how to eliminate parachute effect ?
 

Which way is better to eliminate parachute effect in rear bumper:
1) Cut opening in bumper and glue aluminium mesh to make a vent (like those aerodynamic body kits have)
2) Cover open space between underneath of trunk (where spare tire is) and bottom of bumper

Right now I have installed front bellypan, 70% grill block and rear wheel skirts. Should I work on my rear bumper ? How many more mpg I'll gain if I do it ?

From what I have seen posted here, don't count on too much.

My Insight has a vent right above the rear license plate mount. From the way the body panels are running underneath it seems to be designed to vent belly air flow

I vote for option #2 ( may be the only vote I get this year,but that's a different issue). Between driving techniques and mods I can't really point to any one thing and say I got "X" mpg's from it,but all together I still gained mileage. Something like that with little to no cost can only help, so why not give it a try?
PS: I think the "vent" is for the license plate light.

Right at the top of that white box is where the vent is located. The entire region behind it is hollow and it leads right back to the spare tire well and the fuel tank. There isn't any other reason for it to exist besides being some kind of under belly vent, far as I can see.

I second that. All those things add up. Last summer I had several tanks over 30 mpg, in a car with revised EPA of 17/22. All of the gain from those little things that add up. Now getting mid-20s in winter, again due to a bunch of mods and techniques that combine their effects.

Especially in my case with a pre-OBDII car which has to run without a Scangauge. Fillup calcs let me know my mpg but it's nearly impossible to credit any one mod or technique. Even with a Scangauge, identifying gains takes good careful methodology, as noted in the sticky in the "Experiments" forum section.

For what it's worth, I hope to do a full belly pan going to the bumper this spring. I plan to use aluminum screening as pioneered by Hateful.

I plan to use 2x10's for ramps. Layer them up to get the wheels 6"-8" off the ground. My driveway's uneven so I don't feel real safe using jack stands. I've experimented using 2 layers of 2x10, with ends cut steeper than a 45 deg. angle. Even without any attachment between the layers it's worked well.

# 2 for sure !
It is easier to do and is fully reversible.
I also have a Civic and I have just used a Coroplast piece to fill in the gap.

https://farm3.static.flickr.com/2052/...1bc76d9a3e.jpg

The packs blower vents into the passenger side rear wheel well

I have a similar modification on my LeBaron.

Decided to do it after I noticed there was about 1/4" of dust and gravel in the "C" channel that forms the actual structure of the rear bumper underneath the plastic cover. Driving on gravel roads did it, but if those things are getting up in there, air has to be as well.

If anything, it should increase stability on the highway by reducing lift.