where to start
 

I've been lurking here for a while and figure its about time i start trying out a couple of inexpensive changes. I'm driving a 94 civic sedan with 210,xxx on the odo. I coast in neutral as much as possible, average 65 on my 20mi commute. My tank to tank average this winter (michigan) has been 41 +- 1mpg.

I was thinking about starting with a couple sheets of coroplast from a sign shop ($25 per 4x8' sheet) and shaping an air dam with tire deflectors, under tray and maybe rear wheel fairings.

Which of the above will give me the best gains in mpg? i've read that the undertray is not as necessary with the air dam and partial radiator block.

for those with civics-- how are you attaching the undertray to the bottom of the vehicle? i'm leaving a gap on each side of the exhaust system to allow for cooling and prevent melting/fire. are you just using self tapping screws straight up into the floor of the car?

any general tips/suggestions?

Do you already have a partial grille block? That's where I'd start.

(Standard disclaimer applies: watch temps closely - cover progressively so you don't overheat. And realize you may have to remove blocking as the weather warms or if you do any driving with higher than usual loads, like high speed or climbing)

No grille block yet, but i figured i would just use 4 individual panels. 2 over radiator side and 2 over air-conditioning condenser which would be more permanent (ac inop). warmer months I'll remove panels as necessary. This is just my work car so its rare for me to have any passengers or any load other than myself.

Grille block has multiple advantages over other aero mods. Higher return on investment among the "small" individual mods.

You could also overinflate your tires. On my liberty i have the tires inflated to 40 psi (45 is the max i can infalte too)& I have my toyota camry at 35 psi.

the sign shop that i'm going to get the coroplast from sells a 4x4 for 15 or 4x8 for $25. regarding an increase in mpg, is it worth the extra money and time installing the air dam & undertray vs. just blocking radiator?

If you're looking for the highest gains, slow down from 65 avg to 55 avg. That will net you a bunch.

$25 for a 4x8 is pretty high. A sign shop buys from a plastic supplier, and they are marking it up quite a bit. Call some more sign shops and find out where they get their supplies, and go directly to the people who sell plastics and you'll get a better price.

bellypans almost allways" pan out" if the bottom of the car is dirty aerodynamicly speaking, as to how to mount it ,i drilled holes in the existing plastic under my car and used bolts and washers,search echo bellypan install, there are quite a few how to's on this site for bellypans, i only did my front and rear as the middle of my car is pretty smooth already. coroplast is cheaper at plastic sales stores . they sell lexan, acrylic styrene etc, you can get it for free if its election season,but its usally smaller peices and harder to work with,i vote for pans and grill block.

In my limited experience, if you have a front air dam where the overhang is slightly more then the height of the lowest hanging part behind it (oilpan, control arms, exhaust etc..), then you are all set and imho that is the best mpg gain you will ever see. As far as belly pan is concerned gains are almost negligible in comparison to a well designed air dam.

As a general rule of thumb for an airdam what would be a minimum ground clearance to avoid scraping?

3-4" of the ground would be ideal.

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.

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

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.

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.

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

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.

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

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.

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.

it took a while for the parking lot to get completely cleaned up where i didnt mind crawling around. I started with just a basic air dam, but have some questions about maximizing its effectiveness.

I currently have it set up with 3 inches of ground clearance and just paralleling/contouring the lower end of the bumper. my first observation/appreciation for it was how quite the it is now at highway speed. There are few hills here so i can only do modified coasting measurements. I have shifted my coasting points to turnoffs on my usual route to/from work by about .2 miles:)

i haven't done any tufting tests so i don't know if i am creating too much wake to get the most out of the air dam. How far should it extend laterally to minimize wake and drag?

Pictures to come later.

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.
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when you did this did you try different angles or just at a flat angle in front of the tires? I'm wondering if it's best to angle them in a little or send the air to the outside of the car. thanks

I can't help you with the tuft testing but I also installed an air dam on my 95 civic. I used an old conveyor belt and set the clearance to 2.5 inches. it did scrape some but didn't matter with the belt. I gained 3 mpg with it but have to take it off in the winter. was thinking about doing an undertray just so I wouldn't have to remove it. the only thing is I don't know if it would work as good as a airdam and it's a lot of work to install an undertray. maybe I'll let you do it first. :)

a couple pics. where would you make changes to it if any? Grille block pending still, i want to wire in an led to the radiator fan first. any diy's on how to wire it?

why take it off in winter?

laack any gains with your mod?

...from my college years in Flagstaff during the winter: the idea is to drive over the snow not "snow-plow" your way through it...that's why it's removed.

I'm still on the same tank, but I'll post the first tank numbers. I'm going to take a 3 tank average since weather has warmed up a bit since the start of this tank plus I just started using a different fuel injector cleaner, which netted an extra 1.8 mpg on the last tank.. I got too antsy with the air dam so i didn't get to do a multiple tank average to see improvements from injector cleaner (lube control fp plus). It has however smoothed out my idle and resulted in starting up quicker so even if it doesn't improve fuel efficiency my engine is running better.

I am pretty excited to see some numbers though, i'm at 260miles at the 1/2 mark on the tank. I'm usually at 180-210 at a half tank.

Congratulations on your first mod. Those are some encouraging numbers (though to tell for sure how much is the mod and how much is you attempting to get the best fuel economy possible, you'll need to do some A-B-A coast testing and/or cruise control testing).

As for how far back to go with the air dam, I'd say go back as far as the bumper/fender does. You want to direct the air as smoothly as possible down the side of the car, which means trying to not throw air out to the side of the car. You might be okay simply following the lower curve of your bumper, as seen here.

http://i78.photobucket.com/albums/j1...g?t=1268670068

Even a partial undertray can help, a lot of the aero mess under my car had to do with the wide-open underside of the engine bay, and it practically ducted air up into the front wheel wells. Having even a short undertray like this helped the air to go past that more smoothly. Though of course with coroplast you'll need to make sure it doesn't melt.

If you're going to use an undertray I think it's best if the bottom edge of the airdam is level with the tray, and that both are no lower than the lowest points on the underbody of the car. Having less air passing under the car is good, but if you lower the airdam too much you're increasing the frontal area of the car, which means the car's pushing more air than it needs to. From what I understand, an airdam lower than it needs to be helps compensate for not having a smooth underbody. (I forget who, but someone on here had a GIANT coroplast airdam on the front of their pickup and it helped a lot because of how aerodynamically 'dirty' the underside of your average pickup is)

first tank mpg was satisfying, but i was hoping for a little more. MPG with a mix of 70/30 hwy/city was 45 mpg. driving style: neutral coasting when ever possible, slow accelerations, 60 on hwy traffic permitting, otherwise 65 following semi's.

I was averaging 40-42 all winter so warmer weather alone would account for at least 1 mpg gain. I use the same pump a the same gas station (shell on my way to work) every time so given my unsophisticated calculations its about as accurate as i can get. I still plan to do an average before i make any other changes to configuration. It will be trimmed up first since i'm scraping a bit still.

What kind of gains would i expect from rear wheel deflector/strakes? any tips to reduce separation at the rear of the car? I thought about trying to figure out how to attach the extra coroplast that i have (smaller sheets) but i can just picture wind catching the leading edge of what ever i connect it to and ripping it off. I'm adding additional weather stripping as previously recommended to the hood. If it doesn't add any mpg, hopefully it will at least quiet the ride a bit.

...although this data derives from an '09 Pontiac Vibe 1.8L (DISI) with 4-speed automatic, it might provide a "closer" estimation of fuel economy versus temperature.

1) 28 data pairs [ one in morning (am) and one in afternoon (pm) each day ]
2) temp range: lowest am temp = 37°F; highest pm temp = 84°F
3) roadway: 4-lane freeway driving 95% of the time (time: 05:00 am, ~05:30 pm) 5% urban street & stoplights
4) distance each way: 26.2 miles
5) slight 0.2% road grade (altitude: 2330' home, 2550' work)
6) two rainy days, two windy days

...the linear regression equation (so far) from the data pairs:

MPG = (°F)/5 + 25

...with correlation coefficient of about: RR = 0.8-0.85

...obviously only 100% relevant to my vehicle, but might be useful as a "rough approximation" guess-ta-mation.

update:

I'm a couple of basic mods in and more than happy with my results so far. air dam=3 mpg increase(alot of variables though-increase in temp+ introduction of fuel injector cleaner lc fp plus) from 40-42 average mpg. injector cleaner btw, more than happy with. less cranking and i still swear by a smoother idle. it is possible that i'm just hoping that it is smoother in comparison, either way less cranking is better on the electrical and starter.

air dam + 80% grille block = 47.8 mpg average over 2 tanks with no regard to speed. i got caught several times leaving late for work and driving 75mph on a 20 mile commute. I assume mpg would have been better doing 60-65.

New weather stripping on the hood and side skirts extending to a clearance of 3 inches are next followed/accompanied by rear wheel skirts. My goal is 50 mpg!

i cant stop bragging to my buddies that my 214,000 mile 94 civic is still running, and better than new w/ engine compression still at the stock 180 psi range. i'm going on my 3rd timing belt this week! w/ that out of the way, I know its just a matter of time before i have engine/transmission issues. as clark howard preaches: drive it until the wheels fall off.

My front struts only are however starting to go. If i were to replace them with a lowered set would i be able to see any return in mpg? It would be an aggressive angle and i'm curious how handling would be affected if the rear is left untouched to save money. stock struts/springs are the default fix no return is expected.

laack, those are good # for air dam and grill block,
I agree, keep up with the major maint and keep her driving, I have an 00 accord v6 with 200k that we just did the major service, the car drives like new

tranny is the only weak spot, take care of it and you will be golden,

with the tires being at max, you will have a horrid ride with old springs and shocks, just get a progressive lowering spring and some econ shocks, while at it, get a new PU link kit and do that too.

Q: how did ya attach the air dam?