Vw pickup MAX mpg build!

[aerohead]

Originally Posted by Sneakybassturd69

What mpg are you getting

Without the recent mods she was doing around 28.4 at 80.
The Diesel Rabbit of which the VW pickup is derived was tested by CAR and DRIVER and registered 26 mpg at 80.
Since the aero of the Rabbit/Golf was compromised a bit to create the pickup,we're inclined to believe that her mpg at 80 will suffer a bit also.

[aerohead]

Originally Posted by Sneakybassturd69

It is definitely more effective at 80 one of the main reasons is the rabbit can't go 80 lol I got to run the guts out of it to go 70

The lack of roof could explain the difference in speed between pickup and the car.(Which means that a bedcover which looks like the original car roof would restore the performance.)
Hucho tested the Rabbit with different rooflines and they were able to drastically lower drag,although they couldn't use it in the production vehicle without going to war with Giorgetto Giurgiaro,who did the design.
It just so happens that the lowest drag appeared when the roofline respected the Template contour.

If she were mine,that's what I'd do for a cover.It's already wind tunnel tested.
Here's your pickup,2nd from bottom.You can just see the separation-induced drag.

[Sneakybassturd69]

Should the sides of the bad cap taper towards the end , if so how much, a foot by the time it gets to the end ?

[mnmarcus]

Should... taper to a point. Don't know if the vdub in Hucho's does.

[freebeard]

Here's what VW themselves chose to do with the GTI W12-650:



Place your cards right and it could even have a roof rack buiit-in.

[aerohead]

Originally Posted by Sneakybassturd69

Should the sides of the bad cap taper towards the end , if so how much, a foot by the time it gets to the end ?

That's a very good question,and after the wind tunnel experience I'm not sure what to recommend anymore.
If you're NEVER going to add boat-tailing,then my opinion is to go ahead and give plan taper to the sides.This would be a safe contour for the sides

VW went ahead and tapered the roof on the XL1 and it ends before the back of the car,so an owner could,conceivably add a little elongation if they wanted

IF you plan to ever add boat-tailing,then I think the plan-taper of the shell only might 'wrinkle' the flow.You'll have a downwash off the 'roof' which is opposed to what's happening around the rest of the bed.You can see what I mean in this photo.

For the trip back to the wind tunnel in 2016 I'm going to kill the plan-taper of the bedcover,and instead,starting from the rail tops,allow a new fairing to just 'tumble',from the cab rear,increasing tumblehome as it proceeds rearward,spanning from the rail to the upper edge of the bedcover.
When to the rear,I'll have a more uniform flow pattern for the onset flow over the new tail.
I don't have a drawing.Sorry! Here's the idea.

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The ideal aft-body would be a new truck bed which begins plan taper just behind the cab,beginning the camber necessary for real drag reductions even without a boat tail extension.
On your VW you wouldn't be able to do this easily,as it's unibody.whereas I can just unbolt my bed and toss it.

[aerohead]

Here are the mpg values CAR and DRIVER came up with for the 1980 Golf/Rabbit
30 mph = 76.0 mpg
40 mph = 67.6 mpg
50 mph = 56.7 mpg
60 mph = 46.6 mpg
70 mph = 34.7 mpg
80 mph = 26.4 mpg
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In testing of the '85 model gasoline Golf/Jetta (Cd 0.35/ Cd 0.36),Af= 20.7 sq-ft,curb weight = 2,277-lbs/2,335-lbs
CAR an DRIVER measured a road load of 13.0 hp @ 50 mph:
8.0 hp aero
5.0 hp friction and tire losses
With 85 bhp:
top speed Golf = 101 mph
top speed Jetta= 100 mph
EPA 27 mpg CITY
EPA 34 mpg HWY
C/D observed 23/27 under very spirited driving
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June '85,the Jetta GLI showed the following road loads:
30 mph = 5.0 hp
50 mph = 13.5 hp
70 mph = 25.5 hp
108 mph with 100 hp

[freebeard]

I don't have a drawing.Sorry! Here's the idea.

While I support all plan taper and a flat roofline for visibility and interior space, for pure aero this is a reasonable strategy. Here's what I found in my own investigation. Granted it's the front instead of the back, but the contour is shaped with a triangle in the middle and twisted, tapering rectangles on the sides.