Belly Pan slowing me down

[NeilBlanchard]

Hi,

The edges of the belly pan do not appear to be sealed, right? The problem is too much air is getting in -- and there is almost always too much air "trying" to get through the radiator. I think on many cars that you get better cooling by blocking off some of the grill(s). Some of the openings on the grills on this car seem to be well away from the radiator, and the upper grill is there for style.

I think that ~half of the lower grill should be left open and it will easily cool the car.

[wildfire8]

I did make a bumper block with the middle open. I am going to try cutting a hole in the back to get better flow threw the engine bay.

[wildfire8]

Originally Posted by NeilBlanchard

Hi,

The edges of the belly pan do not appear to be sealed, right? The problem is too much air is getting in -- and there is almost always too much air "trying" to get through the radiator. I think on many cars that you get better cooling by blocking off some of the grill(s). Some of the openings on the grills on this car seem to be well away from the radiator, and the upper grill is there for style.

I think that ~half of the lower grill should be left open and it will easily cool the car.

What do you mean by the edges appear not to be sealed? How would you go about that?

[LeanBurninating]

Is there a way to make exit holes for any air that is being trapped.. without causing more of a parachute effect?

[winkosmosis]

You can put the holes in a spot where they'd be facing slightly toward the rear

[wildfire8]

Originally Posted by LeanBurninating

Is there a way to make exit holes for any air that is being trapped.. without causing more of a parachute effect?

Originally Posted by winkosmosis

You can put the holes in a spot where they'd be facing slightly toward the rear

That is my next thing i am going to try is make hole at the back of the engine bay in the belly pan to to let air out. I am just busy today. I really want to try it out but that will have to wait till tomorrow.

Not sure if I should make 1 in the middle or 2 off to the sides of the belly pan?
I was thinking maybe 1 foot long by 5 inch wide going the width of the car.

[brucepick]

Nice belly pan work!!

Looking at the big cutouts for the front wheels, I think there's probably plenty room for air to exit the engine bay.

HOWEVER it might have to go all over the place to get out that way - so a nice opening in a location that's 'convenient' to where the air flow wants to go, might be a good idea.

Closing off unneeded air flow through the grill is a good idea - the question is, which air flow is not needed? See notes below.

If you have (or get) a ScanGauge you can monitor engine temps digitally which is WAY better than watching a gauge. That will tell you if your grill block is causing higher than normal temperatures. Otherwise you have a good chance of choking off the air flow so that your radiator fan comes on more often to keep the engine from overheating.

It wouldn't overheat (hopefully) and your gauge will likely stay at center - but you'll be running the fan a lot more than the designers intended. I know because I've been modifying my grill block and monitoring engine temps exactly that way.

[Otto]

Exit pathway is as critical as entry. Exit pathway should be smooth so the spent cooling air rejoins the slipstream as parallel to ambient flow as possible.

Think: Fish gill, with entry at the nose stagnation point (highest pressure) and exit at the point of lowest dynamic pressure along the side or bottom, with flow virtually parallel to the slipstream. That way, the slipstream sucks air through the gill (radiator).

NACA did a lot of studies of engine cowlings in the WWII era, much of which was forgotten in the dawning jet age. Unfortunately.

[aussie_modder]

Exactly. Look at the cooling duct underneath the P51 mustang. It is said that the hot air exiting the rear of the radiator actually provides sufficent thrust to overcome the drag caused by radiator itself.

note the radiator situated underneath





Actually after reading closer, it apparently added a few extra mph to the mustang's top speed.
http://www.ipmsstockholm.org/magazin...il_p51d_01.htm

[Otto]

And, when you get the exit geometry sorted out, you'll find that you can then decrease the size of the inlet, with subsequent improvement in overall streamlining. This because with Bernoulli effect sucking the spent cooling air out the well-designed outlet, it takes a lot less ram air (and consequent drag) to stuff cooling air into the inlet in the first place. Less air will be doing more cooling, more efficiently.

BTW, make sure the cooling air has a nice, smooth path(s) between inlet and outlet.

Google for pics of WWII aircraft, and study the engine cowlings on, say, the B-29. Or, if you prefer a recent example, Google for Arnold AR-5 and have a gander at a remarkably efficient little plane, which despite fixed gear, tractor propeller, and cruciform tail, does amazing things on little power. Study the cooling vent on the side of the cowling, which works great but has no moving parts. Design your cooling outlet on the bottom of your Coroplasted car accordingly.

If you need more air hitting the oil pan (finned aluminum on both my BMWs and my Porsche, for enhanced cooling), then take a carpet knife to that Coroplast and make a nice NACA duct with ~7 degree ramp slope. Bits of Coroplast and some duct tape for duct sidewalls will finish the job nicely.

PS: You did a damn nice job installing that Coroplast belly pan, and once you get the exit done, I'll bet your fuel economy has significant improvement