Thanks judgie :) I was trying to find time to call you today as I would like to talk to you about setting my cars suspension up properly, are you about tomorrow for a chin wag ?

Aerodynamics of a bug
 

Thanks Jadewombat
I did think about cutting the hood but as you have said cutting it would not be something I would want to do .The bumper is from a Rover 400,It has been modified a bit but not heavily.

Aerodynamics of a bug
 

I have been pretty active recently on this site as I have spent the past three or four days on the sofa with the sodding Flu. Anyway this is an idea I have had for a rear bumper/spoiler.It would work by releasing the pressure from the rear of the bug where the cars original design seems to act like a parachute.ie wings,apron,engine lid.The holes/vents in the wings etc would escape through vents and get channelled into the rear bumper at an angle to produce down force.In addition to this, the top of the bumper would be angled to produce more down force.It would be built to fit close to the body to eliminate what seems to also be the parachute shape of the standard bumper.Also the bottom center section could include veins.I have seen engine lids with holes behind the number plate this could be angled to produce more directional airflow.I am not sure of how it would effect the rear of the car but as I see it, it could possibly
1. create and add down force
2. release pressure from the rear wings,apron,engine lid.
3 create some rear end stability at high speed.

I have got an old porsche style body kit rear bumper that I was intending to use as a starting point .

All input welcome :)

Hope it turns out better than my sketches .

http://i291.photobucket.com/albums/l...8.jpg~original

Hey Graham,

I like your sketches! The vents in the rear fenders and apron is something that Remmele has done to his cars for a long time also and I think the reasoning behind that is strong. It will surely help some, same as it would on the rear of the front fenders.

Not so sure there would be downforce as such on a rear closed bumper though as turbulence behind the car is probably very high. I do agree they act as parachutes otherwise. For that reason I filled mine up with expanding foam (PUR) :D

Walter

Couple of aero basics for you:

To get downforce the rear exits would have to be channelled to point upwards, the downforce is a result of a reaction force.

The air over the top of the car would be detached from the surface way before the engine cover, typically at the top part of the rear window.

Downforce is mostly a result of STATIC pressure and the difference of this between top and bottom surfaces of a body. Target is to get higher pressure at the top surface which will result in overall DOWNforce. According to Bernoulli's equation: faster fluid flow results in lower static pressure. Using this, you want to get the air under the car flowing as fast as possible to get the static pressure as low as possible giving any increase in pressure over the body a chance to create the downforce.

Graham, well done so far, a very nice side step to the usual copy cat builds, but do you want all that venting on a road car? i have exactly that type of venting on my race car, but its not subtle. with a water cooled road car, why not work towards a diffusor and flat bottom it up to the bumper line? this was a factor in my water cooled engine choice, together with diminishing DB control thresholds at the races, i'm now 3/4 db quieter over aircooled with water cooling alone. you will need to move the lower shock mounts to make a worthwhile flat bottom workable, and the exhaust needs attention with any engine to get it out of the way. Just my view, but i think a road car, or a race car come to that, should be as understated as possible, its easy to get carried away and the KIS rule always applies.;) but well done so far anyway.

i'm in work next week so give me a call.
this is the sort of thing you wnat under the car
http://wp-content.rpmware.com/wp-con.../08/pw-jdm.jpg
http://www.tamiya.com/english/produc...enzo/enzo6.jpg

Of all the aero. tricks I've tried so far, venting the fenders made the most difference I could feel right away. Took the car out on the highway the next day and it felt much more planted to the road than before. I used a punch and flare tool on mine to make the holes. The turbulent air of the spinning wheels causes the fenders to act like wings and give the car some 'lift' at speed. If you look at new(er) cars they have a fender liner to minimize this distance between the tires and the inside of the wheel well.

http://i52.photobucket.com/albums/g3...9.jpg~original

Made a cheapo. roof spoiler out of garden edging recently. Just couldn't bring myself to spend $200 on a little piece of carbon fiber strip. Seems to help, car scoots off the line a hair quicker, could be my imagination too as I'm not being very scientific here but it definitely doesn't feel likes it's creating any drag.

http://i52.photobucket.com/albums/g3...3.jpg~original

I just found this interesting youtube vid & facebook item and thought I had to share it here.

See: Youtube video VW bug in a wind tunnel

And there was a poll on the face book page, see the top red box. The answer is in the bottom red box:

http://www.gerrelt.nl/roofspoiler/ae..._backwards.jpg
(click on it to get to the entire facebook page, I couldn't link directly to this item)

The beetle has 6% less drag when going backward.
I think it's because of attached flow staying attached to the rear window, which creates drag. Going backwards, there's nothing to attach to after the windscreen point. So the airflow can form itself like a teardrop.

Thats very interesting and sad at the same time. Shows us also here's a lot to gain with aero improvements.
We're probably on the right path Gerrelt ;)

:lmao: Yep!! :D

http://i254.photobucket.com/albums/h...e.jpg~original
Here is my underbody at its present stage. the rear ARB need moving to finalize the airflow, and is next for the chop saw, its going inside a tube running through the cars rear wheel boxes, bugs are hard work aero wise, the exhaust is particularly difficult to package away from everything in order to fit streamlining panels that wont be ripped off in the first race, my car already bottoms on the spring plate bolt heads and its not low enough yet, ideally the torsion tube needs raising and the horns chopping out.

Aerodynamics of a bug
 

My car has been hibernating whilst I am waiting to finish a large building project before work begins again on it. I am still looking at the builds here and seeing peoples ideas and views.

Spanner, it's interesting that you mention raising the torsion tube and chopping out the frame horns .Thats got me thinking.:thinking::thinking:

Part of the next stage of mods on my car will involve cutting the torsion tube in the centre and replacing the frame horns to aid the g50 gearbox fitment.Do you think raising the torsion tube or removing it completely may be worth considering whilst I am at it ????

What are peoples views/ideas on the best possible rear end set up to accommodate the g50 minus a torsion tube.I will be using one of Alex's uniball set up's.I am now thinking of a gearbox cradle/frame horn combo to tie into the cage and hold the uniball kit at the same time raising the top shock mounts.Here's the car as it is at the moment.[IMG]http://i1185.photobucket.com/albums/...1.jpg~original~original[/IMG]

Hi Graham, I would look at Ricolas layout, he made up new horns to suit a G 50, but to answer your question, unless it's a race only car, and running at circuit type ride height, ie, 40mm, raising the t/tube isn't strictly required, what it does is allows the car to run lower with good trailing arm angles for effective launching/traction, on the other hand, a powerful motor needs as straight a driveshaft alignment as you can get, so a gearbox raise is required in any case, removing the horns completely requires either a very strong mid mounted yoke set up, noisey for a road car, or a Porsche type rear engine support bar with lots of body/apron strengthening to hold the weight of motor, trans, and control the dynamics of driving forces on the supports, my racer uses a mid mount yoke, as I originally planned to loose The horns, I even tested with the end bolts removed with no problems, but they got a reprieve for packaging and mounting other stuff off them reasons, race only cars are easy, less compromises than a road car has, more for you to consider.

Aint that the truth!

:thinking::thinking::thinking:

Here we go again…

Thanks for the response Spanner.I was going to base the g50 install on what Ricola has done around the frame horn area. He has raised the box and moved it forward at the same time and built a cradle/engine mount and new frame horns.However he uses a combo of torsion bars and coil overs.I was wondering wether to get rid of the torsion tube completely as I will be using the uniball set up and just coilovers with no torsion bars.What do you think ??

Hi mate, Walter has retained his o.e and runs a G 50, many others have too including Russ Fellows, so it can be done, and it's no mean feat to remove the t/ tube, it's the king pin for the rear chassis stiffness and alignment, the frame bracing needs to be in place before the tube is cut out to avoid distortion, also you can't use uniball with no t/tube, so a new control arm points or wishbone pivots need ploting, I did this on my rally cross 4x4 1303 with a Mac strut rear a arm set up, no T/tube but modified horns and coil springs, the prop shaft was where the t/ tube used to live, ,after all that work, I can say catagoricaly a complex car is no fun and a mare to work on, it needs a team of mechanos to look after it, at least for eventing, my mantra now has changed, a bit harsh, but I've been round the block, and unless you do the work yourself, KEEP IT SIMPLE, As much as you can, the original kit can work really well as I'm now proving with my b/j car, it has no problem with keeping double wishbone cars behind, in Rich's case, he had to go super stiff working with a cab' to avoid chassis flex and he knew what he wanted and was able to do the work himself, I think on balance I would keep the t'tube to use the uni balls, but possibly cut the centre section out to move the 'box forward enough and use coil springs on Existing a arms, or you could shorten the b/housing as Walter did successfully and leave the tube intact, this saves a mass of work and would be my way, indeed it may be on the cards soon when my 'box brakes which it will eventually with 200hp twisting it.

Hi Spanner,I really appreciate your input here so thanks for all your comments.

I have had another look at Ricola's build and I think I will more or less go with how he has done his.I am considering an additional upper top mount for the rear shocks tied into the cage/gearbox cradle.I know Wally has machined his gearbox to fit without cutting the torsion tube but I am going Subi so this is not an option.( Wally persuaded me to fit a Subaru engine as I know he adores them…lol )

Anyway back on topic.

Aerodynamics…..

Ricolas car sits level as far as I can remember @100 mm but his is a vert.I was wondering what would be the ideal ride height for a road car (1303 ).. I like a car to sit slightly lower at the front so I am thinking something with a 20 mm difference,say 90 mm at the front 110 at the rear ??? surely this stance would aid the aerodynamics of the car???? Wally What is the front and rear ride height of your car…Thanks again fellas..

Sounds a good starting point, rake is good despite the purist saying the opposite, you will be adjustable anyway on the coil heights, the lower the better, but road cars are not track cars so 40mm in ride is not an option..

really you should be balancing the corner weights than tyring to get a raked ride height.
I'm like spanners in that i i try and keep things stock if i can, or tweeked stock. its all to easy to change everthing and have a car that handles worse than a worn out stocker.
just because it can be done dont mean you need to.

Yeah, I sure must have twisted your arm for picking that engine hey Graham? :lmao:

The rakes stance may look cool for some, but its not good for starightline performance at all. Reasons are mostly aerodynamically and castor related.
Level is the best compromise imo.

Never really measured ride height, but this pic gives an idea maybe?

http://i174.photobucket.com/albums/w...8.jpg~original

Aerodynamics of a bug
 

Thanks for the replies fellas its all good information.

Something else I have been pondering about is running boards.I got wider than standard on my car as my wings/fenders have been widened.I will be taking them off soon to give them a tweak.
I was wondering about putting fibreglass flat bottoms on them with just access for the fixing bolts.Not sure if this is worth the effort though ? would the added weight of the fibreglass out weigh any aerodynamic gain, any thoughts ???

Looking forward to getting some serious time on the car soon so i'm gearing up for what I want to do.

Hi Graham, quick answer, in general, the more floor area, at the right rake angle and ride height, the better as regards good low drag aero dynamic performance, the big decision for a road car is how low you can run it, given that it's a lot of work to run a bug low enough for racing at the ideal 40mm, which is out of the question for a road car, my running boards tie into the pan to widen the flat floor area, but it's not practical for a road car as the jack points have to go in the bin, and the cost of making GRP stuff these days is a joke, don't ask,,,, I would just use something that looked neat with the wide wings, it's the 100mm road car ride height that offers no realistic gains from teasing out small aero detail, but modern cars do exploit lower ride height for Aero advantage, you only have to look at the world championship rally cars going ever lower,,,,,
The best way to lower any car, especially a Stone Age design like ours is smaller wheels and tyres, mine would be on 13" spun alloy wheels and lightweight hot rod tyres tomorrow if,,,,,, well, cash in short. But You have enough power anyway to relax a bit on drag factor, but my aim is to go as quick as possible as near stock as possible,,,,, there is tho a plan B if the opposition start going quicker than in the past.

Aerodynamics of a bug
 

Thanks for the reply Spannermananger…

I was wondering if it was worth the effort with the running boards but probably not, I didn't think about the jacking points.

Also thanks Judgie on the heads up on balancing the corner weights.

Another area of the car that I do want to play with is the rear bumper.As I have a front bumper spoiler I want to build/modify a rear bumper from an old beetle/porsche body kit I have.One reason for this is to give the car a balanced look when viewed from the side.A standard rear bumper with my front end would look odd.The standard beetle bumper on an 03 is in my mind a kind of box shaped parachute.Just the shape seems to me to be totally wrong and the drag and turbulence it must create surely would add to rear end instability ? Or do you think that the air is mainly detached by the time it reaches the bumper ?

[IMG]http://i1185.photobucket.com/albums/...b.jpg~original~original[/IMG]

I had the same thoughts about the rear bumper and filled the box up with construction foam and rounded it off a little.
It also stiffened up my GRP bumper a bot.
You have no idea how many people asked me at shows why I had my bumper filled with yellow foam LOL!

LOL LOL, :lmao: Yes, this would be a good thing as the last thing a Beetle needs is more rear wheel loadings, either from aero loads or adding weight, the problem is only ever the front and this is where the gains are to be had and all the work is required, i know Walter has a splitter so he's seen the need, in a word, understeer is predominate on powerful beetles, even the s/a cup cars suffered with just 100 hp, also front corner weights are very high on the list of must have sorted things, this is so you can stop the thing without locking wheels, not important for a 'looker' but dont go near a circuit unless the above is addressed, or you will just wonder how the quick guys
go so deep into the turns, i would concentrate on the front, then get it road tested to see whets needed, a sleeper is preferable to any heavily reworked looker, they are lighter for a start, so can turn and brake quicker, i cant get photos up just now to show where im at with no more than a flat bottom, lots of work, and already ive run into more understeer, meaning the rear is working harder than without the underpanels, it will morph and turn into a diffusor proper eventualy, but a, it dont need it yet, and b, it can be ripped off or damaged after hours of work and cash,, and all these add ons make the car a bitch to work on, i have stuff to do at the front and that includes a splitter unfortunately, as i want to keep all stock looking as much as possible, but the rod is gridding up near the front row now days, so really needs add ons at the front, and possibly wider front tyres.. all good fun.:lmao:

I have been looking at the front splitter idea for some time now. Here's my progress on a splitter / bumper setup. The donor bumper came off a BMW e46 m3 circuit car. I do have a lot of data of the car without it, so will be able to see on the logger if it make any difference.

http://s21.postimg.org/twvn572x3/image.jpg
http://s21.postimg.org/fcekad7yf/image.jpg
http://s21.postimg.org/lfw4u9y87/image.jpg

hi 4agedub, hows that turbo coming along? well done on the front panel with splitter, Graham has a Rover version adapted to his 1303 which looks great, these take more air to the underside at the front than a b/j car, but both benefit from a proper air dam with splitter, i have some ideas i will cobble together soon to balance up my b/j car, at the moment i run various fairings and air channeling ducts at the front both to vent my rad' and oil coolers out into low pressure areas and also stopping lift, the rear is flat paneled right through just to help reduce drag by intention, but no doubt the spin off with an increase in under steer points to more rear load being generated. the mystery's of photo bucket on tablet remain unsolved, but ill try the pc to post up a few shots. success, here you can see the floor area extended both out to the sides and also into the wheel arches, ive left enough room to work on the car and support it, all mods have some trade off i guess, under the trans is paneled out with a duct for air to the diff, i will temp strip it to monitor things but have allowed for airflow into the clutch etc. the second one shows the ride height at 55mm before the under panels went on, its come down to about 50mm now, still 10mm above the minimum, but getting there, the exhaust needs yet more work to clear the ground and get the primarys up out the way, but i fancy oiking the motor up yet another inch will be the best way forward, i really should be buying a logger also, but for now i fancy using a small bullet cam to measure suspension compression on the fly, that should prove out things..http://i254.photobucket.com/albums/h...e.jpg~original
http://i254.photobucket.com/albums/h...e.jpg~original
[

I'm about a month away from starting the turbo engine and taking it to the dyno for some tuning. Still got plenty to do.

http://i174.photobucket.com/albums/w...8.jpg~original[/QUOTE]

Walter, did adding the oil cooler holes alter its ability, to aid in your higher speeds?

Aerodynamics of a bug
 

Will be interesting to see the comparisons once you get some info from the logger.

I guess the front spoiler/splitter must aid the movement of air over and around the body.However at the same time it is drawing air in at the front creating drag and probably lift.In your case it seems you have some track time so it will be really interesting to see how the car performs all round, inc cornering and at high speed.As Spannermanager points out it will bit different for a circuit racer compared to a road car due to ride height but keep us posted.

Lastly the old Kafer cup cars is where I got the inspiration for mine,I would imagine there are benefits of a splitter /spoiler or they wouldn't of used them :D

Once I do have data I will post it here. I do want to try adding some canards as well to see if they improve turn in grip.... I'm just worried with the extra grip in the front that we might have to add a wing at the back as well.

We have done some testing with a remelle cup type roof spoiler. On a back to back test we saw a 5km/h difference in top speed at the Zwartkops circuit. Going from 166km/h to 171km/h.

Thats good info! I assume the increase in speed was WITH the roof spoiler?

Effee: I haven't noticed any difference with or without the holes wrt handling.

Yes, the speed went up with the roof spoiler. A simple string test on the roof also showed improvement on the Gopro. I'll look if I do still have the photos.

The splitter produces down force, as it's name implies, it splits the airflow, sending most of it upwards And over the car, and the remainder under it, there by forcing it to increase in speed and lowering its pressure, splitters have been found to work very well at fairly high ground clearance, this makes them more benign and can incorporate a diffuser, unlike a NASCAR splitter which precludes all airflow under the car, but are far from benign for that reason, take off is not uncommon, also these don't use rear wings for reasons of racing purity, just a controlled spoiler, side skirts are not necessary on any car, modern flat bottomed skirt less cars produce huge downforce, a curtain effect is caused by simple physics, low pressure air can't bleed off into high pressure air, plus a boundary layer forming additional curtain effect that can be controlled by the lucky few with wind tunnels, most old Skool ideas have been debunked these days, side skirts and such, and new ideas prove wings can work without too much drag penalty for LOW SPEED work, say at or below about 85 mph, slaloms for example, now here's the rub, the effective wing angle can be up to 35 degs, not the 14 or 15 of the old theorists!
it was obvious last F1season that redbull ran at higher rake angles and ground clearance than most others, indicating they had downforce in hand and were using more rear ride height for other reasons, possibly rear weight transfer, side to side or to the front, or for kerb riding ability, lucky them..
As ever, the trade of is drag and weight, how much extra power do you need to pull it all to a faster lap time, non if it's well thought out and shows on the watch over a race distance, if it's faster over race distance, say 10/15 or more mins', it works.
Road cars have no datum, unless you go to a race track and time test before and after, you can't just say " that feels better", better for what? Speed? Fuel consumption? Passenger comfort? That's the problem with road cars, the right tyres and wheels and good brakes are a better bet for development with these, and good looks for the girlies of course...:)

Aerodynamics of a bug
 

Hi Spanners thanks for the continuing input on this as it is something I am very interested in.When my car was running for a short period before it started having engine install problems:angry::angry:,I took it of a spin and noticed at around 80mph (on a private road :D )it felt completely stable. I think this is testament to how the running gear had been installed by type 2 detectives but I would imagine the splitter/spoiler must help/aid this stability ? I hear what you saying about track testing but as a road car I was able to do that speed with one finger on the steering wheel,with no steering rattle or hardly any scary shaking around you would experience in a normal bug.Obviously its a very different car now but to feel how stable and smooth it felt was a very pleasant surprise :D:D
I have not driven a modified beetle with this running gear so its hard for me to now what to expect but I gotta say it felt great.

Regards

Graham, well you've laid a good foundation by starting with the front air dam and splitter, hence the stability you have already noticed, even with a B/j car, it's the front that needs the work first, even with the much maligned ( unjustly) swing axles, the rear on both IRS and swing, is easy to get right, the reason the rear engined GT3 Porsches are so good in LMS and FIA Endurance racing with virtually no rear aero/diffuser/downforce, (flat engine layout =no room) is the already high rear loadings over the mid and front engined types with more room at the back for large diffusers, wheel loads are good to start with, tho there isn't much to choose between the three layouts, front, mid and rear engined, the advantage swings each season, maybe front engine, BMW, Corvette, Aston, were there at the season start last year, now we see Risi Ferrari holding the aces, tho it's so so close, and we know Porsche have a new car for this year...

I have had my 1303 to 135 on the track and was extremely stable, suspension and its settings are crucial, in my opinion the rear is a big issue at high speed on a beetle, if you are running tortion bars with old rubber bushes the toe is all over the place, unibal and coil over will fix that. I run small amount toe in on the rear and under load and tyre drag the rear is probably close to zero at high speed. The most frightening car i drove was me mates with 2.9 type 4, 230 odd hp, and when it had std rear end it was very dangerous, after unibal and coil overs and the right dial in, we did 140 no problem. Wont like a bumpy road tho!

Think I've mentioned elsewhere, I've had 150mph out of my cabrio, admittedly the aero is probably slightly better with the flatter roof? Only aero on mine is flush Kamei to body.. Rear suspension is torsion bar IRS but with 944 parts and aftermarket outer bushes which are probably stiffer than rubber. I also run a small amount of toe in.

Aerodynamics of a bug
 

Hi Rich,how did it feel at that speed ?