Fast355

iTrader: (2)

Agreed on the 2.5 and single 3.5. My 2011 M56 is making about 480 hp at the crank and the 338 cid V8 revs to 7,000. I saw excellent results with dual 2.5" into a X pipe. Single 3.5 has about the same pipe area as dual 2.5" and will help scavenging over true duals.

2012sergen11

iTrader: (1)

Are these types of crossmembers something I can buy or do they need to be custom fabbed? I have a 700r4 and haven't had luck finding a crossmember with the double hump exhaust clearance

Jorlain

iTrader: (4)

I haven't seen any for the 700R4 except for custom jobs.I think I read somewhere that a 4l60e swap crossmember will fit the 700R4 with some minor modifications, though.

In regards to exhaust, with a cam & head swap I doubt you'll see much advantage with a 3.5" cat-back.

2012sergen11

iTrader: (1)

My mods will include cam, heads, on a 383

Jorlain

iTrader: (4)

Ah, sorry. I missed the post with you switching your crank, too. I guess it all depends on what your goals are, and what they're worth. You'll hit a point of diminishing return. A 3.5" Mufflex is around $800. Everything else that's decent is about $400-500 for 3". Is the $300 worth 10-15HP to you? It's ultimately up to you and your wallet to decide.

2012sergen11

iTrader: (1)

The 3.5" is probably not going to be worth the cost for the minor gains I would see however I am trying to find out what my options are as far as the longtubes headers go.

So far I have found hedman headers 68460 and the eBay knock off stainless steel sets.

Is a modified crossmember like above a necessity with these or can I get by with a standard crossmember and sacrifice the ground clearance until I can buy or fab one with the exhaust clearance?

Jorlain

iTrader: (4)

You have a few options.

1) A "double hump" crossmember that will allow you to tuck up your header extensions\y-pipe.
2) Route your Y-pipe to the outside of the crossmember. This will gain you some clearance, but not as much as going over or under a modified crossmember.
3) Run under the crossmember. This is the most straight forward and least expensive, but you do sacrifice some ground clearance. If your car is lowered it might cause issues. If it is not, most people do not run into issues (within reason).

2012sergen11

iTrader: (1)

My car is not lowered at all and I don't have any plans to really do so. If there is enough room to run under the crossmember I will likely do that and possibly go back later if I need to modify it and tuck the pipes up higher.

Any pictures of the pipes using the stock crossmember to show ground clearance? ( non lowered cars )

2012sergen11

iTrader: (1)

Still looking at parts for this build that I will be working on over the winter months. Any difference in fitment between the Headmann 68460 or the "eBay" stainless headers