Engine bay cooling

Rob. Smith · #1 (**permalink**) 10-18-2008, 04:47 AM

Just curious. My "other" cobra is a DRB and the cooling vents on the sides are dummy vents, there is no exit air flow there. Does any DRB owners have any other probs with heating...mostly stationary in traffic. My other cobra seems to have an issue with radiator fan flow...I think moving it back away from the radiator core will improve flow.....but where does the air go ?
Smithy

tomcat racing · #2 (**permalink**) 10-18-2008, 06:21 PM

get a custom alloy fan shroud fitted to your radiator with a 2800 cfm fan and you wont believe how much air pumps through your radiator, the air will escape from under the car, i checked out a lot of cars at the nationals and hardly any had shrouds fitted,a shroud is the single best thing to improve air flow. i live in NQ and it fixed my traffic light heating. norm at aussie desert coolers in melbourne will build you a custom alloy radiator with shroud and 2800 cfm fan for about $1200. most fans pump about 2200cfm. also for your water pump to work properly the top pulley has to be about 10% smaller than the bottom pulley so it overdrives the pump. what a joke the drb vents are dummys must have been a reason. good luck tomcat racing

acecob · #3 (**permalink**) 10-19-2008, 12:05 AM

I own a DRB, heat has been a killer for me from day one, the reason the vent holes are not open is because the foot wells cover two thirds of where the hole is, I have cut holes in mine where the foot well ends and to be honest I dont think it has made much of a difference. even if the holes were bigger I dont think you would get much cooling from them as most uf the heat escapes from under the car anyway.

By the way in traffic, driving casually I dont get many probs its only when I drive it harder, It seems your prob is getting air through the radiator, like tomcat said a good flowing fan and a shroud could fix your prob

cameron02 · #4 (**permalink**) 10-19-2008, 02:27 AM

I made the vents on my DRB functional. I cut out the accessible 1/3 and made fibreglass tunnels to the engine bay. Simply cutting out the 1/3 will not have any affect as the engine bay is still blocked off, it will simply pull air from the wheel arch area. I would post pics but my car is in for painting at the moment.

The vents offer virtually nil cooling when the car is stationary. As far as I know they work like this.

As you are driving the air passes over the vents. Because the vents are rear facing the air passing over them has a pulling effect (suction). This results in air being pulled out through the vents.

Ceramic coating you headers will also help reduce under bonnet temps but if your engine is overheating then the cuuses could be multiple. Air in the system, unsuitable radiator etc. You could try fitting a thermo fan to the front or rear of the radiator for extra cooling.

Rob. Smith · #5 (**permalink**) 10-23-2008, 03:42 AM

Thanks all, This car has a shroud but it turns out that the fan sux nothing....Will be looking into a faster fan or experiment with moving the fan away from the radiator a bit to create a decent flow without radiator fin turbulence.
Thanks again to all for the input.
Smithy

cameron02 · #6 (**permalink**) 10-23-2008, 04:03 AM

Hi Smithy,

As far as I am aware (which isnt much) the closer the fan the better. The fan will lose pulling power very rapidly as you move it further away because it will start to pull air from the engine bay instead of through the radiator as this is less resistance, this is what shrouds are designed to prevent. You could maybe look at a fan with more fins or fins with a bigger curve so they pull more air. Personally I prefer thermo fans but they are no good if you want the retro look.

bobcowan · #7 (**permalink**) 10-23-2008, 09:00 AM

The side louvers do almost nothing. The area behind the wheel well is a low pressure are, so there's no draw. Airflow inside the engine compartment is blocked by the wheel well.

Phil Hill's car had louvers punched in the hood for air flow. Apparently, that worked pretty well.

A stock 351W should not be producing that much heat. Since you already have a shroud and a decent fan, you should look in other areas for sources of heat - timing and mixture.

Rob. Smith · #8 (**permalink**) 10-25-2008, 03:22 AM

Quote:

Originally Posted by cameron02

Hi Smithy,

As far as I am aware (which isnt much) the closer the fan the better. The fan will lose pulling power very rapidly as you move it further away because it will start to pull air from the engine bay instead of through the radiator as this is less resistance, this is what shrouds are designed to prevent. You could maybe look at a fan with more fins or fins with a bigger curve so they pull more air. Personally I prefer thermo fans but they are no good if you want the retro look.

The fan has multi blades and spins pretty fast...you can feel a small draught through the fan but it seems to be lost a few inches away. The shroud is sealing the radiator to the fan. If you move the fan and shroud back the air flow should become smoother and more effective. This is proven with oil coolers and air condition condensers. There must be a gap between them to allow the air flow to become a "flow" and not a cavitation. I proved this with a mustang I built. It had an oil cooler, air con condenser, transmission cooler and then the radiator. All sandwiched together...Stupid. I seperated each one by1 inch and you could feel an actual draft through the whole lot. The only shroud was around the fan after the radiator. This cooled the big worked cleveland like it had no air or auto. The dyno man suggested a commodore fan and shroud. i feel a little modification will work.
Thanks for all the input every one.
Smithy

TUF-427 · #9 (**permalink**) 10-28-2008, 12:14 AM

Its All about surface area,

A 16inch thermo bolted to an average size radiator would probably only cover 50 -60% of the available fin area,

Thats why a correctly designed shroud works so well as it will pull air thru 100% of the fins with a decent enough fan.

I only use a Davies Craig 16in rated at 2200cfm and never had any real problems,
originally used a 3 row brass radiator and are now using a two row alloy radiator with the same fan bolted straight on.
The alloy radiator definatly better for keeping the car cool on the track..

I have seen some of the cheaper brands of fan are the same size with half the cfm rating so may be worth a look what your using.

I also have to defend DRB here,
the air vents are mostly blocked off to allow for very long footwells;
so people 6 foot+ can sit IN the car and not on top of it like some of the other kits available...

I also have a story of a guy that was having overheating problems in a Cobra,
he had the bonnet completely sealed around the opening,
Someone suggested to him to remove the rear half of this seal to fix the problem,
He thought this sounded like absolute rubbish but humored the guy and removed the bonnet seal,
Problem solved!

Peter..

Rob. Smith · #10 (**permalink**) 10-28-2008, 03:36 AM

Good tips, I'll forward this on to the owner...Thanks again to all with the info.
Smithy