With the onslaught of coverage recently here on Speedhunters, I don’t think I need to go into much detail explaining just how insane many of the builds that frequent Gatebil events are. In fact, more often than not, the body on the surface of a vehicle doesn’t give any indication whatsoever to the madness that lies beneath. After a while, you start to actually come to expect this – it’s something I call ‘the Gatebil effect‘.
Yet in spotting trends it’s nearly impossible for me to not also take notice of the outliers. There is one brand in particular that seems to be a minority in the world of complex drivetrain conversions and monster engine swaps and that brand is Audi. That’s not to say that these cars aren’t often heavily modified and highly formidable, just that they seem to prefer to keep it within the family.
And that’s one of the reasons why this particular A4 struck my fancy at Mantorp, not for what it is so much as what it isn’t. It was a refreshing breath of fresh air back to some dimension I had previously known as reality. In a sense, it was a car I could actually see myself building and driving. In recent years my opinion of Audi has done a virtual 180, largely in part to builds like this I’ve seen in Scandinavia.
Of course I’m not trying to suggest in the slightest that this car isn’t totally bonkers, because it certainly is in its own right. It just seems as though there’s a more particular method behind the way these cars are cut up and welded back together again that differs from the rest of the lot. Perhaps by the time we get to the end of this story you’ll see what I mean. Perhaps not.
When the car first caught my eye while making an early round through the paddock, what initially grabbed my attention was the livery. There’s just something about a Red Bull colorway that screams badass – plus you don’t usually find Red Bull logos slapped on turds. When I moved in and gave it a closer look I dog-eared this car for a shoot later.
I knew from the windscreen banner that this car was an outcast in more ways than one, since it was one of the few cars that wasn’t around to drift over the weekend. Furthermore it had made the long trek from Finland to compete which also piqued my interest, leading to me following the car as it went through tech. Inevitably this ended up being the very first car I shot at Mantorp.
There’s something about the simple no-BS demeanor of a time attack car that I like. There are no huge wings, in fact there are very little I-read-about-this-once-in-a-magazine-about-Formula-One-cars modifications at all. It’s just the basics, a hole here, a hole there, lighten this, lighten that. Voila. But I would soon find out that there was quite a bit of work lying underneath the surface.
From the outside little things like the headlight covers and the way the front bumper’s secured appear to be common track modifications. But what I later discovered was that they were absolute necessities since the front frame rails were shortened by 20cm and the entire front bumper assembly has been replaced by a custom tubular framework.
In the rear is another seemingly ubiquitous modification amongst the time attack crowd (and even the show scene in 2013) – the rear diffuser. However what appears to be simply some sheet metal fashioned from tin snips in a futile attempt to add some downforce is actually significantly more complicated than that.
What’s this, a hole in the roof? I guess it is a Gatebil car after all! Last year I had joked that the rear-mounted radiator had become the staple modification required for entry at Gatebil, but all kidding aside it has become extremely common here. While it’s a bit overboard for a lot of cars, on the front-heavy Audis it actually makes a lot of sense.
The roof duct funnels air through two massive chutes into a custom metal box that contains the radiator.
From there the air exits under the diffuser after passing through the radiator and picking up a substantial amount of heat, thus further aiding in the creation of a low-pressure zone under the rear of the car. If that Formula One magazine has taught us anything, that should be helpful.
The engine set-up is pretty straightforward and budget friendly. When Tero Tuohimaa picked it up the car was basically scrapped and without an engine. He decided from the get-go that this would be a track-only build and took the path of least resistance when it came to finding parts and modifying the car. An NA ADR engine from an A4 currently resides in the bay…
But it obviously hasn’t remained naturally aspirated. A massive Holset turbo has been fitted in conjunction with a bunch of DIY parts like the manifold it sits on and the dual-plenum intake it feeds. To accommodate the turbocharging, Tero upgraded the connecting rods and bolts and had some headwork performed to allow the new cams and valvetrain to soak up all the additional boost.
Nothing says “I’m pretty hardcore and generally don’t give a $#*& about my car” like a side-exit exhaust. While it may be the cherry on top in theory, Tero says that in retrospect the cabin gets really hot having both the coolant lines and exhaust now running inside the car. Oh well. #becausegatebil.
The set-up might not be flashy, but it’s good enough to produce over 600hp which is plenty enough to get the job done. The main issue with forced induction is the additional heat introduced by the system, hence the complex rear radiator set-up and massive oil cooler.
The inside of the car, however lackluster it may appear, is probably the most extremely modified area of the car. Obvious things like the fact that the entirety of OEM paneling has been removed stand out. There are some less obvious things as well like the fact that the entirety of OEM wiring, a stereotypical problem area for VAG cars, has also been discarded.
The driver’s seat has also been transported miles away from its original location and now sits some 50cm or so aft, completely behind the B-pillar. Tero mentioned that he got the idea from a scene in Police Academy where one of the characters drives a car from the back seat. After all, “comfort’s important!” In order to accommodate for this new comfort, a number of other bits had to be moved around.
The pedal box was the easy part. Next the steering column had to be extended, which also wasn’t too bad. The major hurdle was the fact that Tero could no longer reach the gear-shifter, so Mikkis Metal custom fabricated a relocated short-throw just for this application. Perfection.
With the seat repositioned and the dash completely removed it was obvious that something had to be done to house the instruments. A simple metal box was all that was needed to neatly arrange the STACK gauges and switch panel in plain view.
I was really excited to see how the car would perform over the weekend, unfortunately it didn’t end up making it trackside much. At first I figured there must have been some kind of mechanical problem, but Tero assured me that it was the driver who was at fault. Gatebil is really a 24-hour festival and it would appear that Tero participated a little too hard in the after-hours festivities if you know what I mean.
Nevertheless, he has assembled a pretty radical car if I do say so myself. In the land of never-ending face-melting conversions and four-digit power figures, it’s refreshing to see a build that’s a little more focused and attainable. As Freud would say, even at Gatebil, sometimes an A4 is just an A4.
Tero Tuohimaa’s 2000 Audi A4
636hp / 654Nm (482 lb/ft)
1.8L turbocharged ADR engine, Holset HX40 turbo #16 by KKD Motorsport, Tatech ECU tuned for E85 by Motest.fi, TiAL 38mm wastegate, custom 33mm DIY turbo manifold, custom DIY dual-plenum intake manifold, custom intercooler and piping, ported cylinder head, Rosten Performance valvetrain, Catcams 3652 camshafts, stock pistons, Eagle connecting rods, ARP rod bolts, custom side-exit exhaust, rear-mounted radiator w/ custom box and ducting by Mikkis Metal, 1700cc injectors, 2x Bosch 044 fuel pumps
Quattro five-speed gearbox, custom relocated short shifter by Mikkis Metal, Sachs 240 sinter clutch
KW V3 coilovers, 32mm(F)/ 29mm(R) swaybars, 034 Motorsports adjustable suspension arms, Seat Leon Cupra R front brakes, Porsche Cayenne Turbo rear brakes, Ferodo 3000 pads, custom floor-mounted OPB pedal box, hydraulic e-brake, roll cage, shortened front crossmember (20cm) w/ custom bumper bars, faster ratio steering rack
Wheels and Tires
18×9.5″ Lenso PD2 wheels, 245/35R18 Federal RS-R tires, wheel stud conversion
Custom front splitter, headlight covers, roof scoop, rear diffuser, rear spoiler, vented hood, smoked taillights
Gutted OEM panels, covers, seats, wiring, driver’s seating position moved back around 50cm, OMP bucket seat, Radelli harness, Momo steering wheel, custom steering column, STACK gauges on custom binnacle, fire extinguisher
That roof design is really cool looking, but that creates a ton of drag that way. A NACA duct flush to the roof would be just as effective and way less draggy.
What kind of steering rack did you use? I noticed you listed that it was a faster ratio. I am trying to find one for my Passat project.
Didn't going with the rear radiator blowing down interfere with the rear diff position, or did it just port behind? I presume you kept the car a quattro for time attack, but I've learned never to assume when it comes to Scandinavian cars... could you wrap the exhaust pipe passing through the cabin to reduce the heat build up? So many questions...
@Kirk_B From what I could tell (it's very difficult to see under the car) the radiator and venting is all behind the rear diff. Also the exhaust is wrapped, still pretty warm.
Anytime you are pulling 600hp through a 1.8L turbo, it has to be running hot.
Just wondering if you could ceramic coat the exhaust pipe to reduce heat... I know it would add weight, but it would allow the exhaust heat to be contained a bit. I was trying to think of a way to utilize the Seebeck effect, by using electric current to the floor pan above the exhaust pipe creating a cold barrier inside the car. It's popular for cooling computer CPUs (Peltier effect), but you just need to think of the cockpit of the car as the CPU.
On second though... it's Gatebil. You get to roast in the car for only 3 or 4 months of the year. The car looks great, and would be a blast to glide around a sweeping corner in. I wouldn't change it!
@seanklingelhoefer: A low pressure spot is only created if air is sucked up through the radiator. If you use it like it's done here, you will only create high pressure under the car....
You're both kind of wrong. If there is a large amount of pressure at the inlet for the radiator system (on the roof at the NACA duct) relative to the pressure in the diffuser, then pressure up top can theoretically blow through the radiator assembly with enough velocity to energize the airflow in the diffuser, increase its velocity, and therefore lower its pressure. The problem is that it is very unlikely that there is an area of high pressure that exists at that part of the roof and this approach would be sloppy at best and far too technical to just guess at what the airflow is doing.
Obviously, it could be the case that there is an area of high pressure at that part of the roof, which is not something that one could simply eyeball, but on most cars, there is lift (read: an area of low pressure) present at the roof which would certainly not encourage any airflow into the radiator ducting. Now, you could argue that the sole function of a NACA duct is to create that high pressure area, and you may well be right, but I highly doubt that the NACA duct could supply the pressure differential necessary to flow enough air to justify blowing into the diffusor. Naturally, fans could draw in the necessary airflow to make the radiators work, but that does not create the purported aero effects that are claimed here. There's a big difference between getting air to flow through all of this stuff thereby making the radiator work and getting it to flow through it the radiator and actually produce some aerodynamic benefit.
Furthermore, unless I am misinterpreting what I'm seeing in the pics, the diffuser is not technically a diffuser at all, it's just some hollow space under the car. The whole idea behind a diffuser is that it is a smooth, raked plane that allows the air to transition from the flat underbody (ideally) to the rear of the car. It is not just some thing that makes a hole in the bumper. So the diffuser shown here is already quite flawed, but by dumping radiator exhaust into it, that's not really helping. A better system would be to have the diffuser actually smoothly connect the underbody to the rear of the car and then duct the radiator exhaust out the back ABOVE the diffuser (not INTO the diffuer), which would have the benefit of "blowing" across the exit of the difusser which delays the flow separation at the exit of the diffuser.
The way that a proper diffuser works is twofold: First, by taking the fast-moving air that is rushing between the flat underbody and the ground and then allowing it to slowly reach a slower speed (as opposed to have a flat body the entire way back that just abruptly stops and creates a ton of turbulence in the process, which creates drag and in turn slows the airflow under the flat underbody), and second, the diffuser has the added benefit (on a production car) of blocking the airflow from encountering all of the normal, non-smooth doodads that hang down from the bottom of the car. If what I see in the pics above is interpretted correctly, it looks like the radiator ducting exhausts right into the what should be the flat plane of the diffusor, which kills both of the aforementioned elements that makes a diffusor desirable in the first place by making it not a flat plane and not smooth. You have effectively just created some new cavity for air to get hung up on and are shoving additional airflow into said cavity.
And just for the record, I'm not trying to be a jerk but that diffuser setup seems really flawed.
@Kevski Style Yes I know best solution would be air exiting in the rear of the car or even radiator flush on diffusor for smooth flow, BUT, lowest pressure should be just before beginnng of diffusor. Diffusor slows air exiting under the car so there is higher pressure anyways. And exit as it is now is so high and near the end of the car ,shouldnt be that much of a problem when going forward. And its just gatebil car, dont take it too seriously ;)
@MrEG @sean klingelhoefer Normally a Naca duct wouldn't have a big pressure buildup. It's kind of the same as a diffusor. It also has minimal disturbance to airflow. Thats why it's largely used on planes to direct cooling without inducing drag. Velocity is key, but it can only be induced by velocity of the hole car. Not by only airflow, as it also creates more lift by pumping air under the car. A diffusor also works by creating a vacuum.
As for the solutions, you are absolutely right! And the same goes for the cavity. It's kind of working as an air brake, and a big one at that....
@terotuohimaa As far as cars are concerned I'm taking it very seriously. But that doesn't mean it's a cool build though :) Built it yourself?
BTW, small tip: The naca duct has a space in between the piping thats closed of. You should open it up, use an extra pipe and connect it to rear decklid in the middle in front of the spoiler, or connect it to just above the diffusor in the bumper. The first creates a little bit extra downforce and less drag. The latter creates less drag and a boundary layer for your diffusor, which would result in the same improvement ;)
@MrEG You didn't come off as a jerk at all, quite to the contrary.
Since your design is very sleek, and is not based on radical aero, but rather a sleeper like appearance. Even though @MrEG and @Kevski Style had some very interesting posts about tweaking the aero of the diffuser area and cooling flow, I would suggest not to start fidling with the diffuser setup too much, for atleast two reasons, if I'm judgin these pictures correctly. Firstly your car does not have flat underbody and secondly it sits quite high from ground level to achieve necessary airflow velocity to actually lower the pressure at the diffuser leading edge.
What I am suggesting is, you should consider moving back that firewall and engine as far as possible, after that you would only need rear wheel drive and could save some wheight over the 4wd system. It would maintain that sleeper looks but be very fast around corners. This is not a professional conclusion but it should be faster than having a spot on aero package in your situation.
Offcourse it would be good to streamline that diffuser area too.
And yes nice build you have here, I like seeing proper welded rollcage and proper seating arrangements. There is just too many crazy builds with flimsy bolt-on-cages, scary!
@TeroK I don't think it is allowed to move the firewall in Finnish time attack series. As for the aero I would suggest to duct the cooling air trough the bootlid and make that underside as smooth as possible. After all a smooth underbelly isn't that expensive modification. Also as the exhaust is is out of the way, why not make the car much lower.
It does have smooth belly from splitter to rear + L shape rubber seal visible if look closely. but its not the whole width of the car tho. They use to rub ground but i rise the car because higher tires were fitted. Will be making aluminium side valance later this year for less "leaks". I drive in modified class. Unlimited is for tube frame and slick tire cars. Thes cars never come ready..
@terotuohimaa Oh yes i see it now. That looks pretty good actually, especially if you can get the seals to the ground. Just make a smooth diffuser into the back and it will be super. A lot of nice ideas in this build.
Yeah, we're in total agreement. I added that in there to avoid someone simply dismissing my comments by saying, "It doesn't matter that there is an area of low pressure on the roof, the NACA duct will create a concentrated pressure differential that will flow all the air you need." In other words, I was trying to head off a rebuttal preemptively, but I agree that the NACA duct likely does not create the pressure differential needed to drive enough velocity so that this setup would theoretically work.
When you said, "Yes I know best solution would be air exiting in the rear," I would agree.
But when you say, "even radiator flush on diffusor for smooth flow," I have to strongly disagree. While I am sure that it is technically possible to have a radiator duct into a diffuser and have that be a beneficial thing, I think that it's far more likely that you are just going to disrupt the airflow in the diffuser in ways that a lay person can't possibly predict (that's not an insult, I'm a lay person too). When dealing with underbody aero, it's already so complicated that you're just buying trouble if you start adding further complexity to the mix. Let me explain that better with an analogy. Many people in the time attack crowd will see some part, say a canard, on, say, a GT3 race car and they will then conclude that their car can benefit from a canard setup in the same fashion as that of the race car. Surely they are right that their car may benefit from canards in SOME fashion, but to expect that a setup from some professionally designed car will translate to another car is folly. The missing link that seems to be ignored by said time attackers is that no single aero part works y itself. The whole setup of the entire car has to be viewed as a complex system working together. So by extension, there may be some car out there that if properly designed, tested, and tweaked, can indeed realize a net benefit of a setup like yours (ducting from the roof, blowing into a diffuser). However, that is a setup that is borne of compromise and has to be meticulously dialed in. It can't be estimated or guessed at. As such, what I'm suggesting as it relates to your car is that you are introducing a degree of complexity and you're skipping some of the basics when you probably don't have the resources to make the complex system work. In other words, I'd keep it simple and not do anything to complicate the situation in the diffuser.
Also, when you said, "BUT, lowest pressure should be just before beginnng of diffusor. Diffusor slows air exiting under the car so there is higher pressure anyways," that's right but it is right ASSUMING that the dissuser is allowed to work properly. Think of it like a river. At the mouth of the river as it opens up into the bay, the flow of the river slows down substantially, meanwhile, further upstream, the water flows very fast, but the two are related. If you complicate the flow in the bay, the river is not going to flow faster upstream. The same thing applies. The airflow under the flat underbody is where all the downforce magic happens. Obviously, you want high velocity, low pressure flow under the passenger compartment. But, obviously, you want the flow coming out the rear of the car to return to close-to-ambient pressure smoothly, rather than abruptly. But why?
The reason is that when fast-moving airflow under a flat-bottomed car suddenly is ejected into the atmosphere, the airflow becomes incredibly turbulent, which creates drag and an area of high pressure behind the car. Guess what, that high pressure behind the car then restricts the airflow under the underbody and it loses its velocity and the downforce goes away. So to suggest that the airflow in the diffuser is already ripe with high pressure so it doesn't matter if you do something to increase the pressure further is simple a bad conclusion because the so-called high pressure in the diffuser is actually still lower pressure than you would have in the absence of a diffuser. You see what I'm saying? In order for the diffuser to work right, it has to slow the velocity of the underbody airflow, which creates higher pressure in the process, but that's not to say that a diffuser works BECAUSE it creates higher pressure, ergo, adding additional pressure into the diffuser is a bad thing. The high pressure is not the diffuser's job, it is a byproduct of the diffuser's job.
Not sure how The Minority Report, Tom Cruise, Precrime division, Precogs and dystopia have to do with this A4 :P
"At first I figured there must have been some kind of mechanical problem, but Tero assured me that it was the driver who was at fault. Gatebil is really a 24-hour festival and it would appear that Tero participated a little too hard in the after-hours festivities if you know what I mean."
Why does a driver/builder put "partying" on a higher priority than "track time"? Because Gatebil.
@terotuohimaa Excellent build dude!