New HPR Best

Had a fun test outing a few days back in the F1000, trying to shake off a bit of the rust from not having run much this season.  Got some good new video with the new SmartyCam HD, and happened to run a new personal best, approximately two seconds under the track record, while scrubbing in some new tires.  Enjoy!

What’s old is new again

Just over ten years after selling my 1997 Corvette to a good friend Mike Feldpusch, the ol’ car has come back to me, and once again finds itself in my garage.

With the continued decline in participation in the Colorado Region SCCA, coupled with the difficult logistics of racing far away with a one year old kiddo, I’ve found it hard to find events to run in the F1000 with any competitors.

So, I’ve brought the Corvette back into the fold to go Time-Trialing and Racing in NASA.  With their focus on local racing, and the fact that so many of my friends from the autocross years have moved on to NASA and not SCCA, the draw is not only for better competition, but for better camaraderie.

The next few months will be getting the car prepared for track use after many years as an Autocross car.  Should be a fun project re-learning how to work on the ‘vette!

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 –, 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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