aero-mods,installment#9(internal drag)

[lunarhighway]

@holypaulie

you should check out autospeed.com

they did some articles on hood vents. wich where pretty well researched
if you want to get it all right you should measure the pressure in different locations under and on the hood to see where the vent needs to be, finding the right spot is much more important than getting the right shape i think .

also this may show your car has other areas like the wheelwells wich you might (also) use to your advantage

[holypaulie]

Thanks for the info lunarhighway. I've just find out the best spot it would be close to the upper grill. Look at the picture, the blue color is low pressure area, green is high pressure and red is the highest pressure area.

[NeilBlanchard]

Hi,

Here's another example:



I think the location differs depending on the SHAPE of the nose?

[Otto]

Originally Posted by holypaulie

Thanks for the info lunarhighway. I've just find out the best spot it would be close to the upper grill. Look at the picture, the blue color is low pressure area, green is high pressure and red is the highest pressure area.

Methinks inlet at red, outlet at purple, or put the vent about a foot forward of where it's shown on that picture of the 240SX.

Do I have my low pressure color (purple) wrong?

[holypaulie]

Otto you are right.
Here is a picture showing where I am going to make a cut on my hood. I think that's the closest I can get. If I move more down to middle, my exhaust manifold will rust after rain.
Upper grill block and half of the lower one is already blocked(pic is not showing my car)

[holypaulie]

I could cover additional exhaust manifold with thin aluminium to protect from rain

[AXMonster]

My Westfield Seight has a fully ducted nose cone rad with ducted outlet onto the top of the nosecone. Its a really smooth transition with an angled rad and does work very well.

The rad has a pre & post glassfibre moulded duct that bolts onto it. Something like the attached drawing

A pic of the outlet here

[gascort]

AXMonster, I think the little drawing with your previous post is one of the better ideas. I think that's how all the production heat extractor hoods are set up.

[Otto]

Originally Posted by holypaulie

Otto you are right.
Here is a picture showing where I am going to make a cut on my hood. I think that's the closest I can get. If I move more down to middle, my exhaust manifold will rust after rain.
Upper grill block and half of the lower one is already blocked(pic is not showing my car)

Why not do a cowl flap? That's what NACA designed for reciprocating aircraft engines such as B-17, B-29, etc.. In other words, put a hinge on the leading edge of the rectangular piece you cut out, and control its upward deflection with a cable or just let Mother Nature set the angle as a consequence of pressure differential below and above the flap. Do internal exit ducting with Coroplast or similar to make a smooth exit path. You want the exiting air to be as parallel to the slipstream as possible, i.e., point it to go smoothly back over the hood. The only downside is that such heated air may be drawn into the cabin via the vent inlets of the high pressure area just in front of the windshield, but that won't amount to much if you are not racing.

When parked, the cowl flap sits in flush position with the same contour it now has, and keeps the rain out.

That's what I plan for my Porsche 944 Turbo, which has a well engineered intercooler inlet, but they sorta forgot about the outlet. Stock, the cooling air is supposed to find its way somehow down and out the bottom of the engine bay past various obstructions to flow. Ungood, especially since heat rises. I figure that in addition to sucking the spent intercooler cooling air out, it will also draw off radiator and underhood air, with otherwise heat soaks the engine. BTW, this reduces nose lift on the car, as undercar flow and pressure is reduced, and the flap also acts as a lift spoiler for the hood. So, she rides a bit lower, less drag from that and less lift on the nose for better high speed handling. Win, win, win.

For a hinge(s), I'm considering those nylon ones used on RC model aircraft from a hobby shop. Gonna fix it in position on the underside of the sheet metal BEFORE I make the cut. That way, I know the flap alignment will be perfect.

What do you think?

[holypaulie]

Originally Posted by Otto

Why not do a cowl flap? That's what NACA designed for reciprocating aircraft engines such as B-17, B-29, etc.. In other words, put a hinge on the leading edge of the rectangular piece you cut out, and control its upward deflection with a cable or just let Mother Nature set the angle as a consequence of pressure differential below and above the flap. Do internal exit ducting with Coroplast or similar to make a smooth exit path. You want the exiting air to be as parallel to the slipstream as possible, i.e., point it to go smoothly back over the hood. The only downside is that such heated air may be drawn into the cabin via the vent inlets of the high pressure area just in front of the windshield, but that won't amount to much if you are not racing.

When parked, the cowl flap sits in flush position with the same contour it now has, and keeps the rain out.

That's what I plan for my Porsche 944 Turbo, which has a well engineered intercooler inlet, but they sorta forgot about the outlet. Stock, the cooling air is supposed to find its way somehow down and out the bottom of the engine bay past various obstructions to flow. Ungood, especially since heat rises. I figure that in addition to sucking the spent intercooler cooling air out, it will also draw off radiator and underhood air, with otherwise heat soaks the engine. BTW, this reduces nose lift on the car, as undercar flow and pressure is reduced, and the flap also acts as a lift spoiler for the hood. So, she rides a bit lower, less drag from that and less lift on the nose for better high speed handling. Win, win, win.

For a hinge(s), I'm considering those nylon ones used on RC model aircraft from a hobby shop. Gonna fix it in position on the underside of the sheet metal BEFORE I make the cut. That way, I know the flap alignment will be perfect.

What do you think?

I see your are very creative and I think that's interesting idea.
PROS:
- fixed rain issue
- reduced front lift
- better radiator air flow
CONS
- more cutting
- require ducting
- require holes for hinges
- less airflow at low speed or traffic
How to mount those hinges to the flap without drilling a holes? How to prevent flap falling inside (down) ?