86z28iroc-z

iTrader: (1)

I recently put hedmann shorty headers on a mildly rebuilt 350 tpi motor and they came with a 2.5" y-pipe, the only two y-pipes that come with hedmann headers are 2.5".

Is it even worth it to mate this y-pipe up to 3" piping all the way back, or would it actually flow better even though the y-pipe is only 2.5". or would it hurt the flow by changing from 2.5" to 3" and thus slowing down the scavanging effect/flow of exhuast?

Should I...

A> cut the end of the y-pipe off and weld a new 3" end on, continuing on with the 3"

B> leave it be and just get the 3" it'll flow about the same

C> screw it all and just get new mandrel bent 2.5" the 3" won't be worth it on a mildly built 350 with a tpi intake

David 91RS/Z28

If the collector on the y-pipe is only 2.5", then I would cut this off and weld on a 3" collector. Flowmaster makes y collectors that come in 2.5" inlets and 3" outlet. From there finish running 3" all the way back. I would recommend using Hooker or Magnaflow for a muffler. Or just get their 3" catbacks. Good luck!

86z28iroc-z

iTrader: (1)

Edited.

86z28iroc-z

iTrader: (1)

Reading over all the stickies and looking at other posts and sites, i've noticed that a 3" pipe is ideal for 350 that peaks between 5500-6500 rpms, so knowing that, wouldn't a 2.5" pipe be better for a mild 357 tpi which peaks between 3500-4500 proven on a dyno? Max HP was @ 4300 and Max TQ was @ 3500.

2.5" fully mandrel bent with headers would most likely be ideal? Am i thinking right here?

joeblue83

iTrader: (8)

yes a 2.5 y pipe with the 3 inch collector and 3 inch catback is perfect for your situation. Remember that a 3 inch catback flows enough for 370 horse.
So you should be fine

86z28iroc-z

iTrader: (1)

In my understanding a bigger pipe would actually hurt performance in the low-mid range which my car makes most of it's power, it's only 230hp to the wheels and 310tq in the 3000-4500 rpm range. That being made with the stock crush bent piping and no muffler and no cat.

My thoughts from reading the stickies would that a 2.5" collector and a fully 2.5" mandrel system would be a more ideal system than a 3" system. But everyone is saying 3" would be better going against what the stickies are showing.