Just thinkin' out loud on a Friday afternoon...

Iamchappy's post about the swiss cheese heat exchangers reminded me of something that I mentally revisit from time-to-time. Has anyone considered making proper reproduction 914/6 heat exchangers, in either plain or stainless steel? I assume the tubing bending is no big deal (there are probably CNC tubing benders out that that can pump them out to spec pretty easily), but how good of a set of HEs would you have to cannibalize to make proper molds for the clamshell parts?

Skip

The reason I have been looking to purchase stock ones is that I haven't heard anything good about the aftermarket ones, I dont understand why they didn't make reproductions from the stock design.

money. or better, the lack of ...

John at SSI looked into making those some 10+ years ago and decided against it. the market is way too small (3300 cars made, maybe 1000 left, if that) and the upfront tooling costs did not justify the effort.

the cost would simply be way too high, the asking price would have to be out of most peoples price range. just not a part that makes any sense, economically ...
Andy

But how many 914 6 conversions are out there and growing.

914 owners are notoriously cheap, especially the ones that do the conversions ( ) ...

if you want to sell those at a decent price, how many do you have to sell total just to recoup the tooling and r&d costs?

think about it ...

and SSI already has all the equipment and knowledge. still, he just didn't see a big enough market, and i tend to agree with him ...
Andy

Repro? Please, how about new and improved

I checked into this about ten years ago. The factory tooling was scrapped, if you can imagine that! I have another possible solution, but it needs more work.

Biggest problem is the economics of the situation. Low volume, high cost. How many guys do you know that would plunk down $1600 or so???

How about a simple kit, 2-4 pieces, to wrap around and existing header like bursch or the other one thats flat at the collector. Maybe????

Natta on that. That's how you get killed by carbon monoxide! All Porsche heat exchanger exhaust systems have tubing that's stainless, not a high grade stainless on the earlier cars mind you, but it is stainless. Newer air cooled Porsches have a very high grade stainless. In addition there are no weld joints inside the heat collectors. A few people got killed by CO1 poisioning back in the mid 60's from some of the early style heat exhangers and that's why.

Also from my experience Bursch headers suck anyway.

That doesnt make sense, Perry. If you set the system up correctly; force air into the HE boxes from a clean space, then there is no way for CO to get into your system unless you suck air or draw air from the wrong place. That is why we draw air form the engine side of the tin, and not the under/exhaust side.

I think that doing clam shells that fit over existing headers is a great idea (been discussing it with someone reacently), but the main problem is that not every one has the same type of headers. This woudl make productiona PITA. The only way to solve that problem is to have the supplier buy the headers themselves and then fabricate the boxes onto them. This keeps production costs and effort down so prices could follow. Theoretically this would keep a set of exchangers to under $1000 a set.

Or, you could build the whole darn thing from scratch and improve it over the original design. This only remains feasable so long as produciton cost can be kept down. The main problems wiht the current set ups are price and utility. They cost too much, way to friggen much IMHO, and do not work that well. the originals work best according to all of those that I have talked to, but they are serious coin usually and still are not stainless.

Untill "someone" makes a good functioning, stainless, inexpensive set there will not be a good alternative, IMHO.

Fear not, though, there are forces at work in this very direction

I was looking into these same alternatives as I needed some heat for my 914-6 conversion. Went as far as purchasing a gas heater to try to hook up into the heater tubes, but never totally trusted the gas fired heaters.

Finally, I settled for a used set of factory 914-6 heat exchangers that had been patched on the outer envelopes, then had them Jet-Hot coated to try to minimize further corrosion. Somebody had a new set on EBay a while back, and they went for $3000. In retrospect, probably not a bad deal for the purchaser.

My mechanic is also a certified airplane mechanic, and very strongly suggested getting a CO detector if you're using older heat exchangers. They are cards wih a little green dot that turns black if exposed to CO. I guess that this is a problem in small planes, as they can get exhaust header leaks, and often use gas fired heaters.

Though John Daniels of SSI decided against producing them, it sure would be a beautiful project if he would ever reconsider. Better than spending $1800 on a set that don't really work or fit well.

George, you touch on another good point about the CO hazard that I didnt address above. Yes, the exhaust tube is running through the HE box, and yes a breach of the tubes integrity would cause a leak of exhaust gas into the heated air stream that positive pressure would not keep out. This is not such a concern with stainless steel pipes, however. The old pipes are old tech and sub standard given todays materials and tools. If people with stock /4 and /6 HEs are not dying left and right (or at all as far as I have ever known) from CO poisoning, then why would an upgraded set with heartier materials be any more of a risk factor? The old ones have lasted for many years, the boxes rot first due to being thinner and more exposed, the positive pressure keeps CO from gaining access to the air stream throught he rotted holes. The concept is sound so long as you take precautions to maintain the exhaust gas within the tube and not the box. SS tubing would give such a gaurantee, so I see no need for a CO meter or concern of such agents in the cabin at all via the E/C system.
I am still waiting to hear of any good counter argument to such.

Not much of a concern for new tubes, etc. However, many of us are now using some used (ie. corroded/patched/etc.) HEs. If you've seen any of the older ones, the tubes do corrode, so could possibly leak exhaust gasses into the heat exchanger envelope. Since you can't see the integrety of the exhaust pipe on the inside of the outer sheetmetal envelope, I think a CO monitoring card is a good idea for the older exchangers. I actually went as far as using an endoscope to view the units from the inside before bolting them up.

Since the monitoring cards are cheap ($5-8/each), it seems like cheap insurance. Luckily, Porsche never put any welds inside the exchanger envelopes, and the outer sheetmetal has a radiused flange around the tubes and it is not welded to them, there should not be any reoccurance of the original 911 exchanger problems.

Yes, I do get a bit paranoid on things such as this! Be Safe!

I get what you are putting down, George. I have a ratty pair of OE HEs for my /6 and they do look like something that was on the ocean floor. How about getting a battery powered CO meter at the Home Depot? You could mount it in a way so it will sample the air coming in.

Sounds like a good idea, maybe put it under the dash by the heater vents. You could also hear it at night. I'll have to look to see what they have available.

I've seen low mileage factory h/e's that look like you both describe, and I believe it is in part due to the original forming process.

As I stated in my prior post; the exhaust tubing for the factory h/e's is not mild steel, even on the four cylinder boxes. Haven't you wondered why the shells turn to swiss cheese paper and yet the tubes still look pretty good??? Haven't you wondered why the shells aren't welded to the tubes? Granted the tubing isn't 304 stainless. It's not got enough nickel in it to make it anti magnetic either, but it's a low grade of stainless.

The problem starts trying to find someone that can form seamless stainless tubing.

Primary reason the aftermarket fabricated stainless h/e's don't work so well is because the collector is really small, and that's because the h/e's are fabricated using premade bends and straight tubing. So there isn't much of an area to enclose that doesn't have weld seams. You can't put a weld seam inside the heat collector.

Years ago in Germany you could purchase new shells for the four cylinder h/e's. I don't know if those are still available or not.

I have done some homework on this.

Is it just a snug fit or is there some sort of "glue" between the shells and the tubes?

S

I started to look into manufacturing replacement heat exchangers for the 4's a few months ago. Found a supplier of stainless steel tube in
304, 304L, 316, 316L, 316 Ti, 321, ASTM A-276 and in metric sizes.

The sheet steel is even easier to get and I think I have a way of forming the clam shells.

Once I figure out the end flanges all I need is a spool of stainless wire and a better welder.

Pretty simple shape, why not cast a form in sand, then hammer out shells on the form? Never done it, but it seems it would be the way to go

You've got to use seamless tubing. And then you've got to bend it. That's the touble. Making smooth kink/wrinkle free bends in seamless stainless tubing is a whole deal on it's own, trust me.

Fixing the problem of the winkles is easy.

I have the flanges figured out now.

I've always wondered about winkles myself.

Wrinkles are natures way of giving you tan lines at the nudest colony

The flanges are necessary as you don't want to weld the outer envelope to the tube, and you want a tight joint. The factory ones also had tabs on the envelope that would attach to the engine case or exhaust stud to keep them from rattling and driving you crazy. Really a nice, neat design.

I imagine that if someone could program the tube specs into a computerized tube bender, the outer envelopes could be fabricated and the exchangers manufactured, but it's not as simple a process as one might think. Even welding stainless is a royal PITA.

Re: Welding Stainless

I have a buddy that works at a place that makes guess what.....heat exchangers......well compleat heating/cooling units actually. These are the big commercial units that are found on top of buildings and when I say big I mean really big. Some I have seen are as big as a small house. They use tons of stainless a year fabricating the stainless heat exchangers that go into them. They have the right equipment and people who are used to working with stainless so if I have any problems in that area I have go to people in place.

I'd like to see some of the tubing when you get it bent.

I've got a friend here with a stainless fabrication business. They have a pressure rolling die to emboss sheet stainless, and he's said he can help me with the collectors (envelopes as George calls them).

The factory design for the exhaust is actually pretty good. The 3.0 215 hp engine that everyone reads about in Bruce Anderson's book, with the back dated exahust is a 914-6 exhaust.

My plan was to duplicate the factory system, with a little improvement on getting the primary tubes a little closer to equal length.

Please let me know if you get anywhere with this Bruce. I can probably help with the collector part of the deal. In a few months that is.

I wonder who will get a set done first It is good to see so much interest in solving a worthy problem.

How about a "boxey" style Racer Chris makes for his headers??? The shape doesn't necessarily have to match the exhaust or look pretty just functional. Just a thought and yes I already asked Chris if he ever looked into making these for "stock" exhaust systems......He just told me no, maybe I was just

My plan was to start with the 4's first. I figure there are 15,000-20,000 of those still around compared to 1,500-2,000 6's left. This is a future project that I have been working on. Next yr before I start anything on it.
Thanks for the offer on the collector part Perry. I'll be in touch.

I wouldn't even consider doing the four cylinder h/e's. Take my word, SSI will make more and the old ones won't ever die anyway. Just my .02. Also, how many four cylinder guys would pay what it's really worth??? Seriously, go to the right crowd of buyers. You'll sell four cylinder sets as long as they are $300 a set.

i wouldn't bet on it.

john seems very happy to be out of the 914 HE biz ...
Andy

I would agree that the 914-6 exchangers are the market to go for. There are many people doing the conversions from -4s, and these are not cheap projects. Most people would be interested in heat if it was somewhat reasonable priced. The $1800 price for a set doesn't seem to be the sticking point for the currently available ones, it's that they don't fit or heat very well.

Best of Luck on your project, I hope it becomes reality.

Then perhaps Dansk.

BTW, I want that book Andy!!

Why bother making them when these are available:

<a href="http://photobucket.com/" target="_blank"><img src="http://i102.photobucket.com/albums/m96/pipsqueek_84/your-head-is-tiny.gif" border="0" alt="Photobucket - Video and Image Hosting"></a>

Maybe this will work better:
http://www.ghlmotorsports.com/Merchant2/me...gory_Code=PH-NT

I have a set of the original 914/6 HE's. They are practically new. If anyone is interested, let me know. I also have a set of SS 914/4 HE's. dcafro@snet.net

I also tried the gas heater. I never could bring myself to cutting holes in the firewall to run it under the gas tank, or to move the tank. There was no room in the engine compartment either. So, I have a new Eberspatcher heater sitting in the parts bin.

I eventually put a 12 volt hair dryer in the dash for defrosters. Worked wekk the few times I actually needed it.