SU test pipe - 2.5" vs 3"

[MShreve]

Sorry if this is a repost, I searched and didn't find anything.

Does anybody have an opinion on the 2.5" vs the 3" SU test pipe? The only reason I ask is that SU just called me to ask if they could substitute my order with a 3" because they're out of 2.5". They did such a good job of selling me on the 2.5" (on their own website (uhm)) that I'm wondering if there will be any noticable difference...although I doubt it.

I'll be installing it on a stock exhaust system.

[dagmz6s]

you dont want to run a 3" test pipe on the stock exhaust. It will create turbulance in the air flow because you'll be going from the 2.75" stock downpipe, up to 3" TP, down to the 2.5" exhaust. Imagine an hourglass but the thin sections are at the top and bottom, when sand goes into the larger middle section it'll go every which way instead of maintaining control.

I have to imagine that mating a 3" tp to stock stuff will also create a mating nightmare and likely an exhaust leak.

[sxyspeed6]

you dont want to run a 3" test pipe on the stock exhaust. It will create turbulance in the air flow because you'll be going from the 2.75" stock downpipe, up to 3" TP, down to the 2.5" exhaust. Imagine an hourglass but the thing sections are at the top and bottom, when sand goes into the larger middle section it'll go every which way instead of maintaining control.

I have to imagine that mating a 3" tp to stock stuff will also create a mating nightmare and likely an exhaust leak.

+1

[tunersteve]

^What they said. If you're staying close to stock, stick with the 2.5"

[MShreve]

I was afraid you'd say that.

The guy at SU told me that all the flanges are the same between the 2.5" and the 3". So I told them to go ahead and ship it. They charged me the price of the 2.5".

Now that I've thought about it a little longer, I can't figure out why they would sell a 3" TP with stock 2.4" flanges on it made to mate to a aftermarket 3" DP. It doesn't make any sense. I'm not going to be very happy if this thing shows up and won't mate to the stock flanges or has other install issues.

I just hope my impatience doesn't lead to a lesson learned the hard way.

[MShreve]

Well, I just called SU again, and they assured me that the 3" TP will connect to stock exhaust without any modification. So hopefully I'm in the clear.

[MShreve]

I think I can live with a little turbulence, since it will still have better flow than the stock cat.

In theory it should sound slightly better than the 2.5" because of the resonance, right? Or am I just making up lame justifications? :P

[Sifu]

Better yet, use all of this as an excuse to go 3" from turbo all the way back! (thumb)

[amilliems6]

su said they will have some 2.5 tp in stock in about 2 to 3 weeks, means i gotta wait