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daqcivic · 02-17-2010, 04:26 PM

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.

02-17-2010, 04:26 PM	#20 (permalink)
daqcivic EcoModding Lurker Join Date: Nov 2008 Location: Portland, OR Posts: 53 Daq Civic - '92 Honda Civic DX sedan 90 day: 42.54 mpg (US) The Hardbody - '91 Nissan D21 (pickup) The Hardbody - '91 Nissan D21 (pickup) Thanks: 1 Thanked 7 Times in 5 Posts	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.