Closing up the bottom of the cradle, is this a terrible idea? (Page 1/2)
Threedog SEP 04, 02:45 PM
So I recently changed the oil on my 2014 Jetta TDI, and it was an incredibly clean process as the bottom of the engine bay cradle was "sealed" by a plastic "underbelly".

I was thinking about doing the same thing on my L67 Fiero. Creating/reusing a piece of plastic underneath the cradle. Is this a bad idea? I am a little concerned about heat issues. I would only cover the inside of the cradle, so the exhaust and control arms would still be obviously free to move around.
Flying_Dan SEP 04, 02:48 PM
I think that would be a bad idea. There is airflow needed to keep things cool back there.

Had a an early Boxster years back and it had a plastic shield. But, there were openings to allow airflow from bottom and exit out.

I guess if you could ensure you still had airflow?
cvxjet SEP 04, 02:59 PM
You have to manage airflow around the engine- the newer cars have had a lot of designing/research/testing to make sure the needed airflow is still there. Air can do some odd things; When I talk to "Hot zhit" teenagers who "Know it all!" I like to to show them the venturi effect; Take two pieces of paper, hold them an inch apart, and ask the kid what will happen if I blow between them- which way will the papers move? Everyone, without fail, says "OUT!" and then I do it and the papers come together....Faster moving air creates lower pressure...Then I tell them, "Don't think you know everything- You don't!!!"

Seems to work well.....
Blacktree SEP 04, 05:58 PM
That's funny. I consider the belly pan on my Jetta to be an annoyance... another piece of plastic that has to be removed to get at the engine.

That said, having a belly pan on the Fiero engine cradle might clean up the aero a bit. I would suggest leaving a gap between the cradle and the firewall, for air circulation in the engine bay.

[This message has been edited by Blacktree (edited 09-04-2019).]

olejoedad SEP 04, 06:30 PM
Exhaust routing and heat could be an issue....
hyperv6 SEP 04, 07:01 PM
No you do not want to do this.

GM spent considerable amount of time to create airflow on these cars. They pick up air under the car and flow it out the top. This helps keep the air flowing around the engine and electronics and keep them alive.

VW and others today are using belly pans for better aero numbers but they also have the airflow compensated for the pan.

What may sound like a good idea is not always as it appears.
Spadesluck SEP 04, 07:51 PM
Aside from any possible heat problems, I certainly understand some of the why but aesthetically no one would even notice it at all. Then the question would be why would you want to if you can not even tell what you did.
WKDFIRO SEP 05, 09:14 AM
I say go for it. The space you are talking about may not affect the air flow for cooling as much as everyone thinks. You would have to make sure that it is very secured at the front so highway speeds don't try to peel it off. If you are going to drill into cradle be reminded that it is hardened steel and structural rigidity will need to be watched or cracks may form. Once you have it on, test it, watch the Temps and see if you gain anything from cleaner air flow under the car or throw all in and "clean" the whole bottom of the chassis between the front axle to the front of the cat. If it heats up, you can take it off. Big deal. Yes they did research on airflow under the car, but it's doubtful they would have spent an extra nickel improving highway airflow under the car any further than cooling.
fierofool SEP 05, 09:30 AM
On FWD cars, air comes in at engine level and even if the belly is closed, the air flows over the engine and out at the bottom of the firewall, in most instances. The old VW Beetle had a sealed engine compartment so to speak. Air was forced up at the front of the engine fan shroud and was routed through the fan to pass across the cylinder heads. Excess air passed up through the engine bay and exited out the vent grill just below the rear window.

The Fiero uses air turbulence underneath the cradle created by a low pressure area in the engine bay as the car moves along. That is accomplished by allowing the air to exit through the vents at the top. To close off the bottom would allow what would be cooling airflow to just pass on out underneath the rear bumper. In my opinion, if modificatons were to be done underneath the cradle, it would to place deflector airdams underneath to catch and direct air up into the engine bay. I know this would probably create other problems such as water, dirt and other road debris being drawn up into the engine bay but it would probably add to cooling.
Blacktree SEP 05, 02:16 PM

quote
Originally posted by fierofool:

The Fiero uses air turbulence underneath the cradle created by a low pressure area in the engine bay as the car moves along. That is accomplished by allowing the air to exit through the vents at the top. To close off the bottom would allow what would be cooling airflow to just pass on out underneath the rear bumper. In my opinion, if modificatons were to be done underneath the cradle, it would to place deflector airdams underneath to catch and direct air up into the engine bay.


I think you have it backwards. The Fiero uses the low-pressure area behind the rear window to pull hot air out of the engine bay. Look at the total area of the decklid vents, and compare it to the total area of the underside. There's an order of magnitude difference. You could block off a large portion of the underside, and still have enough open area to allow airflow through the vents.

Also, I would advise not to install any kind of scoop or air dam in the engine bay area. Air dams belong on the front bumper. Scoops belong on the outside (not the underside). Putting something like that underneath the car can really mess up the aero.

[This message has been edited by Blacktree (edited 09-05-2019).]