Frustrating myself with deciding on a single or dual exhaust setup

[Fellow_Moron]

I recently picked up a set of LT headers as the exhaust that's currently on there is garbage and the manifold flanges are warped and constantly leaking. Anyway, the headers join into a 2" x-pipe. I've tried googling every possible word combination to try to answer my question before making an account just to make this post.

Is running dual 2" exhaust from the x-pipe excessive for the M20? The current exhaust is a single 2.25" from a y-pipe right off the manifold and crush bends all over the place. Should I just cut the x-pipe in half and turn it into a y-pipe and run a proper mandrel bent 2.25" single exhaust? I know there's a bunch of talk about back-pressure and exhaust velocities and loss of torque etc etc but my smoothbrain is still unsure of exhaust diameter relationships and to me going from dual 2" into a single 2.25" seems to be too much of a neckdown.

However, the headers collecting 3 cylinders into a 2" pipe before the x-pipe seems excessive in the other direction, as I've read a bunch of posts about people running single 2.25" setups. I feel like I'm overthinking things and while I'm keeping the car relatively stock, I want to at least have my exhaust setup as efficient as possible.

[reelizmpro]

All depends on how much power you are making.

[82eye]

stock dual piping is 1.75". stock single piping is 2.5" pretty sure both flow a similar volume. if you run a single 2.5" you should be fine.

[Northern]

I'm pro single 2.5"
Lighter, cheaper materials, cheaper/easier to fab. Slap a couple Vbands on it strategically and it installs and removes like butter.
Ground clearance is no issue as long as you think through where the vbands live.

[ForcedFirebird]

2.5" tubing will have a CSA of 4.91" (area), 2.25" tubing will have 3.98", each 2" tube will have 3.14", or 6.28" for the pair. Stock area (1.75" dual) is 2.41" x 2, or 4.82".

I build a lot of dual 2" for the racing guys. True dual with an x-pipe at the center support bearing seems to work well all around. Not quite as much area as a 3" (7" CSA), but I can tuck the 2" completely under the frame rails in the front, up near the CSB in the center, and really makes a difference for ground clearance when going under the rear sub frame.

Here's a pic in an e36, but I do the same for e30's: https://www.instagram.com/p/B4n9fLtgqtr/

[Fellow_Moron]

2.5" tubing will have a CSA of 4.91" (area), 2.25" tubing will have 3.98", each 2" tube will have 3.14", or 6.28" for the pair. Stock area (1.75" dual) is 2.41" x 2, or 4.82".

I build a lot of dual 2" for the racing guys. True dual with an x-pipe at the center support bearing seems to work well all around. Not quite as much area as a 3" (7" CSA), but I can tuck the 2" completely under the frame rails in the front, up near the CSB in the center, and really makes a difference for ground clearance when going under the rear sub frame.

Here's a pic in an e36, but I do the same for e30's: https://www.instagram.com/p/B4n9fLtgqtr/

Thanks Firebird for that info. So it's sounds like running dual 2" shouldn't affect performance even though I'm mostly stock? I do intend on an all-motor ITB build down the line. I'm partial to how duals sound anyway and I'm not out to set records, so I'm okay with the extra weight, I just want to make sure it's done properly.

As an aside, I bought a muffler for the ratty exhaust that's on the car before I got the headers, would it impede exhaust flow too much if I y-piped the dual 2" into the single 2.25" right at the muffler? Thanks again for the reply.

[moatilliatta]

If you go duals you go duals all the way. IMO

FF may know best place to put an X pipe for your power band, which would be good place for a wide band. But then a street car resonator may take up that space. I really like XR1 muffler in the middle and Magnaflow oval race in the back. Could be like a boss and run dual wide bands.

I wouldn't try and mix and match stuff. and now you need a really nice X pipe, the stamped ones arnt that great...

[Fellow_Moron]

If you go duals you go duals all the way. IMO

FF may know best place to put an X pipe for your power band, which would be good place for a wide band. But then a street car resonator may take up that space. I really like XR1 muffler in the middle and Magnaflow oval race in the back. Could be like a boss and run dual wide bands.

I wouldn't try and mix and match stuff. and now you need a really nice X pipe, the stamped ones arnt that great...

That's good to know. Which XR-1 have you used? I've looked on their site but I don't see anything for my dual 2" setup.