This is another pain in the butt part of scratch building maybe even worse then retracts.
If you are into scale scratch building most likely sooner or later you will have to make or get someone to make for you a one off header and box.
I have made a few and none were first off successes mostly they fall apart on the first few flights and need improving.
I have found that you can run a new header and box on the ground for testing and it all goes great but as soon as its in the air the extra vibrations and stresses tear it apart.
My latest effort has been for an old 80 inch span Mick Reeves Hurricane i made 15 years ago that i had flown the nuts of, this aircraft goes back to the time of John Piggot some of you may remember him, the Gerry shed has a small brass plaque on the center support pole in his memory he was the spotter for the first flight and that was even before the heavy model requirements that are now in force.I flew it so much it became fuel soaked and i got bored with it so its been hanging up for many years in my work-shop.So now i have resurrected it.
It started life all those years ago with a 120 Enya 4 stroke and no retracts.
Now i wanted retracts and retro fitting retracts into a 15 year old foam wing is not recommended for anyone that wants to stay sane, but nowadays you must have retracts, so in they went a painful job with more then a fair share of swear words.
The exhaust header was next.
From my box of Aluminum bits and pieces i pulled a tube and a flat, i cut the tube at an acute angle and used the soft Ally braising rods you can buy to braise them.
I tried cutting,bending and braising an ally tube to fit into this header for the bend back to the exhaust box but the direct blast out from the engine was to much for the soft braising used and it fell apart on the first fire up from the engine. So next i used a 1/2 inch copper plumbing bend, attaching it into the ally tube on the header i fastened this with 3 countersunk bolts and JB weld. the exit from the engine is a rectangle and faired this with the JB weld into the round copper pipe.
The JB weld has been taking a direct blast from the exhaust for about 20 engine runs so far and is holding up no problem, great stuff.
Next cut, bent and silver soldered a copper tube and put a pressure nipple in for the fuel tank pressure.
Next i used a heater hose from an auto shop, there are so many shapes and sizes of hoses to pick from you are sure to find what you want.
I find heater hose much better then silicone tube its a hell of a lot cheaper and lasts longer and you can get it with built in bends.
Next i cut a normal aero spray can open and took the end with the nozzle off, the hole left fits tight with a 1 1/4 inch heater tube and is a force fit.
Next the exhaust exit tube was put through the side of the can the tube goes all the way to the bottom and has many holes drilled into it this works to break up the sound wave and reduce the noise like a baffle. This exhaust exit tube had a bolt through it attaching it to the back of the can, i have had these exhaust tubes come loose to often so with the bolt through no chance.
Next where the tube exits the can i have used JB Weld and a clamp no chance of that coming loose as well.
Next i shortened the spray can and rejoined it with silver solder.
You can get an estimate on the size of the exhaust box and the diameter of the exhaust exit tube from the standard muffler supplied with your engine, if you keep your box and exhaust exit tube to about the same size it should be fine these sizes are worked out by the engine manufacture and should be approximately the same.
I have had 8 flights with this third version i have built and its held up so far.
Also you need to have like i have a vibration section built in between the engine and can as you can see i am using a rubber heating hose.If you build it solid i can guarantee it will break.

One more shot of complete exhaust out of the aircraft.

15 years ago....um..I got one of the first large model permits for my Fokker DVII for Dan Reece's first Air Pageant in 1982....I think that was about 27 years ago.

John Piggot was in the pageant and wore HUGE handlebar mostouche.....a lot of fun....

Hi Dave, Did that rubber heating hose stand the test of time? Is it an auto heater hose.
Cheers
Stan

hi Stan i dropped it into the bushes,i have had a problem with dead sticks and after 4-5 it got me in the wrong place and in it went. but its back together again and ready for further testing, with the recurring dead-sticks i changed just about everything i could get my hands on to try and cure it.
Started with plumbing and re- plumbed all the way to the tank pick up with large diameter tubing, then repositioned the tank pressure nipple, then smaller exhaust box outlet tube, then smaller exhaust box after about 20 flights i found out what it was in the back garden while testing (The neighbors love me) the bloody throttle servo had an intermittent fault where it would go back to tick-over or lower when it felt like it and killed the engine.
When i stuffed it in the bushes the tank pressure nipple broke off and while re- soldering with silver solder i melted the Aluminum header so had to start again and make a new header,knowledge gained is that silver solder melts at a higher temperature then Aluminum.
I tested it all last Friday in the garden and it all held together with a new throttle servo of course.
The car heater tubing has held up so far there is not much tubing exposed to hot engine gas i have kept that to a minimum i have changed it with the new header and i found that the old one tubing had thinned out where it was over the copper tubing and clamped but well usable.
Dave.

Hi Stan as an after thought i lent Colin a book on the War time test Pilot for Supermarine and i understand he has passed it onto you could you bring it to the Xmas party next Saturday.Thanks Dave.

Well i can say with confidence that i have sorted all the problems out with the constant dead sticks i had been having after about 35 flights and 15 dead sticks and a few trips into the bush, i pulled the OS 160 out ( i should have done it before ) to try and find the problem with bench running, i had changed everything i could think off except its nappy to try and find the problem.
After about 30 minuets on the bench with a perfect engine set up i found that the head gasket had blown.
In the first pics. you can see the exhaust marks next to the tooth pick.
I an guessing that the head gasket blew due to the engine overheating in my cowl set up.
I spoke to Brian Winch and he said that he was doing an article on making head gaskets, so being me after his explanation i had a go.
What i did was with a set of Staedtler drafting compasses i attached a scalpel blade to one end and used a coke tin stretched out and attached to a flat surface it takes a bit of practice but after a few go's i had a good gasket marked out with a deep etch.
I then took the aluminum coke tin and by bending back and forward carefully around the inside hole etch mark first, it cracked and out it popped and then carefully eased the ring out of the can.The idea is not to crease or scratch the new gasket.
I had about 5 attempts at the etching before i had one that was not marked or creased and its now been running in the OS160 for about 1 hour with no problems. Also in Brian's instructions he explained that the head would have to be ground flat onto the liner with some grinding paste, so i took the liner out and put some fine paste onto the Ally head and with some backward and forward twists against the hardened steel of the liner ground a smooth good surface you will know when its ready as it has a uniform flat Grey circle where the new gasket will fit, that took about 30 minutes and then i finished off with some Brasso, now i dont have to tell anyone that before putting all this back you must clean it very well and get all the grinding paste off i used petrol as it tends to stick very well.You will not damage the liner as its hardened steel rubbing against the ally head. The next 2 shots are of the liner with the blow marks and the nibbled gasket where the heat had burnt the edge.
CU in the pits Blackfingernail

As you can see from my previous post my set up in the cowl of the Hurricane was causing the OS 160 to overheat,so some modifications were called for.
First i will go through the changes that have been made to the exhaust from the pics you can see in the first post on this heading. The first 2 pics below are of how the exhaust looks now and i am happy to say at last it all works well i have just had 6 flights over the week-end and nothing fell of, broke or seized.
So to start with the Ally header that bolts onto the engine is new i had to make a new one as when i was silver soldering the copper pipe further up the exhaust the Ally melted, the lesson learned there is that ally melts before silver solder. Ally melts at about 5-600C.and so silver solder must be about 700C.
I am using corrugated steel tubing for the S bend, where it joins the can and the copper tubing the engine end, the join is sealed over with car heater hose this lasts much longer then the silicone that i have used in the past.
Where before the heater hose was fitted directly into the can i found the heat and vibration was causing wear around the outside of the heater hose and after a few flights it became loose and not gas tight.
So i fitted the can entry with an entry pipe so the heater hose can clamp directly onto the can entry pipe see the next 2 pics.This inlet pipe was attached with J.B.Weld and bolts.
I cannot say enough of how good J.B.Weld is. In one of the pics. of the complete exhaust you can see J.B.Weld on the outside of the Ally header where the copper pipe go's in, also the J.B.Weld is inside the header taking direct blasts from the exhaust gas, i am using J.B.Weld there to fair in the round copper pipe to the square ally header where it matches the exhaust stub on the OS engine, i have measured the temperature of the copper pipe where it meets the Ally header and it is over 200C on the outside so inside your guess is as good as mine.
I have also added another stinger on the can to try and clear the exhaust gases quicker.
If you look at pitts mufflers and enclosed exhausts in general you will see that very near to the engine exhaust stub you will find an expansion box, this is to enable the hot compressed exhaust to expand and hopefully go out the other end, if like my set up that is incorrect and added to the overheating problems the can/expansion box is 15cm.from the engine exhaust stub the hot gas has nowhere to go or takes time to get back to the can so a lot of the gas go's back into the engine and overheats the head.so as i have explained i added the second stinger.
Now to get more air over the engine i have remodeled the cowl and exhaust can cover see the next lot of shots.
The front on shot shows how i have reduced the front air intake area and lowered the top of the cowl to within 1/8 of an inch of the engine head this has the effect of forcing the air to go between the head fins thus high pressure cold air in, you can also see the many louvers along the bottom that causes low pressure turbulence so low pressure out so you have cold high pressure air in getting heated by the engine expanding and getting sucked out by the low pressure surrounding the louvers, basically a constant high speed stream of air going through from high pressure to low pressure, and it works.
I have also just to make sure where the exhaust pokes out of the cowl a small bit put a
louver in front of the pipe to create low pressure again and on the other side of the cowl cut 2 more small louvers.
Boy i wonder sometimes why i play with model aircraft.

More shots
Now i have run out of excuses not to finish the scale detail and repair all the bumps and bruises from the dead sticks and the bush walking that the aircraft enjoys.
So this is the easy part i know it all works now to spend time on trying to make it look like a 2C Hurricane.
One observation.
From past experience i have learnt , always to test my aircraft with the minimum of finishes on them just enough to fly, and this is a prime example of why.
There are many who spend hours on the finish before it flies good luck to them but gravity rules and then there is dear old Murphy always looking over your shoulder.
CU in the pits Blackfingernail