Exhausts and Silencers

So, you want to fit your own exhaust pipes? You're mad.
AK will do it for you. But if you insist, here's what you are in for.

The AK supplied system comes with a flange that connects to the headers, a link pipe (also known as a 'J' pipe), and catalytic converter (cat) and the long, heavy but beautifully made silencers.



You will need an exhaust gasket. CBS sell a kit to make your own.
My headers have a small recess in which a circular gasket will sit so I cut a circular piece of thin gasket for that and a second piece for the whole flange. To cut the metal gasket I bolted the two flanges together either side of the metal material and used a hacksaw and drill to cut it to rough shape, then finish of with a file.

Also supplied are four angled brackets. These can be bolted or welded onto the underneath of the chassis rail. I bolted mine as I wanted the flexibility to be able to move them slightly to properly line up once the silencer is in place.

The sequence is as per the notes on the Body on Chassis page.
If you have fitted the body and will be damned if you are going to go through the rigmarole of taking it off again, then you are going to have to jack it up in the air as far as you can so you can get underneath to tack weld the link pipe and the cat.

So, fit the silencer roughly into place. I used a small jack and a wood plinth with the silencer tied in place. Fit the rubber mounts and the angled brackets. Mark on the chassis rail then drill and tap for 10mm bolts




The rubber mounts will flex and distort with the weight of the silencer.
So, obtain for yourself some 1" diameter pipe with a fairly thick wall. Cut four pieces the same length as the rubber mounts. Using a long bolt and nut, fit the silencer to the chassis brackets using the short solid pieces of pipe and once the silencer is in place, tighten the bolts. The silencer will then be held properly in place while you figure out the cat and link pipe.

Inside the body, fit the cat, the link pipe and bolt the flange into place.
The cat needs to be horizontal and low down, about 5-10 mm above the chassis rail immediately below it.

Now, here's the main thing.
Originally AK supplied silencers in 4" diameter. I dunno, maybe they looked a bit weedy, but anyway, now they are 5" diameter silencers. The original pipes had a straight bracket welded on, these ones have a pronounced angle that lowers the silencer down enough so there is reasonable clearance when the the doors open. I don't know how the original ones looked but these ones have a upward sweep as they enter the body.

If you look at Cobras built with custom made headers, the headers sweep down from the exhaust ports and out through the body. So looking at the pipes entering the body, there is an impression that they are pointing up at where you expect the exhaust ports will be.
Well these things have a similar slight upward sweep, except instead of continuing up towards the ports, the pipes enter into a short tube which then enters the cat which is laying flat, horizontal.
And there are two things about that.

The first is that there is an awkward angle twixt the cat and the pipes.
The second is that I didn't know all this. It is number 296 on the list of things I wish I had known.
And I wish I had known number 296 when I cut the holes in the body for the pipes.
So what we now have is the pipes sweeping up into the body from a low angle and in my case a hole that is a bit far north of where it should be. Not a problem, I just opened it out at the bottom and later I'll fill the top edge and fit escutcheons.
For the record, the hole you want starts about 12-15mm from the very bottom of the bodywork. Measure the exhaust pipes and work out the height and width from there.

So this is how it is.









Anyway, never mind all that. The interesting bit is yet to come.
So we have the silencer fitted and the cat and link pipe in place.

Here is what the cat to short tube joint will look like.












If the angle is too severe to contemplate the weld, then cut a slice out of the pipes tube, at an angle similar to the angle the cat presents to the pipes tube inlet hole.
That makes the cat fit closer to the tube and gives a smaller gap to weld.
If you like, think of the silencer tube where it sits in the car, it will be at an angle. Draw a line around it from the edge of the top lip in a vertical plane. The result should be a cut that then has a horizontal face to the cat.
But be careful. The more you cut, the closer the cat will fit into the tube. That means it is being pulled away from the link 'J' pipe. Make darn sure you have enough link pipe to fit properly into the cat.

Check how flush the link pipe is to the flange. You can afford a small gap but if it is more than 1-2mm you may need to shave some metal off the link pipe to get it to be flush with the flange.

Here you will notice there is bugger all clearance to get a nut onto the stud in the exhaust header.
In any case you will need to cut the studs down. Actually there is just enough clearance on the stud where the link pipe aggressively curves its way off the flange to run horizontal in to the cat, but it is a tight fit.

Right. Now. Next thing is to buy borrow or steal a MIG welder. Then sit for hours in front of a computer watching youtube videos on how to MIG weld.
You can use TIG, but probably not arc or stick weld. The cat and pipes are only 1.6mm thick.
I borrowed a 140 amp MIG welder from my son (thanks Allen).
Next up is to practise on a lot of scrap metal and when you think you have the settings and technique correct, you actually won't, but you will still go ahead and do it for real anyway.

So, get underneath and with the silencer, cat, link pipe and flange in place, tack weld the link pipe to the flange and the cat to the silencer tube. Wear thick clothing with tight cuffs. Only a really stupid person would do this wearing a thin workshop coat with loose sleeves so that molten metal falls down your sleeve and burns its way through your flesh.

Ok, so after some first aid, take the whole thing apart and weld it up properly making sure you don't leave any holes or gaps for hot exhaust gasses to escape.

And here we are.

The joints are painted with high temp exhaust paint.
And if anyone makes any remarks about my welding, I'll ban you from this blog.

Refit the exhausts now with the rubber mounts and connect it all up.
The link pipe to cat has a U bracket around it, and you should probably put some exhaust paste in to seal it. They could be left in place but I have taken mine off and put into storage until ready to fire up the engine.