Exhaust flex section needed in this case?

[Ludachris]

I'm considering building an exhaust system that will terminate just before the rear axle with down turn pointing toward the ground. With an exhaust system that short is it necessary to run a flex section? I'm thinking of not using one.

 

[Burnett03]

IMO yes it is still needed.. Mostly because you aren't really eleminating much, just the axle back it sounds like. You need something to flex, unless you have very stiff motor mounts.

 

[bastarddsm]

do you have prothanes? You probably should, that flex section help keep harmonic vibrations out of the exhaust which will fatige the mounts. On a racecar this may be ok, but not on a street car.

 

[turboglenn]

Yes, unless you're running just a adown pipe, you'll need a flex section. Other wise over a few months the bend in the DP where it goes under the oil pan will split and start to peel like a banana. Mine did this once, i welded the crack and it did it again. I put a flex section in teh 2nd time and haven't had an issue since, except for when the flex wore out and got a hole in it after 8 years, not bad!

 

[Ludachris]

I've had prothanes on the car for a while now and have some poly exhaust hangers sitting in the garage that I've been thinking about using.

 

[spoonman]

My set up is about a foot shorter than your planned exhaust and I run no flex section. I do have solid steel motor mounts so my engine has zero movement. The hangers support it very well and there is only a slight amount of movement at the end of the exhaust if you try and physically move it. I have been running the exhaust for a year and it is in perfect shape with no cracks or broken welds.

 

[turboglenn]

With prthanes or solid mounts you may get away with it, I was on stock mounts when i split mine those 2 times. You could tell the down pipe was "peeling" from the motor torquing back and forth so you might get away with it.

Hell if you're building your DP and stuff yourself where it doesn't cost an arm and a leg like buying pre-built ones, then it's at least worth a shot.

 

[DSMunknown]

I still would be concerned about the exhaust studs.

 

[99gst_racer]

There's a big difference between solid steel mounts and prothanes. With Prothanes, I was really surprised at how much my engine moved on the chassis dyno - especially after coming off of a load.

With prothanes, I would recommend running a flex section just to be on the safe side.

 

[DSMunknown]

You gotta be shittin' me. I just bought Prothanes.

 

[99gst_racer]

You gotta be shittin' me. I just bought Prothanes.

There's nothing wrong with the Prothane product. Just make sure you have a flexible section in your exhaust to avoid potential problems.

 

[Ludachris]

Don't the exhaust hangers take up some of that movement?

 

[dsm-onster]

Yes, and they do enough to do away with the flex, IMHO. I hate to take away from the other's advice. This is just my experience. I ran my FWD with stock motor mounts and zero flex section for over 3 years. And the previous owner who sold me the car drove it that way for who knows how long.

The thing is, the FWD system has to run up into the chassis to go over the rear stabilizer bar. No issue with removing 4 different turbos about 3 times each over the years. Plus the countless headgaskets and bent valves. The exhaust manifold studs have held up just fine. There is VERY little room for error fabicating 3" exhaust as it wanders up into the chassis and very close to the fuel tank. Much less, the travel from a hard launch will show any fault in not having a flex section. But, everything was fine. Since then, I've welded up my mounts. . . The point is if it works for a FWD, then it should do just fine for an AWD.

This is just my opinion based on my own personal experience. Somethign could go wrong, but over the years on stock motor mounts (some broken), there was no problem with any bolts or leaks or anything.

 

[Burnett03]

I don't see what the big deal is about running a flex section? Even just a small one? Better safe than sorry.

 

[99gst_racer]

Don't the exhaust hangers take up some of that movement?

The hangers do absorb energy from the car's driving and normal uses. But, they aren't designed to handle all of the movement of the engine. The engine will want to "roll" using the crankshaft as a centerline. The front and rear mounts are what limits it's roll. But this roll movement is what can damage anything that is connected/fixed to the engine that is not designed to roll on the same axis (the exhaust system). That why we use a flex section as a sort of compensation to absorb that movement. The exhaust section before the flex joint will move with the engine, whereas the section after the flex joint should stay (for the most part) level with the underside of the car.

Picture your engine rocking from front to back. Without a flex section in the exhaust, all of that motion is going to put immense amounts of stress on all of the weakest links (IE: the flanges/gasket surfaces and welded joints). In a nutshell, all energy does is transfer from one mass to another. If you don't have a provision to absorb potentially harmul energy, it very well could cause another part to fail. Some systems are fine without a flex section, while others will constantly have problems. It's a gamble.

 

[Ludachris]

Might as well just pay a little extra and put one in I suppose.

 

[treebonker]

It's been 5 years since Buschur Racing has been selling their EVO exhaust without a flex section and doesn't use the factory ball-socket type joint at the O2 housing either. I don't think they had a single issue with their exhaust cracking. They do use slip joints but I can't imagine it being any help.

 

[99gst_racer]

It's been 5 years since Buschur Racing has been selling their EVO exhaust without a flex section and doesn't use the factory ball-socket type joint at the O2 housing either. I don't think they had a single issue with their exhaust cracking. They do use slip joints but I can't imagine it being any help.

Actually, there have been several reported issued with BR's EVO exhaust system. (I'm not knocking BR in any way here either). Just ask Jake Montgomery - when the exhaust hangers rip off, they will leave a golf ball sized hole in it's place. Like I previously said, that energy's got to go somewhere.

 

[treebonker]

I do recall the hangers ripping off with a portion of the piping back in '03 when they had an issue with the earlier made exhausts but nothing afterwards. I don't know if you're talking about recent events but seeing how they still don't have flex couplings on their std exhaust and manage not be bashed on evom seemed to make a good point on the subject.

 

[Defiant]

You'll crack a pipe or a header if you don't allow for flex. Use one.