Need advice on exhaust flex sections

[RebekahsZ]

Finally getting around to designing and building the exhaust for my LS2/240z.  I have never had an exhaust with flex sections-my old L24 exhaust was bad about breaking hangars and slapping the differential, so I'd like to do better this time, even if it costs me more money-20 years later, I thankfully have more!  I'm putting together my parts list to take to an exhaust shop for assembly (no mandrel benders in this area).

 

I see flex sections of different lengths: 2 inches of flex to 6 inches of flex.  My engine is mounted with poly mounts.  I will be using high-temp silicone grommets where support to the chassis is needed.  Clearance between the 2.5" exhaust and the JCI tranny mount will be very close, as will the clearance under the differential.  Running front to back, I plan to have 2.5" head pipes from the header to a Burns Stainless merge-collector-y-pipe to a 3" single pipe passing under the diff then routed to a 3" Borla XR-1 oval muffler in the stock location.  I will be using v-bands at the header, then another after the y-pipe (so that I can drop the forward section of the exhaust for servicing the engine and tranny, or drop the rear section to service the diff or rear suspension), then another v-band to attach the muffler. I'm planning to put a flex section on each headpipe before passing under the trans mount, so that things can be pretty solid as I pass under the tranny mount with its tight clearances.

 

Questions:

1.  Are short flex sections adequate for absorbing typical vibrations-or should I use longer flex sections?

2.  Do flex sections "sag" - I mean, if I have an unsupported solid section between two flex sections, is the solid section likely to droop noticeably? 

[johnc]

1.  Yes.

2.  You don't need two flex sections on one exhasut run

 

Only one flex section needed on each exhaust run.  Put the flex section as close to the engine as possible and then you mount the rest of the exhaust as solidly as possible while still isolating it from the chassis.  You can run two flex sections, one after each header, and then solidly mount everything after that.

 

Also, do not use a flex section to make a bend.  Flex sections should be kept straight.