Aeromodability of a VW Bug?
 

Howdy everyone. I probably should have posted this question before I went out and got myself a Bug to tear apart and redo, but I felt it still possible. Still do though.

Anyhow.

I'm going to try and strip down my VW bug I just got down to the chassis, and put an aeromodded body on it. I read somewhere that the reason why the VW Bug gets such limited gas mileage**(Mom's informed me that her 68 got 30-40mpg, current non project 69 gets 14, current project 75 doesnt run yet) because of the aerodynamics, the Cd of .41.

Would it even be worthwhile to try and continue this project and make a custom aeromodded 1975 VW Bug designed for fuel economy (As in try and get a Cd of say.. .18 or lower for a beginning goal), or should I just rebuild the carb that's on it an enjoy it as the baja it currently is (29's up front, 32's in rear, haha)?

I can post a basic outline of what I was planning on trying to make if anybody is interested, but it's nothing fixed yet. Right now I've got the bug set aside, and I'm trying to sell the tires to fund the project, but if it's best to keep it bajaed, I'll take down my ad and have some fun. Or just fix it and sell it or something.

I would say that there are a lot of different things you could do to an "old-school" Bug. I think .18 Cd is a little on the optimistic side, i would set a beginning goal of .25-.30 Cd. Then again if you look at basjoos's Aerocivic, you can drop it down quite a bit. i would drop the ride height for starters; depending on how tall you/your passengers are you might want to chop the top down a couple inches. a boat-tail is pretty much a given, maybe you could extend the wheelbase back a little to help weight distribution(though that could take quite a bit of work)

go to The-Blueprints.com - Frontpage and you can get a profile view of an old Bug, they might not have a '69 though. then use paint or some other photo editor and draw up some ideas.

Here's one an applicable analog with another ambitious plan. >150 mph on only 36hp!
Bonneville VW Challenge - Page 9 - The VolksRodders Forum

I'm glad you asked this question.

I don't have a Beetle myself, but I wouldn't say no to one. Kids' tuition, house payments - you get the idea. No time or money just yet.

But: Hot VWs magazine picked up the idea of building an engine, optimized for fuel economy. The project dropped off the radar a couple of years ago when fuel prices dropped, but prices are heading back up - maybe they'll get back into it, hey?

Anyway. Their stocker racked up a dismal 22mpg as found. With a chassis tune and a fresh alignment, they got up to about 27-29mpg. Big improvement!

Then came the engine. Contrary to what you might think, the motor they built is no slug. It makes good torque, it gets a big power bump. A little more stroke makes for good twist. Their assessment was that the car with the new motor was downright fun to drive.

Hot VWs' project was almost exclusively engine mods, and a "Freeway Flyer" tranny swap. They added a small spoiler to aid airflow separation, which was good for 2mpg, this after having already gotten solidly into the 30s. But bellypans, rear wheel skirts, smoothie wheel discs? None of that was ever done.

At its best combination, with a CBPerformance throttle body injector, the Freeway Flyer and the spoiler, the Beetle would tool down the highway at 65mph, delivering 36mpg. That's pretty good by any measure.

Do all the aero mods you can think of, and I bet you could get it into the 40s and keep it there.

CBPerformance has the entire run of articles archived on their site. I used to have them all in the mag, but needed to make room for more comic books.

http://ecomodder.com/forum/showthrea...why-12732.html

This thread has some good information on the Beetle's unimpressive aerodynamics. The basic body shape isn't great, and an air cooled rear engine is far from ideal from a FE perspective. So I would say an aero rebody is a great place to start. I would also make it a point to get modern, LRR tires and an efficient engine.

An aero rebody is a very ambitious endeavour. I can only think of a handful of people on EcoModder who have attempted it. How far along into the process of planning and allocating resources are you?

Well I'll be using a 1975 chassis. I got it specifically for this purpose. I plan on using only the chassis and engine, not the body. I want something with a suPer low Cd. Since I won't be using a bug body, a Cd of .18 should be possible. Not adding onto it, just a one peice body. I'll post up an idea of what I was thinking when I get home.

i would say .18 Cd is definitely achievable since you're ditching the stock body

Ah, to be able to type on something that doesn't have a touch screen.
Anyhow.

Robert- So far I have the bug. Picked it up for 50 bucks and some of my junk, so I got it for a steal. It's been bajaed, so I get to undo that. I'm selling the tires, shell, and some other minor stuff off of it to help fund the body parts. I've got a standard arc stick welder, and a tiny little oxy-mapp welder I can use if I need to. I've done fiberglassing before, and I don't think working with rivets should be too hard. Right now I'm at the planning phase, but I at least have the car. Soon as I get a solid idea, I'm going to start selling things and dumping funds into this. I think the hardest thing for me to get ahold of will be the steel tubing for the roll cage.

As for the engine, right now it is nowhere near FE goodness. I have to dump raw gas down the carb, rev the crap out of it, and feather the clutch to move it. I found some stock wiring I'm pretty sure went to a stock fuel pump for the stock FI engine, so somebody swapped engines in this thing along the line. So I plan on switching back if I can, or just seeing if I can get this one running well enough to use it for a start engine.

Although if you know of a more FE engine that'll bolt straight up to a standard VW Bug transmission (I -really- want the Freeway Flier), let me know so I can look into it.

Elhigh - The freeway flier is the trans I want to end up using. 3500rpm @ 75mph would be better than most cars I drive now (that data is on the mid-america motorworks website I think). I think for the first phase of the project I'm going to just stick with a carb, mostly because it's cheaper to work with, and I kind of already have one installed. The stock engine was supposedly FI, which I love (I did injector cutoffs in the car that's my avatar, that was awesome). I was actually trying to find a small single cylinder diesel engine to use like the single seater VW concept (I forget the name) used, but I remember two things:
A: I live up 600 feet. I have to commute to sea-level, and back up. I don't think that would work for me, unless I want to get hit.

B: I want to retain the haulability of four passengers. I figure for the rear "seating"/cargo area, I would leave the basic lap belts in, but remove majority of the comfort factors back there. No padded seats, more like a hard dense plasticy foam, or just plastic seats. Nothing fancy, more like something you'd find in the back of an old school classroom.

I somehow doubt that a 10hp diesel engine could putt me and three passengers, a full tank of gas, and say a 50 lbs guitar amp up a rather steep grade, at least at 20mph, with all the lights on. So I kinda said forget that.

Botsapper - Is it just me, or does it seem at least slightly impressive that a 36hp engine can hit such high speeds? Interesting link at least.

JoeNavy - Aerocivic has had a huge impression on me. I kept a tab of that open for months, just drooling over that car. That's just about the main driving reason behind this. I want to drive a car that costs pennies to run distances in. Granted he did an engine swap, but 80mpg at 60mph?! I've got no problems driving in the slow lane. And where I'm at, If I had 20 bucks to burn, I could get bored and almost do a 600 mile road trip. I could do it comfortably on 50 bucks (Granted that's if gas goes back down to 3.27 a gallon when I calculated that).

I'm still toying with body designs, but one of the popular threads up was the one about the pillbug car? Seated seven, but dissapeared to england after WWII from what I got. The prototype had a Cd of .117 I think? I'd have to rearead the thread to find out for sure.

Here's an American-designed version. http://blog.hemmings.com/wp-content/...liner_1000.jpg

...design to your heart's ($ and fab capabilities) desire.

Why not turn it into one of these ?

http://image.automotive.com/f/featur...speedster+.jpg

There was an aerodynamic bug in 69 - it was called a Karmann Ghia. My dad and I had a three or four of them and I don't remember that it got appreciably better mileage than a beetle, but then I wasn't really paying attention in the days of $0.35 gas!

http://mycarblog.org/wp-content/uplo...01-300x181.jpg

Have you considered a modern look, like the VW XL1?

Oh man if I had a Ghia I would restore it and enjoy it. I respect people aeromodding them, but I couldn't do that to a car I've loved since I was 8.

Jakob- That was the new vw concept I couldn't think of. Something like that would be awesome, but it would look funny jumboed I think. I don't want to cut the bugs chassis much. The body would be fine, just not the chassis.

Botsapper - I like that design. Pity they didn't make it mass though.

I'll try and post basic sketches today sometime. They're not pretty, but it's at least on graph paper. I know I'll need to put it in scale with a vw chassis, I just have to rip mine that far apart.

Our '71 Squareback (air cooled with mechanical fuel injection) routinely returned mileage in the low 40s on the highway. Goes to show how much difference aerodynamics really make.

I'm wondering though, with how basic the original system was, should I look at getting a FI setup or keep the carb setup?

Also, how is a rear engine worse for FE. I know it effects handling, but FE?

A natural donor for a great retro project.
http://i429.photobucket.com/albums/q...pillbugbug.jpg

There were FI versions of the VW flat 4 in Brazil in the 1970s. The advantage of FI is fuel cut off and better metering of fuel delivery.

The later Type IIIs (like the Squareback mentioned above) used an analog electronic fuel injection system. The later Bugs (and Super Beetles) used a different version, also controlled by analog electronics.

I would recommend not using the original systems. They are quite primitive, all in all, and very difficult to tune and modify reasonably. I would consider something like SDS (Simple Digital Systems EM-4) or one of the Megasquirt variants. The latter requires you to learn a lot about how injection works and do your own fabrication and such.

The single-carb setup is less than optimal as well, I think. The long-ish intake runners tend to promote manifold wetting; the heat risers from the exhaust combat that but take a little while before they get warm enough. I might consider a pair of little tiny single-throat carbs instead, but I'm not a carb guy.

The need for getting cooling air into and out of the engine bay (into the top, out the bottom) will make for extra aerodynamic challenges.

-soD

Well considering the SDS costs about as much as my last car.. I'm gonna have to hold off on that. I'm guessing a primitive FI system is better than a carb, but I might end up with a spare of each of those to tinker with if I play my cards right.

Botsapper - Thanks for the overlay. I didn't realize how close those actually came together. Granted one might be stretched a little more than the other, but they still seem to fit just fine.

Arragonis - I thought they were standard by '75. My bug has the plugs for the fuel pump up front at least, but I thought it was converted back to a carb.

My '80 Fiat has a Bosch Jet-tronic FI system I think, and as far as I know only the warm-up injector fails now and then, decreasing mileage.

Right now I'm gonna try for the FI system and run it stock, just to see how much an aeromodded body would help.

Aircooled vws don't live very long with a lean fuel map. They historically have used excess fuel to help with engine cooling.

If you really want fuel efficency, swap in a small water-cooled motor.

It is possible to do some aero work on a stock body. There is a diesel (current production) bug that used to have its own web site with the different things done to it and some rather lengthy economy runs. As I recall it, the owner made a run up to Alaska and got very good mileage compared to an unmodified one.

That said, you can pour a lot of money into trying to make something out of an old Beatle engine that it really is not and you would need to put a bunch of effort into the transmission. My dad had a '61 Beatle and it turned a lot more RPMs at highway speed that any modern car does. And then there is the matter of the rear suspension.

Anyway, why not make it a beach buggy like you were thinking about and have some fun with it.

If you still feel the urge to build an extreme aero car after that why not start with a modern engine and transmission? If you do not have welding skills, take a course at the local community college and build a chassis to suit things or look into a kit car of some sort?

I just think the odds are that you will put a lot of time, effort and money into the old car and the chances of success are not that good.

Well, the Bug body is not very clean from an aero standpoint, and the driveline is not very efficient either, but things can be improved.

Using adapters from Kennedy Engineering would allow almost any kind of modern water cooled engine to be fitted. Also, there are all kinds of gears available for VW Type 1 gearboxes. My diesel powered Porsche 356 uses a Type 1 trany from Rancho that has a 3:44 r&p, and a .7 4th gear. With those cogs, 2000 rpm means 62 mph.

That kind of driveline with a cleaner body (maybe some kind of kit car?) could yield big mpg numbers.

The scaling doesn't look correct. I think the Pillbug is much, much larger vs the Bug than portrayed.

Low 40's in a Squareback?!? Our family had several of them and I've no recollection of any of them getting anywhere near that. All were efi.

swap in a subaru EJ20

How many miles is your commute? If you're going super-aero, maybe an EV conversion is an option?

This looks like one of those cars that would do better going rearwards ;)

http://i494.photobucket.com/albums/r...racerSmall.jpg

Responding to posts. Always fun.

I think for now I might just stick with the stock VW engine. If I get a FI one, I'll put that in there because I'm slightly more familiar with a FI engine for fuel cutoffs and such than a carb. I still gotta learn how to tune the carb on my '69, as 14mpg is NOT nice. Anyhow though,

Clev - I don't really have a commute. But I do enjoy going to Canada. That's about a 600 mile round trip from where I'm at (southern WA), and having something that would get good gas mileage would be awesome. I think I just need to set up some project goals and see how close I can get to on a stock VW chassis and engine. The body has got to go though.

Is it bad that the only thing that makes me nervous about this -entire- project, is making the doors?

moTthediesel - I'm planning on trying to get the Freeway Flier transmission for the car. (link) Hopefully that way I could get away with lower crusing RPM. That won't come for at least quite a while though.

Pendragon - A beach buggy would be awesome, but I don't have the money to go out and just romp around with one. The truck we has gets 12-14mpg Highway ('97 F-350 XLT), and it's at least an hour's drive to the coast. That and I would rather have something economy. I know the whole time and money thing might not add up to what my goals are, but since I seem to generally have free time, and I'm using craigslist to get 90% of my stuff, I'm not really putting in much cash. That's another reason I want to start out with the stock setup. No point in dropping $$$ if it just won't work right.

Also, do you have a link to that website? A diesel engine (if I could) is the only modern engine I would put in there. Mainly because I could run SVO or Biodiesel. And it would probably get up hills better than with the gas engine in it now. I'm just curious to know if anybody makes a small flat 4 diesel engine that could fit in a VW. Granted it won't be stock, but I don't want to modify the chassis -too- much. Because if it turns out that this is a good idea, I want to be able to work on it easily and run with it.

I'll start working on a goals list and try and get those images uploaded already. They are just idea sketches.

Also, anybody know the mpg difference between a carbed Bug and a FI'ed one?

Okay - wrote up some basic goals I want to hit for now.
Use a stock(ish) VW Bug chassis*
Use an all custom aeromodded body
Have a drag Cd of at least .18
And a lot of you might think this impossible but..
I want to hit 80mpg highway.

I figure if Aerocivic was able to improve his cd by about .14 and get a 45% boost in gas mileage (If I did my math right), then improving my cd by .23ish (VW bug has cd of .41 stock, right?), I should hopefully get a higher than 45% mpg gain. Although it probably won't be close to 80mpg, it's still what I want to shoot for.

* Bug chassis can be modified if needed, but not like chop the whole thing apart and just use parts of it. Although shortening it could be interesting too.

If the 36hp engine could get a Beetle to freeway speeds, maybe one of the Kubota diesels can do the same with your car? I think people have done Honda swaps as well. If so, the Civic VX engine with lean burn might get you to 80 mpg.

Your other diesel option might be the one from the Smart, but you'd have to import it.

I hadn't thought of using a tractor engine. I'd probably have to get a custom adaptor plate, but that really might be something to consider.

Clev - According to the Aerocivic website,
And that's with the lean burn engine. I know there's a lot of differences between a new Honda engine and a VW bug engine, but hopefully the VW engine with a two cylinder fuel cutoff would work closely to the Honda engine.

check out kennedy engineering, they make tons of adapters for the VW transaxles for different engines.

Home

Whoa- what? If you've been around here at all you know that's a dead end.

Previously... lotsa numbers floating around that look like they came outta thin air... kinda pointless until you have a plan...

That includes the diesel engines from the early Rabbits. Another option.

Unlikely to ever happen with the regular thirsty VW Bug engines.

Don't forget Mike's Aerocivic is a lean-burn Honda, that he aeromodded to get and keep it in the lean-burn mode despite going faster.
He started out with a far more efficient engine than the Beetle. ;)


Shortening of the body will generally result in worse aerodynamics if width and height are kept the same.
Additionally, the short length will force you towards steeper angles while you want smooth curves.

The bulbous front isn't the real problem on a Beetle - it's the back.

and that "hood"-windshield angle doesn't help much either.

i would say keep the stock body, chop the top a couple inches (not so low that you can't sit comfortably) and slant the windshield back by about 10 degrees

Also, as far as swapping in a Diesel, depending on how much torque you're planning on having you may want to put a 1st gear lockout on the tranny, one of my dad's friends swapped a small block chevy into a Porsche 914 and the torque was enough to strip the teeth out in 1st gear (luckily it didn't damage much else and he was able to use the trans, after he took it apart and pulled the chunks out)

And then what? Will the Cd be much better? Another dead end that just won't die... Chances are, the only improvment from those actions will come from frontal area reduction and it will still have +30 or even +35 Cd. The entire rest of the car, especially the rear, is still a disaster, except for the relatively smooth underpan and lack of forward compartment venting.

It is the windshield/roof transition angle that matters; if and only if there's a problem there that's solved by re-angling, will re-angling help.

Lifting up the rear of the hood so it's angled could relatively easily cure that - to some degree.

... Seriously? I'm on here but I guess I missed that one. I tried it with my Prelude, but I was never able to get a definitive result. I guess I'll search around and try and do some more reading before doing that again then.

Right now I'm more focused on the body than anything else. I know the engine plays a huge role as well, but for right now my concern is with the body. I was playing around with the idea of using a prowler style front end, but I think the distance between the front wheels and the chassis is too short. I am gonna try and do at least 3 revisions of the car if I have to (not the entire body though), but that way I can change engines and such.

But,
Joenavy - If I used one of those adapters, I would try and use an old diesel Rabbit engine. I don't think I'd need a first gear lockout with one of those because they're not super-powerful as far as I know. Having a hard time bringing up specs on one, go figure.