I had a lot of fun with the ISF at its first trackday.
Bottom line: the ISF got down to 1'10.2, which is only a wee bit slower than the FD was at 1'09.9. And I have to remember that the FD was on really good Endless MX72 pads and Advan AD08R tyres at the time, so it isn't really comparing like with like. At the FD's very first trackday, it got down to 1'10.2 as well; but that was on Kumho KU36 tyres, which are many magnitudes better than the ISF's Michelin rubber on a racetrack. So I reckon the ISF is good for a high 9 on road tyres and quite possibly a low 8 with proper tyres and brake pads.
My fastest laps were with the driving aids in Sport Mode, which is to say that the traction control is slackened off and allows a little sliding. When I turned it all off, which I only did for one session; I was about a half second slower.
But it's interesting to compare the lap traces against the FD's best lap of 1'09 (the FD is the red line):
Starting from the left, the ISF is 10km/h up on the FD's top speed, with the ISF clocking 186km/h before braking. The lines then dive under brakes...ISF's braking point is a little bit earlier, but the big Brembos allow better modulation than the FD's brakes, so you can see that I'm bleeding off the brakes a bit better and getting a slightly better corner entry speed. As the line rises again for the run up the hill, it's roughly line ball, but as the line goes down again for Turn 3-5, you can see that the ISF's trace is jagged, as it has to slow more for the corners, and then accelerate out. In comparison, the FD can take that whole section at a more constant speed, hence the red line is smoother as it heads to the second deep braking point. Then the line rises again, for teh run down the hill into the right hand sweeper, and you can see the FD's red line smoothly arc upwards, because the FD can turn into the sweeper with just a brief lift. The ISF needs a longer lift to settle the car, and so you can see the trace dip a little halfway up as the line climbs.
Then it's hard on the brakes at the "1.21" point on the chart, which is the Bus Stop hairpin. The FD gets a higher entry speed, while the ISF brakes to a slower entry speed, but then you can see the ISF's brute force as it outaccelerates the FD up to the right hand sweeper on the back straight. As the line climbs to the final peak of the lap, again you can see the traces for both cars dip, as they back off to turn in for the sweeper, but there is a bigger dip for the ISF which needs a touch of brake, whereas the FD makes do with just a lift, with the FD recording a higher mid corner speed. Then finally the lines dive for the last time as the two cars brake for the final hairpin, with...surprisingly the ISF logging a higher mid corner speed...probably due to the slow point and squirt nature of the corner handing the advantage to the ISF, which gets a much better acceleration out from the apex.
So overall the analysis isn't a huge shock; the light and nimble, good-tyre shod FD gets a small advantage in midcorner speed in the long corners, but it has a huge advantage in the series of tight corners (which is where it gains most of its advantage). The ISF wins the race out of the corners, but needs to slow more for the entry, and the tighter the corner, the more it sees the FD motor away into the distance. But given that the tyres and brake pads of the ISF are nothing special, I'm a little shocked it's as fast as it is. The tyres are Michelin Pilot Super Sports, 225 at the front and 255 at the back. Exactly the same footprint as the FD, but the Michelins fade quickly on the track and it's hard to coincide the sweet spot of the tyres, with a clean lap with no traffic. I'll upgrade to Advan AD08R when the time comes, and I'll upsize them to 245/275 which fits fine on the stock ISF rims, and should make a huge difference.
The ISF brakes were the oem brembo pads I fitted a couple of days before the trackday. They were really good for the first two sessions, with huge, beastly retardation but after that they got a bit overtemped and began to wear out really fast. After 42 laps, the brand new pads got down to 2mm of pad material, and you could even see them getting thinner and thinner with each session :) The brembos are now in the bin, I'll do it right and get Endless MX72. It's a shame, the Brembos had great feel under road conditions.
...and here's where all the brake pads went :)
And here's the vid!
What's it like to drive? Well, first thing is that there's plenty of accessible power, and the 8spd snaps off aggressive shifts making the whole package feel pretty mighty. In a couple of corners where 2nd and 3rd were both useable, 3rd felt quicker, with enough low down torque to dig the car out of the turn...the top end power can be a bit spiky as it comes in and kicks the tail out, so going a gear higher felt like the better compromise. In terms of balance, it's great...very resistant to understeer, and power oversteer on corner exit is the dominant characteristic. It actually feels like it has more power than it can use, and you have to be quite progressive with feeding it in. And for a big ol' gal, it always hung in gamely and never felt like it would collapse into understeer, and it sure felt nimbler than its 1680kg would suggest, and it sure doesn't feel like a sedan. As for the driving aids, I was a bit slower with them all off, and only ran it this way for one session. There isn't the same feedback as the FD, and rather than ease into a slide smoothly, the ISF tends to transition into oversteer in a bit of a messy spill. So with everything turned off, it could be hard to walk the fine line between sliding just enough, and going way too far with a smoky drift; it was hard to find the middle ground, but maybe I just need more practice. Certainly the traction control is really well judged for track use, it would allow a little power oversteer, and keep the power on for a good drive out of the corners. And you could even feel it straightening up the car, when I'd over-rotated it a little on the ripple strips mid corners. Pretty clever system, I think I'll need a lot more practice before I can better it.
Proper brakes and rubber will transform this, I reckon. I'm having a lot of fun with this, this is a damn fine car :)