question about radiators, single pass or double pass Options

[ldscamaross]

hey im looking to be getting my radiator setup install under progress soon and wanted to get your guys oppinion. Im doing the subi swap and putting in a 06 wrx turbo motor and planing on running a vf39 stock sti turbo on it. it will probably be making around 350 horse and 380 torque at the fly wheel. i am also using the subi tranny.

my question is on radiator selection. i have been looking at a duel pass radiator because of there claimed increase cooling capibility but i have also read some things against it. what are your guys oppinions on them. have you used them? im looking to mainly drive it on the street not the track. would i be better off just using a good two or three row single pass or get the double pass.
thanks in advance

[6freak]

Real 914`s dont have radiators.....but i can tell you about some cheese i once had (IMG:style_emoticons/default/poke.gif) ...

[Phoenix-MN]

Real 914`s dont have radiators.....but i can tell you about some cheese i once had (IMG:style_emoticons/default/poke.gif) ...

Hmmmmmmmmm................

Technically, what's an Oil Cooler? (IMG:style_emoticons/default/poke.gif) (IMG:style_emoticons/default/poke.gif)

[6freak]

good point ...DAMNIT (IMG:style_emoticons/default/headbang.gif)

[rick 918-S]

I don't have a suby but I run a double pass.

[charliew]

I have a stock wrx radiator and have gotten a two row aluminum radiator the same outside size. I will be running ac so I thought the stock size would be ok. I found a nice custom rad. on ebay for a toyota truck with a sb ford. The longer undercar tubes and the aluminum suby motor probably doesn't need the cooling of the iron sbc. Although 350-350- still makes the same heat. Course off boost the suby is about 200hp.

[rascobo]

After years of trial & error, (before 914World.com (IMG:style_emoticons/default/sad2.gif) ).
I now run a single pass aluminum race radiator the largest I could fit and tightly shrouded the perimeter. Cut out as much as practical of the wheel wells, installed a fully shrouded high volume thermostatically controlled fan (mine is a 2800cfm, but now they can exceed 3600 cfm) I also installed a high volume water pump (Stewert Werner) and run 1 1/4" & 1" coolant lines. I also believe that because of the ambient engine compartment temps. that an oil cooler is vitally important to cooling and engine life (despite the fact the water temp. seldom rises above the 185 degrees set by the thermostat), I find even synthetic oils cooking off within 400-700 miles with pressure dropping from 80lbs. cold / 60lbs warm to 40/20. Just one more thing, don't let the guys at the local radiator shop tell you don't need so much for your engine size whatever that may be (V8, V6, Rotory, Subie etc.), they're not familliar with these cars.

btw-Temps in this area top out around 100- 105 degrees. (IMG:style_emoticons/default/driving.gif)

[jmill]

As far as cooling goes there are alot of variables. Surface area, time and delta T (temperature differential). I'm not sold on duals. All your doing is pushing the coolant through twice the surface area twice as fast. You get the same cooling with a single pass because you pass the coolant through half the surface area half as fast. In the end it's a wash.

The way to increase cooling is by increasing the surface area (by added rows or increasing size) or larger delta T - ice cold air blowing on hot radiator.

[ldscamaross]

thankyou guys for the information. what i am planning on doing is builing a shroud from the 916 front bumper opening into the car and to the radiator. then im using the stock wrx fans computer controlled and there is two and then building more shroud to vent out the top of the hood. im planning on using the evo grill to cover the hole. i think there will be plenty of air flow and it should work pretty good.

[charliew]

If you can find a v6 fiero you might want to study the radiator setup they use. It exhausts through the bottom and works good. There are many v8 fieros running around. If you can exhaust through the bottom you will get to keep some front trunk space.

[byndbad914]

...All your doing is pushing the coolant through twice the surface area twice as fast. You get the same cooling with a single pass because you pass the coolant through half the surface area half as fast. In the end it's a wash...

not necessarily true*. without getting too deep into it, if fluid is flowing at a turbulent Reynolds value (directly related to velocity - higher velo = more turbulent) the convection is much higher at the boundary layer between the coolant and the aluminum tube than if it is in laminar flow or near turbulent flow.

For pure water, at purely laminar flow, the convection coeff can be around 300 W/square meter-K whereas at highly turbulent flow, that can be well over 10,000! And temperature drop across a cooling device is linearly dependent upon that coeff, so if you can increase it to 30 times its base value, then do so. Having high velocity flow can be very important.

*If you find you are highly turbulent through the single pass, then the dual won't help you.

Here in the laser world I have helped the R&D guys with a few cooling block designs - they tend to drill a single, big hole thru the cooling block to pass liquid coolant through, and they had temps running away on some of the current designs. For the same volumetric flow rate, I decreased the diameter and made 4 reversing runs in the block, getting both a higher conv coeff and a bit more surface area and temps decreased dramatically. It is mostly due to the higher velocity through the cooling block.

[rascobo]

thankyou guys for the information. what i am planning on doing is builing a shroud from the 916 front bumper opening into the car and to the radiator. then im using the stock wrx fans computer controlled and there is two and then building more shroud to vent out the top of the hood. im planning on using the evo grill to cover the hole. i think there will be plenty of air flow and it should work pretty good.

(IMG:style_emoticons/default/idea.gif)
Don't think cutting the hood is going to help that much, a number of owners after have done so reported no greater cooling than a properly prepared system with air exiting through the fender wells or the floor (don't do both) and with the additional drawbacks of being extremely hot in drivers compartment with the roof off in nice weather and the windshield steaming up when it rains. That said, each of us has a vision (and opinion)of the perfect car, We all gain by sharing the knowledge aquired in trying to create them. As long as Your willing to change something if it doesn't look or work the way the way you envisioned, by all means try what ever you like, but We all feel (IMG:style_emoticons/default/sad2.gif) to see someone give up and just live with it afterwards. Keep us posted as to Your progress. (IMG:style_emoticons/default/popcorn[1].gif)