Modified heater boxes for better flow

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ostojo
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Modified heater boxes for better flow

Post by ostojo » Mon Aug 22, 2011 5:54 pm

I'm want to build a year round daily driver but we have cold winters here. I'm contemplating various engine combos for my build, somewhere between 1915 and 2275. The stock heater box bottleneck is killing my potential combos though.

Ideally I'd like a 1 1/2" or 1 5/8" exhaust system with the best heat possible. A gas heater to supplement is plan B but I haven't given up on heater boxes yet.

Yes I know you can buy performance heater boxes but I hear they put out little heat and are expensive. From what I've read most after-market other than the Dansk boxes are simply J-tubes in the box and don't have any fins. I can't seam to track down any 1 1/2"+ heater boxes with actual fins inside.

I have some ideas about how to modify stock boxes. I think I could make something better than just J-tubes for cheaper than the after-market setups by modifying a stock set.

I have searched extensively on the subject. I know other guys have already tried and I'd love to learn from their experiences. I've picked up bits of info here and there. This has been touched on many other threads. But despite searching I haven't found much good info/documentation. I did find this link:

http://www.cal-look.com/forum/cal-look- ... g-my-time/

So I'd really like to hear about any successful heater box mods you guys have done. What works? What doesn't? Do you know of any useful threads/documentation that I've missed? I'm more than happy to custom fabricate and weld something up but any advice from experience would be greatly appreciated. Thanks!

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Marc
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Re: Modified heater boxes for better flow

Post by Marc » Mon Aug 22, 2011 9:44 pm

I'm running the Dansk flanged 1½" from CIP1 on the 1915 in my daily-driver, they go for $300/pr + shipping when not on sale. After a few miles on the highway they put out pretty decent heat considering they're finless...a bigger engine, or even one with higher CR (mine's ~8¼:1) should be even better. It doesn't get all that cold here in Seattle though, so you may need more...I see a gas heater in your future.

My son's building a pair of 1-5/8 (finless) boxes similar to the ones in the article you cited...yes, it's a lot of work.
One could probably band-saw the guts of a stock box apart lengthwise and then contour the inside to fit snugly around the J-tube, we considered doing that but as I said winters are fairly mild here...
Last edited by Marc on Tue Aug 23, 2011 7:15 am, edited 1 time in total.

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sideshow
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Re: Modified heater boxes for better flow

Post by sideshow » Mon Aug 22, 2011 11:39 pm

Well I can tell you for certain that adding 24 feet of copper tubing to the inside of the common 1 1/2 heater box does nothing for interior heat and is a total pain in the ass.
Image
Personally I was amazed, I thought I was really onto something.
Yeah some may call it overkill, but you can't have too much overkill.

ostojo
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Re: Modified heater boxes for better flow

Post by ostojo » Tue Aug 23, 2011 11:28 am

sideshow wrote:Well I can tell you for certain that adding 24 feet of copper tubing to the inside of the common 1 1/2 heater box does nothing for interior heat and is a total pain in the ass.
Image
Personally I was amazed, I thought I was really onto something.
Too bad that didn't work out. The idea of working in copper makes sense. I'm guessing that the conduction between the J-tube and copper was the weak link. Like how if you don't put thermal paste between a CPU and heat sink you'll burn up your CPU because the conduction suffers. Thanks for sharing that though.

Stray Catalyst
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Re: Modified heater boxes for better flow

Post by Stray Catalyst » Tue Aug 23, 2011 11:34 am

Caveat - I haven't tried this.

Any reason not to weld flanges to the outside of a J tube, and add a sheet metal enclosure around it? Welded flanges should give better heat conduction than the copper tube, as the heat will transfer from the tube to the flanges, which convect the heat. Steel isn't as good a conductor as aluminum (the original heater box inner material) or copper, but this should be something you can do. You'd mentioned that you could weld and fabricate, so it might be an option. Straight flanges wouldn't be too difficult, but you could cork-screw them if you're looking for more efficient heat extraction (and a nervous breakdown from the difficulty, of course!)

Stray

ostojo
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Re: Modified heater boxes for better flow

Post by ostojo » Tue Aug 23, 2011 12:42 pm

Well this thread is getting a lot of views but not a lot of replies. I'm wondering if that just means that not many people have actually modifying their heater boxes.

Anyways I'm exploring some options of how to make better flowing heater boxes. I'm a mechanical engineer and want to do some thermal and fluid analysis on these potential designs.

I'm missing some critical information that I'm hoping somebody might either know or be able to measure. I don't have a running engine accessible to me right now. Please let me know if you can shed light on any of the following:

- the temperature range of the exhaust gases I could expect to see coming through the heater box

- the rate of air flow through the J-tubes

- the rate of air flowing around the J-tubes and into the heater channels

These will all obviously vary with different setups and engine speeds. I'm just trying to get a ballpark range to work with to see how effective various modifications could be over a given range.

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Marc
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Re: Modified heater boxes for better flow

Post by Marc » Tue Aug 23, 2011 1:01 pm

Most folks are less concerned with flow than with heat output; the finless J-tube-in-can boxes flow more than stock, it's just not all that hot. In both my and my son's daily drivers we have electric booster fans in place of the driver's side "muffler" under the back seat, which are useful for improved defroster output on rainy days. They're wired via relays controlled by the alternator warning lamp wire, so if the engine stalls they shut off automatically. The fans used were never intended to pump hot air, but they've held up so far (knock wood).
Another tactic is to divorce the heaterbox cold-air supply from the engine and use bilge fans to push air through them...there are kits on the market that use these to recycle cabin air back through the heaterboxes, they're effective but you have to acknowledge the risk of concentrating CO. Also, it's best to maintain some airflow through the heaterboxes when the heat is turned off.
Look at the stock setup on a Type IV, or a `72-up bus. They use a relay-controlled electric fan to push air through the boxes, but there's also air available from the fan housing through little check-valve flaps to keep the boxes cooled when the electric fan isn't running. If you want to engineer the ultimate heater system, that would be the setup to emulate in my opinion. Make it elegant enough and there'd probably be a market for it.

I'm not a mechanical engineer, but it seems intuitive to me that when the only source of air is the engine's cooling fan, any improvement in heater box flow would imply a reduction in the air available for engine cooling...

Bugfuel
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Re: Modified heater boxes for better flow

Post by Bugfuel » Tue Aug 23, 2011 2:20 pm

a gas heater still works much better and the air smells better. Produces instant heat without having to wait for the engine to warm up. You can run it ewith the engine off even. Hands down winner. Older models can be found for a hundred bucks or less. You don't have to buy a new one. ($$$$)

AND you don't need to use rotted out heater channels that leak and cool the air down.

And ass Marc already poointed out, you can use all fan driven air to cool the engine. Heater boxes need constant airflow through them which is away from engine cooling, even when you don't have cabin heat turned on.

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Marc
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Re: Modified heater boxes for better flow

Post by Marc » Tue Aug 23, 2011 2:47 pm

My son had an idea that seems worth pursuing. He wants to take a pair of L-Jet Beetle heater boxes and cap off one inlet so they can be used in place of carb'ed boxes. The header'll need to be modified to line up with the flanges so it won't be equal-length, but we've done similar modifications in the past and the power didn't seem to suffer.

Gas heaters aren't nearly as common in the states so you'll probably pay more for a complete/functional one, especially a 12V. I have a South Wind that IIRC cost me $150, along with a few extra parts. Downside is that it's 6V, so I'll have to do some riggin' to use it.
`74 Things and Type IVs had stock 12V Eberspacher heaters, so there's a chance of finding one of those cheap - but there'll be some modification necessary to fit one in a Beetle. The BN/4s that were optional in buses are quite a bit different in configuration.

http://www.thesamba.com/vw/classifieds/ ... id=1120595
http://www.thesamba.com/vw/classifieds/ ... id=1175003
http://www.thesamba.com/vw/classifieds/ ... p?id=48885

Bugfuel
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Re: Modified heater boxes for better flow

Post by Bugfuel » Tue Aug 23, 2011 3:50 pm

you could maybe look for gas heaters in some boating forums or classifieds. They are used on boats too. If all you can find is diesel models, you'll need a separate fuel tank for it of course. And water-only gas heaters could be used if you fabricated a heater system using a watercooled car heater core... :)

MFG/brand names to look for:

Eberspacher
Espar
Southwind
Stewart Warner
Webasto
Bacho

The last two being more common in Europe (With Eberspacher, which has been common in the US too)

Just sayin. :)

Ol'fogasaurus
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Re: Modified heater boxes for better flow

Post by Ol'fogasaurus » Tue Aug 23, 2011 7:12 pm

I contacted Marc about this (now that we are playing what if/tongue in cheek) but maybe one of those new small catalytic converters in a modified heater box or two may work for some real heat.

Lee

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turbobaja
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Re: Modified heater boxes for better flow

Post by turbobaja » Wed Aug 24, 2011 10:11 am

I ended up making my own heater boxes a few years ago for a variety of reasons, but they haven't been tested yet. I wanted just a little more heat than the regular J-tube aftermarket heater boxes had to offer, and my 091 trans swap in a bug (moves the engine ~1" to pass side) made it much more tricky to route the heater box outlets. So I built my own "boxes" around an aftermarket header and welded ribs down the length of the exhaust pipe to try and radiate a little more heat into the air flow.

Ribs inside look similar the the ones you can see here with holes along their length to increase surface area a little.

Image

I'm also using electric blowers to recirculate cabin air rather than taking any air from the shroud. The fans blow through the heater boxes rather than sucking from them like the common aftermarket "booster" kits do, so the air the fans are dealing with is much cooler that what's coming straight from the heater boxes.

One feature my boxes lack is flow through them when I don't want heat in the cabin (like Marc refered to with the stock boxes). I'm not too worried about it with my setup because there really isn't any large heat sink to soak heat up into the heads w/o flow. The top of the header pipe is actually exposed along the top of my heater boxses, so the welded ribs are only along the bottom portion. I don't expect these heater boxes will radiate any more heat up into the heads than the header would by itself, but I'll be watching my temps closely to make sure they don't cause any heat soak issues.

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Lingwendil
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Re: Modified heater boxes for better flow

Post by Lingwendil » Thu Aug 25, 2011 10:43 pm

Wow, nice clean job! Can't wait to see how they hold up and the amount of heat they give!

Breaker
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Re: Modified heater boxes for better flow

Post by Breaker » Sat Sep 03, 2011 8:47 am

I am also faced with this, I need 1 1/2" exhaust, for 35 mm exhaust valve, but I also need heat.

What is frustrating, is that in a best case scenario, say, you could take apart stock heater boxes, make a mold of the alloy casting bit, re-mold it in sand, insert your whatever size J-tube, and re-cast alluminium around it, and it STILL wouldn't heat as well, because the surface area of the stock boxes is so much greater than any J-tube could ever be.....

I wonder, though, that bit in the stock heater box where the surface area is so much greater doesn't seem to be much of an impediment to flow... the restriction seems to be the pipes leading in and out.

Could one cut the heater boxes where that transition is made, sacrificing a bit of finning, and then weld in larger-diameter entry and exit pipes? Just a thought... I'm sure I'll come accross some really crappy stock ones to cut up some day..

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turbobaja
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Re: Modified heater boxes for better flow

Post by turbobaja » Sat Sep 03, 2011 9:31 am

I bet if someone were to build their own header and box the entire thing, clear up to the collector flange inside the "heater box", it wouldn't require any fins or heat sinks to make a good bit of heat. The problem with the stock heater boxes is they only used part of the exhaust system to make it's heat = restricted, uneven exhaust flow. Why not scavenge heat from the entire header?
Karl

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