Rear Mount Radiator Relocation

casuprock · Oct 19, 2010

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.

talon2gbuyer · Nov 27, 2012

Seems like the rad would take a ton more rocks to the face that way. Plus if you have speed bumps and your careless you can easily smash the bottom of the rad and then goodbye headgasket.

Clew · Nov 29, 2012

Never would of thought of this....

mattmullin · Jul 31, 2013

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heres my rear rad set up

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TAMA_player · Aug 1, 2013

All this rear radiator stuff is awesome!
Mattmullin setup is great, i saw a video some time ago, that car is a beast at the track.

Keep up the good work guys. :hellyeah:

It will be excellent if Casuprock can report how his setup is going and how it looks finished.

serviceguy · Aug 1, 2013

Very interesting projects, kudos to both.

I have been thinking of a slightly different approach though, more specifically I was thinking to convert to a water/air intercooler in order to minimize the compressed air path between the turbo and intake manifold and using a rear mounted heat exchanger.

This would allow to retain the stock cooling and a/c setup at the same time in stock configuration. Yes, it would be for a daily driver.

TAMA_player · Aug 1, 2013

serviceguy said:
Very interesting projects, kudos to both.

I have been thinking of a slightly different approach though, more specifically I was thinking to convert to a water/air intercooler in order to minimize the compressed air path between the turbo and intake manifold and using a rear mounted heat exchanger.

This would allow to retain the stock cooling and a/c setup at the same time in stock configuration. Yes, it would be for a daily driver.

Not to get off topic.... but
I've been running like this (W2A, exchanger in the back) for 3 years, 7 days a week, driving the car to work, super, girlfriend house, track-days and drag-strip. No problems so far, even hit a wall in a track-day isn't an issue..... :thumb:

Kudos for more in detail pictures of both projects! :applause:

serviceguy · Aug 1, 2013

TAMA_player said:
Not to get off topic.... but
I've been running like this (W2A, exchanger in the back) for 3 years, 7 days a week, driving the car to work, super, girlfriend house, track-days and drag-strip. No problems so far, even hit a wall in a track-day isn't an issue.....

Kudos for more in detail pictures of both projects!

That is actually great news, I think you should really post a write-up with pictures then!

End-of-the-off-topic!

Thesethawa · Apr 18, 2015

Now Idk if this is considered a tuner or not, but I relocated the radiator in my 1983 oldsmobile Cutlass supreme and it worked out perfectly accept it leaks a lot.. but that's to be expected on such a low budget, trial and error type project like this. It also has the turbocharger from a Ford Powerstroke diesel on it and the Small block v8 from an older dodge car with 4bbl tbi injection. Quite the sleeper LOL

Anyhow, The thing that worked for me was to bend in the lip of the doors (in a clean, uniform way), put air scoops over the holes, and make large diameter tube channels going back through the bodywork, and I have high power electric fans sucking air through them and blowing it in the direction of the radiator, and vents very specifically placed and sized to minimize drag caused by the scoop by giving the air coming in somewhere to go out. It's a very scientific process, to say the least.

Braeden57 · Nov 26, 2016

Wow now Im gunna spend more time and money messing arounf with these ideas!

EC17PSE · Nov 26, 2016

This is a proper way of doing the rear mounted rad setup!

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Braeden57 · Nov 26, 2016

This is exactly what i pictured in my head. Looks killer and functional. Ill have to draft my own soon.nice to see a finished product

Apache · Nov 26, 2016

Actually, it may be better to pull air from both the sides of the car as well as under the car. It's quite difficult to get enough air to go through a radiator once it's not in the high pressure zone in front of the front bumper. Only pulling from the sides like that probably won't have enough airflow on it's own. If you also could pull some air from directly under the car (with the use of electric fans on the radiator), you could draw more air through the radiator, as well as create even more of a low pressure zone under the car, creating more downforce. Win,win in my opinion. But I will admit that most of my experience in the area of a rear-mounted radiator is purely academic.

ec17pse, where did you see that car at? I'm quite curious to know more about it.

Braeden57 · Nov 26, 2016

Yeah i could see that being good to come from under the car. The only thing i keep worrying about with that is proper protection from bigger rubble and other destructive forces on a street application.

Apache · Nov 26, 2016

True. You would definitely need a mesh to keep out debris, even for a race application. If you had a properly designed shroud for the fans you could easily suck up a lot of shit that you don't want to.

Another point to this is that you would need to have a VERY large opening at the rear of the car to evacuate any excess pressure in front of the radiator. Creating a low pressure zone behind the car strong enough to do that without having the fans running all the time may be interesting as well.

Braeden57 · Nov 26, 2016

Ive fabbed a truck bed mounted rad before and it worked fine on a 383 stroker with a decent rad and some understanding of aerodynamics but even that truck had the occasional bad day when the heat was relentless. However thats because truck beds need some special ducting otherwise they are a big negative space

EC17PSE · Nov 26, 2016

One of my friends in malaysia done this, they do all kinds of crazy over there! he has an opening underneath aswell as just side vents wont be enough on our cars,

If the main opening is from above debris is not an issue but you create aero issues, alot of drifters do the top openings, while underneath may be best it still causes aero issues and messes with the flow under there so is still not ideal really,

Braeden57 · Nov 26, 2016

I live in BC canada so the max i get around here is 30° Celsius. So 70% of the year my fans can do most the work needed. Pretty cold around here eh haha

Apache · Dec 3, 2016

ec17pse said:
One of my friends in malaysia done this, they do all kinds of crazy over there! he has an opening underneath aswell as just side vents wont be enough on our cars,

If the main opening is from above debris is not an issue but you create aero issues, alot of drifters do the top openings, while underneath may be best it still causes aero issues and messes with the flow under there so is still not ideal really,

I can think of a couple of Time Attack cars that pull air from under the car for both the radiator and for increasing downforce.

http://www.speedhunters.com/2012/06/for-my-ally-is-the-force/

That is one such car. Granted, that particular car is also pulling air from the sides of the car as well, but that isn't quite the point. He even designed a rather unusual side skirt to make it all function better. Pretty cool design actually. I'm curious how well something like that would work on the 2G.

EC17PSE · Dec 3, 2016

Apache said:
I can think of a couple of Time Attack cars that pull air from under the car for both the radiator and for increasing downforce.

http://www.speedhunters.com/2012/06/for-my-ally-is-the-force/

That is one such car. Granted, that particular car is also pulling air from the sides of the car as well, but that isn't quite the point. He even designed a rather unusual side skirt to make it all function better. Pretty cool design actually. I'm curious how well something like that would work on the 2G.

If you look his car more in detail his boxes that run through the car start from the side skirts, so he is not pulling any air from underneath at all, the side does the work, the side door gaps do the work and its all been tied in to make it flow as good as it can, how he has it is great as you get great air flow compared to underneath, either way i think a rear rad setup would be cool as heck on a DSM

Apache · Dec 3, 2016

ec17pse said:
If you look his car more in detail his boxes that run through the car start from the side skirts, so he is not pulling any air from underneath at all, the side does the work, the side door gaps do the work and its all been tied in to make it flow as good as it can, how he has it is great as you get great air flow compared to underneath, either way i think a rear rad setup would be cool as heck on a DSM

Look a little closer at the CFD images. His ducts pull air from under the car as well as through the rear doors. The trick side skirts that he has are for the double decker diffuser design that he has.

EC17PSE · Dec 3, 2016

I read abit more on it now as it does say water cooler ducts on the doors, but his engine bay has a rad shroud on the right side! i wonder if thats another water cooler he has

Apache · Dec 3, 2016

Could possibly be for an oil coooler? That would be my guess. Any Time Attack car HAS to keep oil temps in check or they will just meltdown. May also be a transmission cooler I suppose? Or a heat exchanger for a setup that does both? Wish the article was a bit more complete with regards to that.

I drool over the curb weight though. 2750lbs wet. And still AWD. Simply amazing.

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