View Full Version : Russell's AK Gen3 Build log

10-03-21, 07:14 PM
Inspired by Aarons build thread I thought I'd start my own.

I've been building since 2016 and have just about finished the rolling chassis, so not exactly speedy:D I might go back and document some of the other unusual parts of the build (like the fuel tank) latter but for now I'm going to start with the exhaust system. As you may have seen in some of my previous posts I've decided to design and build my own side pipes. Complete madness I hear you say, yes it probably is, but I wanted a particular style of 4 into 1 merge (not sure what it's actually called) so I modelled it up in Fusion 360 and 3d printed a few prototypes.

Previously I'd roughly cut the bends for the 4 into 1 pipes

and milled the required features on them

Then they where tacked together followed by the cutting/tacking of the various bends
http://www.cobraclub.com/forum/attachment.php?attachmentid=39330&stc=1 http://www.cobraclub.com/forum/attachment.php?attachmentid=39328&stc=1 http://www.cobraclub.com/forum/attachment.php?attachmentid=39329&stc=1

10-03-21, 07:20 PM
Once I was happy with the fit I broke the tacks between the 4 pipes and set about welding the sections up.
http://www.cobraclub.com/forum/attachment.php?attachmentid=39331&stc=1 http://www.cobraclub.com/forum/attachment.php?attachmentid=39332&stc=1

I spent most of today, grinding and polishing
http://www.cobraclub.com/forum/attachment.php?attachmentid=39336&stc=1 http://www.cobraclub.com/forum/attachment.php?attachmentid=39337&stc=1

Next job is to make the 4 3" pipes but I've run out of time for today.

11-03-21, 01:37 PM
Just wow!!

11-03-21, 05:54 PM
*quietly packs up his TIG welder and sends it back to R-Tech*

Yep, that puts anything I've ever put together to shame! :)

11-03-21, 06:09 PM
That looks incredible.

11-03-21, 08:55 PM
Nice art work. Polishing out the welds takes time and makes all the difference.
A linisher makes easier work of the joints I have found with stainless.

30-03-21, 07:03 PM
Nice art work. Polishing out the welds takes time and makes all the difference.
A linisher makes easier work of the joints I have found with stainless.

Yes I built a linisher last summer with this project in mind, but in hind sight the type that loop over the pipe would have been better.

30-03-21, 07:11 PM
Not made much progress of late but managed to get a bit done over the weekend.

I had to wait for some end mills to be delivered but I've now finished machining the "crowns"
http://www.cobraclub.com/forum/attachment.php?attachmentid=39374&stc=1 http://www.cobraclub.com/forum/attachment.php?attachmentid=39375&stc=1

Just need to cut off the support pieces with the angle grinder and I can start to assemble the collectors.

I also brought myself a new micro tig torch so that I can weld the inside pieces, spent yesterday evening making a tool to help cut the tungsten to length (27mm!) and this evening cutting and sharpening them, I have this nasty habit of dipping them in the weld pool so I suspect there will be at least one more batch needed :(

with a bit of luck I should get some time out in the workshop over the long weekend.

18-04-21, 06:43 PM
I didin't take any photos of the assembly but both collectors are now assembled, the micro torch made welding up the inside to the pipe much easier that I expected.

Purging the insides whilst welding the outsides was easy I just used a combination of silicon bungs, but I had to get creative to keep an inert atmosphere on the outside whilst I welded the insides, the solution was a piece of aluminium plate a 3d printed flange and a large plastic bag!
I used a small electric vacuum pump to evacuate as much air as I could then I inflated the bag with argon.

To save a bit of time I brought some pre-made 1.75" 4 into 1's and a a reducer ring to bring the 2.25" unto the 3" v-band, at the moment I've just tacked up the nearside
The O2 boss is just sat on top at the moment, but it looks like there will be enough space for it. I now need to decide if it's best to keep it all flat as it is now or add small bend before the v flange so that I can have the pipes exiting the body on a downward angle. If I do that then I will probably have to shorten something so that I can get the pipes up to the exhaust flange on the engine.

I've also added a hydraulic down feed control to the horizontal bandsaw which I hope will make it much easier to cut the 4" outer pipe without it continuously snagging and throwing the blade like it did on the 3" pipe.

19-04-21, 07:14 PM
I think I've reached the point where I need to take a couple of brave pills and cut out the exit holes in the body, I'd appreciate any pearls of wisdom the group has in the regard.

I'll be fitting the exhausts first and then fabricating the headers to match so not quite sure how to go about deciding where to make the holes and what shape to make them, should it be 4 overlapping circles or just a square with rounded corners, should I leave the bottom piece in or cut it out etc?

The body is currently loosely say on the chassis so I guess I could just do it all by eye but I'd prefer a more scientific approach :p

Thanks in advance

19-04-21, 09:22 PM
Should def be a rounded off square. Bottom edge doesn't matter as its not visible.

20-04-21, 05:42 AM
Russ, give us a call as I made my headers too, one tip to help 07932 565091, Lee

20-04-21, 07:17 AM
I think a rounded off square, then fit an escutcheon, such that AK can provide. Makes it all look pretty,

20-04-21, 12:00 PM
Rounded off square for me. The bottom piece ended up so thin it wasn't worth bothering with so I cut it off.
I cut the hole so I could just fit the exhaust and then opened it up gradually with a dremmel and a flap wheel until I was happy.

27-04-21, 07:27 PM
Weekend progress saw me adding extensions to the inside of the end caps to enable a sort of bayonet fitting to allow them to be repacked in the future. The initial idea was to cut a length wise section out of the left over 4.5" outer pipe to allow it to be reduced to fit in side but I didn't have enough left over. I found some 20x3mm stainless bar left over from another project so I formed that into rings instead. It was a bit much for my small slip roller really but I got there in the end.

Once the rings where formed I welded them in place, turned them true(ish) on the lathe then used the mill to cut the bayonet slots.

I then set about making a bunch of pins on the lathe from some 5mm 304 bar stock, then I set about calculating the required pin positions before drilling and welding the pins into a piece of off cut pipe.
The pins used for the trial fitting still have the piece left on the inside end from the parting operations, I've removed those on the remaining pins


They didn't pull in quite a tightly as I would have liked so I will need to adjust the hole positions when I drill the real pieces of pipe. The plan is to drill and tap an M4 counter sunk screw into each end to stop them coming undone, but I will leave that until after they have been mocked up on the car so they can be positioned out of site.

I've also cut both the outer pipe and the inner perforated tubes to length, but annoyingly I've somehow cut one of the inner tubes 10mm too short. Not decided yet if I'm going to weld it back on and the re-cut from the other end or just order some more.


28-04-21, 09:28 AM
Nice work Russell, looking great....I decided to weld my baffles up with the thought that if I ever needed to access them, I would cut the end pipe, do what's needed then tig them back up, 16yrs later they still sound lovely!



28-04-21, 10:04 AM
Steve, wow they look amazing.

Did you do anything inside other than wadding to control the noise? I'm thinking of putting some semi-circle / crescent moon baffles within the perforated tubes but I'm unsure of how many to add or what shape to make them - any pointers greatly appreciated.


28-04-21, 12:04 PM
Steve, wow they look amazing.

Did you do anything inside other than wadding to control the noise? I'm thinking of putting some semi-circle / crescent moon baffles within the perforated tubes but I'm unsure of how many to add or what shape to make them - any pointers greatly appreciated.


I did exactly this for IVA, and they are still in and very effective.
Some have said my car is too quiet - I like to leave it ticking in the garage for a while so its a neighbour-friendly noise abatement thing, at least till the engine has loosened up a bit.
I got some 6mm steel rod and cut some discs with a hole saw slightly smaller than the width of the baffle tube. Drilled a centre 6.5mm hole in each disc and cut in half. Then a mate kindly tack welded a disc half at each end of the rod at 12:00 and 1 in the middle at 6:00 so the exhaust gases have to snake round it. Then loaded into the baffles with the rod slightly bent so they were a friction fit, and then wired to the end of the perf baffle tube with stainless wire. Idea stolen from Martin (Tinka) who did this first. That, and acoustifil wadding knock a lot of dBs off. If you don't wire them in, then the exhaust gases will eventually push the baffle out of the perf tube and they'll clank. Guess how I know? ;)

28-04-21, 01:17 PM
Steve, wow they look amazing.

Did you do anything inside other than wadding to control the noise? I'm thinking of putting some semi-circle / crescent moon baffles within the perforated tubes but I'm unsure of how many to add or what shape to make them - any pointers greatly appreciated.


Thanks Russell, yes I welded a cone to the front of the S/S perf tube and put 3 opposing half moon sections of the flattened out perf down the inside, with a centre S/S ring at the rear, they're reasonably quiet although IVA friendly, not sure :confused:


28-04-21, 01:25 PM
Thank Kevin, that's very useful.

I was planning on just welding the disks in place but I like the idea of making them removable like that, which means I can postpone that bit along with the decision on fitting cats or not until I've got the rest of the exhaust system finished and on the car

28-04-21, 02:06 PM
I continue to be amazed by your attention to detail and the finish you're achieving, Russell! Might have to take a trip to Wigan for a set of headers.. nudge nudge, etc :lol:

should it be 4 overlapping circles or just a square with rounded corners, should I leave the bottom piece in or cut it out etc?

I hole-sawed four overlapping holes for mine, on a square pattern. I quickly realised this doesn't actually work as the hole needs to be longer than it is tall (to account for the inner bend radius) so er.. it's going to become a rounded-off oblong hole instead!

28-04-21, 02:45 PM
Might have to take a trip to Wigan ...

I won first prize in a competition once which was a week's holiday in Wigan.

Second prize was a fortnight!

Only kidding, I have fond memories of Wigan from my younger days, haven't been there for many years though.

28-04-21, 03:51 PM
I'm not originally from Wigan, I'm a southerner really - been here about 15 years and actually really like the village were in.

Aaron, I originally sat down in front on Fusion 360 a few weeks ago with the intention of designing a punch and die set to get the 1.75" pipes into the exhaust flanges - I'm running a SBF with the flange fixing on 2" centres and quickly realised that it was an exercise in futility. So switched to designing custom billet flanges instead, to keep the costs down there actually going to be made from two parts and welded before final machining. Heres a sneak preview of the final design after a few rounds of 3d printed prototypes to check clearances on the car.

I've got the 304 stainless stock in and the required cutters, I've started work on the g-code for the mill, so hopefully I'll have a set knocked out by the end of the long weekend.

28-04-21, 04:55 PM
You know a CNC mill is cheating, right? ;)

Seriously though - I've seen the commercial equivalent of those and they look beautiful, and really simplify the whole process. Much better than me trying to hammer a round tube square ;) and in my case, hammer the end of a 1D 90º bend square, get it into the port, and weld it up - in the case of the rear-most port, have the tube cut at an angle as well!

28-04-21, 08:54 PM
CNC mill? very old school. Surely you'd print them :-)

28-04-21, 09:15 PM
CNC mill? very old school. Surely you'd print them :-)

Additive is is so “last year”, hybrid is all the rage now,

26-08-21, 07:14 PM
Well my attention got diverted to other projects, but I'm back on the Cobra at least for the time being. I've started experimenting with making the billet header adapters.

Are there any Fusion 360 CAM experts on here?

I'm delighted with the 2D operations, but less pleased with the 3D finish, I've roughed out the part with a 22mm end mill and then used a 3D Ramp operation with a 6mm ball nose mill to finish
I'm not sure how well it will show up on the photo but the sloped area has very distinctive stepping. I've also tried a 3D contour operation but the ramp was slightly better and faster. I've got a 10mm corner radius end mill with a 1mm radius on order but that was mainly so I can speed up the operation. Is there a trick to getting smooth 3D contours that I'm missing?


06-09-21, 07:01 PM
Well, I worked out what I was doing wrong with the cam - who would have guesses the setting "Maximum Stepdown" in 3D Contour would actually mean Minimum Step-down unlike in 3d Adaptive where it does actually mean maximum:grin:

Anyway I'm happy with the end result, there is a small ridge inside some of them where the 2nd op didn't quite line up with the 1st but it looks a lot worse in the photos


Just need to make the flanges now.


06-09-21, 07:58 PM
Blimey, they look good. Excellent work

06-09-21, 09:03 PM
Jeez, I think I'm going to have to go and stand in the 'caveman manufacturing' corner compared to that!

Russ, I may have asked this before but .. what mill are you using?

07-09-21, 07:41 AM
Thanks guys.

Aaron, I have a Warco WM18 mill, that I converted to CNC myself, initially using 3d printed parts! I would have loved something bigger/ more rigid, but my workshop is a 10x10 log cabin in the garden. Even if would fit anything bigger would need a crane to lift it over the house! It certainly has it's limitations but I've not found anything yet that I've needed to make that it couldn't handle, it just lakes longer, but that is part of the beauty of CNC it can chug along in the back ground whilst I work on something else. I also have a Warco WM180 lathe that is also converted to CNC, I've considered replacing it with something bigger, but because of the access issues it would have to me another Chinese model and anything bigger than the WM180 has things like gearboxes and power cross feed which would need to be stripped out for a CNC conversion and that seems a waste.

Overall I'm pretty happy with both machine, the only regret is that I made the decision to mount them both on a shared work bench, am I'm really feed up clearing up chips from every surface in the workshop - its quite amazing where the lathe chips end up (like in cobwebs on the ceiling on the opposite end). So I think my winter project will be to build a pair of enclosure for them which will also allow me to use flood coolant. I'm currently researching using GRP to do that as I don't really relish the idea of TIG welding something that big.

Aaron, you're making cracking progress with those headers and I don't want to slow you down but now that i've worked out the process I would be more than happy to machine you a set square to round transitions to go with your flange plates for the cost of the materials. It looks like you have the 3" bolt spacings rather than my 2" spacing so they should be considerably easier to design, however it may well take me a month or so to turn them around

08-09-21, 02:44 PM
I had a long reply written on the laptop which failed to go through, and I can now only access the forum on my phone via the mobile network (not home WiFi) so I assume the forum has temporarily banned my IP again ... Anyway!

I'm incredibly impressed at what you're getting out of that little Warco mill! Maybe I was too quick to dismiss them when I saw them at the model engineering show a few years back.. and there's not much chance of me CNC converting my well worn 60 year old Bridgeport :)

I had a similar offer of machining from another friend of mine, but thank you! What held me up was the modelling.. I'm passable but not brilliant and I'm still figuring out the lofting of square to round. Once I do that I can print a mock-up and see if it will even fit on the incredibly tight rear ports, though. For now I shall soldier on as time allows (been spending a lot of time with my dad rather than down the garage after his recent diagnosis so progress has slowed a little)

Fantastic job as always Russ, anyway!

04-10-21, 07:19 PM
I've made a little more progress with the billet header flanges.

Machining complete and ready for welding (and yes there are 9, I had enough stock to make 10 but I messed the gcode up and milled one of the flanges oversize - still good to have one spare in case I mess up the header fabrication).

And all of them have now been internally welded

The pipe pieces are socketed into the flange and fusion welded from the inside (I made up an external purge fixture/heat sink and used a 100 amp pulse to try and get decent penertration), Just need to decide if that is sufficient or if it would be worth adding external fillet welds on the top and bottom sides - any thoughts guys?