Radiator perpendicularity to airflow, how important is it? Options

[bondo]

I'm working on radiator placement, and wondering if it's super important to mount it vertical. I know tilted radiators have bene done in 914s before, but they're usually very large radiators that wouldn't fit if standing straight up. It seems like some angle off perpendicular might improve cooling by introducing turbulence within the radiator? Too much and obviously there'd be a disadvantage. Do any manufactured watercooled cars have a tilted radiator? Seems to me I saw an RX-7 once that did. I know that the intercoooler on our WRX is pointed nearly straight up (with a scoop directing air downwards into it) and way more bugs hit the back half than the front, presumably meaning most of the air does too.

I figure that at worst I'd lose some effectiveness at cruise, because if the car is not moving, there is no airflow to be perpendicular to. Do most 914 V8s that have cooling problems have them at cruise or at idle?

[bd1308]

from what i have heard some people complain of heat related problems in 914/V8s when cruising or going uphill....


b

[lapuwali]

With appropriate ducting, the angle to the airflow isn't important. What's important is to have higher air pressure on one side of the rad than the other. You could have the rad be completely parallel to the airflow into the inlet duct, so long as you had the outlet side ducted to somewhere with lower pressure. This also means completely ducting the rad so air on one side has to go through the rad rather than around it.

Paying attention to the rad outlet can pay significant dividends in getting good airflow through the rad. If you can duct the outlet to a low pressure area, you'll get much better airflow than if you simply had it dump into the trunk. The commonly seen hole in the floor of the trunk will cause the air pressure in the trunk itself to fall some as the car moves, due to airflow under the car past that hole. A similar arrangement with a hole in the lid, with a flip-up at the leading edge of the hole, will also cause a low-pressure area. If you then seal the rad to the trunk walls so air comes in under or through the front bumper, and can only go through the rad to get to the trunk, you'll get good flow through the rad, even if you laid the rad completely flat.

[Rough_Rider]

Lotus Elises's & Exige's Both Mk1 & Mk2 variants use sloping radiators. They also have large ducting above the rad to extract the air over the car.

Many sportscars are setup like this. Enzo, McLaren F1, TVR's, plus DTM machines & various touring cars.

Getting sufficient airflow is the key, so think about ducting to & away. Mount some electric fans on the backside. Do a ton of research.

FYI i did something similar with a oil cooler on a Corrado, just used a slightly larger cooler.

[bondo]

QUOTE (lapuwali @ Nov 10 2005, 03:46 PM)

With appropriate ducting, the angle to the airflow isn't important. What's important is to have higher air pressure on one side of the rad than the other. You could have the rad be completely parallel to the airflow into the inlet duct, so long as you had the outlet side ducted to somewhere with lower pressure. This also means completely ducting the rad so air on one side has to go through the rad rather than around it. Paying attention to the rad outlet can pay significant dividends in getting good airflow through the rad. If you can duct the outlet to a low pressure area, you'll get much better airflow than if you simply had it dump into the trunk. The commonly seen hole in the floor of the trunk will cause the air pressure in the trunk itself to fall some as the car moves, due to airflow under the car past that hole. A similar arrangement with a hole in the lid, with a flip-up at the leading edge of the hole, will also cause a low-pressure area. If you then seal the rad to the trunk walls so air comes in under or through the front bumper, and can only go through the rad to get to the trunk, you'll get good flow through the rad, even if you laid the rad completely flat.

Cool, that's what was going through my head, from a common sense point of view. It will be fully ducted on the inlet side, with a vane in the middle to keep things even top to bottom. The outlet side will be at least partially ducted, but parts placement there hasn't been fully worked out yet. It will definitely be sealed so there is no way for air to go around the radiator.

(I've been contemplating adding a mid-vane to the WRX intercooler to help even things out, or at least spread out the bugs) (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

[Andyrew]

Most have the problem of cooling while at sustained speeds...

Havent heard of any v8 car that overheated in bumper to bumper traffic. If so... their fan design was very poor.

[andys]

The outlet not only needs to be in a low pressure area, but also needs to be greater in area than the inlet. A rough rule is the outlet area s/b 1.7 times larger than the inlet area. Do not try to ram air into the inlet. Rely on pressure the differential between the inlet and outlet. Seal the ducting (if applicable), especially on the outlet side.

Take a look at your typical shifter kart. Though generally a poor example of managing flow (They just stick the radiator out in the airstream), they normally tip the radiator back (the top). Some years ago, they found out that their coolant temps went down when they did this.

Andys

[jsteele22]

Sounds like good advice. Think of it more in terms of a pressure difference than as wind. My hunch is that the uneven distribution of air flow (and bugs) doesn't have a huge effect. Just means that heat is removed more rapidly from some spots, less rapidly from others. (Of course, removing the bugs will surely help !!!)

I think that, in rough terms, making air change direction isn't too detrimental, but anything that causes turbulence (like sharp turns, abrupt changes in duct size, etc.) will cause less flow, and possibly stagnant zones (eddies).

BTW, what do people make their ducting out of ? Sheet metal ? I was thinking it might be fun (possibly even worthwhile) to try fiberglass. Make a space-filling model of the volume using some kind of packing foam, styrofoam, Great Stuff,etc., cut and shape w/ a hot wire, surform, knife, ... and then lay on the fiberglass. Prolly a lot more work, but I imagine it could be made to look really nice. And then you don't just have a duct, you've got a product....

Also, FWIW, I can't be sure, but I think I heard that on Corvettes (no grille) the radiator is close to horizontal, and the air comes in from below via a scoop, and is drawn back out by a backwards scoop. Anybody know for sure ?

[Aaron Cox]

look at an H1 hummer. the radiator is basically flush with the hood (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif)

[Crazyhippy]

I've seen cars not cool in traffic, but cool fine on the road, and cars do fine in traffic, and overheat at speed... It's all in the radiator design.

exactly what are you trying to do? I'll be happy to discuss specifics, but dont want to type a novel on what not to do.

BJH

[bondo]

QUOTE (Crazyhippy @ Nov 10 2005, 06:59 PM)

I've seen cars not cool in traffic, but cool fine on the road, and cars do fine in traffic, and overheat at speed... It's all in the radiator design. exactly what are you trying to do? I'll be happy to discuss specifics, but dont want to type a novel on what not to do. BJH

I'm trying to make my 914 not overheat. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) I'm also trying to save a little front trunk. I have a radiator that is smaller than the stock firebird radiator, but has 12% more surface area. It should be able to cool the same engine, in a lighter car, considering the stock radiator kept it very cool even with an AC condenser preheating its air. I just have to make sure this smaller radiator gets plenty of air.

[dbledsoe]

QUOTE (bondo @ Nov 10 2005, 08:12 PM)

I'm trying to make my 914 not overheat. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) I'm also trying to save a little front trunk.

I wouldn't worry too much about saving front trunk space, it's not really practical.

The radiator in my 914 Buick V6 conversion is at an approximate 35 degree angle (from vertical) and I have no problem with flow and have space in the front trunk, but I wouldn't want to put much of anything in there, perhaps a deflated type spare tire or a few tools well tied down. From my experience do not count on airflow to come from beneath the car if you have a spoiler up front. It becomes a low pressure area (beneath the car) and air will not flow in freely i.e., without a large fan(s). Duct from the front of the car through a bumper hole cut and vent through the wheel well cut outs (as is the defacto standard) and you'll have no problem with air flow.

If Guy could chime in here I know he has a lot of experience with this subject (living in Arizona with a V8 conversion that does not overheat in their exteremly high daily temps). He sure helped me with my conversion and placing the radiator/airflow openings.

[914GT]

I would pretty much agree with everything that's been said so far. For a basic cross-flow radiator I don't think it matters much how it's oriented. Probably horizontal arrangement would even improve convection cooling assuming the hot air isn't trapped above the radiator and can't flow out. But I doubt if convection is a significant factor as at low speed the fans are doing the work to provide air circulation. So the important things are what have already been mentioned - to create a high-pressure zone on the inlet side, and low-pressure zone on the outlet side, block recirculation, and minimize overall restriction.

As Don said, the angled radiator arrangement with shroud and cutouts in the front bumper (and also some opening toward the front of the trunk bottom) is a proven design. But I do like to keep an open mind to anybody else's ideas to minimize the intrusion into the front trunk. It would be nice to have a radiator setup that would allow a full-size spare tire on top or toward the back of the trunk. I've seen one or two but I'm not sure if they'd work well here in the desert.