Welcome to my Cobra Replica build blog.
Please contact me if you would like to know more detail as i progress."CR3514@live.com.au"

Thursday, December 11, 2014

Headers Part 1.

The space for headers, particularly the rear 2 cylinders, is very tight on clearance to the foot wells, and steering rod between the column and rack on the CR,  This necessitates a custom made header design,
Other criteria for me was to also utilize as much OE emissions controls  as possible to get me through the certification engineering and registration process.
The emissions need to meet IM240 requirements, and noise db, so my header design needs to be able to adapt from OE Catalytic converters and under-body muffled rear exit design to the 4 into 1 of the iconic cobra side pipes in the future if I want to go this way.
At the moment, I'm thinking under-body but exiting to the side behind the doors.

 A while back, I procured the Cats from another CR builder friend, they were to be discarded from the donor wreck he got his Engine and Trans, Diff and several other components from, (thanks Phil).

After figuring out if I could make them fit in the space, which entailed finding short merge collectors, and some tube routing concepts, i made up a stand to hold the cats in place while i played with different tube locations.

Firstly, I decided on 1.75" tubes, a little research suggested this was the ideal tube size for a mild almost stock LS3.
Drivability is all I'm after with this combination and 434HP in stock form in a 1000kg car will be plenty for me.

I bought some exhaust modelling blocks from "Icengineworks" via Summit in 2", 3" and 4" CLR and some straight blocks, enough to do 1 side at a time.

The blocks come in kits as well with all sorts of other bits and pieces, but I didn't need to obtain these and I'm glad I didn't buy the full kit.

After playing with the blocks, and different options of over and under the steering rod, i finally settled on the above.
This design has all the pipes over the top of the
steering rod which will make for easy removal if required.

The blocks are very quick to adjust to make fit and too maximize the use of bends with minimal cuts and welds.
In this design, the 1st 2 pipes have only 1 join each, and the 3rd has 2 joins and the rear pipe has 3 joins.

In this pic you can see the merge collector, I bought these from SPD Exhausts in the US.
Get yourself a catalogue, great bits and pieces.

The ring above it is a flange I had laser cut. Actually i had six cut, 1 each for the headers, 1 for each collector, and 1 for each of the 4 into 1 side pipe assembles.
This is so I can split the collector off the header and mount the side pipes to at a later date.

The 2 flanges will have V-band clamp rings welded to them for connecting together.

So basically, as you can see in the first pic, the blocks have alignment arrows.
Where the arrows align, the blocks are curved in 1 continuous arc plane, Where they don't align is the point of a change in the arc plane, so I marked this point with a marker pen. on the changed plane then separate at the mark and cut the component from the matching radius mandrel bent pipe.

VoilĂ  !

Here you can see the 2 bends tacked together in the same orientation as the model.

You can also see the marker pen on the join at the change in arc plane.

Eventually, you end up with this.

I have never done this before, and I'm really happy with the result.

Next step was too remove the pipes and weld the joins, before reassembling to the flanges again for final welding.

After tacking it all up, remove the header and mounted to a spare LS1 head to keep it from warping when I welded it all up.

In this pic, you can see I've flapped and filed out the MIG welds on the tubes for a smooth flowing look.

Test fitting the collector again before final welding.

Mig welded up all the flanges while clamped to the spare head.

All done except for O2 bungs and V-band clamp flange on the CAT outlet.

A view from underneath.

Next is to model up the left bank and do it all again.