Making Headers....flex pipe needed?

[AWeb80]

I'm going to attempt to make headers for the GP while the trans is out next month. do i NEED a flex pipe in between the front and rear heads? do i need one on the DP?

 

My Motor is poly mounted and doesn't really move....so, i'm not too worried about the rest of my exhaust shaking....plus, i'll be replacing all the old rubber hangers when i do the exhaust.

 

I've heard a flex pipe is needed because the heads expand too much. this true?

[slick]

I would consider it on the crossover and definately on the downpipe somewhere.

[Brian P]

x2 a small one in the xover area and between the collector and catalyst.

[mfewtrail]

I would consider it on the crossover and definately on the downpipe somewhere.

 

^What he said. The expansion of the heads is the whole reason the shitty stock flex joints on the TGP x-overs crack.

[AWeb80]

Ok. Anyone Have Any Input On Where To Get One?

 

IIRC, The S&S headers don't have a flex pipe.....i have no idea where to look for a good one.

[AWeb80]

I'd Get Some SS 2" if i knew where to find them......and what's the best way of connecting them? i'm using mild steel for the header pipe and will be high temp powdercoated....and wrapped by me. is there a good clamp method out there?

[digitaloutsider]

I wouldn't worry so much about a flex on the crossover. Plenty of headers/manifolds don't come with one, including your stock one. That being said, one on the downpipe is absolutely required. I also wouldn't do header wrap.

[AWeb80]

Yea, I'm Leaning Away From One On The X Over. i don't have one on the dp right now.....or anywhere. so why still do one?

 

and why "no" on the wrap? the reason i want it, is the high temp powdercoat only lasts so long....because it will come loose when stuff hits it. i'm doing the wrap to more or less, protect it. the powder is so it won't rust.....and is good to ~1000*.....so, it should be fine for a na 3100.

[Addicted To Boost]

Have them ceramic coated instead?

[AWeb80]

Nobody Local.....

[digitaloutsider]

Moisture gets trapped under the wrap and eventually leads to them falling apart regardless of what they're coated in, which is why most header manufacturers won't warrant wrapped headers.

 

It's been ages since I've seen a 3100 downpipe, but even the stock one out of my Regal has little flexes in it.

[AWeb80]

The Stock 3100 x over has some ribs in it....sort of a flex....but, that is it. a made my own 2.5" dp, and the stock one had nothing on it.

[AWeb80]

How Does Moisture get trapped if i never get it wet? the car hardly sees rain.....

[digitaloutsider]

If you never drive the car in rain, you're probably fine, but I wouldn't ever do it on a daily driver.

[AWeb80]

I am just trying to keep as much heat as possible out of the engine bay.

[mfewtrail]

Those ribs in the stock x-over = a FLEX! 3.1's, 3100's, etc. all have them.

[mra32]

I think thats just how they bend them. I think they are called crush bends. Its cheap and quick

[mfewtrail]

There are no crush bends in the stock x-overs as they are mandrel bent. The flex portion is near the center of the pipe where it's pretty straight. If crush bends were anywhere, they would be closer to the flanges where the x-over bolts up to the manifolds.

 

Here's a picture of a stock TGP flex.

 

EDIT: I'll rip a heat shield off a stock NA x-over at the junkyard next time I'm there and take a picture...

[mra32]

oops i cant read. I thought you meant downpipe for some reason. Yes the crossover has flex joints. no need for extra proof

[slick]

For your flanges, once you have the pipes welded up, cut expansion slits between the exhaust ports, probably 1/8-1/4" should be sufficient. This will also allow for the natural heat expansion and contraction.

 

For example:

 

http://www.kenrockwell.com/bmw/images/m3-2007/headers-784.jpg

 

And yes, I would put a flex pipe on the crossover and on the downpipe. There is a lot more movement (physical movement, heat expansion, etc...) than you would think, even if your mounts are poly.

[SigEpCutlass]

Adam I hope you can pull this off. Your car deserves headers.

[Brian P]

I wouldn't worry so much about a flex on the crossover. Plenty of headers/manifolds don't come with one, including your stock one. That being said, one on the downpipe is absolutely required. I also wouldn't do header wrap.

 

Stock x-overs DO have one. Depending on design and type of flange used, it could probably be done away with in that spot on headers, but if I'm building something from scratch, I see it as a little extra insurance that's not going to have any adverse effects.

 

FWIW I have heard of some of the S&S 3100/3400 headers cracking over a long period of use.

[AWeb80]

For ease of making them....right now, i'm looking at doing 3-to-1 2" collector and running the 2 inch pipe of each down to where the cat should be, and then collecting both into a 2.25 or 2.5 pipe, all the way to the back. that way i won't have to cram a crossover and 3 collectors in the engine bay. i'll only have to deal with 2 collectors in the engine bay. and then one right where a stock cat would be.

 

of course, i'll see what i have to play with once the trans is out.

[J]

Have them ceramic coated instead?

big werd on that

[AWeb80]

For ease of making them....right now, i'm looking at doing 3-to-1 2" collector and running the 2 inch pipe of each down to where the cat should be, and then collecting both into a 2.25 or 2.5 pipe, all the way to the back. that way i won't have to cram a crossover and 3 collectors in the engine bay. i'll only have to deal with 2 collectors in the engine bay. and then one right where a stock cat would be.

 

of course, i'll see what i have to play with once the trans is out.

Any thoughts on this design? i think having that much space between the flanges will be enough for expansion....thus only needing a flex on the DP