TheSamba.com :: View topic - W. B. X-awst!

Sun Dec 23, 2007 7:47 pm

Guess I'll put up the official W. B. X-awst! progress thread, to let everyone have a look at the development of the tuned WBX exhaust and a brief glipse into the tubularly-twisted mind of tencent. I've been having fun with this one.

My blue motor is still on the stand (when will somebody BUY the damn thing?!!) so it makes a handy clothes-horse for the mockup. Here the last runner is suggested in welding rod, while the others have already been taped-together from sections of 3"-radius mandrel-bent tubing U's in 1.5" mild steel:

Here's the final cuts tack-welded together and aligned with the 2.5" collector:

The collector is temporarily mounted to a clamp bracket so it remains as a fixed reference.

The runners all come off and the sections are carefully measured in sequence so I have the data to make copies of the system.

From the straight collector body, which will be shortened a bit, 2.5" tubing will turn the corner and tuck up into the heat-shielded muffler cavity where the muffler and/or cat will mount to it. The collector will also terminate at a tuned length. I'm still researching which muffler will be best for this system without a cat as I'll use it. For use with a cat the selection of muffler will be a bit less important.

The tubing butt-joints will be flame-welded and the flanges brazed on for better strength. This prototype will just get painted so I can get it on the car for testing, but I'm loooking into ceramic or high-temp powder coating as final finishes. Stainless versions may be in the works but I think the cost might be astronomical.

Sun Dec 23, 2007 8:01 pm

That's AWESOME man, good job! I love the bag of snakes look it has to it.

Sun Dec 23, 2007 8:01 pm

So, where's the Turbo bolt on? :D

Andrew

Sun Dec 23, 2007 8:17 pm

I guess my wife didn't order that motor for me for christmas like I thought she was going to... That exhaust system looks really nice. I can't wait to see it powder coated and hear the performance results. Keep up the fine craftsmanship.

Sun Dec 23, 2007 9:09 pm

Yeah. Just, yeah.

Mon Dec 24, 2007 2:29 am

what are the gains expected to be? are you planning on dyno'ing before and after? I'd be curious as to the results.

Looks like good work. And DAMN, thats a lotta tubing!

Mon Dec 24, 2007 8:58 am

It looks very nice, many beers must have been consumed to get to that point. The turbo would fit nicely after the collector, just have to work out the oil supply/return problem. If you can't find a ceramic coating place, we have one that does the flame coating for the Twin Otter landing gear for us. Let me know

Mon Dec 24, 2007 9:06 am

Bless you tencent.

Mon Dec 24, 2007 9:10 am

I'm in.

Mon Dec 24, 2007 9:30 am

loogy wrote: That's AWESOME man, good job! I love the bag of snakes look it has to it.

Bag o' snakes, indeed! It was quite the reptile-wrestling match getting the same-length 3 and 4 runners squeezed into such a small space while the 1 and 2 lean back and stretch their snakey legs. But I'm pretty sure they're all within and inch in length, probably even closer by my running calculations. Once the joints are sealed up, I'll fill each one with water or sand or something and see how close they are in volume, since measuring actual centerline length is near impossible with any real accuracy.

The wbx presents some real challenges because of the motor support beam, and on the left is the water pump inlet pipe and oil filter. I had mocked up a version at first where everything ended on the right side, lots more room there, but then I could already hear the complaints about the muffler tip being on the left of the car. Ultimately, keeping the O2 sensor on the left side so its wiring wouldn't have to be extended swayed my decision to work up a new design with collector on the left, so the cat and muffler cross to the right and exit under the rear corner like the OEM exhaust does.

That doesn't mean you'll be able to use your stock cat and muffler with this header system, oh no, my pretties. I considered it for awhile, but it imposed too many impractical limits on the design, and what would be the point? Put a fine breathing set of pipes on and then choke it off with a restrictive small-bore cat and muff? The collector will terminate at a quarter-wave tune, at 2.5" OD, so for those who have to use a cat, the cat will act as the first resonance chamber and effectively be the end of the tuned section. What muffler you use after that will not be very important as long as it flows at least 350cfm.

But without a cat, using a straight-thru muff and tailpipe to reach a certain length in total will act as a longer half-wave collector, giving a better resonant scavenging effect on the whole. So I've set it up to be tuned in either case, provided you follow my recommendations on installation of the final components, or specify which you prefer and I'll supply them welded and ready to go.

Good quality all-stainless cats and muffs can be had for less than $200 total. Things get cheaper when you wander out of the OEM world.

The runners are 1.5" OD tubing, which is 1 3/8" ID. Actually, the ideal ID for the best gas velocity would have been smaller, just above 1 1/4, but the exhaust ports are 1 3/8", so 1.5" tubing makes a perfect port-match. Stepping to a larger ID at the port outlet can be a positive, but stepping down at all would be very bad, so the heads dictated the tubing size. The 2.5" collector size is dictated by the total runner sectional area. Lengths of both are set to have the most powerful wave scavenging at 4700rpm, which is halfway between two wave-peaks in the resonance of the stock intake. This will help to make a broad torque area in the mid-high rpm range.

The tuning on this set is built around the CB 2254 cam I'm using, but has enough bandwidth to also work well with the stock MV cam. Ultimately I want to have a custom cam ground right between the two, so I won't have to redesign the exhaust again to work well with that. The 2254 has amazing low-end torque but lays down by the high 3k's, so this is designed to wake up that upper rpm range where the high valve overlap is actually costing power. With strong exhaust scavenging the high overlap should turn into an asset.

I can't wait to find out. There is a dyno in 'Burque at Flat-Four Performance, so I'd love to do a before and after. But my shop's two hours away so I know I'll just bolt it up since I won't want to wait. I can't guess a figure for what kind of power improvement this might give, but if I've done my work right it should be decent.

Quote: So, where's the Turbo bolt on?

I had originally thought to do a one-size-fits-all setup that would accomodate a turbine, but after studying this I think a whole different system should be built. Wave-tuning is pretty much moot with a turbine at the end of the line. A turbo system would just have larger runners with more direct paths, equal length being fairly unimportant from what I understand; the focus is on free-flow and volume. Where the turbine is mounted seems to be a bigger consideration than anyting else, and intake design will have a lot to say about that. So that's another project.

Not many beers but a whole lotta wine and other flammable comestibles went down the pipe in the time it took to cook this thing up, but no animals were deliberately harmed in the process.

Mon Dec 24, 2007 11:55 am

pritty sweet work !

just curious...did you ever concider a symetrical dual muff setup ?

Mon Dec 24, 2007 3:00 pm

Me Like !

Mon Dec 24, 2007 6:36 pm

Crankey wrote: pritty sweet work !

just curious...did you ever concider a symetrical dual muff setup ?

I wanted a 4into1. There is a dual-muff aicooled setup with a center collector, but I never cared for that design , plus it would be pretty tough to fit that in the muff attic behind the wbx.

Mon Dec 24, 2007 10:05 pm

Very nice, TC! No wonder I couldn't envision how you were going to get equal length runners for all four cylinders on a header that terminates to one side. What are you planning on running for a muffler? I've been looking at the 6" round Magnaflow mufflers for my application.

At any rate, top notch work as expected. As you know I would be anxious to purchase a copy when you get to that point. I have a very special WBX engine build to share with everyone here at the start of January and a suitable header is still the missing link.

David

Mon Dec 24, 2007 11:08 pm

Very nice!

Tue Dec 25, 2007 8:58 am

Thanks for the props, guys. I just hope my welding skills are up to your praise.

Quote: "Scientists discover the world that exists, engineers create the world that never was." - Theodore Von Karmen

He should have added "and backyard tinkerers build the shit they wish they could buy."

David, There's loads of muffs that would work, I'm sure. I'm looking at a Borla or one of the Dynomax UltraFlows. Both are oval straight-thrus. The Borla is all SS at a reasonable price. I don't think SS matters so much on the header pipes but I do think it's worth while for the muff, due to condensate settling inside the casing. That seems to be what rots out muffs the quickest.

I won't be using a cat so a 2.5" straight-thru with the right-length tailpipe extension will become an extension of the collector tuned length. I'll try to position the collector end so round muffs can be fitted, too. It has to be anyway for cats to work there. The oval muffs with offset fittings let me drop the tailpipe to a lower height than the collector end so it can slip out beneath the bumper.

Those two brands rate well as best I can learn for excellent flow but good damping for a straight-thru. Unfortunately most of the testing and comparison has been done as pairs on V8 exhausts, so it's a bit of a crapshoot sound-wise, although they all flow more than is needed so won't affect peformance provided the sound is nice (or tolerable!).

There's not a lot of independent comparisons of muffs to be found, mostly just anecdotal preferences, but here's a case where they did a line-up of a range of products. The Borla did very well here for sound, as did the Dynomax UF:

http://www.ls1tech.com/forums/showthread.php?t=119518

Here's an Aussie comparo. The Dynomax is marketed as Genie down under, and was their favorite straight-thru. The Dynomax Super Turbo was a favorite for a tri-flow design:

http://www.autospeed.com/cms/A_0383/article.html?popularArticle

It's basically a bit of a crapshoot on the muffler; they only way you'll know how it sounds on a system is to try it out.

As I said, for people who will use their cat, the cat acts as a resonating chamber and effectively terminates the tuned length of pipe, so what you put downstream of that for a muff doesn't matter so long as it flows high enough, and most do, and you like the sound. I can't tell in my Summit Racing catalog if the Magnaflow 6" round is a straight-thru or baffled design. It would only matter if you don't plan on using a cat first. The cats of course should be 2.5" inlet, so the stock one is too small, but the muff could even step down to 2" after that provided flow is at least 350cfm. I would keep it all 2.5" though. There's no real difference in cost once you're comparing aftermarket stuff.

Or, if you use no cat, you can use a baffled muff right at the collector flange, and extend the tailpipe to exit out the right or wherever. That way the muff acts as the terminal resonating chamber at the right tuned length. There's a couple inches leeway here.

I'll have more soon as I weld everything up. I'll get a better idea of the sale price of a copy of this as I go along. The cost for coating them will be a big factor. I may offer that as an optional thing. I'll definitely offer it with and without muff and cat as a package deal. That way I can do the fab on universal-fit muffs and cats so buyers don't need to get any welding done locally, just bolt it all up!

Thu Dec 27, 2007 7:40 am

Awesome, but that is what we have come to expect from you now.

Thu Dec 27, 2007 7:59 am

"Muffs and Cats"? Is that hip lingo for girls and boys? :lol:

Andrew

Thu Dec 27, 2007 8:15 am

Now you're with it, baby. You can grind with my crowd this weekend; all the muffs and cats are collecting for a tubular barbecubular.

RCB sez you can tell if your van's a boy or a girl by where it leaks. I'm guessing he means boys leak out the front, what what?

Thu Dec 27, 2007 10:16 am

Time for some more progress pics. Got all the runners individually welded up:

I like how easily the tubing sections go together; with the right heat level, the butt-welds flow together with no need for filler. I only have to use any filler when I burn thru if the cut joints aren't close enough and too much heat flows thru the gap.

The crappy spots in the welds are where the MIG tacks were. Lotsa slag in a MIG weld with flux-core, and it doesn't integrate well with the weld pool, as I torch-weld the butt joints.

The port flanges get brazed on for greater strength without distortion:

I love brazing. It's so useful for joining pieces of different thicknesses and even different metals entirely.

Then mock it all back up again for the final joining at the collector. The trickiest operation so far was how to make up a spike in the middle of the collector, to eliminate the high turbulence that would occur at this critical point if you were to just put a flat star cutout there.

I cut long 10degree wedges from some scrap tube, but couldn't figure out a way to jig them to weld the little pyramid first on the bench. Finally I used my dial-indicator magic arm to hold each one for a tack weld into place on the pipe.

Then they were bent to the center, and the tips tacked together. Used a very small flame to join each edge and end up with a sealed pyramid.

Looks ugly, but with a half-round file, rotary burr and maybe some edge-work with a highspeed wheel, it'll clean up to a nice, smooth sharpedge spike. Hopefully. That's my job this morning.

Made up a hoop of flat steel to back up the collector area, so the collector welds won't have so much strain on them. This will get brazed into place once the collector is welded on.

That's it so far.