decklid and bellypan extentions for aero

[moonmonkey]

i saw on a race car an adjustable bellpan extention sticking out the rear of the car about 12" of the ground it has tie rods to adjust its angles, and after reading alot on different sites im still not sure what would be the best shape for a decklid extention for my 2002 echo sedan, and how effective can that and the bellypan extention at the rear be compaired to a boat tail? can some of you aeromod gods draw me a picture of some designs to try on my echo, i,ve completed a full upper grill block and am doing the full belly pan this month id love to build a decklid/bellypan extention if they will improve my mpg on the highway,i have free sheet metal and the like as i have a small bodyshop operation so the cost will be almost free except my time. i used to drag race but ,chasing mpg is way cheaper and its also fun. I get 45 mpg now with a 5 speed mostly highway speeds love to get 60.

[alohaspirit]

dont forget to post the tutorial for the belly pan

and please post some pics of that grill block

[sallen]

The idea of a bellypan extension is a very good idea in my book. I am thinking along the same lines for my Golf.

Many aftermarket "splitters" are available with tie rods, so you could buy a boy racer type rear splitter from your local tuner and extend it (that's what I intend to do). My thinking is that it will add a tiny boat tail effect to the air coming from under the car, in a similar way that a small kammback esque spoiler would for airflow going over the car.

With the tie rods you could adjust the angle until you get most gain.

[moonmonkey]

here is my temp grill block, its made of some old seat upholstery i had, it has been on for about 2 tank fulls, and has only made a small difference ,as soon as i run another 3 or 4 tank fulls thru i should have some numbers, it makes the car warm up faster, and run a little hotter in traffic, but only a few degrees, it never goes above 195. but it is winter (sort of ) here in Fla it dos'nt stay cold for long.I will post photos of each stage of my belly pan and decklid after someone gives me a drawing or photo of something that will work on my 2002 echo 2 door sedan, it will take me forever if i have to figure the design my self, i am willing to remove the rear bumper panel and start the upward slope of the rear end sooner, i might even cut my trunk pan and raise my fuel tank if it will aid the design,, by allowing the upward sweep i think is needed at the rear. what im not willing to do is a 5 foot long boat tail, i drive around 700 miles a week mixed city but mostly highway and that extra length would make it to tough to manuver in parking lots and such. id like to keep what ever is put on the rear around 3 feet or less if possible, but im open to ideas, sorry for the poor picture quality ,ill get a computer guy to teach me how to do it right before i post my bellypan job.

[alohaspirit]

it doesnt get very cold here too. and the grill block looks good

i look forward to the work on your coupe

my sedan will soon follow suit

[aerohead]

you can read about and figure the benefit of in the seminars and mod lists.
Also,the aerodynamic template will help you do the design for your car.

[moonmonkey]

i've been reading and reading but im just a little slow to learn, i dont know how to use those templates for a deck lid, calculation, from what aerohead said i would calculate a 15 deg angle from my roof to the back edge of my lid ? and make the decklid hang off the trunk of my car far enough for the air to reattach ? do i stop it right at the 15 degree line or make it alittle longer for the air to reattach, also i think blocking it up a few inches to make it higher ,i can go about 3 inches and still see out the back window i would seal it against the trunk lid so no air would flow under it and also rubber gasket it against my back glass, also would vertical "wings" like the fusion flats racer help or is that for stability? i have a hard time figuring out what is for CD and what is for down draft. You guys are doing great work with this site and i have Too much to learn, i will post all my work with photos and a how to, if i can make the mods = good demonstrable gains. thanks for the template and seminars aerohead!

[aerohead]

Originally Posted by moonmonkey

i've been reading and reading but im just a little slow to learn, i dont know how to use those templates for a deck lid, calculation, from what aerohead said i would calculate a 15 deg angle from my roof to the back edge of my lid ? and make the decklid hang off the trunk of my car far enough for the air to reattach ? do i stop it right at the 15 degree line or make it alittle longer for the air to reattach, also i think blocking it up a few inches to make it higher ,i can go about 3 inches and still see out the back window i would seal it against the trunk lid so no air would flow under it and also rubber gasket it against my back glass, also would vertical "wings" like the fusion flats racer help or is that for stability? i have a hard time figuring out what is for CD and what is for down draft. You guys are doing great work with this site and i have Too much to learn, i will post all my work with photos and a how to, if i can make the mods = good demonstrable gains. thanks for the template and seminars aerohead!

moonmonkey,all these materials are for members to use at their own pace.Life is stressful enough without adding extra pressure,and slow can mean methodical which is very good!
With respect to the template,imagine a sheet of plywood or stiff sheetmetal with the streamlined teardrop cut away where you could literally place it over your car.
Any part of the back of the car which does not "meet" the curve is a candidate for flow separation and the drag it produces.
Adding the rear spoiler is a compromise between the more ideal teardrop form and the real world.
Going straight back to the curve is drag friendly and allows low pressure to get underneath creating a suction if you will,under the tray for downforce.If you hung a 100-pound weight at the back of the shelf,measured the suspension deflection with that 100-lb load,removed the weight,and then drove to a speed which created the same amount of suspension deflection,then you'd know it was producing 100-pounds of downforce at that speed.That's how hot-rodders measure their spoiler's performance.The shelf has to be pretty long!
By angling the spoiler up at a shallow pitch you can get your drag reduction with less material,as you can "reach" the curve with less distance to the rear.
Anything you do should pay dividends.
Cardboard and duct tape are a great way to prototype a spoiler.If you like the results you see on your Scan-Gauge or MPGuino,tank mileage,then you can commit to a more permanent and costly unit.