Monthly Archives: November 2013

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.