Lemans Lemons Unnecessary Aero Build

Sleepy Head suggested I start a new thread after steering a few threads off topic, so here we go.

Bit of history, we're the 3rd owners of this car, and the second ones to take it racing. It started life as a fairly straight and clean 1989 Pontiac Lemans, with about 350,000 original miles when it first went on track. The 2nd owner (first racer?) tracked down some eibach springs, and a full euro body kit to complete the look. He left the very tired 1.6l (74hp new, at sea level), the very poorly spaced 4 speed, and the very compromised suspension geometry. With a fancy paint job, and many badges from the many names this daewoo wore, they managed and IOE in Lemons, and it was then tarped behind a house in norther Colorado for a year or so.

Enter an engineer that had been following Lemons for years, 2 engineers who think racing would be fun, a retired computer programmer in his 70's who's been following and working in racing for decades without getting behind the wheel himself, and 4 Covid checks, one thing led to another, and it's been my problem since.

For our first race, we changed the oil, changed the brake pads, and off we went. We had a blast, but it only led to bad ideas for making things faster.

Fastest lap 2:36.9, 271 laps 14.5 hours

Race 2 saw weight reduction through any means necessary (the hood is now a bit floppy, and there is no glass besides the hatch), we got stickier tires, and made lower control arm extensions to fix the roll center and add about 3 degrees of static camber.  Wheel bearing and poor lights hurt our finish, but the car is on rails, making it much more fun to drive. 

Fastest lap 2:32.4, 388 laps 24 hours

Race 3: Facebook brought a major daewoo fan into the mix, and the many layers of badge engineering started to show themselves. A close ratio 5 speed from a much newer car, an abandoned saab provided 4 wheel disk brakes, 5 lug wheels, and larger wheel bearings to better hold up to racing. This was the most flawless race, besides being down one driver. Compliments for the handling of the car, and the surprising speed without power started to grow.

Fastest lap 2:31.2, 299 laps 14.5 hours

Race 4: 5 speed used more fuel, longer stints were desired, we put in a fuel cell. This probably made the front a little light, and flooded the throttle body efi, but we could go 2 hours. But, it rained, we had electrical issues, and the lights worked poorly. Did I mention that wipers were seen as extra weight, and it rained. The car was parked most of the night, but came back out with the sun, and was still a blast.

Fastest lap 2:32.1, 326 laps 24 hours

And it's kind of sat since fall 2022. We've all been busier, and the transmission came with a 2.0, which lead to a standalone ecu and a bunch of new problems.

Enough about the backstory, we've addressed handling, we're adding more power, we may have (not) become better drivers, it's time to take advantage of aero.

The plan so far, we have a number of 4x10 sheets of Alumacorr (https://www.grimco.com/catalog/products/alumacorrpanels), we're planning on a flat floor front to back, along with a large splitter. We've started 3d printing sections for a rear wing, and conversations came to mounting and endplates. I've noticed that a lot of top tier motorsports have one piece continuous wings, ie the mount is the endplate, and it goes smoothly into the main wing. I'm curious how this works, and I think 3d printing with a wrap of fiberglass may be the easy way to go. 

I'm up for wing ideas, splitter ideas, or general aero ideas that barely make sense on a time attack car, let alone a 100-120hp lemons car. 

The car currently, and a lot of general photos for me to drag into solid edge later to get sketching. 

I like the dazzle paint job. Does your competition find it difficult to gauge your velocity and displacement? 

Turbo_Rev said:

I like the dazzle paint job. Does your competition find it difficult to gauge your velocity and displacement? 

Nope, slow is pretty apparent. We barely hit 85 on the half mile back straight. After starting the straight at 65...

In reply to SDet :

Not bad for a ship-of-the-line. :) 

If you search "CFD", you should find a very good series of articles about getting setup for simulating aero on a computer. It might be difficult to acquire or create a model of your car, though. 

I'll also plug another forum, EcoModders.com. They're more interested in hypermiling but, to that end, that have put out a LOT of info on practical aero, to include very simple implementation schemes (hope you like balsa wood). 

In reply to Turbo_Rev :

In reply to SDet :

Not bad for a ship-of-the-line. :) 

As a well known non- slang friendly, I looked that up, to see if I could figure it out on my own. 
No avail. All I found was the standard definitions that I was aware of. 
What is the reference here?

While there are easier ways to drop laptimes I admire your spirit. Just make sure you get air to the front brakes when you construct your splitter. For the rear wing aluminum uprights are the easiest way. Simple, effective, and could become the endplates depending on construction. Or just buy a big Wang and be done with it. I saw multiple cars at high plains with them, and the judges didn't seem to care.

so, my first contribution are these two videos:

one note of caution, SDet, is that those studies are on a GTI... which looks like it's rear hatch angle is steeper than the LeMans.  I'll measure it in a little bit, but I suspect the LeMans rear hatch is right in the middle of where mosts texts advise they not be.  Which, I suspect is part of the reason behind the "raised spoiler" that got tacked onto the top of the rear hatch from the factory.

In reply to 03Panther :

Dazzle Camouflage

With a lower powered car I'd be looking for drag reduction beyond all else.

It looks like the rear window slopes away too quickly and flow would detach early. That would be my first area to modify.
Smoothing out the front end will also help. Fill gaps and seams other than the radiator inlet.

Agreed, I'd be looking at drag reduction. I like the flat floor and the splitter, but I'd put something over those empty windows. You might have saved a couple of pounds by taking out the rear quarter windows, but you're paying a big penalty for that with drag. I'd also look at doing a long tail and some tuft testing to see how attached that airflow is over the rear hatch.

Along with your flat floor, consider a diffuser in the back. It'll help drive your wing.

so, yeah... 25deg "OEM base hatch" and ~= 18deg with the rear "spoiler" attached.

In reply to sleepyhead the buffalo :

I just came to add that.

I'm assuming that is in the avoid range?

Would increased understeer above 60 and very floaty steering above 65 be relevant aero wise?

We'll look at patching up the rear windows and smoothing out everything we can. 

Side not, solid model has started.

SDet said:

Would increased understeer above 60 and very floaty steering above 65 be relevant aero wise?

We'll look at patching up the rear windows and smoothing out everything we can. 

Looking at the side profile... and noticing how similar the front part is to the shape of an NA miata, which is known for "float steering" at 60mph... what you've described makes sense.  The front fascia to the hood is creating lift, and it's getting add to by the way the front bumper looks like it's effectively scooping flow under the engine compartment.  although, it's probably not as scooping so much, since I doubt there's any underbody panels under there like in modern-er cars.

getting a splitter under there, with a bit of angle (~5deg), and an airdam to seal it to the existing bumper will go a long ways to firming up the front end "at speed".  although, there'll be some issue with using the AlumaCorr, which will have a sharp edge.  that sharpness will create a bubble of flow instability on the lower side known as a "laminar separation bubble".  the good news is... it looks like there's lots of vertical space there to add some thickness to the splitter (which will also help it to be strong), and allow some way to get some rounding to the front bottom edge of it.  the rounded edge, and the 5deg angle, will help to create low pressure (suction) on the underside; and the two together should help that to be more consistent despite changes in 'pitch' due to accelerating/braking.

another caveat along the lines of Racebrick and buzzboy... be careful about cooling after blocking the bottom off.  definitely try to make sure there's something (duct or turning vane) pointing cooling flow at the front brakes.  I agree about trying to seal the bumper to the radiator... kind of like a "poor mans duct", even better if you can eventually reduce the opening in the bumper for the radiator (assuming the duct is smooth enough to the radiator).  but, you'll want to think about ways to get the heat from the back side of the radiator out of the engine bay (since it used to just escape out the bottom).

Try looking at Vauxhall Astra or Opel kadett as it was used in Europe in rallying and circuit racing

Yes, but they didn't do much aero at the time. Most period correct photos are showing smoothing of the front bumper, and maybe a gurney flap on the rear "wing".

This is one I haven't seen before.

https://www.youtube.com/watch?v=IctrtaH5QJc

Okay, I haven't forgotten about this, and the car has most of the pieces for a running engine.

I've been learning how to use OpenFoam and Solid Edge through youtube, it's been great......

My main goal was to see if I could get a sim that looked mostly right to justify buying a better model, they're like $30.

My basic knowledge of CFD and FEA is garbage in equals garbage out.

With that in mind, I present chineese resturant dumpster that's been in the Louisiana sun for a week or 2.

I don't know what the pressure units are, the speed is about 88mph, and there are no wheels, but it shows some of what sleepyhead was saying about the rear window etc. Still seems cool though. 

I'll guess the pressure is in kPa (kilo Pascals)