More Exhaustion

 

After the last update and the start of the exhaust system I continued with making my slip couplings on the newly fabricated first section. These are made of some slightly larger diameter steel and have been welded on to the two horizontal sections. I initially had two stainless steel slip couplings (clamp on) to attach the pipes together however they were basically dog shit and wouldn’t compress/clamp onto the pipe so they were done away with in favour for these slip couplings. I welded a nut onto each end after drilling a hole through, this will allow a short M8 bolt to nip up through onto the sliding section and stop it sliding out. It’s a relatively good friction fit anyway and will have some exhaust paste on final assembly however prevention is better than cure. 

The next section was to weld a 45 degree angle onto the leading 90 degree leg. This will now direct the exhaust horizontal along parallel with the sill. This is just a case of mocking up on the car and marking accordingly before a few tack welds then checking everything before fully welding together. Just after the 45 degree bend I have also welded an expending cone which goes from the 38mm diameter up to 45mm this is the same as the original spitfire exhaust which in theory should keep the back pressure equal and not restrict the performance. 

It was all coming along quite nicely but the next bit was to notch the secondary down pipe and weld into the primary pipe. Another reason to have the slightly larger diameter pipe just after this join to cope with the increase gas flow. Before I cut this for real I used an off cut of pipe and made a thin cardboard sleeve in order to cut with scissors and practice the angle and cut for a good fit. This was all fairly good fun, and whilst I’m sure there are other ways to calculate these angles as long as I get the end result I’ll be happy with that. I’m no professional fabricator this is all part of the fun of kit car building you have to be a jack of all trades.

So after I was happy with the fit of my practice piece  I simply used masking tape to make a template then transferred it onto the secondary down pipe. And I’m pretty bloody happy with how it turned out. The notch cut was nice and uniform all the way round so will weld up nicely. I marked the circumference of the secondary with a pen so when it was all removed I could see the area I needed to remove before welding up. Then it was out with the grinding disc again and start cutting away. I have sacrificed another Dremel multitool during this project my first one lasted years and years and now I’m lucky if a get one to last 18 months…and I’m not giving them a hard life. 

 Once cut out I filed everything smooth everything was welded into place, after a few tack welds and trial fit first. Then when fully welded I dressed off the top with a flap wheel and then I could make a start on the exhaust wrap. I managed to get 30 meters of exhaust wrap online for only £10 so was happy with that and it’s a nice titanium colour so looks great also. I wrapped the exhaust in two sections first the upper pipes that come off the manifold up to the slip couplings, then the further two pipes as they come out the body and down along the main side pipe up to the edge of the drivers seat access. This should help keep the heat down directly under the carburettor intake filters and also reduce the risk of burning your legs getting in and out the car…. Not that I have ever done that in the Cobra either but it will help soften the blow if it does happen.

I can’t continue any further yet as I’m waiting for two further 90 degree bends to be delivered that have gone AWOL in the post. But when they arrive I will be able to finish the exhaust up to the rear silincer, which will be another custom fabrication idea that I have. I’m really pleased with how this exhaust is looking so far and it will genuinely be exciting to hear what it sounds like when I get the engine running still need to get the carbs built up properly first. 

Exhausted Beyond Belief

So on this update it’s all about the exhaust really. I wanted to try and do one blog update to cover the full exhaust fabrication and install, however everything escalates and takes a slight tangent so we’ll have to cover it over two or three. I started off ordering some mandrel bends and sections in mild steel, I’m not setup for stainless steel welding so mild steel will have to be ok and in fairness it should be more than durable for its use. I have a good idea how I want the exhaust system to look and the style to suit the car so I’m fabricating the full system to achieve this. Starting at the manifold end I used the original down pipe and cut the old pipes off the flange plate, I will be using this still as my fixing point onto the manifold. The original down pipes are a 38mm diameter (1 1/2”) so my new pipes are the same to hopefully keep the exhaust pressure equal and not restrict performance from the mighty 1500 engine. 

I started by fitting two knuckle 90 bends to the flange plate, these are welded in place and the spigot into the flange slightly to give strength as the rotation of the engine under power and vibration. Then off of these two knuckles I have added two straight lengths which will take this new section up towards the body tub inner wing.  I have been tack welding this all up first and making small adjustment and alterations as needed then fully welding and dressing when I’m happy with the fitting. 

Next stage is to cut some holes in the wing and fit some 90 bends to run the exhaust down the exterior of the body. With the first section temporarily fitted to the manifold I used a straight edge to follow its line to the inner wing and made some markings roughly marking the diameter of the pipe and where I needed to cut the hole. 

Then it was out with the hole saw and make a few nervous cuts. My idea is to have a slip coupler fitting the vertical section here to the 90 degree section as it exits the body which will also make the exhaust removable at a later date and for service reasons if needed. Once the two holes were cut out I filed and rounded the edges off slightly making sure there was adequate clearance around the pipes. The exhaust front section will be wrapped in heat wrap which will help keep the engine bay temperatures down slightly and also help cover all my welding joints.

I now am able to fit the two 90 degree sections which will send the exhaust down the external of the wing where I need to make a two into one collector or Y piece as such, I’m still working on this as I’m wanting to also increase the diameter of the exhaust section after this point to something closer to 2” as it travels along the length of the car parallel to the sill. I don’t have this bit of tube yet but I need to keep its diameter to something close to whatever silencer I use… and in mild steel also so I can weld it. 

 This has all been fairly trick to get fitting correctly so far as the horizontal section of the first section runs close to the steering column and I can’t risk any potential voiding, especially when the engine is under load. But the tight knuckle 90 bend directly on the flange plate lift this section just enough to give a good clearance even when taking into account the exhaust wrap later on. 

 My next little task was to run the main battery feed from the battery in the boot along the nearside inner sill and up the front firewall to the solenoid. I used 170amp cable to achieve this which is really overkill for a small capacity 4 cylinder engine, but this lesson I have learned previously with the cobra build as I only used cable then which just meets the amp demand for the engine size and it can struggle to turn over when really cranking for a period on a cold start. The battery cable now runs the length of the sill and I will clip it down at a later date but I have also fitted a batter isolation switch just in front of the passenger seat which is easy to reach in case of emergency. The cable now passes through the front bulkhead and directly up to the starter solenoid using some good heavy duty crimped ring terminals. I’m paying huge attention to the routing and clipping of all cables that are viable as this is wha will help push the quality standard of the whole build and help towards the final product presentation, making it look less of an afterthought installation. 

With the battery feed now installed and the battery negative to the chassis also I could now actually spin the motor over using the solenoid. I’m now sort of at a stage where I can make a start on the full electrical system and start to make some decisions in regards to the custom loom and fues/relay layout positioning. Wiring I find extremely satisfying but also complex to get the correct rated wire and colours for each circuit. Luckily I purchased a USB Spitfire service manual from Rob T (the online Spitfire guru) which has a wealth of knowledge and many many many PDF files covering all aspects of the Spitfire which is going to be really helpful and provide much further specific detail than a Haynes manual.