| [ Total Views: 9394 | Total Replies: 37 | Thread Id: 90645 ] |
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 markd89
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| posted on May 26th, 2011 at 12:54 AM |
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Belly radiator -- Scoop or no-scoop?
Hi,
I'm working on a conversion of a 1Z TDI engine into a 78 Bus. I live in Los Angeles which has a relatively hot climate. I'd like to be able to drive
in 100*F heat without overheating.
I have an aluminum radiator with a core that's 13"x27" with dual 12" fans.
Ideally, I'd like to mount it without a scoop so I retain ground clearance, easier maintenance, less fabrication.
I realize that most here like Subaru's. The difference with the TDI is that it throws of less waste heat.
I know that I can mount dual radiators without a scoop and be fine. I know that I can run a scoop with the one radiator and be fine. The question is
whether I can run the one aluminum radiator without a scoop and be OK?
I'd appreciate any opinions.
Thanks!
Mark
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ElusiveStranger
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| posted on May 28th, 2011 at 09:49 AM |
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Have a little looksee over at VWKD
http://www.vwkd.co.uk/bb/viewtopic.php?t=16
Hellbus and EJ71van are running good setups on here, but there's not much info.
At the end of the day, scoop's the way to go. Belly mount - go the full width of the rails on the scoop. It costs you SFA in materials (in
comparison) to go full width.
Best design is to go for a blower fan mounted above the rad with the cool air flowing above, hot air going down.
I intend to go flat mount rad next time around, XJ40 size but with a hinged scoop. Why? Because I can't fit the surfboards under when camping 
HTH
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dlrecord
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| posted on June 1st, 2011 at 06:37 AM |
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Mark,
I just got my belly mounted radiator and Subie 2.2L on the road! I test drove it on a day picnic yesterday and am sorting through some cooling
questions. I do not have a scoop on mine. It sits between the rails on my Bay and has a slight half inch tilt from front to back (front down). It
has two 14" pusher fans and blows air down and out the back (obvioulsy)
We had it modestly loaded with 2 kids, a 110 pound dog and some picnic accessories, drove highways, biways, and gravel roads at elevation with some
sustained and steep mountain climbs. Totaled about 150 miles round trip. Ambient day temperature was probably in the low 70*F. Hottest reading I got
was 212*F. My fans were kicking on around 177*F, which I think is way too low (hence my cooling questions). So, take it for what its worth. I'll
keep more data on the radiator set up withouth a scoop but don't believe its necessary.
You can see more details on my blog if you're interested.
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General_Failure
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| posted on June 1st, 2011 at 07:00 AM |
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| Quote: | Originally
posted by dlrecord
Mark,
I just got my belly mounted radiator and Subie 2.2L on the road! I test drove it on a day picnic yesterday and am sorting through some cooling
questions. I do not have a scoop on mine. It sits between the rails on my Bay and has a slight half inch tilt from front to back (front down). It
has two 14" pusher fans and blows air down and out the back (obvioulsy)
We had it modestly loaded with 2 kids, a 110 pound dog and some picnic accessories, drove highways, biways, and gravel roads at elevation with some
sustained and steep mountain climbs. Totaled about 150 miles round trip. Ambient day temperature was probably in the low 70*F. Hottest reading I got
was 212*F. My fans were kicking on around 177*F, which I think is way too low (hence my cooling questions). So, take it for what its worth. I'll
keep more data on the radiator set up withouth a scoop but don't believe its necessary.
You can see more details on my blog if you're interested.
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I was just looking at your other post elsewhere. Glad I'm not the only person that does it.
edit: whoops where'd my content go. I've been wondering about the scoop too. To be honest if it were done right I think a plenum setup utilising the
Bernoulli principle would work even better, but I haven't seen anyone do that ...besides me when I had the brain fart and put my scoop on backwards.
If at first you don't succeed. Build, build again.
Vehicle: 1975 Special order delivery walkthrough panel based LCA pop-top camper. Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.
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dlrecord
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| posted on June 1st, 2011 at 07:29 AM |
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I was after the Bernouli effect with my set up! I figure I can always add a scoop or plenum to the set up later as I get real data on temperatures.
I have not blocked the sides along the frame rails or rear support to create the high pressure area...though I am not sure I actually need to as
is.
I'll keep driving it and see what my coolant readings say.
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markd89
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| posted on June 1st, 2011 at 07:51 AM |
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Thanks Dan. I've been watching your blog and your Samba thread too. I'm glad the cooling system is working nicely.
I ended up getting a smaller radiator and am most likely going to do a scoop. It's an experiment as the scoop itself is pretty small. 7"x15"
opening.
My bet is that it will work as the diesel doesn't create much waste heat. We'll see. I'll post when I have it built and of course when I'm all
assembled and running!
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ElusiveStranger
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| posted on June 1st, 2011 at 08:23 AM |
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177F (80C) is way too low for the fan
Stat's operating temp is 78C (172) - 82C (180)
Fan should kick in around 95 (203), but this is dependant on speed if using ECU control
With my setup I fully sealed the chassis/floor gaps etc so the scoop is pressurised
General_Failure "but I haven't seen anyone do that" - you've not looked very hard
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dlrecord
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| posted on June 1st, 2011 at 12:46 PM |
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Mark, keep us posted and snap some pics!
Thanks ES for the info on coolant temps. Confirmation is always good.
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General_Failure
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| posted on June 1st, 2011 at 01:35 PM |
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| Quote: | Originally
posted by ElusiveStranger
177F (80C) is way too low for the fan
Stat's operating temp is 78C (172) - 82C (180)
Fan should kick in around 95 (203), but this is dependant on speed if using ECU control
With my setup I fully sealed the chassis/floor gaps etc so the scoop is pressurised
General_Failure "but I haven't seen anyone do that" - you've not looked very hard
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Probably not 
you are talking about a relatively small entrance for the radiator so that and the position and surface area of the radiator creates some awesome
flow?
Once my setup is back together and registered I might do a test with the scoop the right way (ram) and backwards (plenum) to see which works better.
If at first you don't succeed. Build, build again.
Vehicle: 1975 Special order delivery walkthrough panel based LCA pop-top camper. Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.
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webwalker
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| posted on June 12th, 2011 at 12:56 AM |
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| Quote: | Originally
posted by ElusiveStranger
With my setup I fully sealed the chassis/floor gaps etc so the scoop is pressurised
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ES:
I saw old pictures of your install but haven't been able to find anything recently. Do you have a set of current pics? I have my own ideas of what
should (from a physics standpoint) work well for an NA EJ22 with Hx mounted between the frame rails of a 72+ bus. But I'm trying to suck up all of
the practical experience people who've gone before have had. I've watched dlrecord's build closely, and I'd love to hear more about yours. I'm
not looking for a Hx rig that can cool an SVX motor, just one that will let me drive a bus year round without ever thinking 'am I running too
hot?'
M
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Philadelphia, Pennsylvania, USA
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markd89
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| posted on June 12th, 2011 at 02:07 AM |
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Since I posted about using the scoop, I've changed my mind again #*!&@^
I mocked up the scoop with cardboard and it just looks like there's not a big enough opening to flow enough air. This is all very non-scientific --
i.e. what is "enough"?. The TDI doesn't produce as much waste heat as a gasoline engine, so it MIGHT have been OK.
Previously I had my mockup larger and I was concerned about the loss of ground clearance.
So now, I'm going the route of dual radiators. This is definitely more cooling than what's needed. I' have two new radiators which are replacements
for mid 80's VW's. They're 31" long including tanks. I'm going to put two fans only although four would fit. I just know this is already
overkill. Once I have something built, I'll post pics.
Part of my logic here is also cost. These radiators can be had for USD$70 each. The dual radiators is a proven setup from others. The cost is probably
less than one with the scoop.
Mark
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ElusiveStranger
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| posted on June 12th, 2011 at 12:57 PM |
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Webwalker: if you've had a pog on VWKD... nothing's changed. You don't say where you're from. Our air temp is approx -5 to + 30C
Scoop's the width of the frame rails, approx 5" below the rails. It's wide, well it'd be rude not too as it's free space. I did run a front
spoiler but it severely limits airflow to the rad
I don't understand what a "Hx" is - I'm a Pommie (ps - nice 1st post,
I'm in the Avionics industry. We were all stoodents once)
Mine's based on Hellbus's and EJ71's set up but with "hairydymaniccs" theory behind it. COR copied it Hot air *down*, not stagnating above.
Mark - simple rule of thumb... modern cars.... 1/3 rad size into the rad (well it's mostly solid) 1 times the rad outlet (the air's changed
density)
Post up some more info on what you're doing. We're not mind readers
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mactaylor
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| posted on June 12th, 2011 at 05:31 PM |
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what about a coupla naca style ducts on top of the rad with some fans to push thru. the idea being that you start with a smaller opening say 40% of
your rad size each then slowly open it out over the top of the rad into a thermo. just make sure your ducting keeps expanding in volume so it keeps
drawing as th pressure increases!
EVERLAST CONCRETE TANKS
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VinoDubber
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| posted on June 16th, 2011 at 10:23 AM |
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Just wondering if anyone has had a radiator with scoop but with suck through thermos with a shroud?
I have heard that these are 15% more efficient than blow through but not sure it this is only when mounted on the front.
[size=6]Not just a vehicle.. more a way of life[/size]
20% off wine for members, just email luke@patrickofcoonawarra.com
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ElusiveStranger
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| posted on June 17th, 2011 at 09:26 AM |
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| Quote: | Originally
posted by tocaciu
Just wondering if anyone has had a radiator with scoop but with suck through thermos with a shroud?
I have heard that these are 15% more efficient than blow through but not sure it this is only when mounted on the front.
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15% more efficient doesn't really mean much if you get the design/flow good enough for them to hardly come on in the first place (Yes a sucker's more efficient though)
I've seen a few scoops where the air inlet comes in below the rad. Fans are mounted above, this blasts the hot air up towards the floor - not a very
good design as it hits stagnant air/loading bay floor.
The stagnant air being caused by chassis rails/top hat sections etc
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markd89
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| posted on June 27th, 2011 at 06:57 AM |
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I've done some mockups..
I'd like your feedback, but I'm leaning towards building the mountings for two radiators but only using one radiator initially. I'm thinking with
the TDI's low waste heat I may be OK with one radiator. One radiator simplifies things -- 1 is less than 2 -- it also means I don't have to deal
with the air pocket between the radiators.
So since I'm laying groundwork for two radiators, all of the pics show that..
Here's was an idea. It didn't work because the connection between the two radiators was hitting the clutch cable, e-brake cables under the bus. It
would have worked, but the radiator would have been hanging low.
http://realityisreality.com/tdi/cooling/coolingdidnotfit.jpg
Next, the layout which did fit:
http://realityisreality.com/tdi/cooling/cooling-newlayout.jpg
I'm going to start with installing radiator#1 only, and add radiator#2 only if needed.
The annoying part is bleeding air from the connection between the two radiators. I'd plan to have a hose barb welded in to the pipe between the two
90 degree hoses. If anyone has any suggestions on how to decrease the vertical distance between the red lines, please let me know!
http://realityisreality.com/tdi/cooling/cooling-radiator-joining.jpg
Here's the clearance at the rear (about 10")
http://realityisreality.com/tdi/cooling/cooling-clearance-at-rear.jpg
I plan to tilt the radiator down at the front about 1" to encourage the air-bubbles to exit from the rear. So figure 1" less clearance at front.
http://realityisreality.com/tdi/cooling/cooling-clearance at front.jpg
Other specs... each radiator is 31" x 12". The core is 27" x 11.5".
I appreciate any comments and suggestions :-)
Mark
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boof2332
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| posted on July 2nd, 2011 at 04:50 PM |
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I have looked at cooling alot on the vw conversions...bus and bug... just remember it is the creation of a low pressure behind the radiator that draws
air throuh.....if air can flow directly behind it there will be no pressure drop and you will get hardly any flow....
That is why modern cars have the black plastic piece from the front bumper to the front suspension...when removed in a wrx the engine bay had more
pressure than the air hitting the scoop and flow was backward through the intercooler.
Easy to achieve, just have sides and a flat bottom that goes a couple of inches past the radiator.
Good Luck
Matt
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Joel
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| posted on July 6th, 2011 at 06:49 PM |
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Belly mounted radiators would work well in the city but not much chop out here on rural roads.
I called into the subi joint the other day and it was nice to see another subi powered vw up on the hoist, even if it was australias most roughest
EA81 converted kombi with a cooked engine.
I was looking at the radiator thinking no wonder this thing nuked the fins are completely caked with mud.
Till I realised thats the A/C condenser 
Granted thats the original dealer fitted A/C and probably never been cleaned since the car was new 36 years ago but slow travelling on dusty roads
especiallly with the fans running alot would pull heaps of dirt and crud in.
its a good example of how rads underneath can clog up if you don;t keep your eye on them.
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General_Failure
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| posted on July 7th, 2011 at 12:34 AM |
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I don't take the title? That's good.
If at first you don't succeed. Build, build again.
Vehicle: 1975 Special order delivery walkthrough panel based LCA pop-top camper. Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.
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markd89
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| posted on August 8th, 2011 at 12:35 PM |
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Here's the radiator setup.
These are two radiators which fit 80's VW diesels. They're each 31" x 13". Each core is 26.5" x 12.5". The inlet and outlet are the outside
connections.
Mounting is simple. There's a flat steel bar running beneath the radiators at the rear. At the front, a steel bar is also used but it's bent to give
the radiator a rake effect - lower at the front. I have long carriage bolts which attach the bars to the bus and which can be used to adjust the
height. Even in a worst case scenario, I seem to have over 9" of ground clearance which should be plenty.
The rubber hoses are Gates 21528. The U is made out of aluminum. Naturally it's 1.25" OD and I believe the bend is a 1.8" radius. For the bleed I
got parts from McMaster Carr. There's a 90 degree 1/8 NPT and then a 1/8 NPT to 1/4" barb fitting is screwed in with some teflon tape. I had a local
welder Heli-Arc the 90 degree fitting into the U tube.
The fans are Chinese from ebay. They're rated 1000 cfm in pull configuration. I reversed the blades and polarity to make them push. With 13.8v across
them, they seem to blow nicely. The fans mount with a zip-tie like arrangement through the core. I bought some improved mounts which came with little
springs. I think this is useful as the aluminum is going to deform a little and I still want the fans to be snug.
I'm using a temp sensor in one radiator to control a relay which switches the fans on and off. I actually wired in a second relay for two more fans
just in-case. I don't think they'll be needed.
There's a lot of seat of the pants science in judging what cooling is enough. I know Greenbuspilot from the Samba who has a water cooled VW engine.
He has a copper Chevy truck radiator which is less square inches than my double radiators. Another guy on the Samba has a custom aluminum radiator to
cool his Subaru. I have more square inches than him too. Gas puts out more waste heat than diesel so I should have plenty of margin for error.
Two radiators is a PITA because of the need to join them together and deal with the resulting air-pocket. However, I liked the idea of using a readily
available cheap radiator. If I need a replacement, I can get one for $100.
I did find an even cheaper radiator. $60 shipped, but it has flattened tubes rather than round ones. I blew through it and it felt more restrictive
than the round tube version. Since I'll have more plumbing than stock and double the radiators I wanted to avoid any additional unnecessary
restriction so both of these are of the round tube variety.
Pics:
Close-up of the bleeder and U tube:
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pete wood
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| posted on August 11th, 2011 at 12:30 PM |
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| Quote: | Originally
posted by boof2332
I have looked at cooling alot on the vw conversions...bus and bug... just remember it is the creation of a low pressure behind the radiator that draws
air throuh.....if air can flow directly behind it there will be no pressure drop and you will get hardly any flow....
That is why modern cars have the black plastic piece from the front bumper to the front suspension...when removed in a wrx the engine bay had more
pressure than the air hitting the scoop and flow was backward through the intercooler.
Easy to achieve, just have sides and a flat bottom that goes a couple of inches past the radiator.
Good Luck
Matt
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Matt knows what he is talking about here. The key as he said is not the air being pushed in, it's the HOT air getting pulled back out. A gurney flap
or similar can make a HUGE difference in this regard.
Re Rad size; I think you've overdone it. Look at the vehicle the motor came out of. What did it weigh? Was it doing roughly the same revs at 100km/h?
If it was similar or heavier, then you only need the same size as that. Two rads to me says you've not got the airflow sorted out. Races cars pumping
out twice the heat load use flat mounted small rads, the trick is getting the heat AWAY from the rad. Fix that and you're sorted.
Re belly rads and country roads; if you mount the rad AHEAD of the front wheels, the air that gets to it will be a lot cleaner. A little more work,
but worth it. My bro is talking about putting a watercooled in a split. If he does so, that's where we'll put his rad.
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markd89
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| posted on August 11th, 2011 at 02:40 PM |
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Pete, I appreciate your suggestions as well as Matt's. I'm trying to understand...
I took a look at Wikipedia on the gurney flap. If I understand correctly. I would make a small flap which extends down from the front of the radiator.
I made a sketch which follows. I'm thinking that this flap will block a little of the air flowing under the radiator which will create a low pressure
area. Does this look workable?
Thanks for the help!
Mark
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pete wood
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| posted on August 11th, 2011 at 05:58 PM |
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You can angle the rad like that. But you want a flat bottom on the box. Then the air rushed along under it. It should hit the flap, create a vacuum
and suck the air from out of the radiator.... if I understand it correctly. I've drawn you a pick of the way I understand it.
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pete wood
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| posted on August 11th, 2011 at 06:42 PM |
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Imagine the same setup but upside down at the front of the car... and you'd have this car... Flat air intake under the car, flat air exit on top,
smooth surface and a gurney flap just before the opening.
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vlad01
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| posted on August 11th, 2011 at 08:28 PM |
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Something like this?
black is aerofoil
Green is air flow (tight lines are high pressure, wide spaced lines low)
red is rad
blue is fan.
71 notchback,
Past owner of, 70 NB, 73 SB and 72 FB TLE |
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pete wood
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| posted on August 11th, 2011 at 09:14 PM |
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Yes. That's the literal upside down expression of the race car nose, but the flap doesn't need to be anywhere near that deep. Think about this way,
if a NASCAR gurney flap on the boot is big enough at 4" high to hold the back of the car down at 100km/h, then 2" in depth should more than suffice
behind the radiator. And the other factor is, the closer to the ground, the better it works IIRC. Also, because the air will stick to the surface, a
longer surface under the car (prior to the flap) for the air to run along makes for a bigger disturbance --> then vaccuum when it gets to the
gurney flap. ;o)
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cam070
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| posted on August 11th, 2011 at 09:38 PM |
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Guys this is a fascinating thread. But who would have expected such a thing from people who drive bugs with vertical windscreens and kombis that
resemble house bricks!
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markd89
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| posted on August 11th, 2011 at 11:05 PM |
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Pete, Vlad:
Thanks so much for the explanation and pictures. I think I'm getting it now.
In my current setup, I did not plan to have a box. There's no sides and no bottom.
I could rework things to have that, but I'll need to stare at the radiators and think about it.
If I were to stay without a bottom and sides, could I achieve some of the effect by adding the flap shown in my sketch?
Thanks again,
Mark
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ElusiveStranger
Officially Full-On Dubber
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| posted on August 12th, 2011 at 08:42 AM |
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| Quote: | Originally
posted by markd89
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Make the inlet large, box the whole lot in so the air will have to go through only the rad & that'll work a charm.
Just re-reading through the thread - whoever suggested Nacar ducts on the underslung rad, forget it. They're only effective on laminar flow
systems.
Now I did hear (from a very learned colleague) that the Spitfire (aircraft) actually had an increased power output because of the rad design - despite
the fact it increased drag.
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pete wood
A.k.a.: figure itout
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| posted on August 12th, 2011 at 09:27 AM |
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| Quote: | Originally
posted by markd89
Pete, Vlad:
Thanks so much for the explanation and pictures. I think I'm getting it now.
In my current setup, I did not plan to have a box. There's no sides and no bottom.
I could rework things to have that, but I'll need to stare at the radiators and think about it.
If I were to stay without a bottom and sides, could I achieve some of the effect by adding the flap shown in my sketch?
Thanks again,
Mark
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Definitely box it in. It allows you to control the air so it only goes THROUGH the core. This is extremely important as it makes sure you don't get
hot air turning round and going back through the rad in funny sorts of ways. This is the other side of the 'suck it through' concept. If your system
is about drawing the air out rather than pushing it through, ALL the hot air exits. This is the principle on which all new cars now work.
BTW, The chassis rails can count as two sides of your box.
ES; I'm going to have to disagree with you again on the "big inlet idea". In fact, it's not nearly as effective as a BIG outlet and large vacuum.
Matt will tell you this too. The air comes in cold and goes out hot, so straight up it takes up a bigger volume when exiting. The other part of this
is, as it exits it expands dissipating heat and creating more vacuum. You'd be surprised how little air the car needs to stay cool if it's properly
directed. It also means you don't have something hanging down under the car like the preverbial and hitting every speedhump and bit of roadkill.
Re the Spitfires; they found over a certain speed that the expansion of the hot air from the rad actually PUSHED the plane along. I think the magic
number was 300km/h. This encouraged them to redesign the radiator system to increase this. The upshot was it lowered fuel consumption dramatically
during long missions.
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