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…