Exhaust Collector Issue, Need Suggestions
 

So I picked up a Rotary Engineering exhaust header for my 6-Port 13B at the RX7 BBQ we had this weekend and was looking it over. Its a bit heavy and I love how thick the pipes are, its pretty nicely bent and made.

Unfortunately it did not come with a collector, but I was given the gasket and flange to make my own. No biggie, nothing half an hour in the shop can't fix. But the problem I am facing is this:

I've gone ahead and searched the forum and while there are plenty or good header length discussions; I did not find any real data on what the collector length and diameter should be. I was thinking of going with a roughly 6" section that combines and ends with 2.5 or 3" diameter.

I don't really want to ruin the gains that the header will give me so I was just curious what a good collector shape/size would be. :dunno:

A good collected size is 2.5". A good angle is 30°. Or if you're measuring perpendicular, it would be 70°. I modified my chop saw for just this task, to cut a very sharp angle so I end up with two pipes that converge at 30° like the RB collected headers.

As for a good length, yeah 6" sounds fine.

Do you think I'd run into any issues if I just went with a 3" Exhaust? From what i read it doesn't detract from the performance that much and I'd like to have it there for when I decide to turbo so I don't have to build a new exhaust system ya know?

I used to believe in 2" until I found out how small it was. By small I mean how quickly it ran out of breath at high RPM. So 3" is probably ok. I'm going to run a 3" system in my FB pretty soon.

i run 3"... I'd say collect at 2.5 and expand to 3" with a megaphone or cone.right at the collector
kinda like this
http://www.racingbeat.com/photos/16119.jpg

Thanks guys, I'm going to go ahead and draw up some ideas and look around for piping. I'll post a picture of the header and collector later.

Okay, So I found some piping that will work to collect with but I am having a hard time trying to figure out how I'm going to be taking these 1.25" (I think) pipes and expanding to 3". I'd rather make my own adapter but I want it to flow properly, unfortunately I cannot find out any information on how to actually create this section of the collector. Any ideas?

So here's the update on the collector! I managed to finish it and it actually came out rather well! Though I could have done better with my welds... but I was in a rush and didn't set the machine properly. :scratch:

Here's a few pictures showing the start of the project and the finish of it:
The bits and parts before-

http://i230.photobucket.com/albums/e...pawn67/1-2.jpg
http://i230.photobucket.com/albums/e...pawn67/2-2.jpg

Here's a picture of the primary tubes, I decided to continue with the thick walled primaries that the headers were made with:

http://i230.photobucket.com/albums/e...pawn67/4-1.jpg
http://i230.photobucket.com/albums/e...pawn67/6-1.jpg

Here's a picture of the modification I did to the 3" pipe for it to fit around the two primary tubes. Interestingly enough when you squish the tube into a 2" tall oval it makes the ends roughly 3.75" wide, give or take a hundredth or two. The two pipes together are 4" so if I grind down the thickness of the wall of the two pipes which gave me a roughly acute angle, a few welds later and some sandblasting later we have the finished product!

http://i230.photobucket.com/albums/e...awn67/10-1.jpg
http://i230.photobucket.com/albums/e...pawn67/8-1.jpg

And that's that! The only thing left for me to do is weld some press in studs onto the flange and then paint it in VHT FlameProof header paint again.

nice work!

Thanks! Now I just need to get the 3" piping and a 3" catalytic converter and a 3" muffler and hangers... oh and gaskets... :rolleyes:

3" without a turbo's gonna be loud as hell. I'd get the biggest pre-silencer I can find. Exhaust volume increases with pipe diameter.

You'll want as many mufflers as will fit. I just picked up two 3" RB presilencers and their 3" universal muffler. I'm wondering whether I'll be able to run it out of breath with the Camden on a streetported 13B. I hope it will be quiet enough.

The two presilencers will be inline. The "large" one in the cat location and the "medium" one in front of the rearend. I figure they were designed for a rotary so they should work better than anything else, right? Then over the rearend and into the universal muffler.

So far the exhausts have been way too small for the Camdens so I'm hoping that going overboard will solve the tendency to run out of breath at like 5 grand I've been experiencing. Hopefully my low end isn't killed off in the process.

I'll need to make a collector maybe similar to yours. I'll see what I come up with.

What are your exhaust plans? Which type of muffler? How thick of pipe?

Well Jeff, since I am just running a 13B N/A and I'm not going to be really trying to push the motor to its limits I think I can just use the normal thickness from the collector down, the header and collector primaries are made of what looks like 1/8" steel so they should be more than adequate for heat dissipation.

Unfortunately, I am not sure what I am doing for mufflers, I plan on running a 3" Catalytic converter and then most likely will try to run a pre-silencer and muffler.

Worst case scenario I will run a removable section of piping that restricts the tube diameter down to 2.5" for a length...


Keep in mind the only reason I am running a 3" system with my stock S4 13B is because later down the road I plan on running a turbo engine and don't want to replace all the cats, mufflers, and piping because it was a smaller diameter even when the system still works you know?

3" with the turbo isnt bad, na can be.

ive never done a 3" system with a cat, but we found this http://racingbeat.com/resultset.asp?PartNumber=16425P in the middle with any thing else in the rear works great on a turbo, or NA

Hey Mike, isn't this the same presilencer without the pipes? I got one. http://www.racingbeat.com/resultset....rtnumber=16434

I also got the medium version. http://www.racingbeat.com/resultset....rtnumber=16435

There should be enough room in the cat location for the large presilencer. I'm hoping there is also enough room for the medium one right before the rearend. This location is where RB's dual pipe street strip center section has its rear presilencer which fits nicely. We're talking 4" high x 6" wide. The medium presilencer measures in at 6.25" Wide x 4.875" High. Think it'll fit? The width puts one eighth of an inch extra width on each side, so no problem there. The height kind of worries me a little. That's almost 5" tall.

And lastly I got RB's universal 3" muffler. http://www.racingbeat.com/resultset....rtNumber=16030

Would you recommend these RB products to DemonSpawn67 or will they end up too loud?

Like DemonSpawn67, I'm planning something bigger in the future so I want my exhaust to be ready.

DemonSpawn67 I just noticed something about your collector. It collects directly to 3". I was told that you actually want to collect to 2.5" first then expand out to 3" through a megaphone style 6" long length of pipe (where 12" length = 1" in diameter increase). This gives the pulses a chance to first collect then expand along a gentle path.

The way your collector is set up, the pulses travel at high velocity down the 2" primary and then encounter an instant expansion chamber slowing velocty way down and hurting performance. Or I could be wrong. hyper4mance2k and rotarygod should see this thread and correct me if I'm wrong.

Hmm... now that you mention it. I was hoping that the fact that the pipes end up flat and sort of expand into a circle from an oval would give a similar effect, but I have no real design data for the collector, it was just designed to adapt the header to the 3" piping LOL.

paul, it looks awesome :) lets just hope it works well

it lost the first one.... um so yeah plenty of room, but you have to have a couple slight bends to get more toward the middle of the car, because the floor is not flat.

RB mufflers are quieter than anything else, and they are also heavier duty. we put a generic muffler in the FC race car, and we broke it every event. it just couldn't handle that kind of a pounding. the RB one, which was used, lasted 2 years before we melted it.

What the hell is this catalytic converter you speak of?..
3" NA sounds like this...
http://www.youtube.com/watch?v=U0vbPTuvCzs
http://www.youtube.com/watch?v=-jGFVon0Fc0
http://www.youtube.com/watch?v=MdmIgmxvjuc
This is how I feel and many others, but my exhasut which does work well is designed just like this one. Except the merge pipes were cut and welded together. kinda like this
http://racecarfab.co.nz/colweld.jpg
Once I finish building my BP I will redo my exhaust once again...

I wish I could have TIGed mine, but I am so out of practice with TIG it'd look worse than these mig welds... :(

Looks good, great work!

^Yes that's almost exactly how I'm doing mine. Two pipes cut at a steep angle to be at 30° when joined. Then output to 2.5" and expand along a 6" length to 3".