where to start

[rav]

3-4" of the ground would be ideal.

[moonmonkey]

if your bellypan is smoothed out, then an airdam mostly serves to increase your frontal area, (not good) . although small spates to divert air around your tires can be good.

[k.civic.f4i]

the only time I ever saw an issue with my full grill block on my 94 hatch was when i was climbing an incline. i have a removable piece that exposes half the length of the radiator and that solves the problem. mind you this is in the sunny CA(100 plus in the summer). other than in the summer, I leave my grill completely blocked

[MetroMPG]

laack: just a terminology clarification...

"radiator block" is technically different than a "grille block". Most of us use grille blocks.

Blocking the radiator may give some benefit in terms of thermal management, but it still lets excess air into the engine compartment, so the aero benefit is limited.

[busypaws]

You said A/C was inop. If you don't plan on fixxing it then pull it out. Mine weighted in at 57lbs when everything was removed. Go to a shop and have it drained of freon (lets be green). You also save by removing some rotating mass which is even better. It will only cost you 20-25 bucks to drain and a couple of hours work.
I also removed P/S since A/C and P/S were on thier own belt. This way I removed a whole belt and didn't have to play around with getting a smaller belt.
For my grill block I used some of the 3M window film. The stuff you put over your windows in the house in the winter and then shrink with a blow drier. Cost $1.67 at Home Depot and took 15 minutes.

[laack]

Originally Posted by MetroMPG

laack: just a terminology clarification...

"radiator block" is technically different than a "grille block". Most of us use grille blocks.

Blocking the radiator may give some benefit in terms of thermal management, but it still lets excess air into the engine compartment, so the aero benefit is limited.

Clarification: what is the difference between the two in attaching panels? i'm still new here... feel free to dumb it down

[thatguitarguy]

A radiator block will normally go behind the grill and in front of the radiator in order to limit the airflow through the radiator keeping the engine temp up, but doesn't do much to force the air up and over the vehicle, which is the main purpose of a grill block, which goes in front of the grill and will also restrict airflow to the front of the radiator, but will still allow some cooling airflow.

So a grill block will generally show an aerodynamic improvement, but a radiator block will not.

[k.civic.f4i]

unless you are concerned about looks... a grill block is the way to go

[laack]

Grille block is the plan.. I picked up some coroplast over the weekend. Now i'm just waiting for the snow to stop and the parking lot to get cleaned up.

[daqcivic]

So I have essentially the same car as you, laack, with similar miles too. I have a grill block, full undertray, and front tire deflectors. Here are my thoughts about your options:

Grill block: very easy to do, and since the radiator is so small, you can really lower the amount of air going in without risk of overheating. I don't have AC, so I don't know how much grill area that takes up. I would make the block adjustable (with different removable sections, for instance) to cover from 50-75% of the radiator area, depending on ambient temp and engine load. I've found that I have no cooling issues in city driving up to 95 degrees with a 50% block; during winter in Michigan with mostly hwy driving you are probably safe down up to 75% if not more. I chose to block the width only, not the height, but either or both will be okay, the main thing is total area. The easiest place to mount it is on front against the bumper grill slats, which makes it look almost factory as well. If you are willing to go the extra mile, you can construct a duct from the grill to the radiator so the grill area is working more efficiently.

Front dam and undertray: go with the dam, at least to start. It will help on this car in particular since the lower edge of the bumper is far higher than the rest of the car's ground clearance. And a dam is far, far easier to do than a front undertray, especially on this car. The latter was extremely difficult to get right, and recent testing of mine shows very little difference between the two, with the dam perhaps marginally better. Coroplast or one of the various lawn edging products will work fine. For how low to make it, find a happy medium between the minimum ground clearance of the underbody (as viewed from the front) and what you need to clear driveway ramps etc. with minimal scraping.

Other easy mods:
Seal up the hood all around with foam or rubber insulation strips. The factory rubber seals do not seal completely, especially after +200k miles. Pay special attention to sealing up front and back, as both are high pressure zones, and the latter can disturb flow over the top of the car if lots of air is being sucked in.

Rear undertray from the gas tank to the bumper, re: parachute effect, which is significant on this car. The angle from the gas tank to the bumper is near perfect for aero. It's a bit difficult to find places to attach the front of a rear undetray, but I did it by loosening the gas tank straps enough to loop zip ties around them (of course it's critical to tighten up the straps again when you're done). Other than that, I just screwed the rear of the undertray to the bottom of the bumper.

Front tire deflectors. Find some mud flaps or something similar, and screw them into the wheel well lining. Place them to cover from the inner half of the tires to 3-5 inches inward of the tires, as viewed from the front. You will see that the car companies do it this way, and it is for a good reason, aerodynamically speaking. You can play around with how low to make them, but I would start with them extending 5-6 inches from the ground.

Slow down. With my mods I can do 50+ mpg at a steady 65mph. But I only do that speed on longer trips; you'll take barely over 3 minutes longer to do 20 miles at 55mph, and you will see a significant gain in mpg.