Gedankenexperiment: Rear mounted radiator

69427

The Artist formerly known as Turbo84
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Clinging to my guns and religion in KCMO.
Had the '69 up on the lift doing some fit measurements for the replacement radiator crossmember supports (aluminum), and kept noticing the big open space where the spare tire used to be. While kicking around ideas to cover up that big gap I got to wondering about a rear radiator. I'd love to move about 35# of radiator and coolant weight (and possibly a portion of the radiator support structure weight) off the front axle and place it on the rear. There looks to be a decent amount of space back there to put a good size radiator, and the biggest fitment issue looks to be the routing of the coolant lines in the axle areas. An electric fan would be necessary, along with a bit of (aluminum) sheetmetal ductwork to direct some air to the radiator. As much as I'd like to think that there's minimal air (and lift) under the car with the low ride height I have, I have to think there's probably a bunch of air moving under the car at speed. Currently I have all the front grill area blocked off, and the radiator is getting its air from the two factory cutouts underneath the outer grills. With this configuration, the engine never overheats, even in 101* track days (and hopefully won't with slightly higher ambient temps at the rear of the car). The radiator would be lower than the engine, but the expansion tank should still be able to allow air to burp out of the system.
So, my main question here is have I neglected to consider any issues that would prevent this system from working? I've got plenty of other issues to deal with in the near term, but my ADD keeps distracting me with other possible projects.
Thanks!
 
that's where I moved my gas tank to to lower the CG (pictures on my build thread).... I do wonder what to do with the space above the tank. I also considered moving all the support systems back there (efi computer, vacuum pump, etc).

In my 4x4 experience with rock buggies, rear mounted radiators are a pain to keep air bubbles out of - we'd mount our radiators to the roll bar with an electric fan - and it'd work well keeping it cool, but at least once per run (10 rigs), someone would start to melt down and we'd be stopped bleeding a system.


The Detomaso cars have issues with their radiator systems too - because the fluid goes down then back up to the radiator....

That said, simply because no one hasn't done it doesn't mean it shouldn't be done, also given the body of knowledge of people who are doing it now should help you avoid most of the major pitfalls....
 
Naive stuff popping out of my mind:
-That's gonna be a lot of tubing, filled with coolant, I see weight gain here.
-Tubing will probably follow more or less the same path exhaust do.
-Air at the back is surely hotter, with the exhaust line and the engine coming from engine.

Why not fill the space with those rear turbo and forget the whole weight loss thing altogether? ;)
 
Lower the tank, put the radiator on the rear deck and fabricate some kind o ducting to ra air through it. Mr Blue Glenn had that on his car.
 
Naive stuff popping out of my mind:
-That's gonna be a lot of tubing, filled with coolant, I see weight gain here. I can offset that by using a slightly smaller radiator (I seem to have excess cooling capability with the DeWitt radiator in there presently). The tubing will conduct some heat out during the flow loop.
-Tubing will probably follow more or less the same path exhaust do. Front to rear direction yes, but separated by a large gap.-Air at the back is surely hotter, with the exhaust line and the engine coming from engine.
True, but remember that the airflow won't contain all the extra heat that comes from a hot radiator up front.
Why not fill the space with those rear turbo and forget the whole weight loss thing altogether? ;)

I got enough horsepower. What I don't have is enough cornering power or braking power. I can't fit any wider tires under the stock bodywork, so easing the workload of the tires is my only option.
 
How about staying front mount and going with a C5/C6/GTO plastic and aluminum radiator?

They are cooling plenty of 600-700 HP late models that see track use and are typically used with the AC almost constantly on in street mode.
 
Flip it forward (not the aft leaning tank),
Build an airbox to seal to hood,
Add a splitter/Dam to Ram air in,
And an electric fan setup to modulate tehmperatures,
Then, cut a hole in the hood to exit the air.




1269510a46ead9460.jpg
enhanced Greenwood Photo

That will be my Gedankenexperiment!

Cheers - Jim
 
Flip it forward (not the aft leaning tank),
Build an airbox to seal to hood,
Add a splitter/Dam to Ram air in,
And an electric fan setup to modulate tehmperatures,
Then, cut a hole in the hood to exit the air.




1269510a46ead9460.jpg
enhanced Greenwood Photo

That will be my Gedankenexperiment!

Cheers - Jim

That setup looks heavier than my present setup. My objective is to get weight off the front axle.
 
with a tiny oil cooler, GM basically doubled the life (at least) of their motors.... so why not follow that principle and change your water-based system into an oil based one? probably a dumb question - but the basics of thermodynamic heat transfer relies on efficiently getting the heat into another substance for transport than back out of the cooler. Having a smaller radiator could be the result of this? thus lighter?
 
Flip it forward (not the aft leaning tank),
Build an airbox to seal to hood,
Add a splitter/Dam to Ram air in,
And an electric fan setup to modulate tehmperatures,
Then, cut a hole in the hood to exit the air.




1269510a46ead9460.jpg
enhanced Greenwood Photo

That will be my Gedankenexperiment!

Cheers - Jim

Im working on that now, except more... stock looking. I think Ill be able to keep the rad in the same location, just flipped forward instead. The way that the hood opens is the biggest issue but that could be solved with a different type of hinge. Rad will be slightly smaller but Im thinking the increased efficiency will make up for that. Obviously your pic is a race car but on a street car the headlight assemblys would be in the way. Unfortunately it looks like it has to sit a bit higher in the chassis to make things fit. Ill get some pics up once I get more than just a cardboard "radiator" mounted
 
Found it chasing down similar Airbox designs. It might have been the Greenwood site.
Here's another - less highlights - from my hard drive:
thum_1269510b96bd0408d.jpg

1269510b96bd0408d.jpg

Nice - Huh? Note the engine and tranny are moved aft too.


This - or next weekend - I should be into Cardboard modeling too. My front is a Flip-Front so a bit different challenge. As I get some "real work done - will move to another thread.

Cheers - Jim
 
Not exactly the same objective but I've been considering installing a smaller radiator in the front, tilting forward and then opening the fender vents and putting an oil cooler at one and another smaller (like heater core) radiator on the other. Of course I am also planning on opening up those vents considerably to make them truly functional.
 
that's the john paul greenwood built imsa covette, check http://www.canepacollection.com/det...msa-greenwood_gt_supervette-used-5468804.html

IMO it's the ultimate C3 race car and has been one of the Rotating VM logo cars since day 1 here.

All in all I think that's a damn neat car (although I always liked the looks of Greenwood's Spirit of 75 or 76 car better), but there's a couple items that make me scratch my head. Given the radiator placement, there's a couple things that come to mind. I like that a laydown radiator will help lower the vehicle c/g (good for cornering and braking), but the placement also moves the c/g forward (bad for cornering, braking, and accelerating). Which change to the c/g position is dominant? Does this change help or hurt performance if the exterior bodywork remains stock?
I agree that exhausting the hot radiator air upward is a good thing (compared to allowing it to flow under the car) to reduce lift. I am assuming that the engine induction system gets its air from the two NACA ducts on the hood, although I'm not sure what the back of the hood does, as it looks in the pictures like there are cowl openings directly behind the injector stacks. It looks like this is an area that would injest warm air from the radiator ductwork exit that gets dammed up at the windshield base. I don't know what the underside of the hood looks like, hence the question.
 
Likewise - the exhaust of the hot radiator (well at least warm) air must be heading straight for the Hillborn(?) intake horns. Raises the air temp and lowers the density.

Not good.

I note the extra wide hood rise and that leads me to that conclusion. Not so sure of the advantage of the mixing of some air from the 2 NACA ducts - but it couldn't hurt. From the site TT posted there are some louvers on the fenders too and may also serve the radiator - but expect more the wheel well.
There appears a bit of shadow that may indicate a slight exit in the hood - if you look close at the left (driver's side) of the yellow paint.

1269511444ad91f2c.jpg


TT - Thanks for the awesome link too!

To visualize my approach - take 90 percent of the JP SUPERVETTE, minus the wide-body Greenwood fenders, add flares instead, and Kamm-back in lieu of the parachute (rubber bumper) with diffuser. My laydown radiator and airbox - has an exit in the hood - cut last weekend - sorry - still "processing the photos".

Cheers - Jim
 
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The radiator gets air from the lowesd part on the front and exits through the extractor hood

the naca ducts on the hood supply air to the kinsler injector, the air boxes are missing in the pics. They look like this:

Babin09.jpg

more pics here, top & bottom

http://www.greenwoodcorvettes.com/Tubeframe2Gallery.html##22 L. Burgos

I'm not trying to be disrespectful or critical of aspects of the Greenwood designs, as it's certainly obvious that Greenwood was infinitely more successful in the professional race world than I have been, and my questions and comments are purely from an engineer's perspective.
The hood seal gaps at the windshield base leads me to think that the (very small) plenums feeding the injector stacks take in (heated) air from the windshield base, in addition to the NACA ducts. I'm curious how efficient this dual feed setup would be.
Going back to the radiator setup, after looking closer an additional item piques my curiosity. When the radiator is layed flat like this it limits the ability to create a reasonable volume plenum to convert the high speed intake air into low speed pressure. High speed air hitting a flat surface is generally a good recipe for aero drag. Without any actual aero data from this car to look at though, my question is just that, a question.
Again, no disrespect intended for the Greenwood operation. I followed Greenwood's career when I was young, actively rooting for his success, and he and his crew were certainly sharper in their 20's and 30's regarding vehicle dynamics than I was.
 
Here are a couple of interesting comparisons:

12694de3f7452e149.jpg

As an aside, approach "D" is somewhat like what Glen - Love-is-Blue did on the rear of his Vette. Note ther is little drag savings - yet 1/2 the volume of air. Maybe that is why he used 2 radiators? -- Oh, no --they were 1/2 size too?

I believe in the comparison show above the radiators are the same size.
And, here is another one to think on:
12694d212c6b2a6c8.jpg
ANd an implementation that seems effective:
12694c27ec2f393c2.jpg


Cheers - Jim
 
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