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Old 07-04-2015, 10:46 PM   #1 (permalink)
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Thanks to this forum...45.74 MPG wagon

Finally got up the nerve to do some more extensive aero work on my 1993 Tracer Wagon (Escort) with 1.9 auto. I was getting about 33 highway at 65MPH with a partial grill block, sealed front end ( the air leaks around the lights, hood equal the size of the upper grill), and constructing some metal to divert nearly all the air getting through the grill to the radiator. I also sealed around the radiator with AC weather stripping to make sure all the air was going through the radiator. In addition, I put on much better plug wires and pulled out the stock restrictive air intake "muffler" and built a free flowing cold air intake. These last two really boosted power across the whole RPM band and especially at RPMS above 2700 and smoothed out idle and boosted mileage.

I also made some of my own serrated trip material to hopefully get the air to bend down around the rear glass to reduce the wake. Still need to tuft test this now that the roof rack is gone.

The big boosts just came recently.....Full air dam (lawn edging) down to about 6 inches with a front belly pan back about 3 feet attached to the bottom edge of the air dam. I also cut off the roof rack. 6 inches is just about level with the lowest components in the front end. I could feel a significant difference in the air resistance, to the point I have to hit the brakes much harder than before to slow down when at highway speeds. I then added a full rear belly pan that extends forward about 4 feet on the exhaust side and 6 feet on the fuel tank side. In order to cover nearly everything (the muffler hangs down through a cut out about 1 inch), I used lawn edging to drop the bumper edge a couple inches. The rear diffuser angle is probably a bit steep (close to 7 degrees), but it maintains good bumper clearance for the rear bumper when the car is loaded up. Diffusers this length don't loose that much aerodynamic effectiveness at somewhat steep angles and do a good job increasing downf orce for better stability and traction.
I also added a heavy duty ground directly from the block to the battery and a second to the MAF. The car often almost idles smooth and at lower rpms. ( the 1.9 is believed to be the roughest 4 cylinder out there).

The first 2/3 of the trip had full benefit of the changes until a semi tire blew out just in front of us and crumpled the metal on one corner of the airdam ( I could immediately feel the increased drag). We also ended up knocking the front end out of alignment near the end of the trip which also seems to have created increased drag. Overall for the 250 mile trip was still 45.74 MPG. Best previous ever was 37 MPG. ON both trips I spent a good deal of time behind a semi moving at 65MPH.....not too close, but close enough to get some benefit.
The car now has dramatically reduced wind noise and holds the road extremely well at high speeds (semis going in the opposite direction on two laners have almost no effect) and high speed cloverleafs are faster than ever.
Time to go get the car aligned (already fixed the crumpled metal)

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Old 07-04-2015, 11:05 PM   #2 (permalink)
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Congratulations. That's success. The best mileage I ever got (47.5mpg) was when I borrowed someonelses Geo Metro.

I think the 7 angle is OK. Some sources suggest 0-4. It all depends on what's happening upstream with the top and sides.
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Old 07-05-2015, 10:46 AM   #3 (permalink)
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la_voiture_de_courses - '03 Renault Megane Estate
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Hope you can post pics sometime.

Apart from that, congratulations !
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Old 07-05-2015, 10:46 AM   #4 (permalink)
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Thanks.....

I was quite amazed, but not completely surprised after estimating some of the reductions in CD from under tray, diffuser, air dam and tire faring work that have been posted. I suspect that the inherent low rpm design of the engine, coupled with some of the simple mechanical improvements allowed the engine to run more efficiently at very low load than most typical higher HP engines.

This involved no special driving tricks P&G etc. and I didn't notice any significant tail winds at all.

I still have a few things I would like to try.

1)Swapping in late model mirror which probably are much better aero than the originals. They are abetter match the best mirrors in some of the aero studies referred to here.

2) Improve the aero in front and behind the tires.

3) Reduce air flow through grill at high speed with either an active or passive grill design.

4) Test and improve rear aero

5) Partial cover of wheel wells.

I do wonder if the mirrors are actually reducing the wake because in the mirror studies, the rear wake appeared to be reduced with mirrors that threw the air outward. I suspect it rushed in at a greater angle to fill the wake than air just traveling along the side of the car.
I also suspect that the bump up in the roof line may be producing the same effect. This seem to show up in the VW Van aero tests with different tops.
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Old 07-06-2015, 01:49 PM   #5 (permalink)
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Congrats on your success. And welcome to the forum.

I know I'm not the only one here who's wondering if you'll post pictures. There's a 5-post restriction on adding images, but you're almost there.

(EDIT: That was probably the cause of the error message you contacted me about.)

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