Cockpit Airflow

[Neal]

In an effort to reduce the greenhouse effect I've added a 100cfm fan to extract air from the cockpit. Sure, I could have added A/C but 80% of the time it's not necessary in my climate zone and heaven forbid I should lose those extra few horsepower.

Fan and grill were sourced from www.digikey.com for US$25.

Just another idea....

 

[Rick Muck- Mark IV]

Sounds like a good idea to allow for exit airflow however I am always concerned about any opening from the cockpit into the engine area. Any opening poses the possibility of fuel/oil/hot water entering the cockpit in the event of an "event".

There are a large selection of small fans available from www.hosfelt.com as well as some nice wiring tools and parts.

I really think the hot set up would be to duct the fan to the roof exit vent. It would extract air at low speeds and when the speed increases the vent will flow more air than the fan can. As I remember from my copy of "Racing and Sports Car Design" from the '60's the ratio of area is 1:6, that is max airflow will occur with an exit 6 times the size of the entrance. This would require a pretty big roof vent! The early Mk Is had the punched vents across the rear of the spider, the later cars had the reverse NACA duct type exit. Obviously opening the vents on the side windows will help. I am afraid the reality is that the car was designed for "max" airflow in the cockpit.

Remember Ford abandoned the "flow thru" design the earliest cars had due to aero issues that cost horsepower.

I have baked at Watkins Glen in P1116 on a 85 degree day. Some of the 40 owners just removed the side windows for airflow.....bad aero but good ventilation!

Rick

 

[Jim Glickenhaus]

I would also worry about Carbon Monoxide.

 

[Brian Magee]

My NACA ducts behind the headlamps are connected to the eyeball vents on the dash. They have small fans in the pipework for when the car is stationary. To create a flow-through of air, I have grilles low down behind the back of the seats which open into the 1 1/2" space between the cockpit and engine bay. this then vents into the area between the sides of the engine bay and the fuel tanks and exits out of the opening for the lower radius arms. I have no smells from the engine and seems to work very well. Anything over 25 mph, I get a good blast from the eyeballs.

Brian.

Editor, Fortyfication.

 

[Jim Glickenhaus]

You can't smell CO and that is why it is so deadly. If you pressurize cabin as you have IMHO you should vent cabin not open into engine compartment.

 

[Neal]

This is set up pull air out of the cockpit. 100 cfm is a heck of a lot of air movement. I also have the NACA ducts opened up to provide fresh air to the cockpit via ball vents. CO is a valid concern. I may duct this to the door sill and maintain a barrier between the firewall and cockpit. Food for though...

 

[Julian West]

Hi Neal,

I reckon the ducting is a good idea. There was an earlier thread about the rear clip 'balooning' at speed, caused by high pressure.

If your fans vent into the engine room they will have to work against the high pressure, which may render them ineffective, or worse!

 

I have also ducted the front side NACA ducts to the eyeballs (no fans yet) which is fine when the car is moving but I think allowing the hot air to escape from the cockpit is equally important.

I would also SERIOUSLY NOT connect the cockpit to the engine bay, under acceleration I have slight petrol smells come from the engine bay (pumpers) as hot air comes up the gearstick gaiter - this indicates to me that the engine bay is under greater pressure than the cockpit, not good for ingress of the aforementioned CO etc.

I plan to fit fans (as Brian has) and take round ducting to a point ahead of the rear wheels in the rear wheel arch (next to the radius arms). This way the driven air should not meet any particular pressurised resistance.

 

[Rick Muck- Mark IV]

It may be possible to fit a "flapper" valve to the air outlet as some street cars today have. This would seal against CO entry while allowing air to exit. I am not expert in aiflow but I seem to recall reading somewhere that having the fan at the exit rather than at the entrance of the airflow can be more effective. The real problem with venting a 40 is the lack of any exterior area to put the exit vent without fouling the appearance. It would be possible to put exit vents on the lock face area of the doors IF the weathersealing was moved inboard to the area where the door meets the inner door panel, that would allow an exit vent area that does not open to the engine bay and is in a possible low pressure area. Not an easy operation. I agree with Jim (J-6) that any opening intro the engine compartment is risky at best. I would not want to find myself sitting a pool of fuel....see the "crash test" pictures in the book SHELBY GT40 for a scary view of what happens when the fuel is pushed up the filler tubes and the caps blow open...like the accident that happened to the guys on the road near LeMans that was posted here.

Rick

[ May 08, 2003: Message edited by: Mark IV ]

 

Not that I would want to copy a Ferrari but looking at a 308GTB I drove a while back, it had louvres in the rear of the sills just ahead of the rear wheel. As I mention above I think would this would be relatively safe exit if concertina style round duct was taken from vent behind the seats. A fan could be used near the rear to pull the air out.

The other issue with the GTD design is that the sills are open to the engine bay on the inside - if these where sealed it would prevent a lot of hot air and gases from being driven up the side pontoons and noticeably through the gear lever gate. I think this might also keep the cabin a bit cooler.

I would prefer to try to get air out of the top of the cockpit but there seems no easy option in this area without it showing bigtime.

 

to solve so greenhouse effects inside your GT40 there is a companty in the uk that make a air con unit that is ideal they say for GT40 customers. You can find it at www.nfauto.co.uk and will cost u around £800 which is expensive but when stuck in traffic on a hot day could be money well spent.

 

[Julian West]

I find this an interesting topic! Some well placed vents and inlets could make the car much easier to live with, without the complexity & weight of AC.

Has anyone any info on the aerodynamics of the car, showing the high & low pressure areas? Presumably the front NACA ducts are in high pressure areas, so it would make sense to fit the corresponding vents in a low pressure area??

 

[Jack Compton]

For those of you using the front NACA ducts to direct air to the eyeball ducts in the dash, how have you attacked the problem of the front clip opening and closing, and the affect on the hose? A fixed tube along the underside of the clip to the front bulkhead? Would appreciate your ideas...I want to do the same to my car.

Thanks-Jack

 

Jack,

Here's how I did it - please see the photos below.

There was very little room to get a vent through so I made a round hole next to the fuel filler. I fitted a piece of black house drain pipe joiner (!) cut down (you can hardly see it). This took a 60mm hose inside the car perfectly.

On the outside I made a channel out of aluminium with a flange to bolt to the bulkhead and used Sikaflex to seal it to the drain pipe.

You can just see the fibreglass channel in the deck underside shot. I haven't sealed it properly to the ally channel just a few layers of foam to keep most air going straight on. I really need to address the problem of water inflow though it will 'leak' at this join so for the few times I expect to be driving in the rain it should suffice.

I should add that it works great, a real blast of air once you get going.

I would like to able to turn it off sometimes as it can get annoying, so a round valve somewhere in the tube/channel would be an improvement. Also I was thinking of plumbing it to the heater unit so that I can use the fan in this unit to draw air in when stationary - this would be a more conventional arrangement.

Dave Champ

[ May 21, 2003: Message edited by: Dave Champ ]

 

[Neal]

Dave,

You might consider a blast gate as a means to regulate flow. These are typically associated with woodworking dust collection systems.

 

[Bo Eliasson]

Dave,
I think it looks great. I like it! I had a similar idea but I must say your solution is better.
To get the air out of the cockpit, wouldn't it be possible to run similar fibreglass channels under the rear deck to exit in a 'low pressure area' at the rear?
Just a thought!

 

Neal, I was thinking of a flap (in the form of a hinge) between the deck and the bulkhead which would divert the unwanted air into the wheelarch.

Bo, if a fan assisted vent was organised your idea could be very effective, I think I'll have a look.

 

[Robert Logan]

At Roaring Forties we collect fresh air from just in front of the radiator and using aluminium tubes and normal air hoses we deliver the air to the air conditioning unit. The A/C unit has 50% of its air fed this way and the other 50% is recirculated from the cockpit. This addition of fresh air is VERY important as it stops carbon monoxide poisioning.

I completely concur with the answer above questioning the venting into and out of the engine bay. This is a very dangerous thing and it would be my greatest concern that the driver would get drowsey.

If engine bay temperatures are high than exhaust the engine bay using fans positioned at the rear vents. We have done this and it has been to great effect.

Best wishes,

Robert

 

[Neal]

I've stared at this with feedback in mind and decided to shroud the exit and duct it to the front of the rear wheel opening. Pics to follow...

 

what about using helicopter vents the small circular ones one each side then you can twist it around to draw air in one side and face the other one backwards so the air can escape that way you always have a flow of cold air very simple but effective and cheap /ubbthreads/images/graemlins/tongue.gif