Rear Mount Radiator Relocation

[casuprock]

I'm posting this information to start a discussion about rear mount radiator relocation in the DSM. My particular application is a complete rebuild, but the discussion may be applicable to those retaining the stock body.

Pros
Relocation of the front mount radiator to the rear of the vehicle is better for weight distribution in vehicles with significant lightening of the rear. It is also better for air flow in the engine bay. Vehicles with body modifications can employ an under body diffuser to channel air through the radiator. The radiator is thermally more efficient and does not pick up heat from FMIC or oil coolers. The radiator is protected from debris and snow pack.

Cons
It adds more pressure head to the water pump. It adds negligible mass to the vehicle. It increases the polar moment of inertia of the vehicle. Custom fabrication work is required for airflow and the fabricator needs an understanding of aerodynamics and possibly CFD.

I have a car that is undergoing significant lightening, with many structural and non structural components being replaced by composite materials. Here is a photo of the recently finished trunk (spare tire well is cut out and replaced with cf floor). The radiator will go to the rear of the fuel cell and a diffuser is being constructed to draw air from under the vehicle and out the rear.

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To address the cons of a rear-mount radiator, here are calculations that describe both the pressure head on the water pump and added mass from potential rear-mounting of the radiator.

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As can be seen, the coolant hose diameter plays a role, and the diameter can be chosen to balance head loss and added water mass to the vehicle. According to the numbers, it looks like a good idea if it is done correctly. If you've had experience with rear mount radiators, please provide insights or data you may have about performance.

 

[agentorange313]

just out of curiousity, what are the different weights of aluminum racing radiators? mishimoto fluydine ebay 2 core?

Are they heavy enough where you will see a difference if you relocate it?

I also have questions about how is this going to be routed. Are you going to use the stock locations, reroute from the water pump and thermostat housing, through the firewall, to the rear?

Are you thinking about putting an actual radiator/heat exchanger in the rear?

this is an interesting discussion and would like to hear some more ideas.

 

[AWDnoobie]

Id go with a V mount setup to be honest.

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[gixrman]

I've had hopes and dreams about this idea with air coming in the two 1/4 windows and exiting out the center taillight area. Keeping the radiator before the rear axle. The problem with the V-mount setup is room, if you ever tried to lay one og our radiators horizonal there is zero room. If you do a total overhual of the turbo, manifold, and frame structure you could more than likly get good results but it would take a ton of fab work.
I moved my battery to the trunk area keeping it low and could still tell a weight difference shift when cornering. Did you notice this when you moved the fuel cell or is this just a straight line car?

You could overcome the cons of the water pressure on the pump with a electric pump and maybe a two stage system.

 

[ninetyfour]

What would you do to route the air that is passed through the radiator? Mount some sort of hood that funnels out the rear of the car?

If i'm thinking about this right, the air flow would be poor if it didn't have an efficiant flow out.

 

[habitatguy187]

Our stock radiators weigh like 4lbs, I don't see the point of relocating it to the rear, increasing the overall weight of the vehicle (longer hoses more radiator fluid), taking all the time to design and custom fab the system, and on top of all that you're just increasing the risk of springing a coolant leak.

You could probably just drop a 10lb weight in the trunk and call it a day.

 

[GsXdSmKingGsX]

That seems like alot of work for not alot of gain..

 

[casuprock]

Has anyone done this modification on a DSM? The numbers show feasibility, but it would be good to learn from success or failure in an attempt. I've got no problems being the first to try an experiment, if it fails I'll be happy to tell the world why.

Here is additional information from a scale:
Stock radiator empty plus one attached fan weighs 13lb.
Stock radiator full of coolant plus one attached fan weighs 19lb.

I designed a coupler to adapt the stock coolant locations (1.375") to the optimal hose diameter (0.75") going to the rear. This adapter keeps the flow laminar through the diameter transition. The head loss calculations show a minimal pressure drop at reasonable flow rates 1-2 liter/second.

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[gixrman]

What would you do to route the air that is passed through the radiator? Mount some sort of hood that funnels out the rear of the car?

If i'm thinking about this right, the air flow would be poor if it didn't have an efficiant flow out.

It would all be enclosed and ducted, with the opening in the rear being the area were the center taillight is as the exit. You would still use two pulling fans. As far as lines you can cut down on the weight by using Carbon fiber tube fabrication, it not that hard just time comsuming and attention to detail are key. Not to mention the the cost to fab up cores and molds. Two 1.5" lines running from the engine to the rear can be made to weight less that 10lbs.

As far as weight bias, you really want that 50/50 weight distrabution so any that any weight you can move to the rear will benifit, as you keep it between the axles.

 

[ninetyfour]

I don't see weight being so much of an issue on this platform. From my own experience its the room in the front of the engine bay that would be OH SO AMAZING!

 

[casuprock]

It would all be enclosed and ducted, with the opening in the rear being the area were the center taillight is as the exit. You would still use two pulling fans. As far as lines you can cut down on the weight by using Carbon fiber tube fabrication, it not that hard just time comsuming and attention to detail are key. Not to mention the the cost to fab up cores and molds. Two 1.5" lines running from the engine to the rear can be made to weight less that 10lbs.

As far as weight bias, you really want that 50/50 weight distrabution so any that any weight you can move to the rear will benifit, as you keep it between the axles.

Nice drawing. I'm thinking of something like that. Since the diffuser I'm building will pull air from under the car, I was thinking of ducting the airflow down under the rear subframe and doing the side scoops through dummy quarter windows in the back

 

[nuclearr]

Just out of curiosity what are your plans for this car? Is it a race car? Also are you removing the rear seat?

 

[Locke]

I'm assuming you will be lowering the vehicle, as well as installing some form of front splitter and possibly skirting, with the goal of biasing airflow over the vehicle, rather then below it. With this in mind, have you considered the volume of air available at your underbody pickup point, and its pressure delta against your chosen exit location? The rear quarter windows, as gixrman suggests, may make for a better choice, allowing for the lowest possible air pressure under the vehicle while still bringing an adequate volume of air to the radiator.

 

[casuprock]

Just out of curiosity what are your plans for this car? Is it a race car? Also are you removing the rear seat?

It is a race car that will be driven on the road occasionally. Here's a picture of the rear seat... before I cleaned stripped and primed the area.

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I'm assuming you will be lowering the vehicle, as well as installing some form of front splitter and possibly skirting, with the goal of biasing airflow over the vehicle, rather then below it. With this in mind, have you considered the volume of air available at your underbody pickup point, and its pressure delta against your chosen exit location? The rear quarter windows, as gixrman suggests, may make for a better choice, allowing for the lowest possible air pressure under the vehicle while still bringing an adequate volume of air to the radiator.

I am considering a front lower lip. Side skirts are an interesting thought. I have BC coil overs so I'll be able to experiment with the ride height of the car. I'd like to generate lowest pressure under the rear subframe since the velocity is highest at this point due to the venturi effect. That's why I was going to duct the radiator out before the rear subframe. Venturi effect - Wikipedia, the free encyclopedia

The rear quarter windows (one or both) could be replaced by ducted inlets for the radiator. It's not like they serve a good purpose right now.

If the basic setup is a success;
The inlet flow rate could be choked by iris valves in the ducted inlet, enabling adjustment of volume flow rate and "tune" the pressure under the vehicle. A lofty goal would be to have a pressure sensor under the body and adjust the inlet diameter according to the RPM to control pressure at speed.

 

[gixrman]

I don't know if you have ever seen the older F1 cars that had hugh fans (now banned) on the tail of the car that used to suck the car down to the track for better grip, even the side skirts would "ride" or follow the ground.

 

[casuprock]

I don't know if you have ever seen the older F1 cars that had hugh fans (now banned) on the tail of the car that used to suck the car down to the track for better grip, even the side skirts would "ride" or follow the ground.

Yeah! I've seen pictures of those. I don't follow F1 much since it's frustrating how constraining they make the technical rules. It's almost like racing for lawyers. Although admittedly, it is a test of driving skill since all the vehicles are on the same level.

There was a recent fiasco in F1 relating to the design of rear diffusers... with people making double diffusers under a loophole in the rules. Double diffusers 'banned for 2011′ | F1 Fanatic - The Formula 1 Blog

 

[casuprock]

Here's an update about the radiator positioning.

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[Absit]

Subscribing because anything that gives more room in the engine bay is ok with me.

 

[casuprock]

Machined coolant adapters...

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[Tanro]

This is a really cool project. You sir, are slightly insane. i mean that in a good way.

 

[gho5tone]

I hope you finish this because I would really like to see how it turn out. Could always use new ideas on future track car.

 

[spawn87]

i can see you have been doing your homework so im not gana bash on the concept even if some beleave it to be a waste of time. i in the other hand think this is a neat experiment that deserves the time for at least a trial.

one thing i can say is i dont think you should get a defuser and have the air flow from bottom to top and come out the quarter windows i think you should to the opposite. have ram air dams come from the quarter panels push air through the radiator and then have it collect into two hoses that go around your fuel cell and dump at your back bumper/lights.

reason i say this is, the resk factor of having something on the track/road get pulled up at a high speed could crack or damage the radiator and cause a leak.

sorry my paint skills suk but hope you get the idea. (top box shows front view.

 

[casuprock]

i can see you have been doing your homework so im not gana bash on the concept even if some beleave it to be a waste of time. i in the other hand think this is a neat experiment that deserves the time for at least a trial.

one thing i can say is i dont think you should get a defuser and have the air flow from bottom to top and come out the quarter windows i think you should to the opposite. have ram air dams come from the quarter panels push air through the radiator and then have it collect into two hoses that go around your fuel cell and dump at your back bumper/lights.

reason i say this is, the resk factor of having something on the track/road get pulled up at a high speed could crack or damage the radiator and cause a leak.

sorry my paint skills suk but hope you get the idea. (top box shows front view.

That's a good idea, I was considering ducting in through either the sides, small rear windows, or the sunroof. I made a carbon fiber sunroof plug I can modify to have an air scoop. I have an old (cracked) carbon fiber hood off an STI that I might harvest the scoop from...

 

[bryan305]

This is a very interesting idea...wonder how this would work as an angled mount along with a diffuser at the bottom of the rear bumper....

 

[gixrman]

i can see you have been doing your homework so im not gana bash on the concept even if some beleave it to be a waste of time. i in the other hand think this is a neat experiment that deserves the time for at least a trial.

one thing i can say is i dont think you should get a defuser and have the air flow from bottom to top and come out the quarter windows i think you should to the opposite. have ram air dams come from the quarter panels push air through the radiator and then have it collect into two hoses that go around your fuel cell and dump at your back bumper/lights.

reason i say this is, the resk factor of having something on the track/road get pulled up at a high speed could crack or damage the radiator and cause a leak.

sorry my paint skills suk but hope you get the idea. (top box shows front view.

Nothing like stealing my idea (post #9)