Exhaust fabrication (from headers back)

[Crazy2287 1,886]

I put together for my crossy a wee while back. Just going to highlight a few points of building one.

First, Get a metal drop saw. Building exhaust without one is painful, not the cutting, but filling the gaps when welding on the un-square cut's made from using inappropriate tool "X"

Choosing between mild steel or stainless.
Obviously mild steel will rust, I'm not sure on current life expectancy for mils steel exhausts.. 10 years??? and you will have to paint it with ceramic (flameproof) paint at about $20 a can. It is however cheaper overall to use.
Stainless is more expensive but will last a lot longer, Most likely the life of the vehicle, especially if you weld with stainless wire. (You can weld with normal steel wire but obviously it will be susceptible to corrosion at the joints.

Your local exhaust shop will sell the mandrel bends in mild steel for $20-35ea Any more than this and shop somewhere else! The hot tip here is to get 180º bends. Because you can get 2 bends from a single piece.


A hanging system or a hard mounted one.
Hard mounted systems can drone through the car, using the body of the car like a speaker. Finding rubber mounts to hard mount that will stand up to the heat and remain flexible can be interesting (if you know of such material let me know!) So it's not recommended for a cruiser.

Hanging systems, like the stock one, are suspended by hangers and rubber supports. The bonus is they are a little bit cheaper to build (the flexible couplings are expensive) and you can have a louder exhaust without so much drone in the cabin.

Here im building a hard mounted system. Bonus with it is it can sit up under the car, a few mm from the body allowing maximum ground clearance for lowered cars.
Few points:
-Get the longest flexible coupling you can fit. The longer they are, the more deflection they can withstand and the longer they will last. Longer ones also give less resistance to engine movement meaning less force on your mounts and extractors.

- You need to support the extractors at the bottom, onto the engine. On a fixed system, Heat as well as engine movement puts a lot of mechanical stress into the extractors and you could end up with cracking around collectors, along the manifold flange plate or crack studs/bolts.

Here is an example of both my flexible coupling and the brace i used to support the bottom of the extractors to the engine and prevent the force from engine movement straining the extractors:





In that last pic you can see one of the bolts that hold the end of the flexible coupling to the body of the car. There are 2, one on each side. These were done with the long nuts you can get form the local nut and bolt man, welded to the body of the car, painted in stone guard and some angle steel on the exhaust. Between the mounts is some HD rubber but the heat eventually killed it.



Preventing these bolts from undoing is also a bit of a challenge. Vibrations and heat make short work of undoing them. In the end i can't remember if i used bolts cut to the length so they would bottom out and bind up, loctite, split washers or a combination of. Another option would be to cross drill the head of the bolt and lockwire them, but you will need a drill press and a suitable drill bit, of which i had neither.

For the remainder of the bolts, i overcome the undoing issue be double nutting (locking 2 nuts together) ... (gigiddity)

Mounting of the Cat and EGO sensor.

The best cat converter is none at all, But if your going to drive on the road you need one to stay legal. Stainless steel high flow 100cpi will look good and appear "legal" but you should not expect to pass an emissions test. This is a whole other topic but if you wanna do it properly, do your research.
The cat and EGO sensor both need to be HOT to work properly. As such they need to me mounted as close to the engine as possible. There are limitations where these things can get too hot, but generally in a NA car the base of the extractors is already far enough downstream to ensure this is not an issue.
Do not mount your EGO sensor in a primary or secondary runner, unless you running multiple sensors, otherwise you will not be monitoring all the cylinders. It needs to be mounted after the final collector.
EGO sensors with internal heating elements or Wideband EGO's can be mounted anywhere in the exhaust as the internal element ensures they reach operating temperature.

Here is the base of my pacemaker extractors:



There are 3 things going on here. To fit the flexible coupling and maintain ground clearance i needed to shorten the extractors, but this worked out well as the outlet of the extractors was only 2"1/4 so in shortening the final collectors, and taking to it with a hammer to make it round, i was able to make a good taper to the 2.5" pipe i was going to use and The mounting point for the EGO sensor.

Looking back, the taper in that collector before i shortened it may have been important for the venturi affect but for now i will just continue to decide doing what i did improved flow just to keep my brain happy. Comments on this welcome.

Everything else is pretty straight forward, Keep the pipes straight as you can. If your using a MIG to weld it all together don't worry about grinding off the excess to make it flat, leaving it there will give more strength.
Prepair yourself for a lot of time and interesting methods for holding bits in place as you line up, cut, tack, check, weld, check, grind, cut and weld. Did i mention welding sparks going down the back of your neck? Enjoy that =P and if you have a hoist then STFU.

Remember things move when you weld them, Support things in a jig or in place on the car putting big supporting tacks on 3 or more places around the pipe before removing it all for your final weld up. One problem i ran into at the very end was one of my flanges rotates when i welded it and i could not do it up so had to cut it off and try again. Make sure there is pretty much zero load on the flexible coupling when everything is bolted up and at rest, i till give maximum life from the coupling. I recommend using flanges on the system so you can pull it on and off easily in the future.

Heat builds up at turns, restrictions and intersections. Ie, the heat that comes from a straight piece of pipe is a lot less than that which coms from a 180degree bend, muffler, the cat or the collectors.

To prevent the exhaust bolts undoing, use studs and lock washers. You can buy proper stud kits for a few $$, If your a tight ass like me you can get a hand full of appropriate length bolts by measuring the depth of the threaded holes in the head, add the width of the exhaust flange and the nut + 10mm and get bolts this long. Cut the heads off the bolts, then use 2 nuts locked together on the good end so you can turn them in. Wind the cut off end with a little bit of loctite into each of the holes in the head until the bottom out.

 

[Crazy2287 1,886]

Now have a heap of pics:

[adrianphu123 73]

I would recommend against buying a bend and cutting to make 2 bends. You never the the correct angles and even though mandrel bending maintains the diameter, it deforms the pipe slightly and fitment will become an issue

When fitting the over the diff section of the exhaust, support the car on the rails and let the axle hang to give you more room.Especially good if you've painted diff or exhaust. Useful for fitting the rear swaybar too.

 

When i did my exhaust, i made mounts to suit the stock hangers, flanged it after the headers, before and after the muffler. I wish i had raised the muffler a bit more, as its barely hitting the swaybar but i think i can just get away with it. I would recommend using 3 bolt flanges as they are roughly the same price as 2 bolt ones.

 

Good write up mate, lots of good ideas there

[slydog 7,873]

Good work bruz...lots of ideas for people

[Thom 6,650]

Good work Q, is that the same exhaust you had on at heathcote?

[Crazy2287 1,886]

Yep

[SAM 5]

Hello guys

 

Any difference or access using a 3 bolt flange as apposed to a 2 bolt flange ?

[slydog 7,873]

None at all

[PRO250 1,506]

i did not take pictures of the system for my ghia but its gold the welds are so good you dont even know its welded 

[Neil Armstrong 92]

The welds are so good you don't even know its welded?

 

how do you know they are good if you cant see the welds? could of been shit as fuck and they where just talented on the grinder lol

[Gandalf 144]

Another nice story to compliment a few coldy's.

 

 

Cheers - Steve

[L6=:) 18]

All useful information here, thanks for putting it up

[Neil Armstrong 92]

Hello guys

 

Any difference or access using a 3 bolt flange as apposed to a 2 bolt flange ?

 

Definatly, having 3 bolt flanges is far superior cause it apply's even pressure onto the exhaust flange surface, 2 bolt flanges have a tendency to leak and always have to fix them up from time to time etc I even have gaskets with my 2bolt ones and used exhaust temp silicon and they still leak from time to time over the years. 

[Crazy2287 1,886]

I only use 2 bolt flanges on the 3" and 2.5" zorsts i have built and am yet to get a leak at the flange. I see where your coming from but the only connection that truly puts even pressure on the joint is V band couplings. 3 bolt flanges are still susceptible to distortion that could cause leaks. The rigidity and thickness of the material used for the flange will have a lot to do with it's susceptibility to distortion. You'll notices the "normal" 3 bolts and 2 bolt flanges are different thickness.

It is my opinion the requirements of the instillation should more importantly dictate the requirement for 2-3 bolt couplings, like space, ease of assembly or availability. Rather than a fear of the coupling failing to seal properly.

 

It's important to note that you should check your flanges for flat with a rule after you weld them, the heat from welding could easily distort the flange. Just as your exhaust can move as your welding the pipes. It's important to weld the flanges on LAST, while its all bolted on the car or on a jig. If you weld them on first or during and the pipe happens to move, even only a little bit, during welding it can cause very annoying alignment issues. If you leave the misalignment uncorrected and install the exhaust anyway it can certainly cause leaks/cracking.

 

If your feeling picky you can weld the upstream flange on so that the exhaust tube protrudes a couple of mm, and the downstream is recessed a couple. This way when bolting the flanges up they will "locate" themselves square when the protruding exhaust pipe is slid into the downstream flange. Couple also help hold the gasket in place. This wont always be ideal, just a thought.

[slydog 7,873]

Well said Q...people often forget the basic's.Mis-alignment and over tightening can warp em and using gaskets and silicone as the your placing a bigger bridge/pivot point between what is supposed to be two flat surfaces.I'm yet to have any of em leak aswell but I also prefer a overlapping slip joint for extractors and bolt on flanges for the rest.