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Discussion Starter · #1 ·
First off, this is all just me thinking out loud.

We've all seen the tail aero on 18 wheelers by now I would think. I read that on average the tail aero on these trucks increases fuel economy by 6.6% at 65 mph. Lets face it, the R model isn't the best for fuel economy. So why not try to help it out a little bit? In theory reducing the drag generated at the back of the car will also make it more aerodynamically "slippery" for lack of a better term.


Now before anyone jumps to conclusions, the material I'm planning to use is clear, so this will in no way obstruct the tail lights, etc. Plexiglas or lexan will probably be the material of choice. Another reason for using clear material, so that the kit doesn't stand out. I mean, this is a down right silly idea for a passenger car to begin with, right?

But lets put it into real life terms. . . if (and I stress IF) the same increase in fuel economy were to transfer from the 18 wheeler, (6.6% at 65 mph), and my V70R averages 27.5 mpg at that same 65 mph on level ground. Then a 6.5% increase would equal 29.28 mpg, which in itself doesn't sound like a huge leap I know. . . but enough small things like this add up to big increases in fuel economy. What other kind of things you ask? Well, I'll save that for my next post.

Until then, here is a (very rough) version of what I have in mind. Again, this idea is in its infancy, I've been thinking about it for a while, and just now beginning to determine things like how long the panels will need to be, etc.
 

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Please don't disfigure that beautiful car (assuming that VR is yours). If you were looking for 30mpg+ all day you bought the wrong car.
 

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I highly doubt youll be seeing any increase in mpg. Those trailers have a lot going them to start with. So any thibg aerodynamic they apply to them already helps in the long run. You want to get bette mpgs lets start with some weight reduction.
 

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You won't see that much of an increase, not 6.6%. The reason those tails work on 18-wheelers is because it helps to diffuse the pressure/drag on a square-ish object which has a much higher coefficient of drag than what the shape of the v70 is. the height also plays a factor because it gives more surface area to exert the drag on, which is why you see such a large increase in efficiency. the v70/s60 has smooth lines and aerodynamic(ish?) curviture, so it will not experience as much drag and the decrease in drag created by the tail aero would be much less dramatic. think of it as blowing air against a 2' piece of tile vs. a 1' piece of tile, the 2' piece will experience waaaay more drag because it has a larger surface area. i'm sure you thought of most of that but i just thought i'd put in my 2 cents.

if you really want better milage, you shouldn't have bought a 300 hp station wagon. 27.5 is actually really impressive. reducing weight like psy said or using gas additives/new filters/tune-up/FMIC is probably your best bet if you really need to get better MPG.

apologies in advance if my thought process on the aerodynamics is wrong. i'm only a sophomore :D
 

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People on the Ecomodder forum do mods like this. It does work and would benefit a square back wagon a lot. But I don't think it's worth the hassle

Now if you can come up with a way to increase city mpg that would be great. Going from 30mpg hwy to 35mpg doesn't save much gas. But going from 15mpg city to 20mpg would save a lot. Those are the mpg numbers my 2.5T gets...

BTW the tail needs to taper otherwise you don't get much benefit. The idea is to let airflow converge at the rear of the car and leave less of a vacuum behind you. Think of the fastback design of the Prius
 

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Aero's just one part of it. I've hit the magical 30mpg mark with a little patience. Drop cruise to 60 and hang out in the right lane with the trucks, keep tires inflated relatively high (37-39psi), and use the throttle in such a way that you stay out of boost as much as possible.

It might feel a lot slower, but unless you're on a very long trip, 60mph versus 65mph will only take a few extra minutes.
 

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People accomplish really amazing things with areo mods. check out http://ecomodder.com/


I have a 1996 honda civic that came stock with non V attck Yo! 1.6l 4 banger (d16y7) good for 105 hp or so and a 5 speed manual transmission. I was and still am very interested in mixing performance with efficiency so I put the lean burn d16y5 head and ECU on the block, bumper the compression to 10.5/1, added headers, a modestly bigger exhaust, and nearly completely smoothed the bottom of the car with coroplast and aluminum. I also blocked a bunch of the grill opening, closed in the wheel wells on the inside, put eibach sportline springs, koni yellow dampers, ST sway bars, and disk brakes from a larger car on the 4 corners, pads, fluid, ss lines, .... Plus some other stuff. The net result was a faster car in a strait line that gets allot better mileage and goes around corners like no volvo ever will. When I bought it and did 'stage 0' the car returned an average of 28 mpg with enthusiastic mixed driving. Now it gets 40 going 80 mph and just returned 37.5 mpg getting the **** flogged out of it on a 1300 mile road trip filled with gear.

So you are on to something even though I could never do that to the lines of a V70R!
 

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I will be doing some type Areo mods on my VR, although not for mpg. Looking to gain in the 1/2 mile races but mailny for the Mojave Magnum 1.5 miles race in April
 

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You won't see that much of an increase, not 6.6%. The reason those tails work on 18-wheelers is because it helps to diffuse the pressure/drag on a square-ish object which has a much higher coefficient of drag than what the shape of the v70 is. the height also plays a factor because it gives more surface area to exert the drag on, which is why you see such a large increase in efficiency. the v70/s60 has smooth lines and aerodynamic(ish?) curviture, so it will not experience as much drag and the decrease in drag created by the tail aero would be much less dramatic. think of it as blowing air against a 2' piece of tile vs. a 1' piece of tile, the 2' piece will experience waaaay more drag because it has a larger surface area. i'm sure you thought of most of that but i just thought i'd put in my 2 cents.

if you really want better milage, you shouldn't have bought a 300 hp station wagon. 27.5 is actually really impressive. reducing weight like psy said or using gas additives/new filters/tune-up/FMIC is probably your best bet if you really need to get better MPG.

apologies in advance if my thought process on the aerodynamics is wrong. i'm only a sophomore :D
As an aerospace engineer I was going to make the same argument . . .

As far as volvo aero data goes, lots of good info here . . .

http://forums.turbobricks.com/showthread.php?t=287934
 

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The rear wing already does that. It gets rid of some of the vacuum.
 

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You bought the wrong car if you really want good MPG.

Instead of messing up the good looks of the V70R with crazy aero mods, spend the money and buy a beat up Honda Civic Hatch 92-95.

Even with tons off mods, the fuel effiency of a Civic Hatch even stock will kill a R in the MPG dept.

I had a 93 CX hatch with a single cam D16z6 out of a 2 door Civic EX in it and got 42-44 mpg every single day. Even in town.

Buy a Civic VX and get 55 mpg on the highway.
 

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The easy and boring way to reduce drag is to stay in the slow lane close behind a transport.


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Back when gas was getting crazy expensive I enjoyed trying to get 30+ by drafting behind vehicles around 65 MPH.

My moments of misbehavior would always drive the overall average down though, lol.
 

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Yep. I'm happy to average around 20 mpg in suburban / city traffic driving. My country road MPG is lower :D unless there's a slow person in front of me.
 

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haters will hate. if you want to do it then do it. its your car after all.


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I have had more time to sit and think, I would do aero mods very last.

1. Step, bring car to stage 0 with a full tune up. New plugs, possibly high output coils, run some Mopar combustion chamber cleaner through it, get a brand new Bosch Wideband upstream 02 sensor. Fresh synthetic fluids in all the different systems of the car.

2. Step, I would a tune, down pipe and exhaust, better filter, simple bolt on mods.

3. Light weight wheels plus LRR tires. Tire rack has 17X7.5 OZ wheels that weight 16 lbs each.

4. After everything else I would do aero mods.


When gas was $4 a gallon I was driving my Lexus SC400 back and forth to work 112 mi a day. That car got terrible gas mileage, like 22 mpg on the best days. I spent time trying to make it more fuel efficient, but in the end buying a Honda Civic hatch for $1400 gave me better MPG than I ever saw in the SC400.

The truth is if you can get over driving a tin can, the Civic Hatch is one of the cheapest to own cars on the planet. Tired are 14/15" so they are super cheap. Lots of aftermarket, you can do your own engine tuning to tune the car to run lean, which you can never do on the R. You can buy light weight 15" wheels for nothing on the civic. Find a set of aluminum brake drums for the rear from a insight, do all sorts of cheap things to make the car lighter.

I put a turbo setup on my civic that I got pretty much free, and that car is so light that they are pretty quick/fun even with only 4 psi of boost. Even with a turbo setup on, I still got 42-44 mpg when not beating on it.
 

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I almost want to pick up a Honda Insight and strip it to make it more efficient. Seats? Gone except for 1. Carpet? Gone. Headliner? Gone. I had a conversation with a friend and it really escalated... By the end the doors, hood, trunk, and roof were carbon fiber or plastic bags :rolleyes:...
 

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All things considered, a big heavy power sedan like the R being able to cruise about 65 with the A/C on and get close to 30MPG while doing it is quite good which is one reason I really like the R.
 

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Discussion Starter · #20 ·
Loving the negativity and the doubters. If I wanted to daily drive a soul sucking hybrid then I would buy a first gen Insight or a Prius, then subsequently chop my balls off and die.

Pennies make dollars. . . the same way tenths of a mpg add up to a whole mpg.

Again, aero is just the tip of the iceberg.

Full Synthetic fluids, vortex generators, under aero, light weight wheels, weight reduction. . . it all adds up.

Baselines will be set, data recorded, and bars set.
 
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