Belly Pan slowing me down

[winkosmosis]

I don't understand how the heat could result in thrust from the exit port. The heating and expansion of air wouldn't push air out the back any more than it would push it out the front. The way I see it, it should have no net effect on flow.

[wildfire8]

Here are the pics of my bumper block.
The hole cut out of the left front is for my ram air kit for my intake.
It is not attached to the bottom of the bumper.

[NeilBlanchard]

Looks good (though you may find the cooling and aero might be better with the upper grill blocked and then open up the lower one a bit). Any initial impressions of whether this addresses your issue?

[wildfire8]

Originally Posted by NeilBlanchard

Looks good (though you may find the cooling and aero might be better with the upper grill blocked and then open up the lower one a bit). Any initial impressions of whether this addresses your issue?

My number seem to me normalizing out with the bumper block. But its hard to really tell cuz my scan gauge calibration changed a few %'s with the last fill up. I did make an opening in the belly pan that should exhaust the heat and the incoming air from the engine bay, and rejoin the air stream. I have not yet tested. Made the opening and didnt leave the house after. I will post some pics tomorrow.

My temps did rise a little.
Normal was 182f 184f.
With the belly pan it stayed at 184f (+/-)(didn't check to much).
Then with the bumper block 193f.
I hope this opening helps with some of the heat.

[lunarhighway]

seems to me like this might be more of an intake air temp issue than an aerodynamic one, in wich case, fining where the engine picks up it's air migth be a good thing.

i've had lower FE with grillblocks that extended my coastdown, so they must have helped aero, but they blocked the area where my engine picks up air. so it removed the ram effect and made the engine injest warmer air.

decreased engine efficiency might overrule aero improvemens as these are only very effective at higher speeds. it might be the wrong conlusion that the undertray is ineffective by itself. perhaps rerouting the engine air picup migth help things.

[aerohead]

On my CRX,I have used stamped-steel 45-degree louvers from HVAC application to form the bellypan section under the firewall area of the car.Air passing from the nose shingles over the louvers with little disruption,and the louvers offer positive engine bay ventilation for the cooling system.I have as much free area of louvered outlet opening as I do grille inlet opening.The louvers are available at building supply or HVAC supplies outlets.

[Bicycle Bob]

Originally Posted by winkosmosis

I don't understand how the heat could result in thrust from the exit port. The heating and expansion of air wouldn't push air out the back any more than it would push it out the front. The way I see it, it should have no net effect on flow.

The theory is that the assembly is like a mild ramjet. Instead of adding fuel and burning it, it just adds heat from a heat exchanger. However, the pressure inside is higher than the air around it, and the back is bigger than the front. Hence, a tiny thrust. As to Net thrust, there are skeptics. . .

The folks who flew Voyager around the world on one tank of gas had to re-do all the standard tables on heat exchange at low speed, and wound up with 20% cooling drag overall, even with careful adjustment of flow by the co-pilot.

[Otto]

Count me in as a skeptic on the heat-from-thrust question. Could be, other aspects come into play, such as drag reduction because the rear flap on the P51 radiator nacelle may act to prevent backwash from the rapidly constricted shape, and/or the hot exiting air attenuates the drag from that shape. Maybe "pressure thrust" per Goldschmied/Bushnell at NASA is at play here. One way or another, apparently the thing gets less drag, which is tantamount to an increase in thrust.

For a good, recent application of careful thought and design of a heat vent into the slipstream, Google for the Arnold AR-5 and note the configuration of the forward right fuselage wall where engine heat is vented. Also, have a look at the various aspects of the Arnold AR-6 racing plane, especially the cooling inlet at the front of the cowling, which is designed to let max ram air in during climb (when the engine gets hottest) but more streamlined in cruise (when the angle of incidence is less, for less air entering).

For purposes of efficient venting of engine compartment air on a ground vehicle, I suggest starting with a horizontal application of the side vent shown on the Arnold AR-5. Perhaps you could have one sheet of Coroplast from the front bumper on back to near the firewall, then an exit gap where a second sheet curves down to and meets the same horizontal plane as the front sheet. Or, perhaps the rear sheet curves down to a parallel horizontal plane perhaps an inch or so higher than the horizontal plane of the front sheet. This way, the slipstream acts to suck air out of the engine bay per Bernouli and/or Venturi effect(s).

[wildfire8]

Been busy.
I made an exhaust port on the belly pan. Check the pics.

I did try a grill block but 5 miles of driving and I saw my temp hit 220f so I pulled off the free way and took it off. Then just last night with the bumper block temps where hitting 200f it was fine when I was in motion but when I stopped at a light is when the temps started going up. I noticed that when my intake air temp went down my engine/water temp went down.

I took that off bumper block on just drove home on the streets 43mph and saw my MPG numbers go quite high and the load go lower then usual. And that was with no bumper/grill block and just the exhaust port. I don't feel the parachute effect any more. Temps where at normal 182-184f.

If you notice the middle dipping down in the exhaust port I fixed that. I tied it up so it stays up. Pic later.

Going to try with just a grill block and leave the bumper open and see how that works out.

[winkosmosis]

I'd say this illustrates why the concept of a rear grill block makes no sense. By letting the air flow through, you decrease drag.