Road going rear mount radiator idea? Disscussion

[De Ranged]

This is something I'm contemplating doing to a 40 series Landcruiser...... I'm posting it up here because of all the groups I'm part of this group has the best bunch of thinkers I've come across and the least of the web crawler mentality where they have to be heard even if they don't know anything, or can't extrapolate lol 

Now to set the scene, this is about road going vehicles with a rear mounted radiator at sustained open road speed .... we all know it works on slow offroad toys.

The issue is at road speed, there is a vortex behind the cab that does two bad things first it recycles the same air and there is a slight reduction in air pressure  

Now my idea is to open up the transmission tunnel behind the motor vertically so the air forced into the engine bay to flow above the gearbox and back to the radiator mounted at the end of the new transmission tunnel at the back of the cab, sealed to the deck and guards 

- The lower pressure in the deck should help draw this through from the transmission tunnel ?

- will the turbulance under the vehicle destroy this flow ?

- Is there a vacumn under the cab that would cause this to want to flow from the back of the cab to the underside ?

- I don't think the engine heat will be an issue ? (I've done a few buggys and there are alot in competition that have a low mounted rad that draws past the engine and from below, and they work)

- will the vertex in the back, flows forward towards the cab and up the back of the cab impact flow ? 

 

If I can pull this off I gain two big bonus's from an offroad perspective..... first is the fact the radiator isn't in the front pushing the bow wave of sloppy mud when you enter a bog, and second by drawing the air from the engine bay under the cab I stop all the steam from the engine and exhust when you hit a wet crossing or bog going up infront of the windscreen effecting vision 

           

The setup I'm planing on running in the 40 series is an LS1 (5.7L), running the biggest Davis Craig electic water pump and controller, with Alloy water pipe lines between the motor and radiator, and a Nissan Patrol TD42 alloy radiator (basicly the biggest radiator short of a truck one lol), I was planing on 2 x 16" radiator ducted fans (one on a manual switch and the other on the Davis Craig controller) 

 

Any thoughts... experiances....... before I carve out the floor on my 40 lol 

[lo-fi]

You've already identified the biggest pitfall, being the stagnation area behind a square vehicle at speed. I've seen some modeling on race machines showing that flow actually reverses in some situations in a totally non intuitive fashion, which explains some oddly shaped louvers on Le Mans P1 cars. Without modeling it, it's impossible to know what's going to happen unless you're Adrian Newey! All sorts of odd pressure gradients and suchlike on a brick shape. 

How about tape some ribbons on it and see what's going on as it is, then maybe tape some temporary ducting in somehow and see what effect that has before cutting anything? 

Or if you fancy being really cunning, we could design up a scheme to use the exhaust as an ejector to create draw over the rad... Plenty of waste energy to be harnessed from 5.7 litres huffing down a tube! Added advantage that it works harder the harder the engine works. 

[FridgeFreezer]

@miketomcat ran his rear-radiatored Tomcat on the road all the time with no problems, likewise Richard's Dlander, Jez's Petal and Mouse both had rear rads with no issues. All of them had roof scoops.

Most of the comp safari boys have rear rads and they're not hanging around.

[Blanco]

38 minutes ago, FridgeFreezer said:

All of them had roof scoops.

My thinking exactly, ... the best way to secure the flow is to duct it directly either over or under. Pressure reduction under the vehicle will be modest at worst because its isn't contained by skirts or anything, (I presume), it is more about flow control.

[miketomcat]

Roof scoop, radiator vertical on bulkhead, vents on rear roof. Worked so well the fan never came on no matter what I did.

Mike

[FridgeFreezer]

58 minutes ago, Blanco said:

My thinking exactly, ... the best way to secure the flow is to duct it directly either over or under. Pressure reduction under the vehicle will be modest at worst because its isn't contained by skirts or anything, (I presume), it is more about flow control.

My concern with picking up from underneath is it's just channelling dirt, debris, road salt, etc. into your rad rather than the somewhat cleaner air going over the top.

Petal:

Petal Mk2:

Mouse roof scoop:

 

D-Lander, bit of an Elvis quiff:

 

[Blanco]

4 hours ago, FridgeFreezer said:

My concern with picking up from underneath is it's just channelling dirt, debris, road salt, etc. into your rad rather than the somewhat cleaner air going over the top.

Fair point but wasn't Deranged talking about creating space behind the engine, up over the tunnel? Under the cab rather than the whole vehicle?

[De Ranged]

Yep you guys are right, a roof scoop works and works really well..... your drawing dust free air, and good flow..... catch is while we are allowed to blackout/interfair with the vision throught the back window it is only for commercail vehicles lol there is next to no way I could get away with it 

I have considered ducting (over the sides of the roof, and around the sides of the cabin) but this is the open conditions for alot of tracks lol 

I don't have any pic's on the computer of the tracks where the bush is trimmed back to keep the tracks open, I'll leave it with the comment it is common to slip a branch down between your exo and body and break the stick as you bend it between cage and body... and yes this F's pannels.... This is why I'm getting "inventive" lol 

The other thing is we don't have a dust problem in New Zealand lol over winter its the oposite.... why I see keeping the engine steam off the windscreen such a big gain 

For the books we don't salt our roads and I'm not a big fan of beach runs 

The road going side of it is going to be limited 1-3000k's/yr, I want this for club runs and the ocasional epic... and I'm going to setup the radiator up so it can be removed/tilted for cleaning... some of the play areas have a sloppy mud that is very deep and once it touches anything warm it drys on, but washes off easily 

20 hours ago, lo-fi said:

How about tape some ribbons on it and see what's going on as it is, then maybe tape some temporary ducting in somehow and see what effect that has before cutting anything? 

Lol I would have if I could, my knowledge of flow dynamics is F all, so something like this would have been the way....... catch is what has prompted this build is the flywheel almost fell out so the truck isn't a runner lol 

My understanding so far on the aerodynamic's is from watching the tonneau cover of my ute (which has a way lower cab and almost twice the deck).... and from past vehicles I've built for the road (I solved one with ducting, one with extra radiator core (I used two radiators), and the rest with HD fans (Audi ones I think from the A4's, these fans will pick themselves up off the floor and fly! but they are a huge draw 80amp fuse) and some non-realated posts on a commador forum about drag from racing utes that backs up my observations driving my ute

Lo-fi your comment about using the exhust gas flow was intregging untill I did some math..... I started with the best case option (I can cause as much flow as the exhust via ventui/heat) 

I started by converting everything to the same standard "flow per second" 

The engine 5.7L @ 2000rpm = 190L/sec of gas flow (1L =1000000mm3)

Wind 1km/hr = 277.8mm/sec

The surface area of the radiator is 735mm x 438mm = 323244mm2 

So 190,000,000 / 323244 = 587.8mm/sec of flow or less than 3km/hr of wind flow.... math can really steal the fun out of an idea lol 

[FridgeFreezer]

Could you make the ducts out of perspex therefore not diminishing the rear-view? Or fit a reversing camera as rear-view mirror?

I think you're over-worrying about hooking a tree on it, Jez never damaged the scoops and they were ploughing through trees all day.

[De Ranged]

My idea so far..... and I'm getting to the piont its going to be a try it and see thing lol is 

Is lift the floor between the seats as much as I can (legal safety limits to protect occupants) possibly around 400mm wide by as much as 500mm tall with a rolled top (curved corners part of the occupant protection), the firewall and under dash will get a cone as wide as I can push it without interfering with the pedals and an equal amount on the other side (symatry looks good lol) and as high as I can take it up under the dash 

At the back of the cab I'm guessing mounting the radiator on a 45 degree angle "\" to the cab.... and will be sealed into the deck/guards

I'm guessng the flow dynamic is going to get all screwed from what I've seen with my ute, to my eye the wind flows over the cab and is hitting the rear half of the tonneau cover forcing it down, most of this turbulance flows over the back, but a small amount flows forward towards the cab and cycles up the back of the cab lifting the front of the tonneau 

Given the 40 is a brick, is twice as tall, the deck is as good as half as long and I'm going to have an exo interfering with the flow Im expecting the area behind the cab to be a mess of turbulance with no real flow, but due to the flow around and over at enough of a pressure differentail it will draw through the radiator if it is sealed 

This is why I'm' guessing at a 45 degree angle, I see it as sorta hedging my bets lol 

I'll try and keep the exhausts out the sides and put some sheilding to try and limit there heat impact and I was thinking of some sheet metal deflectors around the base of the engine and possibly in the transmission tunnel to keep the bulk of the flow through to the radiator and limit debris... but I'll try and keep these minimal as I don't want them acting as mud traps 

Any thoughts ? Anything I've missed ? 

Thanks for the feedback it helps with my thought process lol 

[De Ranged]

5 minutes ago, FridgeFreezer said:

Could you make the ducts out of perspex therefore not diminishing the rear-view? Or fit a reversing camera as rear-view mirror?

I think you're over-worrying about hooking a tree on it, Jez never damaged the scoops and they were ploughing through trees all day.

It has been done with perspex and it is about the only way I could do it catch is it depends on the certification tester and the yearly warrent testers opinions.... if either feel the qaulity of vision is impacted then I'm screwed and have to remove it 

its not trees its the shrubs on the side of the track.... imagine hedges of branches from finger width to 50mm thick and these are just off the track lol thats Minginui forest. This truck was built for it 

Notice the fiberglass roof.... look closely at the top of the windscreen, the orignial roof has a gutter that sticks out not much about 20 or 30mm if that but it was catching enough it damaged the roof so this one was made..... personally I prefer "Camel trophy" wires to lift the branches over 

Those issues aside a roof scoop doesn't address the issues I wanted to solve and one of them is steam on the windscreen you might laugh at that but when you have to stick your head out the window to see and your driving clay ruts and a hedge of branches to the side lol its not good I'd rather my head was inside the cab 

[miketomcat]

A while after I sold my tomcat it was rebuilt by the factory. They fitted two small radiators on either side and ducted them in from just behind the doors, I believe it worked well.

My limited know of aerodynamics is the flow coming off the cab rolls in on itself creating an up draft directly behind the cab. So if your out let is as high as you can get it and as close to the cab as possible it should draw on the up draft. The out let on my tomcat was two big holes in the rear roof which used the roof flow to draw the hot air out. I've seen some with the exit on the back, this tends to draw air in at the bottom and out at the top creating positive pressure in the rear roof.

Mike

[elbekko]

Your underbody idea should work just fine I think, as long as it's enclosed. You're basically just building a big diffuser, ending in a radiator and a low pressure zone (which should help).

[Escape]

I'd be worried about airflow and possible mud etc getting in the diffusor when used in deep mud. To keep steam away from the windscreen you'll have to seal the bonnet pretty good. In Mouse there was no lack of steam when the water reached the hot headers, and it will go up rather than to the rear if it can find any way at all. On the other hand, if you close off the intake too much, you'll be limited to hot air from the engine bay in slow moving conditions.

When looking at flow and cooling, it's usally better to focus on getting air and heat out rather than getting cool air in. If there's a good draft behind the radiator, air will always find a way in. Maybe from the sides? Testarossa-style intakes between the doors and rear axle maybe. Ideally with an opening beginnen in the doors, like a NACA duct. I could see this work on something like a 110.

As an aside, a lot of mid- or rearengined cars actually have the radiators at the front. Possibly because the better airflow and easier packaging offsets the added weight and complexity. Those who don't often have a roof scope to get air into the engine bay.

Filip   

[FridgeFreezer]

I wanted to fit a rear rad in the 109 when I rebuilt it to stop mud clogging it up, in the end I couldn't see a nice way of doing it without too much other compromise, ended up just fitting a wide-cored (earthmover or "caterpillar" core) rad in the front and it's never clogged.

[Bowie69]

Thought about side scoops?

Often done with track/racecars when moving radiator into where the rear seats should be.

[Arjan]

"..the vision throught the back window it is only for commercail vehicles lol there is next to no way I could get away with it.."

A rear lookingcamera / screen in the mirror is not an option ?

[De Ranged]

6 hours ago, Arjan said:

"..the vision throught the back window it is only for commercail vehicles lol there is next to no way I could get away with it.."

A rear lookingcamera / screen in the mirror is not an option ?

I know this is going to sound daft lol but the whole technology thing hasn't been confirmed yet..... using a camera as wing mirrors, your example etc......  there is one vehicle that is leading this issue and that is a disability conversion with electronic steering and controls, this vehicle is pushing very hard so they are writting rules to cover this. Till then it is a case by case thing and I'm back to the discretion of the certifier and the warrent tester 

Bowie its not as simple as it seems, there is a big thread up on a local FB group about fitting radiators into the rear side windows (Patrols and Cruisers) and the concensous was that ducting did little to help.... it was all about the fans, some of the guys had put alot of develpment time in on this and on long sustained climbs (road) they still had cooling issues..... now one thing I did notice is there was no talk of where to vent, the discussion was about fitting the whole system in a window inclosure, maybe if you were to vent somewhere like the top of the rear door it would make the scoop work? 

Fridge lol 25yrs I've been working around and with heavy earth moving gear (even washing mud out of radiators) and I never thought of this lol I will remember this for the next toy 

Escape thats not a bad idea, I'm trying to visualize a 40 series with racing door vents lol..... just a thought would the exo tubes interfer with the surface flow ?... just realised that would stop the windows winding down bugger 

I've got a mid mounted PTO winch so the radiator will go above this just below the rear window (I'm allowed to lift the floor behind the seats as far as I want, as no issue with occupant safety), as for sealing the bonnet I was going to run a length of door seal under the rear of the bonnet.... the sides of the gaurds come up under the sides of the bonnet so should create a bit of natural seal.... if I have to I'll seal them as well. Stopping this is a big bonus to me. There are guys here with winch trucks that run trans cooler fans under the bonnets to push the steam down to lessen the issue, I'll probably do the same if this isn't good enough 

There are alot of transaxle buggies here that use the rad fan to pull the engine heat back to cool it down for the occupants (google NZ 4wd trials its good to watch) and I've never seen a rear rad setup that struggled to cool,  I think its a combination of the extra volume of coolant and the cooling gained from the hard lines. All that said I've never seen one sealed into that airflow like I'm looking at 

 

 

[Bowie69]

I wasn't really thinking windows in this case, more likely grilles similar to a supercar type setup, just a bit higher.

[FridgeFreezer]

1 hour ago, De Ranged said:

Fridge lol 25yrs I've been working around and with heavy earth moving gear (even washing mud out of radiators) and I never thought of this lol I will remember this for the next toy

Why not this one? You can get a rad made any shape/size with this core in it, mine didn't cost much more than a genuine parts brass one.

[De Ranged]

21 hours ago, FridgeFreezer said:

Why not this one? You can get a rad made any shape/size with this core in it, mine didn't cost much more than a genuine parts brass one.

Because I've already bought the Radiators for my current projects lol Alloy ones at that! 

 

22 hours ago, Bowie69 said:

I wasn't really thinking windows in this case, more likely grilles similar to a supercar type setup, just a bit higher.

Your suggesting just behind the doors ? That would be an interesting challenge as I'm going to be trying to keep the exo as tight as I can on the outside and the seats on inside hmmmm do-able tho.... not going to allow me to draw off the steam from the headers and motor tho 

[Bowie69]

Yeah that was the idea.... :)

[FridgeFreezer]

15 hours ago, De Ranged said:

Because I've already bought the Radiators for my current projects lol Alloy ones at that!

Depends if price of another rad is less than the price of all these other mods to make it work?

[De Ranged]

9 hours ago, FridgeFreezer said:

Depends if price of another rad is less than the price of all these other mods to make it work?

Lol I modify things, thats my fun..... to be honest the journy/process of design, problem solving and creating is of way more interest than actually having and using the end product, I'm an ex logging contractor and farmer so I've spent 25+ yrs driving and opperating where most wouldn't lol I won't say I'm over it, but 4wding is almost more about the social thing for me... I'm just as happy in the passanger seat motivating a mate to have a go even if its my rig lol because if its broken its back in my workshop for improvements 

To that end.... I hate to compromise an idea

And while the industrial radiator is a good option it doesn't solve the issue, at rallywoods putting that upfront would get me another bog maybe 2 or 3 before I have to wash it out and it will be easyer to wash... the clay in the slop drys on in layers lol its not uncommon to see an inch of mud stuck to the front of the radiator there 

Edited April 4, 2020 by De Ranged
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