Category Archives: Projects

Tunnel Vision

Had a chance to do something over the weekend that was cool enough that I thought I’d share, since obviously it’s been a while since I’ve put anything up here.

Last year at the F1000 Pro Series race at Miller, Ryan made a contact with the owner of a new full-scale wind tunnel that opened up in Ogden, UT.

The tunnel is operated by Darko Technologies –, and since they were interested in seeing some race cars in the tunnel, and obviously we were interested in data, we worked out the details and finally got the car out there this past weekend.

The tunnel is a fixed-floor, open circuit, full-scale tunnel, with maximum wind speed of 60(?) mph. The whole day ran smoothly, and the tech was helpful and friendly. 

We showed up in the morning, unloaded, and rolled the car right in the tunnel. We spent some time getting the tunnel configured for the car (load cells and such for the measurements), and then spent our time working through a test plan that Zebulon put together. Zebulon used a cool boundary-layer control technique to help mitigate the ill-effects of the fixed floor, and a few other tricks from tunnel work they’ve done before, so it was really handy having somebody there that knew their biz.

I have to say, it was an incredibly fun experience – and TOTALLY scratched the nerd/engineering itch! 

Each run was around 5 minutes long, as we would take 3 data points, each about 80 seconds apart, plus a few seconds to spin the fans up and down.

Ultimately we were able to answer the age-old question: “Does an F1000 generate enough downforce to drive upside down?”

The answer? No. Not even close. At least, not this one. But, it was surprisingly efficient in L/D – hats off to Jesse Brittsan/BRD’s bodywork on that one. Obviously rolling road and wheels would affect this number.

The data we gained was fascinating – effects of front and rear wing changes, beam wing angle changes, ride height changes, and tested a few of the aero whizzy bits to see what they did. In particular it was very interesting to see the relationship between the aero balance we typically run on track that feels “balanced” to me, versus the static weight distribution of the car – not exactly what I expected.

Most encouraging of all is that the data produced by the wind tunnel had outstanding correlation with the CFD that Zebulon has been doing as we sort through the car’s aero, which means we can continue to pursue the simulation avenue with a high degree of confidence. Zebulon’s plan is to mimic the conditions in the tunnel in CFD and validate the correlation as tightly as possible.

Also, as an aside, the driver was happy that the strong correlation between CFD and tunnel also means that his butt dyno is the largely accurate (and exquisite!) device that he’d hoped!

By the end the car had so much yarn on it it looked like I’d crashed into Hobby Lobby.

As a last step, purely for cool factor and extra validation, we did some smoke visualization to get a sense of airflow over the car, and in the underbody, which was also incredibly fun to do and see. The behavior of air around the front wing and front tires, and the resulting vortices is wild to watch. Encouragingly, the airflow we saw in smoke trails also matched up extremely well with what the CFD simulations have shown us, so a big nod to Zebulon on that one too. Never would have guessed what happens behind the front wing and front suspension.

Lots of data to go over and analyze now, to see what other conclusions we can draw from the numbers.

Incredibly fun experience to have, can’t wait to see what it gets us in terms of analyzing the car’s development and competitiveness. Not something that many of us at this level get to do, so I thought I’d share, and also to dangle the hook:

Darko and Zebulon’s hope is that others will think the value is there for visiting the Darko tunnel with their race cars, so maybe we’ll see more cars in the tunnel moving forward.

Contact Ryan at Zebulon MSC ( to get a test plan set up, and they’ve arranged for discounted rates at the Darko Tech tunnel if you bring them with for engineering and consulting.

Overall, a true bucket-list day, still shaking my head at getting to do it

2013 Development Review

So, we made a huge number of changes to the car this year, some of which I haven’t mentioned on the blog until now. Our essential goal in 2013 was to try and reduce the massive drag on the car. At the 2012 Runoffs, I had a top speed of approximately 137mph, down in Canada Corner at Road America, compared to the 147+ that the best cars had. We were approximately 3 seconds off the pace. The same delta was true at the season opener in Texas, where we had the same ~136-7mph speed limit, compared to other cars in the mid-140 range. So, finding and eliminating drag was one of the biggest goals for the year.

At this year’s Runoffs, The car’s top speed was in that needed high 140 range, with the car touching 147-148 as we got the car dialed in. Had the week gone better, we would have continued to dial out rear wing due to the extensive rear grip, and found even more rear grip. Broken endplates and everything else made that a lower priority.

In short, we fixed the drag problem, and the car is now at least somewhat competitive in terms of straight line speed. Next will be to try and gain some corner speed to try and keep up with the pace-setting Citation and JDR cars.

So, some of the changes have been obvious, some of them not-so-obvious.

BRD Rear Diffuser
I want to mention what I think was the biggest change first. Jesse Brittsan made me a copy of his rear diffuser, which we installed on the car for Runoffs. The rear of the car was SO PLANTED that we continually had to keep reducing rear wing throughout the whole week, as well as raising the rear of the car. The amount of extra rear downforce is something we haven’t had all year, and even better, the car’s top speed was excellent – high 140’s, and within shouting distance of the smaller cars. In short, finally something that you could fight a little bit with, rather than being tens of miles-per-hour down.This seems to have been the largest single contributor to the car’s increase in top-speed, as even at the race before, at Miller Motorsports Park, Jose and I in our Stohrs were still stuck around the 137mph speed limit that the factory diffuser apparently had on our cars. Flow-Viz on the factory diffuser showed huge amounts of air rolling around the top of the diffuser and infiltrating in the holes for the lower wishbone, resulting in huge separation on the inside of the diffuser. Whatever the interaction, it seemed to create tremendous drag, and it’s nice to have off the car.I’m really looking forward at continuing forward with the BRD diffuser, and the level of grip it appears to give the car. Gathering some more data at High Plains Raceway, where we have lots of comparative data, will be really interesting as the 2014 season starts.As with Jesse’s excellent Dry Sump systems, contact Brittsan Racing Development for more info.

Brand New Diffuser

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Front Anti-Roll Bar
Halfway through the season, Dave from FRM developed a front anti-roll bar for the car. This not only allowed us to lower the front spring rates, but lessened the roll of the front of the car. By making the bar adjustable, it provided some in-race adjustment, which was very useful at the very hot Miller Motorsports Park race, where the front tires really suffered from the big heat and long, high-speed turns.These ARB kits are available from Dave at Front Range Motorsports, if you would like one for your Stohr.

Zebulon Motorsports Front and Rear Wing
I’ve been lucky enough to spend most of 2013 working with a pair of bright young engineers who make up Zebulon Motorsports. One of our first studies was to examine the wings on the Stohr, as our first attempt at finding and reducing the drag on the car. The result was a slight reshuffling of the rear wing configuration, which is now the Stohr factory setup – a large single beam wing, with a dual-element upper. The Stohr elements for the rear tested quite favorably in CFD. Zebulon drew me a nice swan-neck mount for the Stohr factory beam wing, which maximizes rear wing performance over the traditional bottom-mount. style.

These are available for purchase if you’d like one for your car, and Stohr has the shape for the top-side Swan-neck wing brackets – you can see the final version of the swan-neck mount in the diffuser shots above.At the front, CFD showed significant problems with the factory front “flat bottom” wing, so Zebulon designed an outstanding front wing, with an innovative endplate treatment that makes outstanding downforce. The wing was CFD optimized for a low drag coefficient over a wide range of downforce settings, while minimizing downstream flow disruption.The rear wing changes, combined with a new front wing, netted a 20% increase in downforce on the car as measured by the shock pots, and a few MPH of top speed at High Plains Raceway. At high downforce tracks like Sonoma, this enabled me to outpace the other Stohrs with room to spare.I highly suggest Zebulon’s replacement front wing package, which is also available for sale.

Bodywork Modifications
This has become commonplace on all of the Stohrs now, but one of the biggest bodywork problems exposed by our CFD study were the large “flip ups”
just inboard of the rear tires. in CFD, not only did these make substantial drag, but these contributed lift as well. We ran a 3-part test with stock bodywork, modified bodywork where the flip-ups had been extended out to the tires, and then a third test with the flip-ups removed.Predictably, the factory configuration was worst. Moving the kickups out to actually
shroud the tires did pick up 1-2mph, and removing them entirely also picked up the same 1-2mph. As such, you’ve now seen that most Stohrs have removed those flip-ups. Owing to this
change, Stohr has now developed a new sidepod shape that tucks in tightly to the rear spar, that streamlines the rear of the car substantially. This should be even better
than the raw cut edge that the car has now, once they make it available to more than just the factory car.

Rear Tire Fairings

Copying a bit from the Citation guys, we made some rear tire kickups out of some foam from Home Depot, and a bit of gaffer’s tape. These seemed to net
about a 1-2 mph gain on the data at High Plains Raceway, when coupled with the front wheel spats. As with many of the other modifications we did this year, Stohr has taken
our idea and will be making production rear tire fairings you can get for your Stohr. Or, you can get the originals from Mike Devins at Hurley Racing Products, since he’s about the nicest guy in the business.

Wheel Spats
Taking a page from the Formula Atlantics, we developed some simple front wheel spats that cover off the front wheel space. With brake cooling requirements so low on our F1000’s, covering the wheel reduces drag and lift. Fitting the fronts along with the rear tire fairings made a measureable increase in top speed, as well as a definite change in seat-of-the-pants feel in the car.Copies of these are available from Dave at Front Range Motorsports.

Wheel Spats

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Busy Busy

Boy has it been a busy couple of months!

New Spar

Much to report from the race car side of things. Many projects and changes. The biggest is the replacement of the factory aluminum spar with one built out of chromoly, built by Jesse Brittsan of BRD. This new spar aims to be stiffer than the aluminum one that it replaces, is lighter, and also makes room for an oil tank for the BRD dry sump system.

In initial testing, the spar did not result in any additional stiffness, disappointingly. We added some additional X-bracing at the front, and will add the engine-bay bracing to see if that gets the stiffness measurements to improve over the factory spar. Interestingly, it only reduced in stiffness slighltly when not attached to the floor, unlike the factory spar, which is almost 300% weaker without the diffuser attached.

On the upside, it is 9-10# lighter than the factory spar, which offsets the weight of the dry sump system almost completely. As well, initial indications are that I will be able to remove one of the two oil coolers in the Stohr, thus saving about 6-7# of cooler-and-oil weight, as well as the extra lines. Another plus is that it makes it a much faster job to get the differential in and out.


I finally decided to try moving back to a bump shifter, like I had on the DSR, after a couple of particularly difficult weekends shifting. With the Stohr paddles,
at the end of a long race, or when the gearbox is a bit balky, the effort to shift starts to get very high with the paddles, since only your forearm strength is available
to pull the paddle. This was beginning to cause me issues with work (typing), so it was time to go with the paddles.

A local welder friend helped me weld in the spud on the chassis for the shifter pivot, and Stohr did an awesome hurry-up job of duplicating Jose Gerardo’s bump shifter, left
over from JR Osborne using it. The shifter installed without too much trouble, and feels great, all I did was bend it slightly with a torch to get the offset
where I wanted from the steering wheel. Shift feel is fantastic – it makes shifting the car very enjoyable. Highly recommended if
if you’re having second thoughts about the cable actuated Stohr paddles.

Cockpit View

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Clutch Pedal fix

I may have mentioned it elsewhere earlier, but at HPR earlier in the year, and to some degree at Laguna Seca, I had an odd issue where I would lose the clutch pedal after just a few turns, and have to re-bleed.
Replacing masters, slaves, etc, nothing fixed the problem. Gary Slahor reported a similar issue Here on ApexSpeed. Long story short, I replaced the Wilwood master cylinder with a
Tilton one, and the problem is solved. Live and learn.

Dry Sump

As mentioned above, Part of the new spar install was making way for an oil tank, which is now integrated into the new spar. A clever O-ringed tube provides feed from the tank into the engine, meaning there are only two external oil lines – the scavenge, and the return from the coolers to the tank. Very nifty.

Initial readings show the promised 25-30* temperature drop, and pressure is as good as ever – in the 50* neighborhood.

We did an initial shakedown at High Plains Raceway, and experienced no issues. However, at Sonoma, we had significant scavenge issues, resulting in pressure dips, high oil temps, and blowing oil out of the engine breather. Initial culprit is apparently the Peterson filter I placed on the scavenge outlet, which folks are telling me is a big no-no. We will reconfigure with no filter on the scavenge, and see what develops from there.


In the continuing effort of getting the aero package refactored to reduce the substantial drag we have on the car, we re-did the rear wing mount, in addition to having a different wing package at the rear of the car. Following the lead of the LMP boys, Ryan designed a swan-neck style mount, similar to what the car originally came with from Stohr, to work with the new wings. As you can see from the oil traces on the underside, there’s no sign of the flow separation due to the (not present) lower wing mounts, so that much seems to be working well.

Sure Feet

From the “Small Details that matter” department: Go get some non-slip tape from your favorite auto-parts store. I found a roll of adhesive tape at an Autozone, in with all the rest of
their adhesives and tapes. Cut it into small squares and place on your pedals. Next time it rains, or you have racing boots wet from the gras in your paddock spot or whatever,
you’ll be happy you did

No Slip Pedals

How To: Shock Pot Install

It’s been a very long time, but after CoTA, I embarked on a project that was new enough to me, and what seemed like uncommon enough in the formula car world that I decided to
do a how-to writeup on something, in case it helps other folks out there. This time, it was the installation of shock pots on the car, to help with gathering data on suspension travel, downforce, and more!

All of us with formula cars wonder how much downforce the cars really make. We hear all kinds of numbers, some realistic, some not-so-realistic. With that in mind,
and with an eye towards trying to back up what by highly calibrated buttometer tells me about the downforce and grip the car has, I decided to install linear potentiometers
aka “shock pots” on the car for the 2013 season to get some real measurements about downforce, suspension movement, chassis roll, and all that kind of good stuff.

Here is what it took on the Stohr:


What Why Where
shock pots (x4) 100mm is the ideal length for our car, as it allows for the pots to be installed almost 100% in-line with the shock, without having to worry about droop travel. Veracity Racing Data
Upper Mounts (x4) An easy/cheap solution is plastic cable tie mounts with a hose clamp (see below) McMaster-Carr
hose clamps (x4) For clamping the above mounts to the shock bodies Autozone, etc.
1.25″ button-head 10-32 bolts (x8) For screwing through the plastic mount to act as a stud for the shock pot Any fasteners store
-3 AN Nuts (x20) attaching shock pots to the studs Pegasus, or any racing supply
1″x1″ Angle Alum. for making extension for rear bellcrank (see below) Home Depot Racing, etc.
1/4″ and 1/2″ 10-32 alum. spacers for spacing eye-end mounts updwards Home Depot Racing – specialty fastener boxes
1 1/2″ 10-32 hex-head bolts black oxide or stainless, for welding to bolts (below) Any fasteners store
AN5-13 Replacement Suspension Bolts (2-4x) to weld a threaded stud on for mounting the pots. For the Stohr, this was AN5-13 Pegasus, or any racing supply


One goal when installing shock pots is to try to get them lined up as closely with the shock as possible, to reduce the motion ratio between the shock and the pot. When the shock
moves 1″, you want the pot to move 1″ as well. This makes the calculations as easy as possible. On the Stohr, this was possible in the front, but not in the rear, as we will see.

First, take your plastic saddles, and install a 1.25″ button head in it with an AN nut and washer, with the bolt head on the inner/curved surface of the saddle. Next, put a hose clamp through the mounts of the saddle, and attach the hose clamp to the top of the shock body, above the shock collar. This provides you with a stud facing upwards that you can attach the shock pot to. Use a second AN nut to act as a standoff that will set the height of the pot when it’s installed. A third nut will secure the pot after it’s in place, further down the line. Do this for both front and rear.

At the front, for the Stohr, you will need to move the factory shock canister mount. Set them aside for now. Weld the 1.5″ 10-32 bolts to the head of the replacement suspension bolts, so the threaded portion of the 10-32 is straight up in the air. Install another AN3 nut to act as a spacer, similar to before.

To relocate the shock canisters, I suggest putting them in the middle, inboard of the shocks, as pictured. If you need them, I have more of these shock mounts, drop me an e-mail.

Some pictures. Note that in my install, we used 50mm fronts, as I worked with CSU, and donated the two fronts for their FSAE Car. With 100mm pots, you would not need the aluminum extension that we used.

Some notes from the pictures: Set your height of the “standoff” nut so that it will clear your spring and collar. On my car, the challenge was clearing the Hyperco hydraulic perches, hence the need for 1.5″ standoff bolts to be welded on the eye-end suspension bolt. The canister mounts I had cut locally on a water jet, and I have many extras. Pictured are a similar mount from Rick Iverson, found on

In the rear, things are a bit more complicated. The bodywork is close enough to the suspension bolts on the bellcrank that you cannot do the same weld-a-stud-on trick as the front. So, you have to make a lever arm, which means that there will be a motion ratio for the rear. We’ll cover that later in the setup.

Up at the body end, attach a plastic saddle with bolt and hose clamp, similar to before. This time, angle it inwards approximately 30*, since we’ll be moving the other end of the shock
pot mount inboard as well.

To make the pivot for the rear bellcrank, cut a piece of 1×1 angle aluminum into 4″ lengths. Cut three inches off of one leg, as pictured below. Line up the edge with the “leg” still on it
with the end of the machined relief in the bellcrank, and mark/drill your hole for the lower shock bolt. The remaining leg should fit flush up against the flat portion on the inboard, forward-facing surface of the bellcrank.

Drill a 3/16″ hole for the shock pot 1 3/16″ from your shock bolt. 1.25″ is too short, as the bodywork will interfere. 1.5″ is too long, as the pots will interfere with eachother as the
suspension travels through its motion. It’s a tight fit!

Use one of your 10-32 button head bolts, and push it up through the bottom of your mount. Put a 1/4″ 10-32 spacer on the other side, then an AN nut to secure the bolt. Your shock pot will rest on that bolt, and can then be secured with one final AN nut on top.

Do the same on the opposite side, remembering to make a mirror of your first mount, rather tha a duplicate.

Run the wiring for all four pots, and tighten the small locknut at the very bottom, near the pot’s rod end.

Configuration and Setup:

Now that the pots are installed, the next challenge is in configuring them. I’ll talk about configuration on an AiM EVO4, but the concepts are similar for all dashes…I hope ;-).

One easy way for wiring them is to plug all four into an AiM expansion box. This makes them easy to remove as a unit if desired. However, one of the uses for potentiometers is to get a histogram of shock velocity, which you can use for making damper changes. To get meaningful information for the damper traces, you must log at high frequencies – 500Hz or more. The AiM expansion boxes support a max of 100Hz per channel, so you will likely want to install the pots directly into the EVO4 logger itself, which supports up to 1000Hz per channel, for a total of 5000Hz logging.

Next, you must configure the pots in AiM. You want to set these up as “Distance Based Potentiometer”, and set the low as “0”, and the high to the size of the pot, in our case 100mm. Depending on how you oriented your pot during install (typical is with the body on the side of the shock body), at the bottom of the screen, you may set a negative or positive number for the max travel used on the pot (i.e. 100 or -100), so that the pot’s outputted mm reading changes in the direction you want for your calculation:

You will want to name them LF_POT, RF_POT, or similar. This is so you can later multiply by your motion ratio in your math channels to get to shock travel:


Finally, to zero out the pots, set the car on the ground, do your setup, and in the AiM studio, click on “Device Calibration.” The four pot channels will be listed, and you
can simply click the “auto calibrate” button. You’ll have to do this each time you make a ride height change etc, so that you are always starting from zero on your suspension
travel inputs.

Calculations and Math Channels:

The next number to be aware of is any motion ratio between your shock pot and the shock itself. In our install, the front is exactly linear with the shock,
which means it is 1:1 with the pot, so no motion ratio adjustment is needed. For the rear, remove a spring, and move the suspension through its travel, and compare
the ratio of movement between the shock and pot. For us, the shock moved .7612 for every 1″ of pot travel, so that is our motion ratio for the rear.

For calculating things like downforce and roll, you will need to know the motion ratio of the wheel/tire and the shock, what is commonly known as the motion ratio. On the
Stohr, it is approximately .92, depending on where you are in your suspension travel (it is regressive as you move into bump).

Those motion ratios, plus your springrates, can be plugged into math channels to calculate downforce levels on your car, as well as roll angle and much more. For getting those
math channels, I would suggest contacting David and Ellen Ferguson at Veracity Data.

I would suggest using the “Constants” feature for things that will hold relatively constant, such as your front and rear motion ratios, front and rear shock-to-pot ratios,
and your springrates. Remember you’ll have to update your springrate in your calculations every time you change them, or your downforce calculations will be off!

Finally, note that all these math channels will slow down loading of your channels, as it has to run through all the additional calculations. Here are some of the additional calculations you
might want:

        LF_SUSP = LF_SHOCK * MR_F                                  --> suspension travel from damper travel and motion ratio
        FrontRideHeight = (LF_SUSP + RF_SUSP) / 2                  --> ride height from average of pot readings
        FrontDownforce = FrontRideHeight/25.4*(2*Ks_FRONT*MR_F^2)  --> front downforce from ride height, front springrate, and front MR.
        FrontRollAngle = atan((LF_Susp-RF_Susp)/(53*25.4))/DEG2RAD 
        DownforceBalance = 100*FrontDownforce/(FrontDownforce+RearDownforce)

Happy Testing!