Boat tail on a normal car? (3-box sedan)

[Weather Spotter]

I would say that my matrix (linked to above) is a good starting place. I went 4' past the back bumper and tapered it to the size I wanted the back to be ~15 degrees. I also used a large piece of Plexiglas to keep my rear visibility.

I think your idea of a bike rack might work, or just buy a hitch for the car and use that (which is what I did).

I am happy to answer questions if needed

[Weather Spotter]

Oh, also look thought the wiki page on boat tails:
Full boat tail - EcoModder

[cliffyballs]

I traded with my brother-in-law for this car, when i got it it already had high/cold air intake and performance exhaust. It also has aftermarket wheels on it which will be coming off soon.

I have attached a picture of kinda what im thinking.

I am thinking of having the "butt" of the boat tail rounded is there any aero gain to that?

Also i am in the process of getting one of those scan gauge things for testing my MPGs

Side note Someone suggested getting an air splitter for the front of the car you negate a belly pan...anyone ever heard of this?

[Weather Spotter]

I would square the back end up. It will make it easier to mount the licence plate and tail lghts.

[cliffyballs]

Yeah i think the flat "butt"" is the way to go. Something i should add, i don't mind this being a permanent boat tail, i want it to look like it came stock, i don't want to spend a million dollars either... any suggestions would help!

I haven't been able to find a blank aero streamline template, any links?

[Pendragon]

Originally Posted by cliffyballs

I traded with my brother-in-law for this car, when i got it it already had high/cold air intake and performance exhaust. It also has aftermarket wheels on it which will be coming off soon.

I have attached a picture of kinda what im thinking.

I am thinking of having the "butt" of the boat tail rounded is there any aero gain to that?

Also i am in the process of getting one of those scan gauge things for testing my MPGs

Side note Someone suggested getting an air splitter for the front of the car you negate a belly pan...anyone ever heard of this?

You are well on the way already.

I agree about the present wheel/tire combo. They are nice, but are not really what you want for an aero package. I am guessing that you are looking into some narrower low rolling resistance tires with either moon caps or something similar and rear wheel fairings.

You might give some thought to lowering the car. VW showed a concept car. They cleaned up the front end and lowered the car either an inch or inch and a half...nothing radical which meant the car should have kept a good ride in the real world. I don't recall whether there was a belly pan on the show car or not. It was a part of their planned Bluemotion (diesel) attempts to field a 70 MPG vehicle.

You might want to establish some baseline speed/RPM charts at the speeds you expect to travel at and then do some digging around to see what alternative gear sets or transmissions there may be to get the cruise RPMs down. That is one of the good things about VWs, there have been a lot of parts over the years. Lowering cruise RPMs is one of the ways that the manufacturers have been getting their EPA highway figures up. It also makes the cars quieter which is not all bad. I think there are also some pulleys to spin the alternator slower, but you have to be careful not to overdo it if you are using the AC in hot weather or driving at night a lot.

You might also give some thought to the influence of exhaust gases on the airflow.

You might take a look at the drawings of the Formula XL1 Concept for a little inspiration about the aero treatment of the rear wheel areas. It is an outgrowth of the original 1 Liter project. Wiki

You might want to first think about the materials you intend to use to fabricate the boat tail with as they may have a practical impact on what shape you can easily build.

[cliffyballs]

I figure i would not need to get a rear bumper (because of the tail), but the front and side skirts might not be a bad idea instead of lowering the car?

Link to front bumper: seems to have a front air splitter on it as well

Extreme Dimensions OTG Body Kit - Front Bumper for 99-04 Volkswagen Jetta at Andy's Auto Sport

As far as transmission gearing it could use some lower gears, it runs about 3500 RPM at 70MPH, which seems really high to me.

[COcyclist]

Welcome Cliffy, Here is the link to Part C with the template you asked about.

http://ecomodder.com/forum/showthrea...rt-c-9287.html

Part A has photos of various cars under the template, IIRC. I have found the VW to be low clearance already. I put on an aluminum skid plate under the engine right after I got the car. My stock bumper cover scrapes sometimes so unless your roads are totally flat I might hesitate to spend much on a different bumper. I have gotten good results from cleaning up the underside with a belly pan from just behind the cat to the back bumper.

[Pendragon]

Yea, 3,500 RPM is a lot at cruise speeds these days. I am not up on just what parts swap out on VWs these days (I used to play with Honda stuff, but the VW guys in the club were always playing with gearing), but here is a link to a comparison of the gas and diesel transmissions. I don't know if they are bolt up swaps so check carefully. I would look for some VW specialty shop or start looking in forums.

Just as an example though, swapping these transmissions out should get you down to a bit over 2,500 RPM if my calculations are close. (Obviously, do your own calculations before making any sort of decision/purchase.) There may even be other options.

[Edit] P.S. I forgot to ask about the wheel/tire package on the car. Have you compared them to the stock setup for revolutions per mile?

[cliffyballs]

Did i do this right (the streamline)?


I did not compare the new wheel/tire package to the stock one, the new ones have low profile tires, and I believe they are slightly wider. I have the stock tires at home I'll get the specifics off of each. I think the diameters are the same.

You guys are really giving me some good places to start and what information i need before i dig in Thanks