Thoughts about aerodynamic improvements in a 550 Spyder

[ghamauricio]

First of all, hi everybody and congratulations for the excellent quality of the articles and discussions.

I'm an architecture student from Brazil who likes to know at least a little about almost everything you can think of (so please be patient with me because I'm not an expert in mechanics, aerodynamics nor anything like that - just a bit curious).
For the last two months or so, I've been wondering: "what if I built a Porsche 550 Spyder replica?"

And since then I've been considering a few things like suspensions, engine, gearbox, interior and, of course, aerodynamics.
The first thing I think I have to think about is the chassis.
The chassis design is influenced by the engine to be used and the suspension i guess.

In the original car the engine was air cooled, and I think the suspension was like the one used in the "Type 1" in the front, and a "de Dion" in the rear.

First I don't really like the "de Dion" suspension for a city car, but I also don't know which is the best for this scenario (a city car, to be used sometimes in long road travels - 3h or so).
Second, I pretend to use a water cooled engine. Where would the radiator go then?
There's a company here in Brazil which makes replicas of the 550.
They have two options for the chassis: air cooled, with the infamous de Dion; and a water cooled version, with "independent suspension" (according to the guy, based on the Gol's (a simpler and cheaper version of the Golf) rear suspension). The problem with this chassis is that the radiator goes where the extra tire used to go, and the extra tire goes in the front (he sent me a few pictures which I can post later).

The problem with this setup is that the underbody of the car is flat from the front to the part of the engine. At the part of the engine, it's open because of the radiator, making it kinda hard to make a flat underbody with a splitter.

So I've been considering putting the radiator in the front part of the car. There's a small "grill" on the front, and from some pictures you can see there's a hollow place which I don't know what it's used for, and maybe the radiator could go in there.
Here are a few images:

Here you can see the underbody from a replica, but I don't know who makes them, I just think it's as close to the original as possible. The exhaust pipes would go in those "splitter-like hollow spaces".
The water cooled chassis from the http://www.autoclassics.com wouldn't have that "splitter like" part, it would just be open.


The hollow part in the front which I don't know what it's used for. I also don't know if the replicas available to me around here in Brazil have that part like that.

Images are from the great http://www.type550.com, I hope he doesn't mind I used them here. :S

Also, for a flat underbody with a splitter to work as expected, would I need side skirts? Notice the design of the car doesn't allow for sideskirts without making it weird.


Well that's it for now.
Thank you all for your time!

[747heavy]

Hi, welcome to the forum

the hollow part at the front is the air chanel for the oil cooler.
If your replica, has it, you could use it to mount a radiator for a water cooled engine. For a "small" engine with <100hp it should be sufficient, but routing and bleeding the water system is my a bit problematic.
Sticking with a air cooled engine, makes it a lot easier, and the car will be lighter as well.
But it´s up to you, off course

as for air cooled engine options, maybe have a look here
http://www.cbperformance.com/turnkeys.asp


if you are not too concerned with original apeal, a Subaru 4 cylinder flat is maybe a good option as an alternative engine.
You will also need to consider a suitable gearbox to go with your engine.
Again maybe a complete Subaru unit is not a bad option, other than that look at a VW bus engine/drivetarin combination (T2/T3 models)
Not sure if a Gol engine is the best option. I think you have plenty of cheap T1 VW Bus (Combi) engines/gearboxes in Brazil, and sure enough people to tune them a little bit.

I would not be too concerned with flat bottom or any other type of underbody aerodynamics. If you plan to use the car on Brazilian roads, chances are that you can´t run the car low enough, to make good use of it anyway, and for most of the time, you want go fast enough, for any aerodynamic effects to take place, especially not inner city.
A good suspension package with a good setup will go a long way, and be more important/benefical - IMHO

just my 2 cent
Good luck

[ghamauricio]

Hello hermano 747heavy, thank you for replying!

The problem with air cooled engines is that I can't seem to find engines other then the Beetle's (they're also used and old). Also, is it reliable enough in traffic jams and slow moving situations?

There are some "wide body" versions of the Spyder "shell" with a "grill" over the rear wheel which I don't know what it's for, but maybe that could be used to cool the engine, right?

I don't really mind about the appearance of the engine, I'm more concerned with performance, economy and reliability (I know performance and economy are opposed, but you can always get a mean term).
Why are the Subaru boxer engines so popular with Spyder replicas?
I saw some Audi A6 engines cheap enough, wouldn't they be a good choice?
Also, how do I choose the gearbox to be used? What are the variables involved?

The flat bottom would be used in longer road trips; when I wanted to benefit from the underbody aerodynamics I guess I would lower the car a few centimeters with a couple of twists with a wrench and I'd be all set, right?
This involves a good suspension package, but what would that mean in terms of chassis modification (and price, of course)? Can I get good suspensions (with a few adjustment options like ride hight and maybe spring stiffness) cheap enough?

Thank you very much for your time!
Best regards!

[747heavy]

Hola amigo,

I´m not really much into the kit car scene, so there are probably others better to comment on it.
I only mentioned the Subaru engine because it is a flat four, same as the original engine, and it´s water cooled. So for packaging, and a bit of original sounnd it would make sense - IMHO
Other than that, they are probably cheaply available and you get them from ~100 to ~300 hp as a oad car engine.
Now, having said that, the car (Subaru) is probably not the most comon in Brazil and as it is not produced in Brazil, parts are may expensive.

Sure you can use an inline four engine, such as the VW/Audi engines which are produced in Brazil.

As for the gearbox, it should match the power output (torque) of your engine of choice. If you mate a VW Bettle (Fusca) gearbox which was designed for a 45 hp engine with an 120 hp engine, it may does not last too long.

I still don´t think, you will get any meaningful aerodynamic forces with that car under normal conditions, so IMHO, it should not be too much a concern fo you.
The flat floor/underbody as such/by it self will not create much downforce. Yo wold need a sort of an diffusor or at least a bit of rake with the car to try to create a lower pressure under the floor.
The large radiuses on the bodyshell, does not make it any easier to keep the low pressure under the car, as the air will rush in from the sides.
You would need to un the car lower then 100mm from the ground to make that sort of aero work in any meaningful way - IMO
Knowing some of the roads in Brazil, and the "love" for speedbumps it´s not so easy to make this practical - IMO
But I accept that others may have a different opinion on this matter.

You may find some informations here:

http://www.chamonixcars.com.br/site/en/index.html
http://www.motorrad-fuchs.com/en/single ... PLICA.html
http://www.beckspeedster.com/beckspyder ... ntory.html
http://www.autosportlabs.org/viewtopic. ... 3ba53c53cc

photo of a replica with 2.0 ltr VW engine



Good luck
Abracos

[Flummo]

As for the gearbox, it should match the power output (torque) of your engine of choice. If you mate a VW Bettle (Fusca) gearbox which was designed for a 45 hp engine with an 120 hp engine, it may does not last too long.

The type 1 has not been sold here in Sweden since the early seventies so obviously I do not have any idea about what gearboxes has been used since then. But most of the gearboxes are rather weak, apparantly the late models with an S last in the model (as 1303S) have the best gearboxes. The bus had more powerful engines, and therefore also better gearboxes.


The rear engined old VWs are popular for banger racing here, they have the weight of engine and gearbox right on top of the rear wheels = very good grip when you take off, and as all qualifying runs are only three laps a good start is very important. The original aircooled engines are ofcourse way too weak, so they are almost always replaced with B20-21-23-230 engines from Volvo (brute force and ignorance needed to make space for it), usually tuned to 150-200hp. However, broken gearboxes and driveshafts are not uncommon...
http://www.youtube.com/watch?v=xotnuqkV ... re=related


Enough irrelevant rambling... You could make skirts some distance in from the side, I'm thinking horizontal sheets of polycarbonate plastic. Survives abuse from hitting the ground (as it no doubt will some times) and should do some good if you get any useful under car aero...

[ghamauricio]

Hola amigo,

I'm not willing to use an old Fusca or Kombi engine; only if I could use new parts and tune them to get at least 130HP. But also I prefer water cooled engines.
I'll try to check how much would cost me a Subaru engine. Also, is it too complicated to turbo-charge a normal engine? Or just out of curiosity, can I super-charge a turbo engine if I want to?

The problem with the flat underbody and adding downforce without visually altering the appearance of the car is that I'm kind of concerned with lift and poor high-speed handling in such replicas. I know the Fusca has terrible lifting problems in high speed, and I wonder if the changes and adaptations in replicas would cause similar problems in the 550.
For example, there's this company in Brazil which makes replicas, but the underbody is flat until the firewall. From the firewall rearwards it's open so you can cool down the engine. And I'm worried if this wouldn't alter the aerodynamics characteristics of the car.

As for the ride hight and rake, I'm aware that the car would have to run very low (below 10cm, ideally 8cm from the tarmac), but I guess I could lower the car for high speed conditions when I need to (ex.: interstate road trips) with a couple of twists in a wrench in each wheel's suspension.
I think the problem with the air coming from the sides could be solved the skirts proposed by Flummo. I was thinking about something else, but I'm having connection problems now. When I get home I'll try to use a Sketchup model to show what I was wondering for the sides of the car...

Flummo, I'll also talk about the engines in more detail later.

Thank you all guys!
Best wishes!

[marcush.]

Hola amigo,

I'm not willing to use an old Fusca or Kombi engine; only if I could use new parts and tune them to get at least 130HP. But also I prefer water cooled engines.
I'll try to check how much would cost me a Subaru engine. Also, is it too complicated to turbo-charge a normal engine? Or just out of curiosity, can I super-charge a turbo engine if I want to?

The problem with the flat underbody and adding downforce without visually altering the appearance of the car is that I'm kind of concerned with lift and poor high-speed handling in such replicas. I know the Fusca has terrible lifting problems in high speed, and I wonder if the changes and adaptations in replicas would cause similar problems in the 550.
For example, there's this company in Brazil which makes replicas, but the underbody is flat until the firewall. From the firewall rearwards it's open so you can cool down the engine. And I'm worried if this wouldn't alter the aerodynamics characteristics of the car.

As for the ride hight and rake, I'm aware that the car would have to run very low (below 10cm, ideally 8cm from the tarmac), but I guess I could lower the car for high speed conditions when I need to (ex.: interstate road trips) with a couple of twists in a wrench in each wheel's suspension.
I think the problem with the air coming from the sides could be solved the skirts proposed by Flummo. I was thinking about something else, but I'm having connection problems now. When I get home I'll try to use a Sketchup model to show what I was wondering for the sides of the car...

Flummo, I'll also talk about the engines in more detail later.

Thank you all guys!
Best wishes!

I think perimeter spoiler /splitters will not destroy the looks of the car as much as skirts would.
perimeter spoiler are simply horizontal plates at the sides extensions of the floor.
having some longitudinal strakes on the underfloor will help there as well .
But i think you will need to go lower than 8omm at the front to make use of downforce created by underfloor aero,especially with a small car the 550 is.

[ghamauricio]

Do you mean front and rear spoiler?
I can't imagine a spoiler on the Spyder man...

And the skirt could be fit under the car so you can't see it if you don't look very close and from below.

I've also been thinking about the air intake possibilities... Could the air go through the tube of the chassis?

[marcush.]

look at the lip the horizotal extesion of the floor between front and rear wheel.
that was what I thought of ...I´m not sure who invented it ,John travis?

[ghamauricio]

Sorry, I guess I'm not following you...

[747heavy]

not 100%, but I think Marcus mean something like this:



or a bit more fenczy (Carbon look)

[ghamauricio]

Oh, I see. Well if that is a perimeter spoiler, what would a skirt look like then?

I can't imagine those on the Spyder either... I wanted something discrete and almost invisible, not messing with the car's original lines.
Something like Flummo said, perhaps made of wood or cheap plastic, but more or less between the wheels...

[747heavy]

skirts in a extreme form would be this:



some other examples:





you try to seal the gap between the underbody and the ground, and create one or two tunnels.


http://www.autozine.org/technical_schoo ... h_aero.htm

[ghamauricio]

Oh I see it!

Well unfortunately I downloaded a Sketchup model of the 550 and it seems a spoiler and rear diffuser would both be well visible, though I don't know how accurate the model is.

As for the suspension... How complex is it to change a suspension type, and what kind of effort is it worth? I mean, is it worth changing from a double wishbone to a multilink?

[ghamauricio]

Guys I just noticed this forum is almost exclusively about Formula 1...
I wanted to post a few questions about the engine intake and I wonder if I'm supposed to post it in "Automotive news and technology" or if I'm supposed to ask for another forum, more general, which deals more frequently with such broader questions (not about F1).

Is there any other forum?
The problem is that I think the people from here are so competent and good that I'm afraid another forum will not be as good.

Or I can post it in this topic too, but I didn't want to run over the previous question before it has been discussed...