DIY Exhaust for a rotary

[MikeLMR]

Having just built an exhaust on the rally car project for next to nothing (scrap from auto exhaust places) I\'m starting to think what I\'m going to do about the exhaust on the 323.

Now I want to keep it fairly quiet as a loud exhaust just attracts the wrong kind of attention. Any ideas ? we are thinking of making our own silencer with stainless wool packing and perhaps doubling the exhaust back through the box twice (think like a U bend but inside the silencer)

Any ideas/experince (from N/A cars of course)

[antnicuk]

I just bought 2 nearly new scooby exhaust silencers from ebay for £20 each.  It will be quiet and you know its good enough for 250 hp minimum, and it has nice twin exit tails

[OLSKOOLROTAR]

Hi Mike,
           Speak to Era he\'s repacked a few exhausts in his time.

Jase

[travellinbob]

Do you have any photos of the scooby silencers that you bought off e-bay? I am in the same position as Mike so am interested in any advice people might be able to give.
 cheers, michael.

[Carl]

The rotary needs thick wall tubing especially on the headers or it will just fall apart.
The boxes really should have stainless wool in them as glassfibre just get\'s burnt away after a few miles.
On full throttle imagine the headers glowing bright orange and it gives you some idea of what you are up against.
Regards
Carl

[antnicuk]

they are certainly very thick and heavy,  very similar to a stock FD box.  things are a little cooler at the back end

[travellinbob]

Aaaah, I actually looked at these in my quest for exhaust stuff for the moggy. What will you be using them on? is it mazda stuff or another project.?
 Ideally I would love to have twin pipes running to just before the diff then a single pipe over the diff to a large-ish staraight through muffler. In ozz( and I know there was no science involed) we used to run the smallest \'truck\' muffler we could get as it was usually straight through and 3 inches in and out.

[MikeLMR]

decent quality pipe seems real hard to find in mild steel, even truck systems are stainless these days. The headers I have are nice and thick and about 4 feet long with no merge so I might be able to use some of our "free" exhaust pipe to make up the rest of the system, its pretty thickwalled, probably 2.5mm. I think it came off a big diesel Audi or similar. I do need to find a good 2-1 merge though.

If we were to make or modify another silencer what design is best ? straight through ?, baffled or A N Other ?

[mullins]

If we were to make or modify another silencer what design is best ? straight through ?, baffled or A N Other ?

Straight through is best - packed with as much stainless steel wool as you can fit! I used one with an "S" bend in it to get an MOT once on my old 3 but it really sapped the power compared to the 2.5" straight through one. Heavy walled tubing is obviously quieter too but then you have the weight problem. If you run a twin system they\'re usually quieter than a single and you can stagger a couple of long resonators down near the diff which all helps.

[MikeLMR]

whats a resonator and how do they work ?

[Carl]

Resonators are straight through presilencers.They take some of the edge off the noise before going through the main silencer at the back.
To give you an idea,on Dave Nixons race car,he has 2 headers that run to the back axle,each with 2 presilencers ( 4 in total) and then the headers join up into a collector with the big back box after.
That runs about 104DB.
Regards
Carl

[kev-yorks]

decent quality pipe seems real hard to find in mild steel, even truck systems are stainless these days. The headers I have are nice and thick and about 4 feet long with no merge so I might be able to use some of our "free" exhaust pipe to make up the rest of the system, its pretty thickwalled, probably 2.5mm. I think it came off a big diesel Audi or similar. I do need to find a good 2-1 merge though.

If we were to make or modify another silencer what design is best ? straight through ?, baffled or A N Other ?

Mike have you got any truck supplies near you deal with TTC (truck and trailor components) they have some mild pipe in there book not sure on sizes though i\'ll have a look in the book tomorrow and get back to you they also do a few bends in the same sizes. If i\'ll of known before the weekend i have a spare book sat on the desk at work but its a bit heavy for posting.
Kevin

[MikeLMR]

I\'ll look them up Kev, sounds good. Its nice to find an industrial supplier of bits n bobs.

Crikey Carl thats a bit loud, how much of that is down to the porting though ? I guess with the standard ports and the exhaust diffusers in place my 323 will be a little quieter ?

Its going to be good fun finding out what works anyway if its wrong the first time we\'ll cut it off and redo it ... I don\'t think I ever make somthing correct the 1st time !

[Ray]

Hi Mike,

104db  :rollin
That\'s quiet for a bridgy, it takes a bit of skill with gently building up the revs to keep it that low... the worst I\'ve seen it tested was a few years back at Pembrey when it hit 119db, but the noise scutineer didn\'t really care because it was Truck racing at the same meeting. I can\'t imagine how loud the early race cars must have been with straight through systems and megaphones.

However on a street port noise is a lot more controllable, my RX-4 is 92db at 4500rpm, that\'s running a Janspeed manifold into a 2 inch system, with 2 pre-silencers and Rotechnics rear box, not ideal for maximum power but ok for a standard engine. I\'ve got an old Janspeed manifold lying about somewhere if you want it?

Ray

[kev-yorks]

Mike TTC do exhausts starting at 2inch dia upwards 1.6mm gauge tube in both mild and aluminiumized mild they also do flex in the same diameters. The bends are 90 degree only in the same sizes. If i remember i\'ll fetch the book home and scan the pages tomorrow for you.
Kevin