2014 Development Review

Normally I don’t find myself writing this entry until after the Runoffs, but this year has definitely been pretty atypical, in a lot of ways.  No Runoffs for me this year, unfortunately…

We only ran a few events this year, but did lots of test days during the preseason and during the season getting the Stohr dialed in with all of its new parts.

There’s a lot of fun stuff we did over last winter that I haven’t chatted about previously, so here goes:

  • Kawasaki Conversion – Over the winter, we converted the car from Suzuki power to the Kawasaki ZX-10R.  With the 07-08 Suzukis getting older and increasingly more expensive, it seemed like a good time to make the switch to a newer engine.   The engine has run without any hitch at all.  The conversion was relatively straightforward, so here are some notes:
    •  For oiling, we went with a BRD dry sump system, which connected to the same rear-mounted dry sump tank that we used with the Suzuki. As with all BRD parts, the fit and function are great, but you’ll wait a long time to get it.
    • The  front sprocket is further towards the left of the car than it is in the Suzuki.  To keep the rear sprocket aligned, we reversed the rear sprocket on its flange, and added 3/16 of spacers to move it towards the left of the car.  This necessitated 3/16″ longer studs on the WRD diff as well.  This has been problem-free.
    • The rotation on the shift lever is opposite than that of the Suzuki.  I rerouted the shift cable for the car, and mounted the shift lever bracket on the front sprocket cover.  The shift lever was a modified dirt bike lever, which we cut and reversed so that the mounting screw could be removed with the large dry sump scavenge pump installed on the engine.
    • Contrary to what I read elsewhere, the Suzuki headers did not interchange to fit the Kawi.  Richard Cottrill at Rilltech made a nice header incorporating his oval muffler that tucks nicely behind the BRD bodywork
    • Just a note, not really a conversion specific thing:  When starting, the Kawi seems to turn over really slowly – don’t worry!  Your battery is fine, that’s just how it sounds.
  • BRD Bodywork – Since we’ve had the Stohr, drag has been a big problem.  Zebulon did a CFD study of the Stohr stock body compared with the BRD bodywork, which showed that the BRD bodywork was on the order of about 40% less drag than the stock Stohr body, even after our removal of the drag-inducing rear body kickups.  Fit and installation of the BRD body was excellent, and the parts are very strong, light, high-quality pieces – they look very nice.  As typical with BRD, the wait was long, but the parts are very nice.  Top-end speed has been substantially up this year as a result, the car cools well, and our wind tunnel testing earlier in the year correlated strongly with the CFD and verified the predictions.
  • Chassis Stiffening: In addition to the aero work we’ve done on the car with the Zebulon Wings and the BRD bodywork package, we did some analysis of the Stohr frame.  It is no secret that the as-delivered Stohr chassis is not well designed as it relates to chassis stiffness.  Triangulation is poor, in particular.  To address this, Zebulon modeled the car using FEA, and by repositioning and adding only 6lbs of tube, we improved chassis stiffness by 65%, and we verified these measurements using the torsion testing rig that we built at the end of 2012.
  • Bonded Aluminum Floor Pan – Taking a page from most other formula cars, when replacing the floor, which was damaged beyond repair after the 2013 Runoffs, rather than continue with the original method of a single floor bolted to the bottom of the frame, we replaced the main floor with a bonded and riveted aluminum belly pan of .080 aluminum.  Borrowing from the Citation guys, we extended the frame rails with 1″ steel strips to provide extra bonding surface for the floor.  I can see why folks don’t do this very often – the amount of work was immense, and took over 700 Cherry and Solid rivets!
  • Spar Updates – At the end of the 2012 season, we replaced the aluminum spar with the BRD chromoly spar, which was a good improvement for chassis stiffness, but not as much as we hoped.  We added more tubes to the chromoly spar over the winter, which addressed those shortcomings.    Along with the chassis stiffening above, and the bonded aluminum floor, the car is now approximately 250% of its original stiffness, and the change in drivability is tremendous – communication from the rear of the car is much better, and the stiff chassis now enables the front anti-roll bar to be a very effective tuning tool.

So…how has it all worked out?  Competitive results are hard to come by, as I did so little racing this year, but one good comparison is with Jose Gerardo and his car.  Last year, we were essentially neck-and-neck on pace at most events.  This year, I’ve been as much as 2.5 seconds per lap quicker in qualifying and testing sessions, so the changes have been hugely effective, and more importantly, the car is now likely very much in the hunt in terms of national competitiveness!

Now I just need to find a way to get the driver there…

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 – http://www.darkotech.com/, 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 (www.zebulonmsc.com) 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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Winter 2013 Update

Plenty, as it turns out. Since our last entry, we have:

Racing Backlog

  • The final F1000 Pro series event at Miller Motorsports Park. It was a THRILLING weekend, with some great racing between the three Stohrs of me, Lucian Pancea, and Jose Gerardo.

  • the SCCA Runoffs was in September, and it appears that my Runoffs luck has finally run out, as it was a pretty miserable week.

Winter Development
But, now it means that it’s time for winter development. So, what’s in store for 2014 to see if we can get the car on pace?

  • New Floor/Diffuser – With my factory Stohr floor being essentially destroyed at the Runoffs, thanks to Captain Asshole in the FA (hit me in the Kink at Road America),
    it is time to start fresh on the floor/diffuser. The performance of the BRD diffuser was such a transformative change at the Runoffs, that I will be continuing with that next year.

  • Chassis Stiffness – Our measurements of the Stohr’s chassis stiffness showed that the car’s torsional stiffness is not even half of the approximately ~4000lb-ft/degree number that is
    a common target for cars of this size and type. As such, we’re going to be looking into stiffening the car’s chassis significantly. The factory spar was the weakest point,
    followed by the cockpit, then the engine bay, so that is where we will be focusing our efforts.

    A little bit of FEA, and some common techniques,
    such as putting a bonded belly pan on the bottom should help us get closer to that 4,000 target. We will see.

  • Kawi Konversion – Owing to the increasing rarity of the K8 Suzukis, I’ve decided to make the transition over to the Kawi, and see if the extra top-end power will
    provide a benefit for the car. I will be using Jesse Brittsan’s proven BRD Dry Sump system to keep the engine happy, and since the
    rear of the car has the BRD Chromoly Spar on it already, Jesse will simply weld on the Kawi engine mounts, to simplify the engine installation.

  • New Rear Endplates – Since my flexi-Stohr endplates finally failed for good at the Runoffs this year, I need to get some replacement endplates. Once again, I’m turning to
    Jesse Brittsan at BRD for some new endplates, since the pieces on Rod Rice’s car, in use with his BRD body kit, seem to be very nice, and importantly, stiff/strong.

  • Tripod Axles – With the Kawi being about 20# heavier than the Suzuki, and the chassis stiffness changes set to add 15-20#, I will definitely be looking to save some weight. One
    way to do this is with the small DSR-sized tripod axles. By eliminating the heavy CV joints, you are left with essentially just the weight of the axles themselves, thus saving approximately
    15# back out of the car.

    At the Runoffs, I was ballasting about 10# to make sure I would make weight, but with adding the Kawi, reinstallation of the dry sump, adding of tubes, I will no longer be all
    that near minimum weight moving forward, without additional weight-savings measures.

  • New Sidepods – Probably won’t be any budget left for this, but if possible, I’d like to take advantage of the new sidepod shape that Stohr developed based on our
    development suggestions.

Great Salt Wounds

Great Salt Wounds

Like the proverbial emotionally battered lover, we returned once again to the site of our recurrent misery, Miller Motorsports Park. It’s an amazing facility, and a varied,
challenging set of circuit configurations. Yet somehow we always emerge feeling run through a wringer. But, it really loves us, right? Right?

At least the challenges show plenty of variety. This time we had no issue with freak snowstorms, inexplicable oversteer (broken tire gauge), inexplicable brake problems (faulty uprights), or any of the difficulties that we have faced and beaten before. That said, certainly there would be new challenges!

Friday: So, Uh, Where does it go again?

Despite having watched and re-watched my video from the 2010 Great Salt Race in my old Stohr DSR, finding my way back around the track took some doing. Amidst the attempt to regain my bearings, we also were running experiments on trying to contain the overheating issue that was afflicting all the Stohr F1000’s in attendance, to see what affect we could have. The first experiment, an intake splitter duct, had no measureable effect. During the second-to-last session of the day, I removed the left-hand sidepod entirely and observed water temps a full 25* cooler than before. Also immediately in effect was a substantial reduction in rear downforce, so let it be said that the bodywork definitely plays a role in getting good
airflow to the rear wing!

So, on the strength of that experiment, in a last ditch effort to keep water temps in check and keep the engine alive, we cut a hole in the top of the sidepod, just aft of the upper radiator
section, and hoped that would make a difference in staying cool on long runs for the race.

Saturday: Low Point

Those of you accustomed to reading my race writeups will know that I tend to have a quip of sorts for various parts of the weekend, but for this, there’s not much to say. Saturday saw
the beginning and near immediate end of the shortest race of my now 7 year long racing career. A combination of a good jump on the flag, a wide field, a dirty line, and some driver
brain fade saw me too late on the brakes at turn 1 and into the tires at the end of the straight. Race won in the first corner, genius. Game over, and a destroyed nose cone to
go with it, and a damaged front wing for garnish. Video is linked nearby.

Thus began the scramble to figure out if I’d be able to complete the weekend. Here came the spirit of sharing that seems to pervade the SCCA. JR Osborne loaned me a spare nosebox,
to which I attached my now damaged front wing. Richard from Rilltech donated the epoxy to repair my wing, the repairs for which were guided by Gary Hickman from Edge Engineering. To the car we bolted four used tires gifted to us by Lucian Pancea, the four on the car having been flatspotted in the shunt. Four guys pitching in to help us out – without their help, I wouldn’t have had a prayer of getting back on track, and would not have made the Runoffs this year.

As always, I’m so very grateful for the competitive and helpful spirit amongst our competitors!

Sunday: Now This is what it’s all about!

I started the morning with a tentative practice session, and found that the car now had a bit of understeer. I thought this might be attributable to the older tires, but it persisted through
qualifying as well – it would appear that our front wing repair hadn’t quite gotten the profile quite back the way it ought to be, especially as the wing now showed about a 1″ difference
in height from left to right. Hmm….something we’ll have to address later.

But now: Let’s go racing!

This race was EXACTLY what we were hoping for getting into F1000, it was a doozy. As you can see from the pictures, Lucian and I were LOCKED together the whole race!

We came around to the flag at a medium pace, and before I realized what was happening, JR pulled out to the left and jumped ahead, followed by Chris Ash in his F1000. Seeing this,
the starter waved off our start, and we went around again. Our second attempt at the start was much cleaner, and off we went! But, right as the green flew,
a huge chunk of something flew up from a car swept across the nose, crashed into my mirror, and bounced off of my face shield. What the heck? The mirror was knocked askew,
meaning I could only just barley see anything in it if I strained. This would turn out to be a crucial factor in the race.

I followed Lucian down the outside lane, having started
P6 overall and P5 in F1000. Chris Ash was incredibly late on the brakes, forcing Lucian wide to avoid being hit. I was EXTREMELY conservative on my braking point owing to my, uh,
indiscretion from the day before, and Gary Stevens came by on the inside as well. Recovering from his wide entry, Lucian got a good exit out of T1 and led me through 2, 3, and 4, and we raced around the opening lap, all of us squirming around on cold tires. Near the end of the first lap at Clubhouse corner, Chris Ash slowed suddenly (shifter problems), and we all swept around.

Crossing the line, it was JR and Larry in their own world, and Lucian and I just feet apart. I noticed that my understeer continued, but Lucian also seemed to have a very loose
car. That gave me the advantage through the high speed turns 2 and 3, and I poked my nose under him briefly in 3 after seeing the advantage, but thought better of it. I followed
Lucian again for the lap, just a few feet behind. We started lap 3, and this time I got a better exit out of the 180* turn 1. Staying almost flat-out through 3, I braked late as
Lucian swung wide to begin the turn, and snuck my nose in. We went side-by-side through the corner, and I was able to sweep ahead as we entered T4.

We continued like this for a few laps, when a I saw Sam Souval in his WF-1 in my mirrors as we came down the straight. I pointed him by and eased slightly, hoping he would go
by quickly enough not to spoil my gap to Lucian, and this seemed to work out. I followed Sammy through the first few corners, with Lucian now filling my mirrors.

Just a few laps later, Sam was in the mix again, having had contact with Gary Stevenson in his Speads DSR. Sammy continued but was going slowly as we came through turns 2 and 3. Neither Lucian nor I could figure out which direction he was going, and he nearly collected us both. I very nearly stuffed my nose into his rear wing, and Lucian locked up and went wide left on the entrance to turn 4 trying to avoid both of us. Somehow I managed to stay ahead through the mess, and off Lucian and I went again. I got a poor exit leading up to the attitudes and had to defend. A poor exit out of Tooele turn saw him right in my mirrors. I defended to push him to the inside, but knew he was going to get by.

I braked early and returned to the outside of the track and watched Lucian sail by and wide, and was able to complete an over-under pass, regaining the lead entering Windup corner just before the main straight.

We continued in this manner for the next 10 laps as the race neared its close, my understeer steadily worsening. It was particularly bad in the decreasing-radius and off-camber turn 1,
as well as the long right-hand T5 sweeper. However, my advantage through the high-speed T3 and Tooele turn allowed me to consistently stay ahead of Lucian, who would close substantially in the slower corners.

As we began the last lap, I tried for one last good go through T1, but just couldn’t make it happen. As I neared the apex, once again I had to lift and slow in order to get the
nose down to the apex. Rather than see him, due to my mirror all akimbo, I could sense Lucian off my right rear quarter. Then I could hear him – his car sneaking up along the right.
Desparate not to make another stupid mistake, AND take out the championship leader in one fell swoop, I kept my line tight just in case he was there.

I’m still not sure if he was or not, or if I could have exited the corner normally, but we’ll never know. Lucian’s better exit from T1 was enough to pull him beside me into T2. Side-by-side we went through 2 and into 3, but he swept ahead through 3, and I could not keep close through 4 and 5, as my front tires simply had nothing left. I could see his car wiggling with oversteer through 4, 5, and the rest of the lap, but I simply could not get close enough to make a move. Of course, I had to chuckle at the irony that the very man who had loaned me these tires had been led by them for nearly the whole race distance. At
just the right moment, they returned loyalty to their owner, and we crossed the line a second or so apart, P3 for Lucian, and P4 for me.