how much exhaust flex?

[driftR420]

so i was logging times on my little stretch of hi-way this weekend, when all of a sudden after my last launch, my exhaust decided to snap clean off right at the back of the flex point(the weird connector with the springs on it) so now i'm looking to replace it with 3 in. so my question is how much flex will the new exhaust need? i'd like to run a 3in stright pipe as close to the exhaust manifold as possible. but this thing that failed me in the first place, this flexing connection looks like it needs to be there. so i 'm kinda wondering how most of you have done it. the guy i bought the car off of had modded the exhaust in the first place and left none of the orignal hangers and hung everything with welded metal, this leads me to belive that there was no room for the exhaust to flex it the first place which may have caused it to snap apart.

thanks guys -Ryan

[driftR420]

nobody can give me any info. i know most of you have gone to 3in exhaust. i'm just trying to find out if i can dump the flex point at the end of the down pipe or not?

[turbovanman]

It all depends on what car you have. If it came with a 2.5 inch dp, the 3 inch dp will fit. If you got the 2 1/4 dp, then you need to upgrade the SV. Now, if you an use the 3inch sv, it will work and move like the stocker. The exhuast system can't be rigid, it needs to move, it will move back and forth roughly 1-2 inches.

[CSXT404]

The donut b/w the down pipe and the swingvalve is there to help adjust for flex.

[driftR420]

right on guys. the cars a 88 shelby z and i'm sure it's 2.5 in. i'm slapping 3 in on tommrow but i'm only going as high as the flang on the bottem of the flex point.

[GLHNSLHT2]

the 3" donut won't fit that Swing Valve. I'd also find some way to convert back to factory style hangers. How about the motor mounts? Have you upgraded them? This will keep the motor from moving as much.

[Mike M]

Some or most 88s got the wide bolt pattern 2.25" SV... which is the same width as the 2.5" + 3". So I think it should work.

My Lancer Shelby has full 3" DP to muffler. The exhaust is actually quite rigid, I can't recall but I think the shop actually welded a steel bracket from the muffler right to the underside of the body. The rest hangs on the stock rubber bits. The motor is held in place with stock rubber mounts filled with windshield urethane, its pretty frickin solid too. 2000KMs and no troubles.

[turbovanman]

Ever watched our engines under load? they move down 2-3inches. I had an inch of clearance from my turndown to the hitch, I run MP and PB mounts with a solid bobble strut and under hard accel, the turndown hit hard enough to mark it. The exhuast needs to move around, hence the sloppy factory mounts. Plus, if its too tight, you get crappy vibration inside the car/van.

[phantomrt]

turbovanman is right. Engines move a lot with stock mounts. I've determined that a good way to determine if your exhaust moves good and any other mods do not hit the engine is to remove the front engine mount and the bobble strut and rock the engine by hand. It swings like its on a swingset. In real world operation, the rocking of the engine does NOT follow the exact same path, but it gives you a general idea.

For all practical purposes, the donut flange (the joint with the springs) HAS to be there.

[driftR420]

wicked info. thanks for all the help. you guy's never let me down.