.advancedstreetperformance...iy_exhaust.php