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Patrick 31st July 2018 20:14

New exhaust
Planning an update to the exhaust, starting early in the morning or coming back late is a bit of an issue. Dispite the sound passing SVA it’s a tad disruptive. Also on long trips at 50mph you get quite a bit of resonance.

This setup using Varex X-Force back boxes gives the best of both. Open it up and it's a straight through perforated style muffler same as the magnaflow boxes on there now and when closed the sound is reduced to stock or lower levels.

Adjustment is via a keyfob, you can set open/close and anywhere in between.

Pipes by Jetex same as the current exhaust - great quality and lots of choice.

V band clamps from eBay, will have to see how the quality lasts on the clamps.

Some jetex parts:

If any of you are classic car fans, we installed a very similar system on Richards 67 Mustang with a 289 small block V8 (Original marked in Video had two tiny bullet mufflers and it literally made your ears ring after 10mins of driving, was also a two pipe system. New varex setup also added an x pipe)

Lots more on this car here:

Now I just need to find time to build the new one! Doing a bit of planning in Autodesk Fusion 360 - which is aviable for free if you're a hobbist, well worth a look if you're into playing with CAD.

This shows some jetex parts to bridge the height differene between the exhaust run and back box height (and moves from the 2" pipe size to the 2.5" input size on the back box):

Patrick 1st November 2018 22:20

Updated design:

Progress on building the new exhaust. The welds a’it purdy but they’re solid and not too bad considering I’ve never used a TIG before and have learned how to use it with YouTube tutorials…

Step 1: Remove the old exhaust:

Step 2: Test fit some pipes, ordered the wrong bend, so either need to modify or get another one

Step 3: CAD (Card board aided design) to get the angles for the 2″ to 2.5″ transition. The height difference is 80mm, the input and output are parallel.

Step 4: Transition parts tacked together with v-bands clamps at one end. The v-band connects the backbox to the rest of the pipes, will allow for some angle adjustment later if needed.

Step 5: Back gas feed, v band clamp in place to reduce chance of warping when welding that part.

Step 6: The two height / size transitions welded up (don’t look too closely). Back gas worked well, clean weld through no sugaring / oxidisation on the backs.

Step 7: Cut down the inputs on the back boxes, they input at a slight angle so needed cutting flush for the v-band to be welded on.

Step 8: V-bands welded on – these were both back gassed

Step 9: Cut out hangers for from stainless tock and cut holes in each.

Step 10: Hangers bent 90º – welded these on, bit of a tough one to get the amps right, melted away a bit much of the original metal but I think I made it longer than it needs to be to compensate.

Step 11: Finishing up welding the first piece – this goes from the exsiting output all the way to the back box

Step 12: Pipe in place, it will be clamped were the colour changes from stainless, to stainless covered in dirt

Step 13: Back box in place on the hanger (into the existing E36 style exhaust hanger).

Step 14: May need to move the head shield a bit as the back boxes are closer to the centre of the car due to the offset inlet.

The bullet mufflers are now no longer part of the exhaust system, in theory the closed setting should be quieter than before and open should be the same or louder!

Step 14: Cut down the output pipes, otherwise the tips would stick out too far.

Step 15: Tip test fit, could move these back further by cutting the tip input down a little which would make the hole bigger.

Step 16: Test fit on car, it’s just push fit to at this point

Opened up the cover that’s over the mechanisum which actuates the volume flap

View from the top, position seems quite good here

Patrick 4th November 2018 00:16

Built the other side of the exhaust today. Welding is ‘better’ than when I started but still pretty uneven. I can’t weld too far consistently around the curve yet. Did punch a few holes in the metal in places which results in having to ‘glob’ in filler rod to build it back up again. This part was back gassed as on the others before as it was a butt joint.

The 45º and straight pieces are sleeve fit, have welded these too so less clamps are needed. It also cuts down on potential exhaust leaks.

Once the two back boxes were hung I used some boxes and various peices of wood to hold the tips in place at the right height, this is with the car on the ground. Nothing on the Sportster is straight so this was done visually.

I used a piece of angle metal to line the tops and ends of the tips up. This helped make sure the tips were aligned straight with the ground, with each other and spaced from the back of the car.

Welding the tips on was a bit tricky, blew a few holes in the metal especially where the gaps were bigger. The left box alignment is slighly off, but it’s not visible once mounted and the tips are in the right place visually.

Both exhaust pipes mounted, the v-bands are visible in this shot. I used a tiny bit of exhaust paste on the mating surface, shouldn’t be needed with v-bands but I’d rather not have to take them off again! Also visible the zip tie exhaust hanger, nothing like attaching your exhaust to your suspension ;o) Kinds tempted to make some straight pipes that can be put in place of the back boxes, but that’s a whole new level of noise (did try running it with just the header and you need to wear ear protection…)

The more permanent hanger, this is a part is from pypes a US manfuacturer of exahust pipes. Had that left over from building an exhaust for the Mustang ( last year (welding with our 'cheap' clarke MIG, very messy process compared to TIG). Available at

View from the otherside, wiring is hanging down. These cables need plumbing in properly and the metal shields putting back on the mufflers.

Car down on the ground from a low angle, the exahust tips are closer together than before (due to the input on the backbox being offset rather than in the middle).

The tips stick out a little further than the old ones, the wall thickness and slash cut work quite nicely.

Temporarily wired up the control box, and now for the noise test:

Closed it’s quieter than old the jetex micro bullet muffers + the large magnaflow boxes. Open it’s a bit of a beast, louder than before so that should be fun! It's pretty much were I wanted it to be, will see what it's like on the road once the wiring is done.

peterux 5th November 2018 15:32

Brilliant work there Patrick. Well done!!

I'll listen out for you at Stoneleigh next year :evil::evil:

Patrick 5th November 2018 18:59

Thanks Peter :smile: :smile:

Patrick 22nd November 2018 20:06

As I was busy Richard sorted the wiring out for the control box:

Wiring, inside the tub running along the tank with the rest of the rear loom

Wiring running along transmission tunnel, protected by a piece of fuel tubing to stop stray debris from damaging it.

Behind the fuse box, hooked in via 7.5amp fuse to an ignition feed

Located the control box in the same area just off the centre console.

Everything back in place under the dash

Just needs the rear putting back together again.

Barber 1st December 2018 11:38

Great thread, well documented and described. Whilst i have no interest in doing the exhaust on my car, this had me hooked. I saw a Marlin on ebay for £2,500, and was sorely tempted, but my wife has warned me off having any more secret projects.

Patrick 1st December 2018 17:50

Thanks :) Marlins are quite small, chuck a rug over it she’ll never notice :lol: ;)

Next time there’s a dry day I’ll shoot some footage of it running it out the red line

Patrick 2nd December 2018 15:53

Video (obligatory no exhaust clip right at the end when everthing was off):

molleur 2nd December 2018 17:47

Like the open sound! Find & fix that fuel leak ASAP.

Patrick 2nd December 2018 17:51


Originally Posted by molleur (Post 97905)
Like the open sound! Find & fix that fuel leak ASAP.

Fuel is just what was coming out the exhaust on start, without an exhaust on there it ended up on the floor! :)

molleur 2nd December 2018 18:38


Originally Posted by Patrick (Post 97906)
Fuel is just what was coming out the exhaust on start, without an exhaust on there it ended up on the floor! :)

Very dangerous condition with fuel pouring out the exhaust. I'm sure you will take care of it soon..

Patrick 2nd December 2018 19:22

This was due to two cold starts in a row, it struggled a little to fire so the engine just pumped the extra fuel out. It’s nothing to worry about as these were not normal stating conditions.

molleur 2nd December 2018 20:15

Happy to hear no worries! Enjoy, exhaust sounds great!

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