Radiator Sizes & Angles?

[Doug Clark]

I've gone and got myself a bit confused so I'm hoping for some information that'll put me straight again...

Originally in my design I'd been planning to lie the radiator flat in the nose of the car, with a 4" gap between it and the floor.
A sealed duct would connect it to the opening in the nose 1/3 the size of the radiator and hot air would be dragged out through an opening at the root of the windscreen and the wheel arches.

Some examples of cars where its done like this are the Ferrari 333SP and the Enzo, P4-5, MC12 line.

So most people tell me this arrangement either doesn't work or is very hard to make work and recommend getting angle onto the rad to improve it.

At the moment I can get about 30 degrees to the horizontal on the radiator and not screw up the lines of the planned body. But is that enough to work in a 'conventional' layout? What is the 'normal' angle seen in a 40?

The radiator I have measures 21"x17.5" across the cooling element, how does this compare with whats in peoples 40's?

I have been searching for information to enable some sort calcs to back up the argument one way or the other but found nothing of any use, if anyone can point me at that sort of info I'd appreciate it?

Thanks,

[Dave Peterman]

Hi Everyone:

I could also use help with an answer to this question

Will a 19" x 29" radiator work in a GT 40?
Thanks in advance Dave

[Mark Clapp]

Dave and Doug, the dimensions depend on the size your replica is between the headlight housings, etc. My radiator is a brass 4-core, triple pass and is probably at a 40 degree angle spreading fully across the opening. I was afraid the air was bouncing off the rad and flowing under the car so I put some ABS plastic on the "floor" of the frame in front to force more air through. This topped off my cooling mods and the car stays at 180F even when it's really hot out.

[Fred W B]

Doug, not that I can help much but I have read that a problem that can occur with the setup you describe is that the local high pressure developed in front of a full screen while the car is moving can stall the air flow out of the nose duct.

Hopefully I have dealt with this in my car by having the duct exit some distance from a low screen.

Cheers

Fred W B

[Dave Bilyk]

Doug,
the alloy GT40 replica radiator from Dockings used in many replicas, is 24" x 12" x 2" matrix size, overall size is about 29" x 13.5"
angle is about 80deg from horizontal.

[Doug Clark]

All,

Thanks for the replies...

Fred, the closest the edge of the outlet to the base of the windscreen would be about 6", hopefully thats far enough away.

Dave, thats interesting, one of the ideas I'd had was to cut 4" off of the height of the rad then I can stand it vertically. 24 x 12 = 288 square inches. 21 x13.5 = 283.5 square inches which is close enough.

The motor in question is a Toyota V8 1UZ-FE if anyone thinks that might be an issue? I assume everyone is using a V8 of some sort?

[Cliff Beer]

Doug, if you're utilizing a large displacement motor (5.0 ltr+) that dimension radiator should work OK (assuming the core thickness is reasonably thick) provided you get sufficient flow past it. With that much rake and limited frontal exposure I suspect you're going to need as big of an electric cooling fan as you can get. Spal makes a variety of dimensions and outputs, and they're highly regarded, but I'd shop around to find the biggest output. In any case, it's likely going to be marginal at best. You could try adding one or even two oil coolers in well placed locations (wheel wells are common) to help with the thermal issues - these work really well if there is a way to include oil squirters (focused on the bottom side of the piston crown). In the end you'll probably have to try a few different things to manage the heat.

[Jac Mac]

Fairly sure the Toyota will already have piston squirters. With the amount of rake you have on the w/screen pressure at the outlet may not be an issue,but plan to have the exit further fwd if possible. Dont get sucked into the bigger is better argument when doing the inlet- the idea is to get quality airflow then slow it down in the area in front of the radiator while turning/directing it thru the core. Its amazing how a couple of curved vanes will help in this area.

[Doug Clark]

The motor is a 4.0L unit BTW and the core is ~2" thick from memory.

Jac Mac, I'd been thinking of the design of the ducting using the same principles as for an airbox (which I've some experience of doing on motorcycles). Its funny to find a real use for understanding Bernoulli.

Boiling it down I think that theres basically 2 options:

1. 21"x17.5" (367.5 Sq") laid over to 30 deg from the horizontal.
2. 21"x13.5" (283.5 Sq") and vertical, but 23% smaller in colling area than option 1.

The outlet issues are going to be identical in both cases, so I think that can be taken
out of the decision making process.

Who'd chose what option?

[Jac Mac]

I would lay it fwd @ the top for the extra area and being able to move the exit fwd as well.

[Fred W B]

I've also read that having the rad at an angle to the air flow, rather than exactly perpendicular to it helps the cooling by the air impinging on the vanes of the rad rather than passing straight through

Cheers

Fred W B

[Jim c]

Doug

I made my radiator.
the matrix is 24.8x12.4" it is leaning at 30deg forward at the top.
it is alloy and 2 row only,I would have to measure but I think it may only be 35-40 wide.

I wouldnt even bother with brass radiators as they will never get the heat away like alloy.
My car has not hit the road yet but I have made another for a GT40 and it works very well.

Ducting I have always used the rule of thumb 1/3 area in 2/3 area out, area being the radiator size.
I gather you will have to make your exit vents = 2/3 your radiator to let it out.
I am proberbly telling you what you already know.

Jim

[Trevor Booth]

I wouldnt even bother with brass radiators as they will never get the heat away like alloy.

why is it so when alum has half the heat transfer rate of brass and an emissivity value of 25% of a black painted brass radiator.

[Jim c]

Yes I have read that as well.
A mill finish alloy is also good I think it comes in 2nd to a black painted surface in the Bosch handbook.
I have scotch brighted radiators and intercoolers to get the dull mill finish.
An alloy painted black I have never tryed but would be interesting.

I have made a few radiators over the years and have come to the conclution that the alloy works more efficiantly.
Back to back I have had better results.
No more than 2 rows it is lighter It generaly will run less water and has still done the job.

I understand what you are saying about the brass but something seems to work better with the alloy in real life maybe it is in the fin pitch ,I dont have an answer to that.

Jim

[Jim c]

Ok Trevor you got me thinking about why alloy has shown improvment over your figures of brass copper.

I think it is the mass.
An alloy radiator 3kg verse copper brass 9kg.
It would be the mass difference, it would be easier to disapate heat from 3 kg than 9kg.
?

Jim

[Jac Mac]

Fairly easy to sort this one Jim, grab a piece of each about 6"x6" of same thickness, heat them to say 200° in the oven, then bring them out to cool, check at say 20sec intervals with pyro to see which cools fastest. Let us know the result!

Jac Mac

[Jim c]

I had thought of that.
If I get a chance I will do it tomorrow.

Jim

[Trevor Booth]

jac mac,
not the same, we are talking about transfer of heat from one side to the other.

[Jim c]

Did a bit of checking,this will help with your radiator Doug.

Bosch Automotive handbook.
Compact high performance radiators have cores which consist of alternating corrugated fins and flat tubes.the heat transfere of this design is so high that some passanger car radiators comprise only of 1 row of tubes and have an install depth of only 20mm.

What I took as the alloy radiator making the difference is not the case it looks like it comes down to the fin design.
If you could get copper painted black in this fin design I would say it would be extreamly efficiant

some other figures I found.

emissivity

black body radiator =1
alluminium unmachined=.07
alluminium polished=.04
brass matt=.22
brass polished=.05
copper oxidized=.64
copper polished.05

Copper does a good job.