Pursuit of the "perfect" Boxer exhaust

I have a Nouvalari Sport exhaust on my '83 BBi. It's okay, but I know the car can sound better. My theory is that I prefer the sound of a quad exhaust (12-into-4); which has a late 60s / early 70s Le Mans sound (eg, 512 S/M and the '69 917) – and of course, the BBLM. This is essentially the opposite of what most modern exhausts do (lots of collectors, cross-overs, etc.).

As far as I know, the only 12-into-4 Boxer exhaust is the Borla. Swap out the mufflers for something more aggressive (eg cherry bombs), and you're in business. Unfortunately, Borla discontinued their Boxer exhaust ~15 years ago, and it seems no amount of bribery will convince them to make me a one-off.

So my plan is to create an exhaust from scratch, similar to the Borla, but more modular (easier to swap out mufflers). I removed the Nouvalari, and (after the obligatory open headers run), I started 3D scanning.

I haven't decided if I will 3D print the entire thing out of stainless steel, or only the connecting parts (eg, brackets via SendCutSend, 3D printed inlets and tips, etc). I am designing it to go either way. The cost is not that different if using good quality steel, mandrel bends, and high quality tig welding (not just some sloppy "Exhausts-R-Us" shop).

My first test is essentially straight pipes. This is mostly an experiment to make sure things line up, experiment with the 3D printed stainless steel, etc.. The sound will likely be the same as the open headers.

Once the "straight pipe" experiment is finished, I'll make a decision on 3D printing the whole thing, or having it fab'd. If I opt for 3D printing, I may tweak the design to have more organic bends.

I'm still working on the designs, but figured I'd share work-in-progress. Both are using 2" diameter tubes, 1.5mm thick stainless steel, with a consistent 50mm bend radius, and 2.5" tips. The muffler section is 18" long. It's mocked up using Vibrant glasspack styled resonators, but the idea is that a lot of different mufflers / resonators could be tested with minimal welding (if any).

"Straight Pipes"
Image Unavailable, Please Login

Borla-Inspired Quad Exhaust
Image Unavailable, Please Login

Thoughts? Am I missing anything? Anyone have a Borla exhaust they want to part with and spare me the exercise?

 

Just a thought...Maybe find out how many systems Borla would have to make to get back into the BB game? 12? 25? 200? etc Then you might get takers on F-Chat for a group buy? But of course, Borla might say, regardless of quantity, "No way!"

One other concept (As it's soo easy to spend someone else's money). Make it out of titanium. Light and very corrosion resistant. But extremely difficult to fabricate and weld.

 

a one of a kind to make and money does not matter everything is possible

 

I could try that. When I spoke to them, they didn't seem at all interested in bringing it back or making a small run. Not quite "no way!", but pretty close. Maybe I could try higher up the chain.

That would be very interesting. 3D printed titanium is currently 10x the price of stainless steel though (Inconel is 30x!). There just aren't enough shops overseas printing large pieces in these metals yet. It's rapidly changing though. I bet in a year or so the price would be half. A super lightweight exhaust would be awesome, but I think I'd rather spend that money on other projects.

 

Hi,
Your concept is currently mounted on my car. I bought a Borla system for my 512bbi from a local Boxer owner that had it stored in his basement collecting dust. Its a nice design being modular with standard EMPI 3 bolt flanges that can be easily modified to your taste. I wanted an aggresive tone so when I did my first engine out major, I sourced (4) 12" SS glasspacks and 409SS tubing see photo on page 1 https://www.ferrarichat.com/forum/threads/boxer-major-in-a-not-so-mega-garage.173325/ I had a friend with an exhaust shop weld the orginal flanges, tubing, and glasspacks together. The modified Borla system is still mounted on the car. If I ever desire to do a concours again, the system comes off easily and I can remount the original Euro system in just a few hours.

Here's how it sounds:

Hand held camera so it's a bit shakey

Go to 4:08 on the below video. from a previous Italian Village Chicago event

 

After sleuthing through all the exhaust threads discussing Bell, Borla, Nouvalari, Larini, Tubi, etc., it was your videos that triggered the "that's it!" moment; which led me down the path of trying to figure out what it was about your setup that I liked – which I think is the 12-into-4 configuration. So yeah, your exhaust is essentially the inspiration for this design.

It'd be great if I could find an existing Borla system to modify, but it seems I'll need to create one from scratch if I want to go the quad exhaust route.

 

I agree. Locating a 512bb/bbi Borla system would be a challenge. I do wonder if the patterns for the system could be purchased from Borla since they arent interested in reproducing the system by an alternate exaust system manufacturer?

 

A good exhaust shop could fabricate what you want out of 304 polished SS. They do it all the time for hot rods

 

I found a biz on the internet that fabs up exhaust systems from Ti tubing. Not 3D printed. For a surgical project we made some printed Ti tubing shapes that were very impressive, but they were small, like 5-6mm Ø X a couple of inches long and around $90 a piece in quantity of ~10.

The raw material for Ti tubing ~ 1.75" diameter was very pricey per foot.

I'm happy with my custom stainless Borla system. But if I attacked the project with price-no-object approach. I like the newer car Ti systems.

 

After doing a little more research, it looks like some of the pre-muffler parts are outside the bounds of most Ti printing machines; which makes it much more expensive. So a few strategic cuts that are convenient to weld can make a big difference in cost. If you do that, Ti is about 4x the price of SS (vs 10x without breaking the larger parts up).

The nice thing about this design is that I can have it fabricating or printed. I can also have it printed in SS, and then swap out components for Ti – or do a hybrid (SS pre-mufflers, Ti post-mufflers).

Speaking of the design, I made some small tweaks. I used standard bend radiuses (2", 2.5" and 3"). The piping is all 2" ID; which I think is slightly larger than what is used on the original Borla design. I also made it so the mufflers can be swapped out (I think the original design has the muffler outlets welded on).

Attached is the current design.

Image Unavailable, Please Login

While working on the CAD for the full design, I ordered four 2" ID cherry-bombs, and 3D printed side exit exhaust pipes out of ASA. They can only handle a few minutes of exhaust temps; which was just long enough for me to confirm this is the sound I'm going for. This experiment was equal amounts of ghetto and awesome, but it did the job. I much prefer this sound over the Nouvalari I had installed – particularly at idle. My plan is to make the full version in plastic (ASA) first, make sure everything fits, and then have it printed in metal (SS or Ti – I haven't decided).

Image Unavailable, Please Login

 

Some of the glass packs are very restrictive, do some research on brands, even that they are straight thru. Titanium is difficult to weld, any the only advantage is less weight. If you use polished 304SS it turns gold brown after heat. Ask me how I know, I have built a few SS exhausts.

 

david, if you could weld SS and also aluminum then it is no magic to weld also titanium. important is to clean right before welding ( TIG ) with pure alcohol or acetone

 

Why choose Titanium

 

Mostly for the weight savings. It does sound a little different too, but that wouldn't be main reason (for me, at least).

 

much less weight

 

Unless race car, not worth the cost.

 

Ti turns a very pretty blue.

 

RE: Ti

Anybody know how it ages for exhaust use? It copes with higher temps than aluminum, but it has limits. I'm thinking about a header right next to the head.

 

The Countach Ansa mufflers are essentially like what you have in mind there. Not really a muffler, sort of a dampening device I suppose

 

It's very inert. I think it's more corrosion resistant than 316SS without weight penalty. It's a total bear to work with. Forming, cutting, welding is pretty specialized. Also, its thermal properties are interesting. Poor conductor and allows exhaust to remain hotter. This speeds up exhaust flow which affects tuning slightly. Pushing a little closer to an adiabatic engine. (Think of header wrap without the wrap.)

And... good enough for F1.


My aging concern comes from the low miles that goes on F1 cars, and exhaust gets really hot.

I found some 'light reading' on the subject: Effects of thermal cycling and microstructure on the fatigue crack propagation in forged titanium–aluminide alloys under thermomechanical fatigue conditions - ScienceDirect

 

Stainless steel 304 is also a poor conductor of heat. 400 series SS has some carbon in it, 17-4 can be heat treated for higher strength. But not to good for exhaust. F1, cost is no object.

 

A little update.

I've been tweaking the design and 3D printing the exhaust parts in plastic for mockups. I've shortened the pipes as much as possible, while using as large of diameter tube as possible, and as large of a bend radius as possible – without having the parts touching or in danger of radiating too much heat near body parts, factoring in O2 sensors (my car is EFI), etc.. The 3D scan is invaluable in this process.

Image Unavailable, Please Login

I've got it mostly there. The manifold attachment area is necked down to 1.75" OD to make it easier to install hardware. After 50mm, it goes up to 2" OD throughout. I then have it expanding to a 2.5" OD megaphone on the exits with a 3mm rolled edge. I'm currently testing the exits / tips to see if I like the look, but it's inspired by some of the white BBLM exhausts I've seen with rolled edges.

Image Unavailable, Please Login

I also some of the parts being made that I know aren't changing. Eg, the "brackets" that everything hangs off of are being cut via SendCutSend in stainless, then powder coated black. I designed the muffler flanges to incorporate 2" length of straight tubing, so I can easily swap mufflers using straight tubing from Vibrant (no welding necessary). The "flanges" are being printed in stainless via CraftCloud.

Image Unavailable, Please Login Image Unavailable, Please Login

My plan is to A/B a few options:

- Straight pipes (control group, for science!)
- Cherry bomb glasspacks (the real thing).
- Porter "shorties". Similar to cherry bombs, but have a lower growl due to a coil instead of perforations and steel packing vs fiberglass.

I was able to shorten all of the tubing to make them 3D printable in SS or Ti without breaking into smaller parts, so once I am sure those parts are fully designed, I'll have them printed in stainless steel. Then it's just bolting it together. Not sure how I plan on treating the parts. Eg, cerakote, powder coat, "white lightning" ceramic coat, etc.. I've never 3D printed SS before, so I think I'll see how it looks with glass blasted before making a decision.

If all goes well, I should have a custom 3D printed exhaust in a few weeks.

 

I don't know much about 3D printing! Isn't this going to be very expensive?

 

I've only done metal printing a few times, and only aluminum (I printed custom intake manifolds for my EFI/ITB conversion). This is my first time printing SS.

My guess is that the cost is similar to a custom made exhaust. Eg, good quality stainless, mandrel bends / pie cuts, purged tig welds, etc..

Right now, the price for the printed parts is coming in at $3,000 USD via CraftCloud. The SendCutSend brackets (both the shock mount and hanging brackets) came in at $100 (with black powder coating). Factor in another $400 for the cheapo cherry bombs, lap joint clamps, and gaskets. So $3,500 – which is less than I paid for the Nouvalari exhaust it's replacing.

Assuming this all goes well and works, I still think I would prefer to have purchased an off-the-shelf exhaust from Borla, but that's not an option. Also, I don't know of any exhausts for the Boxer that are this modular. With this setup, I can swap out mufflers and experiment with different sounds. I can swap out the post-muffler sections for Titanium if I want to reduce weight, etc..

 

Okay cool! But research glass packs, some are straight thru but very restrictive.