Let's talk rear radiators

[Novablue454]

Who here is running a rear radiator setup? I'm looking for pics of installs and also some tech. What material did you use for the piping, upgraded water pump, etc?

I am thinking the stock LS pump should be sufficient paired with an aluminum radiator and -16an hose the whole length to/from the radiator. I have seen people opt to use things like copper pipe the length of the vehicle, but that seems sort of ghetto to me.

[audioscience10]

Who here is running a rear radiator setup? I'm looking for pics of installs and also some tech. What material did you use for the piping, upgraded water pump, etc?

I am thinking the stock LS pump should be sufficient paired with an aluminum radiator and -16an hose the whole length to/from the radiator. I have seen people opt to use things like copper pipe the length of the vehicle, but that seems sort of ghetto to me.

Most of the guys I know running rear setups are running aluminum tube to the rear and back. Not sure on pump.

[jalopi]

+1, i know you're not afraid of spending money on your car, but holy shit that would be alot of money in AN hose.

i was gonna do a rear mount radiator on my v8 e30 before it blew up - i was planning on using DOM tube underneath the car, never got around to planning the cabin piping. DOM might be heavier and more expensive than typical pipe, but under normal (even harsh) conditions it's damn near puncture proof. i was planning on using a regular 50/50 coolant/water mix though, so if you're rocking 100% water you might not be a fan of the inside of the tube rusting up.

mount the radiator flat in the spare tire well and dump the "exhaust" in front of a diffuser so you can tell people your car has F1 tech

also, i think the only time fluid pump strength really comes into play is when you ask the pump to move a liquid vertically. because it has to fight gravity or whatever. your stock pump will most likely be fine

[protomor]

The sikky cars I work on has those. AN lines the whole way. Some huge shit. It can be a pain to bleed if the system is dry. The hoses are just routed under the cars. Not through the cabin. I don't think you're allowed to run fluids through the cabin. Regardless, it's hard to make the rear of the car grab and push enough air to cool the radiator. Most FD cars do it for the crash safety and weight balance. But unless you're that level, why would you want to do it? Not like you'll be cooling your engine any better.

[Novablue454]

+1, i know you're not afraid of spending money on your car, but holy shit that would be alot of money in AN hose.

i was gonna do a rear mount radiator on my v8 e30 before it blew up - i was planning on using DOM tube underneath the car, never got around to planning the cabin piping. DOM might be heavier and more expensive than typical pipe, but under normal (even harsh) conditions it's damn near puncture proof. i was planning on using a regular 50/50 coolant/water mix though, so if you're rocking 100% water you might not be a fan of the inside of the tube rusting up.

mount the radiator flat in the spare tire well and dump the "exhaust" in front of a diffuser so you can tell people your car has F1 tech

also, i think the only time fluid pump strength really comes into play is when you ask the pump to move a liquid vertically. because it has to fight gravity or whatever. your stock pump will most likely be fine


Yeah, the price of AN is what had me curious as to what others were using. It's just about $300 dollars in hose alone, not including fittings or getting a radiator modified to accept AN fittings. I was googling it and all I really found were a few people using copper pipe from Lowe's on Willy's hot rods.

As far as airflow goes, I was planning on cutting out the spare tire hole, mounting the radiator at a 45 degree angle with the top towards the taillights, and then making up some scoops from Lexan for the rear side windows, and if that isn't sufficient adding a roof scoop to the sunroof delete panel, all with ducting to the rear bulkhead, paired with a set of high flowing fans and some vents in the trunk lid.

According to the rulebook, "If cooling system lines are routed in the driver’s compartment or a trunk area that is open to the driver, they mustbe separated from the driver by a crushable metal enclosure made up of .036-inch steel, or .059 inch aluminum.The floor of the enclosure must be designed to prevent accumulation of fluids."

I will just be running water + water wetter, so corrosion is a concern.

[jalopi]

making up some scoops from Lexan for the rear side windows, and if that isn't sufficient adding a roof scoop to the sunroof delete panel

exactly what i have in mind for my e36. i'm personally planning on making the scoops harrier-intakes shaped and doing an aircraft themed paint job :D

only the rear mounted radiator is only going to be supplementary on my car, as i'll still have a front mounted radiator as well. on my old v8 car, a front mounted mishimoto Z3M radiator and a SPAL fan would only let me do 4-5 runs in 80-90* weather before needing a 10-15 minute cooldown break... and those radiators are huge. the biggest problem with rear mounted radiators (based off of the limited information i can find about em online) is that it's hard to get good airflow to them. take this setup for example:

http://i11.photobucket.com/albums/a156/jonocos/111111111111111086.jpg

it looks like alot, but the reality is that pipe isn't even half the surface area of the radiator. even if you used a 3" scoop on the roof, that's only (roughly) 90-100 square inches of intake. even if you used some crazy big 10" diameter ducting from the windows, combined you've got about 260 sq.in. of intake for a radiator with a surface area of about 360 sq.in.

would it work? definitely. hell, it'd still probably work with just the side scoops. but the real question is how many runs could you do before overheating like a bastard. IIRC it's not an uncommon for FD guys needing people to spray their radiators down after a few hot runs

[Novablue454]

Nice! Since I've got so many Subaru parts laying around, I was thinking of trying to mold them off of WRX hood scoops, then riveting those to flat lexan side windows.

[btaLSM3]

I have also thought a lot about doing this with my LS build. I opted against it just because its that much more I have to do before my car is done and running. . But I have found the lexan quarter windows and the ducts like these. . .

http://www.afterhoursautomotive.com/images/spec%20v/naca-duct.jpg

From there I was going to do a sheet metal back and use that as the plenum to the radiator. but like I said I never ended up doing it. .

Talking around . . a lot of people who do this run electric water pumps. All the extra fluid required seems to put strain on your factory mechanical water pump. Most setups I have seen run the aluminum tubing to the rear, sometimes under the car or sometimes inside of the car. Ultimately, i'd look at the pros and cons of doing it. IMO there are more cons - cost, time to build, questioning the effectiveness, possible strains on other parts. Pro - looks cool as shit, frees up space, very effective if you're on a baller budget. . . just my 2 cents.

[jalopi]

these rumors about rear mounted radiators killing stock water pumps need to die. the only times i've seen supplemented pumps that i could justify doing is on monster offroad trucks where the beds' radiator is mounted significantly (at least a foot) higher than the water pump.

toyota was able to use the same exact water pump on their 4AGE, 3SGTE, 5SFE and 1ZZFE regardless of whether it was used in their front engine/front radiator cars or their rear engine/front radiator cars.... none of which (the pump) were insanely powerful or anything, and that was only pushing through four cylinders' worth of cooling passages. i have a very hard time believing that a water pump meant to move enough fluid to cool a v8 with a displacement which - at a minimum, is 2.4x greater than the largest toyota engine - can't handle pumping coolant an extra 15 feet with insignificant elevation changes

[JesterMX6]

these rumors about rear mounted radiators killing stock water pumps need to die. the only times i've seen supplemented pumps that i could justify doing is on monster offroad trucks where the beds' radiator is mounted significantly (at least a foot) higher than the water pump.

toyota was able to use the same exact water pump on their 4AGE, 3SGTE and 5SFE regardless of whether it was used in their front engine/front radiator cars or their rear engine/front radiator cars.... none of which (the pump) were insanely powerful or anything, and that was only pushing through four cylinders' worth of cooling passages. i have a very hard time believing that a water pump meant to move enough fluid to cool a v8 with a displacement which - at a minimum, is 2.4x greater than the largest toyota engine - can't handle pumping coolant an extra 15 feet with insignificant elevation changes

I agree. the water is flowing at the same rate regardless of the distance between the pump and the radiator. Provided their isn't a major change in radiator height, the pump shouldn't be under any more stress than normal.

[btaLSM3]

I agree. the water is flowing at the same rate regardless of the distance between the pump and the radiator. Provided their isn't a major change in radiator height, the pump shouldn't be under any more stress than normal.

Fluid is heavy. . If you have more fluid you're going to create more pressure on the pump. Whether or not that extra pressure and fluid will damage a pump just depends. . but there is additional strain without a doubt, ultimately taking some of the life away from the pump. It may still last 75,000 miles with a rear mount radiator, but it probably would have lasted longer with the normal amount of fluid.

[jalopi]

you're 100% right bro - fluids (especially water) are pretty damn heavy. but we're not talking about witchcraft or magic here, this is basic physics.

for instance, if i asked you to lift a 100lb ball, you may or may not have a difficult time with the task, depending on how fit you are. but if i asked you to roll a 200lb ball across a room you'd probably be able to do it without much difficulty. see what i'm saying? this is why most fluid pumps have a head pressure rating - aka how many vertical feet a pump can move fluid before giving up the ghost. go shopping for sump pumps and that figure is on the box somewhere. here's the wikipedia non-TLDR version of what i'm talking about

https://en.wikipedia.org/wiki/Hydraulic_head

i did some reading through rock auto to find radiator sizes for a 2003 silverado with a 5.3 and came up with a radiator that's roughly two feet tall. even if the pump was perfectly centered at the middle of the radiator, it would still have to pump fluid 1' high and draw fluid 1' high, making for a 2' load. i still don't think that increasing that load to 3' (or staying the same/less with a flat mounted radiator) is gonna kill the pump. after all, it's not like MR2 water pumps were crapping out any sooner than their FWD counterparts.

the only argument i'll merit is that the longer pipe does account for some extra frictional power losses... but i don't think it would even start to make a difference until your pipe length got past 100-200 feet

so once again. rumor. needs. to. die.

[btaLSM3]

I completely understand what you're saying about the head pressure and parts of me agree with this theory. But if it really wasn't an issue why would so many people who do this switch to electric water pumps? People have to be spending money to improve something. I know I don't want to be the guy to just test it out and learn that the regular pump fails and you're out an engine or something. And also I'm pretty sure MOST cars that run rear/front radiator setups factory have multiple water pumps. . but I could be wrong on that one.

[jalopi]

you're not wrong about additional electric pumps - i've seen a bunch of FD car setups that use supplemental pumps just for their superchargers' radiators. it's a different cooling circuit than what the engine uses, but i completely forgot to mention that earlier.

i don't mean to sound like i'm bashing electric water pumps - they do have their uses. one thing that's nice about them is that regardless of what speed the engine is running at (or if it's even running at all) your coolant flow can still be at 100% full blast. i'm sure they're more efficient at cooling your car down while waiting in line after a hot run. the obvious downside is that they're quite expensive - a 30ishGPM unit would work as a supplementary pump, but not as a primary. 30 is pretty much limited to drag cars, 55GPM is necessary for other uses.

so.. i guess the point i'm trying to make is that installing an electric pump won't hurt anything, but neither will rocking a rear mounted radiator without one. especially if the radiator is mounted flat in/on the wheel well

[Novablue454]

Yeah, I've been looking at switching to electric, but holy crap they are expensive. Makes me wonder about installing something like this on the way from the radiator back to the engine, I would just be worried about it having the opposite effect and actually restricting flow.

http://www.jegs.com/p/Meziere/Meziere-Mini-Inline-Electric-Water-Pumps/750520/10002/-1

So after this thread and speaking to some local guys, it seems my best plan of action is to run 6061 Aluminum pipe (http://www.speedymetals.com/pc-4436-8370-1-14-sch-40-pipe-6061-t6-aluminum-extruded.aspx) the length of the interior along the passenger side rocker panel, through the trunk firewall and up behind the dash to the engine firewall. From there weld AN fittings on at both ends so 20AN can be used from the pump to the pipe and from the pipe to the engine, along with 20AN from the radiator to the pipes inside the trunk. the spare tire well will be removed, and the radiator mounted at a 45 degree angle with 2 large pull style fans directing the hot air out the spare tire well. Airflow will be provided using 2 side window scoops with tubing routed through the trunk firewall. A third scoop can be added to the roof if needed. I am also looking in to putting reverse louvers on the top of the trunk lid to grab some of the air coming down the back of the car and direct it in. Vents will also be added to the rear of the decklid.

Thoughts?

[Iteachgolf]

Seems like a lot of expense that really isn't needed and a front mount radiator would work perfectly fine. Why do you feel you must do this? Especially when you're just getting into this.

[jalopi]

yeah, i'd worry about that little 20GPM pump having surge or cavitation issues with whatever flow the GM pump is pushing at high rpms. for the same kind of money, i'd get this instead (though you'd probably be fine without a supplemental pump)

http://www.jegs.com/i/JEGS+Performance+Products/555/50950/10002/-1

i've seen a few guys use them on GT40 kit cars. these are dudes rocking 427+ cubic inch big blocks and the jegs pump seems to work fine for them. only issue you might run into is over pressurizing the cooling system and blowing a hose or gasket

[Novablue454]

Seems like a lot of expense that really isn't needed and a front mount radiator would work perfectly fine. Why do you feel you must do this? Especially when you're just getting into this.

I don't "need" to do it. I want to do it. I am well aware that a front mounted setup would work, but that's no fun. Research, design, and fabrication are fun. Every aspect of this car could be nitpicked in similar fashion. What it really comes down to is that I enjoy the build phase and fabricating things.

- - - Updated - - -


yeah, i'd worry about that little 20GPM pump having surge or cavitation issues with whatever flow the GM pump is pushing at high rpms. for the same kind of money, i'd get this instead (though you'd probably be fine without a supplemental pump)

http://www.jegs.com/i/JEGS+Performance+Products/555/50950/10002/-1

i've seen a few guys use them on GT40 kit cars. these are dudes rocking 427+ cubic inch big blocks and the jegs pump seems to work fine for them. only issue you might run into is over pressurizing the cooling system and blowing a hose or gasket

Good find! Yeah, i'll probably end up just using the OEM pump, and if it seems like it's not flowing well enough then i'll look into adding a supplemental pump.

[Novablue454]

Updating just in case anyone else does a search,

After speaking with Meziere and some other people, we ended up going with:
Meziere MEZ-WP337S, Electric 55GPM Dual Outlet remote pump
Meziere MEZ-WP89U LSx Water Pump Block Adapter -12an
CFR HZ-40016-X3 Modular Aluminum Radiator 31" x 19"
CFR HZ-6064 8"x 3' Aluminum Overflow Tank
CFR HZ-1009-31 Radiator Fan Shroud
CFR HZ 1009CU 16" Electric Cooling Fan

I will update once the car is on the road with how it works out.

[jalopi]

just make sure you run big ass ducts from those scoops and it'll probably work just fine

[MptyWall3t]

So what's the advantage to running the radiator like this? Does the radiator not fit with the LS in there?

[jalopi]

some guys rock rear mount radiators for touchie feelzies

other guys use them for crash protection

sometimes you have to due to fitment issues

there's more than enough space for a radiator in front of a LS installed in an e36

the only downside is you have to put some really good thought into designing your air intake/exhausts to the radiator. very easy to not get enough airflow through a rear mount radiator. and if poorly setup, a real bitch to bleed

[protomor]

Shameless plug: I wrote an article on it a while ago http://yoshi.e30drifter.com/2015/10/15/rear-mount-radiator/

It's useful for the pros. Mainly for the crash resistance and increased amount of fluid. For the rest of us, it's not worth the effort.

[MptyWall3t]

Ahh I see, learn something new every day.

[Novablue454]

So what's the advantage to running the radiator like this? Does the radiator not fit with the LS in there?

It probably would, but what's the fun in that? My plan is to run a 31" x 19" (oem is 23" x 18" ish) radiator at a 45 degree angle with the top tilted towards the rear of the car. From there, I am going to cut out the spare tire area, and run a 2300 CFM cooling fan, pulling the hot air out of the trunk floor. For the fresh air I am going to run 4 NACA ducts, 2 in each rear window, ducted through the trunk bulkhead to the front of the radiator. A 55GPM water pump will handle moving the water through 2 -12an lines to the block and a 1.5" line to the radiator.

Honestly, there is no real reason I am doing it. I want the extra bit of crash protection to keep from damaging my $550 radiator, and moreso I just want to do it for fun.

[jalopi]

plus, when you decide to start feeding it compressed air in the future there'll be more room for an intercooler ;)

[Piner]

For the fresh air I am going to run 4 NACA ducts, 2 in each rear window, ducted through the trunk bulkhead to the front of the radiator. .

How big are these NACA ducts? That seems like a completely inadequate amount of flow for a car that's going to be driven hard. I've heard of guys with 8 3" NACA's to their rear rad complain about overheating due to not enough airflow.

[jalopi]

How big are these NACA ducts? That seems like a completely inadequate amount of flow for a car that's going to be driven hard. I've heard of guys with 8 3" NACA's to their rear rad complain about overheating due to not enough airflow.

100% with you there buddy. when i was doing the math for my ducting (back when i had the e30), i figured that my radiator had about 370 square inches of surface area. even with running DIY 12" ducting from the rear windows (think that pic with the red car earlier in the thread), i'd only have 226 sq.in. of air intake. but i figured at speed the 60% coverage would work out OK, if not i'd add a one or two inch scoop along the length of the sunroof, which would bring my air intake size close enough to the dimensions of the radiator

justin, on the other hand, has a humongo 589 sq.in. radiator that's only gonna be fed with four 3" naca ducts (never seen any for sale bigger than that, though granted i haven't done much shopping for em). by my math that's about 28 sq.in. of air intake. aka not quite 5% of the surface area of the radiator. even 8 is only 56 sq.in, which is easily still insufficient. not sure how well that's gonna work bro, might wanna consider using bigger ducts, i don't think naca ducts are the right fit for this job

[Piner]

Pat goodins S13 I think is the right way to do it. The entire rear 1/4 windows are ducts

[hatfan]

Hey guys

This is the setup that I'm going to use on my E36 sedan. The radiator is from a 7 series and the fan is from a MB Vito. The fan should suck in a sufficient amount of air. The piping will be a 40mm aluminium tube and I will be using the stock water pump (M60B40). Ill post more pictures when its ready. The two small quarters without the 3mm polycarbonate sheet, will be filled aswell.
563091563092

Cheers from Estonia.

[jalopi]

i dunno about that radiator intake placement, but your rear bumper paint sure is dope

to give you some insight as to what i'm skeptical about, here's a side shot of a 5 series in a wind tunnel. the e36/39 profiles are close enough to use this as reference

http://www.m5board.com/vbulletin/attachment.php?attachmentid=110284&stc=1&thumb=1&d=1278643799

here's another shot of a e36 in a tunnel, though at a worse angle

http://i.imgur.com/OLLV8BA.jpg

now i'm not an expert in fluid dynamics or anything, but i have learned a thing or two from this guy who is and his youtube page

https://www.youtube.com/channel/UCHqgnBEbgkljvHQUg9MQfKA

if you watch a few of his videos, you'll see why this inlet design is bad. i too used to think that high pressure airflow would follow the rear glass and skim over the trunk, but that's not how it works (as visualized in the pictures above)

the reality is on cars shaped like ours the high pressure airstream breaks off a few inches below the roofline. this is why you usually see airfoils placed around this area. basically what this means is alot of the airflow going through your radiator is gonna be low pressure, low speed air

also, most fans can only push 2-3000 CFM of air, which isn't enough to keep a car running cool. really your fan is only there for cooling your car at speeds under 10-20mph. for instance, if you have a radiator air inlet opening of about 20"x20", at just 30mph you have approximately 7300 CFM of air passing through your radiator, just from the force of your car moving down the road. at 60mph, this figure doubles. around/a little over this speed and your fans actually become a restriction. this is why some racecars don't even bother with a fan

anyway, will this work for you? probably good enough in cooler temps, just don't be surprised when you find yourself hosing your radiator down with a weed sprayer every other run when it's hot out

[Novablue454]

Pat goodins S13 I think is the right way to do it. The entire rear 1/4 windows are ducts
This is what I wanted to do, however I have yet to find a single clear scoop other then the small NACA ducts.

[jalopi]

what ever happened to molding your own?

[protomor]

Speaking from personal experience, I think you're thinking too linearly about it. The airflow characteristics you're talking about is for full bodied cars. If you're running a rear rad, generally, the bottom of your car is an open void to the world. The fans should help draw air through at higher speeds. Perhaps even a siphoning effect at speed. Though, both for and against our opinions is the fact that we will be sideways. Aerodynamics goes out the window at that point. Not to mention that the extra fluid capacity and length the fluid has to run through will help cooling anyway.

[Novablue454]

what ever happened to molding your own?

Turned out like shit. I guess Lexan is super hard to vacuum form without bubbles. I've searched the internet high and low for other solutions but it seems a roof scoop and NACA ducts are the only options, and even then the roof scoop would need to be custom.

I did get in a discussion the other day about scoops vs ducts, and apparently proper placement of LP ducts will move more air then a scoop, especially when sliding sideways.

I'm not really concerned. My radiator is MASSIVE compared to a stock LS, and I've seen plenty of guys at tracks having no problems with 4 NACA ducts. If it poses an issue i'll readdress it later on.

My major issue is how to get coolant from the rad to the engine and vice versa.

[jalopi]

maybe, though i don't know enough about the subject to debate it. honestly i think the extra coolant is the only saving grace of these setups, i think when i crunched numbers for my car i figured out i'd be adding nearly two gallons of coolant to the system

it would be interesting to see a drift car placed at a 45* or something angle in a wind tunnel though. recently that graysgarage guy has been taking commissions, maybe one day i'll see what his prices are like and send him a model

- - - Updated - - -

? what's the issue with getting coolant to the radiator? water pump lines still hitting the serp belt?

[protomor]

Added weight is bad. But better weight distribution and more room up front. I made a post on my blog about it. Really, I think it's only useful for full on draft cars. Helps with front impacts and not being down for so long. Gotta plan for some kind of impacts!

[Novablue454]

- - - Updated - - -

? what's the issue with getting coolant to the radiator? water pump lines still hitting the serp belt?

Nah, well that's a whole separate issue. I don't want to route the lines inside the passenger compartment, but it seems to be the only logical way.

[jalopi]

so this got me reading alot about naca ducts. i then found this cool calculator that visualizes the best way to make your own custom naca ducts!

http://www.miataturbo.net/general-miata-chat-9/diy-naca-duct-calculator-24534/


*edit - not enough room to run the piping next to the brake lines and stuff?

[protomor]

Most people run them along the framerails.

[Novablue454]

yeah, like my header have a nice gap from the framerails, but it's not enough to fit a -20an through, and I wouldn't want my rad hoses that close to the headers anyway. Unfortunately between the header and the rail is the only way to come up from underneath the car that I can think of. I can go inside the trans tunnel to about the point where my V bands are and then space get's real tight. Not to mention I still have to mount the corvette FPR there and run the fuel lines beside the bellhousing as well. I will also have to get a custom expansion tank made to take the 2 -12AN from the block to 1 -20AN to the radiator as well as tee in my steam vent line.

[audioscience10]

For what its worth my buddy Shane is running a rear mount in his GTO. He has a full shroud around his rad inside the car with lots of ducting. He is running a roof scoop, quarter window vents, and quarter panel vents. I don't know what he is running for fans. I haven't seen him have any issues with cooling.
http://image.thefabricator.com/a/still-building-america-taking-it-to-the-limit-and-then-some-9.jpg