Pictures of custom undercarriage mods.
 

Here are some pictures of the metal work I had installed under my 1997 960.

I hope it will give you some ideas of things you can do to your own car for better mileage.

I gained about 2.0 mpg at 65 mph with these modifications.
One of the guys on a Volvo board was the first to install a rear cover between the differential and bumper using a plastic office chair carpet protector. He saw an instant 1.5 mpg increase on his 94 Volvo. The open area of the rear bumper works like an air brake on these cars.

First starting at the front there was this large void in front of the tires behind the bumper and spoiler. The area was enclosed to help with air flow ahead of the tires.

https://farm3.static.flickr.com/2048/...2a66b1.jpg?v=0
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Next I installed a plate under the IRS rear suspension to divert air under it instead of letting it go through the structure.

https://farm3.static.flickr.com/2332/...760424.jpg?v=0

Behind the plate is a box that was built to divert air from interacting with the
spare tire hump which looks like a big donut and the rear bumper.

https://farm3.static.flickr.com/2162/...a38fc4.jpg?v=0
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Hi ALS,

Looks very nice, almost professional.

Yours looks very nice. You might want to check out Lovemysan's pictures. He did a superb job on the bottom of his Saturn.

Did you notice any fuel economy improvements after doing this?

JESSE69: did you not read the post?

highly impressed. How long did all of this take you? What material did you use?

I saw a jump of about 2.0 mpg. I have looked at adding to this undercarriage modification but the gains would be small for the amount of work and cost of materials and labor. I had a guy that restores Corvettes and builds street rods in the area do the work. Most of the custom street guys use him for metal work.
He is in his late fifties and is old school when it comes to this type of work.
The plate is stainless steel and the rear box is made of Aluminum. The boxes up front I think are made of PVC or a similar plastic.
I am looking in the next month or so of having him make me some custom snap on, snap off rear wheel opening covers for the car. Also my mechanic and I were talking last week about dropping a ring set in the rear end. That change would drop the engine speed about 100 rpms on the highway at 65 mph. Those two changes should be good for another 1 to 2.0 mpg. I want a minimum of 30 mpg in this boat anchor. Right now it is running 28.5 to 29.5 mpg at 65 mph depending on the weather. EPA has this car rated at 24 mpg highway.

Before I spent money on aero mods beyond the low-hanging fruit, I'd look at using Redline or Royal Purple motor and gear oil. Very good stuff.

A new ring set in the rear end for only a 100 rpm gain is not cost-efficient. You could get a 100 rpm change by using taller tires on the rear wheels.

As nice as the undertray work on your car is, it could stand some improvement: Get a can of Great Stuff at the hardware store, for ~$5. Use it to spray on and when dry sculpt or sand some smooth and streamlined deflectors/fairings for the tires, a la Prius. Paint them charcoal black with spray paint. In your case, it would be easiest to remove the undertrays from the car and do the sculpting work on the bench or work table, rather than crawling around under the car.

Already have M1 05W30 in the engine, Redline D4 ATF in the transmission and Redline 75W90 in rear end. There are already metal factory air deflectors under the car right in front of the rear tires.

Is that low expansion foam that "great stuff"? only stuff I've used seems to keep swelling for a week.

That's one reason to take the undertray panel off the car to use the foam. You could make a simple mold out of bent plastic sheet, squirt the foam, and let it rise and cure at its own pace, then sculpt/sand/paint.

Hey ALS, I was the guy with the carpet pad turned undertray on a 94 965. I remember reading your original post on TB and I was very impressed by the workmanship. I'm glad to see the car is still on the road. I don't drive the 960 anymore, moved on to a BMW 318i 5 speed but my GF drives an 850 5 speed. Driving volvo carefully we managed 32.7 mpg on our last 500 mile road trip. I also found that I can get away with taping up 50% of the grill, removed the wipers and folded in passenger side mirror. Theres a lot of room for improvement under the 850 as well. I was also thinking about doing rear wheel covers but I'm not sure what kind of material and fasteners to use.
cheers
Justin

https://farm3.static.flickr.com/2108/...6e309afa_o.jpg

Theres not a lot of Volvo aero information in this forum so I'll add my modifications here in the name of being concise. I'm preparing our volvo 850 for a 1700 mile trip to Seattle. I picked up a 8'x4' sheet of Coroplast at Tap plastics. So far I have the rear of the car finished. Next I will move on to the front.

I cut out a fitted sheet of coroplast.
https://farm4.static.flickr.com/3001/...d1b6d52e30.jpg

Epoxied on some strategically located aluminum right angle strips for stiffness.
https://farm4.static.flickr.com/3060/...e19d07df8a.jpg

This is how the car left the factory. There are huge air gaps underneath the rear end between the fuel tank, spare tire well and rear bumper.
https://farm4.static.flickr.com/3192/...30702181_o.jpg

After. The panel is secured in place with a special mixture of zipties and bolts through the bottom of the spare tire well. I left a lot of room on the driver's side for the exhaust. Probably too much room but better safe than sorry when it comes to melted plastic.
https://farm4.static.flickr.com/3160/...f6a391e0_o.jpg

I'm cooking up something special for the front ;) To be continued

That looks great. You're making me consider spending some money on some nice big sheets of black coroplast...

The rear area of my 960 wasn't as as bad as your 850. My spare tunnel hump looks like a big donut. Justin it is looking good what you have done with the rear area. I'm going to have to link this thread to a post over on the Brickboard. There is a guy that is trying to improve his gas mileage with a 960wagon.

I put about 1 hour of work into the front end this afternoon. So far, so good.
Left front before
https://farm4.static.flickr.com/3255/...008f0523_o.jpg
After
https://farm4.static.flickr.com/3242/...18e450a3_o.jpg

Right front before
https://farm4.static.flickr.com/3131/...1a0c98d5_o.jpg

After
https://farm4.static.flickr.com/3288/...fd776eb1_o.jpg

Center section
https://farm4.static.flickr.com/3150/...93d911f1_o.jpg

Looking across from passenger side to driver's side.
https://farm4.static.flickr.com/3059/...ed1df4f2_o.jpg

Thats all the work I'm willing to do. We'll see how it pans out on the highway. The car does an honest 32mpg at 65mph in stock form. I don't have time to grow old and die in the car so I drive a bit faster. If I can pull off the same 32mpg at 70 or 75mph I'll be happy.

Please keep us posted on mpg gains.

I bet many people here WANT to know how much you can gain from doing these "harder" aero mods.

Since not many people try it we don't have much evidence but I bet that it gives solid gains as much as grill blocks and so on. (and its cheap to do also, just a little harder).

Nice looking :thumbup:

I spy IPD parts. ;)

You should see how many IPD parts my 745T has.
Sways, lowering springs, chassis Braces U&L, and HD Bilsteins.

I want a factory lowering kit for my 960. The problems is, it is over $2,000 through the grey market to get it. That is way more than what the fuel economy gains could ever be recovered by making the change.