Hanchey has two decades of experience, as does Casey and Stuart, and they were all 2 seconds off the pace even after a few laps. That's not a knock on their driving - no, its showing that this mess of a set-up is that hard to get used to. I've co-driven with Weiss and Hanchey many times over the past 20+ years, and they can usually hop into any car and go fast as Hell within 1-2 laps. But when proven, fast drivers like these hop in the car, and it still takes a significant learning curve. Luckily we've already been "learning" this for months. Given another dozen laps they would have been right on pace. Even after 5+ autocross events in the car and dozens of laps, its still
difficult. Costas was literally making throttle changes with his toes thru thin racing shoes - not the typical ankle movements - its that sensitive.
Left: Costas during one of our many tire changes for the day. Right: Hanchey working with some F Stock racers on ASTs in a 2007 Shelby
They all felt that because of the very abrupt power application the car was nearly undrivable, and certainly holding us back. Hanchey was convinced the car had serious throttle tip-in/mapping errors. This was a 30 second test course run entirely in 2nd gear, nowhere near redline but always in the meat of the powerband on every corner or transition exit. Hanchey said to "try a run in 3rd gear" to prove his point. I told him that was crazy, but we humored him. Costas made 3 laps in third gear. It was ~2000-2500 rpm lower than in 2nd gear at every spot on course. He came in and said "No way, that felt SLOW",
but it was .3 sec faster - best run of the day so far. WTF?! Yes, there is a problem with power application and this proved it.
Now it wasn't faster on every lap. He took 3 laps like that to get used to it, and the first lap was slower, the second lap was even, and the last was a bit quicker then all previous laps. It was the change in power application, but also a *large* change in lines he took through the cones. Very different line could be utilized with the less sensitive throttle. More of a "momentum" line than a point and shoot line. But in the end, it was faster cutting back on the power by running the higher gear through the course.
Why is that? Let's explain - modern fly-by-wire throttle systems have the ability to tweak the throttle response (correlation between % pedal opening and % throttle body opening) by both the OEMs and tuners. The "trick" is to make the throttle mapping much more "falling rate" or digressive, which make the cars "feel faster". This means - the first small percentage of pedal opening makes for a LARGE percentage of throttle opening. So when you barely give the car a little gas pedal, its opening the throttle very aggressively, and it
FEELS FAST. Which makes it very difficult to delicately adjust throttle, which is all you do in an autocross with a powerful car. That's been the case all along with this car, both with the stock tune and the aftermarket tune we added via the SCT Tuner. This is actually the 2nd throttle mapping we've tested and its still MUCH too aggressive.
Throttle Mapping Issue = Found!
What we actually need, to make the car easier to control at lower speed events like autocrosses, is
a rising rate throttle map as described and charted on page 36 of Neil Robert's excellent
"Think FAST" book. And I quote,
"A rising rate throttle... provides fine control over the lower power end of the throttle range. That helps you blend cornering into forward acceleration smoothly and early". An example of this from the 1960s was the uber-powerful and light Can Am cars, another quote, "Jim Hall said that a rising rate throttle linkage was an absolute must on the big block Chevy (1000+ hp) Chevy-engined Chaparral Can Am cars to make them anywhere close to being drivable." We don't have a 1000 hp big block underhood but we
are trying to take 400 whp V8 and power it through somewhat narrow street tires, and do so in a parking lot, in lower gears, with abrupt power transitions.
So the throttle mapping is
a big thing that needs to be changed, and throughout the day I kept asking Costas to make a run or two in 3rd gear, every hour or so. And every single time, on every set of tires, and every permutation of shocks,
the car was as fast or faster in 3rd, a higher than optimal gear, because it was so much more drivable. Matching those times in 2nd gear took extreme control and wasn't nearly as repeatable. The shop that is providing our custom SCT tunes for the Mustang was called and we described the issue in great detail; we were already on a supposedly less aggressive throttle map, but now a third custom tune was created, and Paul M and I just loaded it to the Mustang this evening. We'll be testing this in anger this coming weekend at a SW Texas Divisional series 2-day event.
The next big revelation was in shock revalving. We had already had AST-USA revalve the fronts but the rears were still pretty much "off the shelf". Hanchey had a suggestion, we asked them to try the valving change he thought would help, they revalved the shocks on the spot, and it made a huge difference in times right off. It has us thinking about some even more radical shock ideas to test in the near future- which, for business reasons, I'm going to test before we explain these plans.
After this significant jump in times was from the shocks verified on several more laps with the Yokohamas we moved on to the Toyo R1Rs, then the Dunlops, each time re-verifying the shock settings front and back as well as the tire pressures that worked best on the Yokes. So which tire won? Well, it was pretty close between two of them, and I don't want to spill everything just yet (need time to crunch numbers and edit video), but
the Toyos are for sale...
Fresh set of 265/35/18 Toyo R1Rs ..... now FOR SALE!
These R1R tires are still
full of tread and have less than 20 total autocross runs on them, all in the last 6 weeks. Still very fresh, great durometer numbers, so how about $600 + shipping? Probably make great track tires for somebody (and I will keep them for just that if I only get low-ball offers). They won't be going back on this Mustang for STX use, that's for sure. We do really like the Dunlops, even these 3 year old former street tires we tested with. I bet you will see a fresh set on our car soon, for testing head to head with the Hankooks and Yokohamas, and possibly in some unusual sizes. We learned some things that day that we want to verify with even more testing.
We didn't have time to run into town and have the Hankooks mounted - the 265/35/18 Hankook RS3. So we've already mounted those and they will be run this weekend at the SW Divisional here at TMS. But as the day was winding down we did re-mount the first set of ours - our control set, the Yokohamas. We noticed only a slight uptick against the original times, so the temperature creep didn't account for more than .1 sec of our overall gains, from beginning of day to end.
OK, so what did we learn? How much time did we gain, if any? From the beginning of the day, starting with shock and tire pressure settings we'd refined so far this season, to the end of the day, we found 1.1 seconds on a 30 second course. That's.... a lot. This was between testing some unusual tire pressures, the various tire testing, and most of all the shock changes (valving changes uncovered almost a second alone - you can't tell me "shocks don't matter much"). And this is still with 2nd gear power application
almost impossible, and the car quicker in 3rd gear. Will this latest round of improvements + a new throttle map translate to a more competitive car on a full SCCA sized course? We hope so.
THere's a couple of stills from the "tire cam" videos (that I still need to edit/upload) showing sidewall deflection; the Toyo was compared to the Dunlop & Yokohama. Costas also managed to replicate that unusual "limp mode"
error icon on the dash that I ran into event last month. It happened 3 times during the day, but he wasn't allowing any more wheelspin than normal, just the same massive amount we always see in 2nd gear. He'd notice an abrupt lack of power, abort the run and come in to show the icon; I snapped a picture of it. To clear the error you have to turn the key off and restart the car. Odd.
More soon,