Rear mount radiator discussion.

[Future_gohan]

So i'm in the process of doing a rear mount radiator for my car, and over the past few months i've been doing a ton of research to best of my ability wile also look in person at other peoples setups deciding what will work best for my setup.

Now i have the radiator mounted, and have started working on how to channel the air to enter and exit smoothly, and to block the heat away from me as best as possible behind the cage.


Now the big question is for people who have experience with rear mount radiators, is deciding on what water pump to run.

I'm currently running an SR20, possibly later on running an ls platform, but not 100% set on that.

Should i run both my factory water pump, and an inline water pump. Only Factory water pump, or only inline water pump.

I worry about the factory pump and the inline pump somehow working at different speeds and causing the car to over heat, but on the other hand i don't feel the stock pump has enough power to move all that extra coolant it'll have.

Anyone who has experience with this would be great, trying to get this perfect.

Also if anyone knows of the best inline pumps or good bolt on SR pumps would be awesome aswell.

[CaptainVlad]

Are you doing this for efficiency reasons (to run cooler) or just because?

I ask because there are much easier ways to build your system so you do not overheat. Ducting is obviously the most important, but a vmount with a properly ducted set up should yield great results.

Just something to think about.

[Drift_FX]

99% of the time a front mount radiator will cool better than a rear mount solely because it gets more air, if you dont NEED to run a rear mount.... dont... if you do run a rear mount most people just convert to an electric water pump....

[Future_gohan]

I'm doing it mostly out of the fact i tubed the front end from a crash and want my radiator to be safely tucked away. The ducting and such that i have done to my car should be suffice to get it plenty cool, biggest concerns are how to/what to run for a water pump. I know i should go electric but will a single inline pump be good enough or do i need to run two? I haven't been able to figure these questions out.

[dawagarage]

thats a good question that i always wondered as well (water pump.)
if i think about it, i would just run an inline pump, definitely not 2 pumps. im assuming one can find a pump with adjustable pressure/speed.

i have a tubed front and am running my rad in the same place so i dont understand your train of thought.

where is your radiator? in the cabin? in the trunk? tell us about your ducting.

[Future_gohan]

thats a good question that i always wondered as well (water pump.)
if i think about it, i would just run an inline pump, definitely not 2 pumps. im assuming one can find a pump with adjustable pressure/speed.

i have a tubed front and am running my rad in the same place so i dont understand your train of thought.

where is your radiator? in the cabin? in the trunk? tell us about your ducting.

It's in the trunk area behind the front seats, I have nascar style ducts coming from the corner windows with ducks going to the radiator with dual E fans, and the air should in theory exit through the rear window where i have it being vented to with an exhaust fan pulling the hot air out.

IMO thats more than any of the D1 cars i see with rear mount rad setups.

So, in theory i could just block off the factory water pump? Then my question would be would the coolant flow through the engine properly? So many questions i cant seem to answer 100%

[jordaninnovations]

I'd need to see pics to tell exactly what you've got going on, but if you think air's going to come out the rear window, you're in for a surprise - that's a relatively high pressure area unless you've got a huuuuuge roof wing.

We've helped with rear-mount radiators in quite a few drift cars (Conrad's Camaro in 2009/2010, when he swapped back to front-mount, and more recently Tony B's Mustang last year) and it's amazing what works and what doesn't. Where the air exists (pressure behind the cooler) is more important than where you're getting the air (pressure in front of the cooler) - cutting out the floor and the back of the car is the best way to get low pressure behind the core.

As far as the pumps, there's a few issues - flow for sure, and head pressure. You've got a HUGE increase in capacity, so it'll take longer to heat the water up, but if you're not flowing enough you'll have a cool radiator and a warm engine. IIRC, we started with the standard Meziere external (50gph I believe) and it wasn't enough, and went to their HD/super pricey pump and did fine.

Running a factory pump on the engine and an aftermarket electric pump down low, mounted in back sounds like it'd be fine (electric pump would be helping quite a bit at low engine speed, mech pump would start to flow more at high rpm), but I don't know of anyone running the stock mech pump in conjunction with an electric - doesn't mean it doesn't work!

[zerodameaon]

Don't know the quality of this but I have seen one on a SR20DET S14. The rad was in front and the guy was just one of those do it cuz he can guys so IDK how well it would flow all the way to the back.
Meziere WPK510 ises WPK510 Electric Water Pump Kit - Nissan SR20DE (http://www.frsport.com/ises-WPK510-Electric-Water-Pump-Kit---Nissan-SR20DE_p_30270.html)

EDIT: Haha well guess Jeff kinda answered that lol.

[Future_gohan]

I'd need to see pics to tell exactly what you've got going on, but if you think air's going to come out the rear window, you're in for a surprise - that's a relatively high pressure area unless you've got a huuuuuge roof wing.

We've helped with rear-mount radiators in quite a few drift cars (Conrad's Camaro in 2009/2010, when he swapped back to front-mount, and more recently Tony B's Mustang last year) and it's amazing what works and what doesn't. Where the air exists (pressure behind the cooler) is more important than where you're getting the air (pressure in front of the cooler) - cutting out the floor and the back of the car is the best way to get low pressure behind the core.

As far as the pumps, there's a few issues - flow for sure, and head pressure. You've got a HUGE increase in capacity, so it'll take longer to heat the water up, but if you're not flowing enough you'll have a cool radiator and a warm engine. IIRC, we started with the standard Meziere external (50gph I believe) and it wasn't enough, and went to their HD/super pricey pump and did fine.

Running a factory pump on the engine and an aftermarket electric pump down low, mounted in back sounds like it'd be fine (electric pump would be helping quite a bit at low engine speed, mech pump would start to flow more at high rpm), but I don't know of anyone running the stock mech pump in conjunction with an electric - doesn't mean it doesn't work!

Well the z32 has a very low roof line, and i have rear luvers on the back window in junction with the exhaust fan, reason being is i see everyone cutting the center out of the trunk and exiting it that way, but its not an option for me.

I was debating on cutting holes in the floor or not too, and how i should go about doing that but again, haven't touched that section yet.

Don't know if you an answer this or not, but do you think the mech and electric pump would fight each other at all moving at different speeds? Thats my worry as I realize if not done correctly the rad could end up cold and the engine hot, which is obviously what i'm trying to avoid.

Would it be more efficient to run an exhaust fan exiting under the car then instead of the window? I haven't cut the plexi yet for the fan so that is an option to do aswell.

[Future_gohan]

Don't know the quality of this but I have seen one on a SR20DET S14. The rad was in front and the guy was just one of those do it cuz he can guys so IDK how well it would flow all the way to the back.
Meziere WPK510 ises WPK510 Electric Water Pump Kit - Nissan SR20DE (http://www.frsport.com/ises-WPK510-Electric-Water-Pump-Kit---Nissan-SR20DE_p_30270.html)

EDIT: Haha well guess Jeff kinda answered that lol.

I like the block off plate but it doesn't say what that pump is rated at, i guess close to stock would be my guess.

[oni jake]

Here's a really good article about rear mounted cooling. It's for off-road trucks, but the concepts and technical discussion carries over.

http://www.crracing.com/wp-content/uploads/2009/10/COMP_DS0909.pdf

Water Flow Rate

Research has shown us that water flow rate is very important to a cooling system’s overall efficiency. Contrary to old-school thinking, the higher the water flow rate the better the cooling. Flow rate is regulated by the size and speed of the pump, restrictions in the engine water passages, radiator size and plumbing. High-flow rates provide two benefits; insures good pressure in the combustion chamber area of the cylinder heads and raises water velocity flowing through the radiator tubes. The higher the velocity through the cooling tubes, the more turbulence in that tube, which equates to increased heat rejection. Good water pumps will flow up to 100 gallons per minute (GPM) when unrestricted. With cooling system restrictions, your pump should be capable of at least 50 GPM. Remember, a good flow rate will help keep temperatures in check when conditions are adverse as they are in off-road racing. Don’t forget to look at the manufacturers recommended pulley and pump speed.

[zerodameaon]

I like the block off plate but it doesn't say what that pump is rated at, i guess close to stock would be my guess.

I did a little looking and I found mention of 20GPM so yeah not really going to cut it.

[95_S14]

You're running a sr in a z32 ?

[zerodameaon]

If he has the power to push that beast why not, it will at least have more room to work on lol.

[Future_gohan]

You're running a sr in a z32 ?

Yessir. I'm not the only one either lol

[PeaceOnesxWai]

For good ducting set up you should look into this car. Great idea that would work with Z/S Chassis. INTRODUCING "LASUPRA" EVO, AKA EPIC LANCIA - Speedhunters (http://www.speedhunters.com/2013/06/epic-lancia/) Running a lexan box parallel to the rear window with feed coming from top. If the car gets sideways adding dual naca ducts on the quarter panel is also a bonus. Of course with a design like this a tight seal air passage would be needed to run efficiently. Air should go out from below the trunk line, where it is low pressure.

As for pump I would recommend using all electric pumps, its always better to have hot water escape faster. I would also run a external thermostat as the pump would give the system higher pressure along with the extra water. :cool:

Im surprised you have to go rear mount considering the space there is in a Z32 with a SR... Im sure you can get a very nice ducted V-mount set up with the money your gonna spend. But its your money and I have no complaints on a badass race car set up

[The Dude]

I don't know anything about rear mounted setups but putting another pump inline is only going to increase pressure. You need to either get a bigger pump or have 2 in parallel to increase flow substantially.

[brndck]

just a heads up, i have a meziere electric water pump with sr20 block off plate for salehttp://zilvia.net/f/sale-items/296981-meziere-water-pump-kit-sr20det.html