Dave.Martin2008

So the other day I decided to take on a little project... Build my own header, I ended up using 2 1/2" piping for the tubes and 1/2" mild steel for the header plate, and a 2 3/4" collector pipe. once I got the pipes bent into shape and welded in place, I then used Hi Temp header paint to coat the outside and inside, cured it and then wrapped it with Thermo Tec header wrap. now its drying in the sun and I will get it silicone coated this afternoon. I will get pictures up of my set up and give you the exact bend specs also in case anyone else wants to build one... in all this header wrapped cost me around $80.00 and should give me some great flow for my 12A... more info to come.

Customisbetter

2.5" for the primaries? That's pretty huge but I guess this won't be a dyno car so it won't matter.

Dave.Martin2008

2.5 O.D. and that's the size of the exhaust ports on the engine as well as the stock exhaust manifold. So my thought was just to keep it all the same untill the collector and that is brought down 2.75 O.D. should I have used a smaller tube for the header?

diabolical1

iTrader: (3)

$80 ????? awesome!

got any photos?

Dave.Martin2008

Yep Ill have photos this afternoon... and I will give a parts breakdown and cost...

Dave.Martin2008

OK here are the photos everyone wanted to see...

rotorholic

iTrader: (53)

I tested different piping sizes a long time ago, The stock Mazda manifold will make more power than a 2.5 pipe diameter header (Don't ask why, I don't even know)

Cookboy

iTrader: (10)

Good looking work, Dave. Rotorholic, I'd guess velocity, but that's just a cooks guess.

Dave.Martin2008

Piping cost was... $10.00
Steel plate was... $12.50
header wrap was... $40.00
over coat paint was... $15.00
=$77.50

pipes had a large 90 deg. bend in each and the lower pipe had a small bend in it to make the pipes meet up nicely at the end. I used a 2.75" small section and expanded it to fit over top of the joining pipe.
steel plate was 10" X 6" and 0.5" thick mild steel. I used a stock manifold to make a template and then Plasma cut the shape. there as a 2.25" insert pipe 1" long that runs from the plate into the tubes to help with lining everything up and I just welded it in solid on both ends to beef up the steel in that hot spot. I still need to clean up the port holes so they are a nice round hole, and then put a coat of hi temp paint on the wrap to seal it all up. once that's done it will go back on the manifold plain and get smoothed out and be installed. once installed I am going to run a 2.75" exhaust system to a fart can at the rear with a 1.5" pre silencer.

I hope this information is useful and any questions or concerns are welcome... I am always looking to learn more.. thanks for reading. I will have more to come in the next few steps of this little project.

diabolical1

iTrader: (3)

likes:
1. the bends off the engine flange
2. the fact that you actually put this thing together from scratch
3. the anti-reversion feature (if I understood what you said about the 2.25" pipe inside the 2.5" main pipes

constructive criticisms:
1. the 2.5" diameter (I think it would be fine if you weren't running inserts)
2. the length

is that 1.5" presilencer a typo???

I can't tell you how much respect I have for people that can weld. i'm going to get off my *** and try my hand at one very soon. I actually ordered some bends a few days ago and I've had a welder sitting down in the corner for about 2 months now.

Dave.Martin2008

Leigth I am not sure I could get it any shorter. Over all its under 8.5" out and under 2' long. And 11" tall for "box" dimensions... all together my piping ony comes past the stock manifold on the outlet end by 3" and that's because I made such a elongated junction with the two pipes joining together... this however is my first build of this kind, I have done exhaust work before but never built my own header. I hope I can build a resonator pipe for this also, I am still figuring the mathmatical equation for getting the correct leigth and tubular size to cancel out the drone noise with out comprimising exhaust flow. I will post that once I get it done also in this thread

Narfle

iTrader: (16)

Did you cut the plate with a plasma cutter? Could use some smoothing...
Nice project.

Dave.Martin2008

Yes it was cut with a plasma cutter... I did smooth the inside of the tube with my die grinder so those are nice and round now and then I recoated them with heat treatment if I get time tomorrow I will finish smoothing the edges of the outside for a cleaner look but funtionality is my main goal at this point because I would like to prepair to make a turbo header next for my other 12A build.

Dave.Martin2008

So the anti reversion pipes are not needed? Are they not needed on a rotary engine?

Dave.Martin2008

Has anyone had any experience with branch resonators? I am looking to quiet my car down a bit with out hurting performance and this seems to be the thing to do it but every forum I read says that you have to calculate it but all the calculators I am finding are for piston engines. I am trying to bring the db down from 70db so its not so loud in town driving. and that 70db is before I put the header on I almost don't want to put the header on until I figure out this branch resonator stuff.

diabolical1

iTrader: (3)

no. my concern was just THAT. that it's too short to make any power. however, reading your responses, I now gather that the point was simply to build cleanly within the confines of the space you had, not as a precursor to making power. you also mentioned this being a sort of dry run. so disregard what I said.


needed? by virtue of the fact that they are not commonplace, I would have to say no. the question is HOW effective are they when you have them?

Dave.Martin2008

ran it on the planer today its coming along nicely I think... I smoothed out the inside on the inlet to allow better flow.

Dave.Martin2008

I just called Racing Beat and there person told me that there header went back to 2" before the cat connector, mine is 4" away so my header is only 2" shorter than the professionally made headers. my question is how much is that going to affect the power I would like to create if any since they have a longer trailing pipe on there header.

I am hoping to install this later on today is the shop is not too busy... I have to move some stuff out of the alignment bay to get my car on the hoist in there.

Jeff20B

iTrader: (13)

Have you read about long primary exhaust and how it tends to make more power everywhere in the RPM range? Well, according to rotarygod it does. Go ahead and search for his writings on the subject

I recently built a couple of long primary exhausts and the difference compared with a short collected system is dramatic. More power everywhere and it sounds better (more character). It's louder too but if you use enough muffling it's fine.

There are some rules you need to follow. Don't go too large on the primaries. I think your pipes are too big. You want to keep velocity as high as possible while not choking but you also want a thickwall pipe (.120" like RB's) to reduce noise leakage because believe me that close to the engine, it will leak if it's not thickwall. The pipes will ring thanks tot he supersonic blasts that our peripheral exhaust ports make. Since your engine is a 12A, go with RB's 2" OD 1.75" ID pipe.

The length is important. According to RB, they say a long primary is best at 120" to 125" of length. That's pretty long for a 1st gen so knowing something about harmonics and frequencies, I'd say go for a half wave. That will be 60" to 62.5". The long primary I built for my REPU worked out to be about 61" so right within that range.

The collector is important. RB collects too small at 2" on their collected headers. This is too small to make decent power. I don't know what they were thinking. Oh, it was to maintain compatability with the rest of the stock exhaust. In other words, a compromise. However their long primary system (the so called "streetport exhaust") collects to 2.375" OD with a 2.25" ID. It's up above the rearend and pretty far back from the engine. This far back is fine as the gasses cool and contract. Infact the pipes feeding it transistion from the center section's same-as-header 2" OD 1.75" ID thickwall material to the muffler section's 1.75" 14 gauge material which has a 1.6" ID. This step down in size is actually very appropriate this far back from the engine.

Just a note RB's FC header collects at 2.5" with thickwall tube. It also has a 2.25" ID, being thickwall like it is. A long primary would make more power here too and RB sells one. Again the short collected header is designed to work with the stock exhaust if you also get their presilencer (the 2.5" FC one).

So do yourself a favor and read up on the subject as much as you can because it sounds like you're genuinely interested in rotary exhaust and willing to experiment. Your first several systems might suck as mine did, but that's how you learn. Heck my REPU's exhaust went through three major revisions and now it finally sounds perfect and should flow more than enough, even with a Camden.

ultimatejay

iTrader: (1)

Your not making any power because 2.5" is way too big and your primary pipes are way too short. This header would only work on a pport engine and the powerband would be extremely high and short.
Stick with a nice two inch diameter header with longer primary's and the most critical design is a nice merge collector.

Dave.Martin2008

Thanks everyone... going to think this through. I have the exaust system pulled off right now and that first one I made would not fit in with the pitman arm mounted in the car... note to self get a better tape messure or find a person that can read one. Second build in progress

Dave.Martin2008

Ordered new tubing today. 2-5' sectoins to build new primeries. Also you think an exhaust bender will have trouble making the bends I need being 11 gauge steel. Its going to be interesting. Also ordered a new base plate but this one will be clean and finish cut.

Customisbetter

I'd recommend looking at the headers at definedautoworks.com

They are making serious power with long primaries and standalone ECUs...

Dave.Martin2008

I did take a look at the website and wow they are proud of there headers... $850 proud.... you know how many headers I can mess up making before I get to that price point. I hope to get this right the next time.

ray green

iTrader: (14)

You rock Dave, nice work. You'll get a decent header out of this at a decent price, and the rest of us will understand headers better. Thanks!