Flex Pipe In Exhaust System... Needed?!

[medwin46]

Hey all

Im just thinking maybe i should have a flex pipe section in my exhaust system? Car is AE86 with a 3sgte, high mounted turbo and full 3 inch stainless exhaust system made by me. I dont think it will have (engine) very much movement, unlike a east-west orientated engine that rocks under accelleration/decelleration. What are people's thoughts on this?

And before you all cringe at the thought of my hand made exhaust, heres a pic....



Thanks in advance

[jezza323]

shouldnt do...flex pipes generally only used in east-west AFAIK

[SillyCarS]

id put a little one where your wastgate joins to the dump, some people say its over engineering but there is significant heat changes and thermal expansion in these two pipes

this is what i mean:

http://www.toymods.net/forums/attach...5&d=1161749726

[medwin46]

id put a little one where your wastgate joins to the dump, some people say its over engineering but there is significant heat changes and thermal expansion in these two pipes

this is what i mean:

http://www.toymods.net/forums/attach...5&d=1161749726

Na, internally gated into the single 3 inch dump Cheers

[oldcorollas]

i say.. why not...

reduce vibration in the rest of the exhaust which may help with drone and vibrations, increase life of exhaust mounts..

also.. think of the leverage the exhaust will have on your fragile little turbo if the mounts DO break..... or even if they are not prefectly aligned and holding the weight evenly...

oh.. and where is the cat?

[merc-blue]

there is a "test pipe" in there so im assuming he swaps that out for the cat

[japlish]

i'd do it,
my 20v ae86 didnt have it at first and ended up having a big crack form on the extractors

[IN 05 NT]

rwd you dont need it. front wheel drive yes,

but i do recomend running one,

i can supply you a 3" and 6" long flex for about $65-70...

NINJA edit....ohh your in tassie

[GA61XX]

I've seen them on, RWD motor's, as well...
So use one.. as it will stop vibrations & crack's, in you exaust system...

[schnitzel]

All comes back to how hard you use the motor and the movement this causes, if your motor twists more than the amount of twist your pipe will take then you need a flex joint. If you want to hard mount the rear part of the exhaust again you need a flex joint. If your engine has minimal movement and your exhaust is not fixed but is mounted to allow movement you dont need one. Personally I prefer them I have them on an 18 rg in a ke35 and on a chev 350 in a motohome, but not in my standard road cars. Also given the hanging weight and size of your system, and the fact it looks like it is stainless I would be using one in your appplication. Most stainless by nature does not twist as well as mildsteel tube.

[oldcorollas]

if any exhaust pipe is being twisted.. i mean actually being elastically deformed.. you have serious issues with engine and exhaust locating devices

neither will twist, and nor should they.
if system is designed to be perfectly free hanging and mounted such that is can freely rotate on the same axis as the engine.. then all good...
but that doesn't happen. (think axis of engine movement (mounts) vs axis of exhaust movement...

[schnitzel]

Twisting is not necessarily to point of deformity, twisting does occur due to the movement of the motor, even when the exhaust is mounted relatively freely. As I said on a normal road car, (RWD of course) a flex pipe is not required, on a car used for other purposes where motor may move on the engine mounts a twisting or rocking motion may occur greater than the amount taken up by the exhaust hangers a flex pipe may assist in reducing the likelihood of the pipe snapping or cracking. The 2 examples I have 1 is in a car that is used for autocross and motorkahanas and hence engine movement exceeds the normal limits. Whilst the exhaust on the motor home is approx 10 m long and the rear section can often still be moving one way whilst the motor moves the other way causing a small induced twisting motion. Most trucks and buses have a flex pipe installed due to this effect to stop the pipe cracking . Again would note I am not talking about twisting to deformity but the small constant motion induced by the movement of the engine. Agree that twisting to point of deformity and you have other serious mounting issues, and no system can be mounted such that it is perfectly free hanging, there must always be some sort of resistance if it is mounted.

[oldcorollas]

how does the the exhaust on the motor home twist one way, while the motor is twisting the other way? what is exerting a force on the end of the pipe that is greater than the force exerted by the engine??

my previous point was.. if you are actually elastically deforming the metal.. you have issues.
twisting "with" the egnine is normal and is a problem if the design is not thought out properly.
if, for example, your exhaust is solid mounted and the engine is free to `twist`, then you WILL break the exhaust... that is the twisting i was referring to.. from when you said

Most stainless by nature does not twist as well as mildsteel tube.

you will probably find that with the strength and wall thickness differences, there is not much in it in terms of resistance to twisting deformation of the two materials.

[The Real Roadrunner]

i put them in if i feel they are needed (depending on the job), but in any exhaust it is worthwhile to put one in if you can afford it.

if you have a stainless mani it is even more worthwhile because they are prone to cracking by nature and the extra force exerted by an exhaust bouncing around under a car will only do more damage than good.

and SillyCarS is correct that any external gate setup should run a flex if it returns back into the main system as the expansion/contraction between gate open/closed will cause cracking eventually.

cheers
linden

[9000rpm]

It isn't going to hurt putting one in there.

Just make sure you attach the exhaust solidly to the bellhousing then have good flexi jouns from there back.