Miata Data Analysis: NA8 Vs NB2

Published: February 2, 2018

I had an opportunity to compare my performance in a more recent addition to my fleet, the 2003 "Hampton" Miata, to its older cousin, the 1997 Miata that's been with me through most of 2016 and 2017 HPDE events.

While running the 1997 Miata I noticed that it was, infortunately, not competitive in straight lines to NB Miatas, even when said NB Miatas are driven by intermediate drivers. This video of me running in Chin blue (intermediate) group at VIR demonstrates the issue perfectly - NB Miatas are walking away from me even in a draft.

Thus I made the decision to obtain an NB Miata for my HPDE efforts, which is what the 2003 car is. Let's look at how the two cars stack up.

Test Setup

Conveniently, the aftermarket parts on the two cars are almost the same because most were transfered from 1997 car to 2003 car: roll bar, shocks and springs, sway bars. The front sway bar on the 2003 car is actually slightly thicker than the one that was on the 1997 car, but since the 2003 car is heavier this is probably fine. The difference between the two cars is power level (both stock, 2003 makes about 20 hp more from the factory and more torque), weight (2003 is about 100 lbs heavier), and tires.

Summit Point Main

1997 Miata in green, 2003 Miata in red:

The 1997 car was equipped with the stock 4.1 open differential and used 225/45-15 Toyo RR. It also drove on the old Summit Point pavement. The 2003 car was equipped with the stock 4.3 factory LSD and used heat cycled out 205/50-15 NT01 fronts and totally heat cycled out 225/50-15 NT01 rears, but drove on the new Summit Point pavement.

The new pavement is much stickier than the old pavement, permitting the 2003 car to accelerate earlier and harder, despite having a grip disadvantage. The track probably became about 2 seconds quicker after the 2017 repave, hence the 2.5 second difference between cars is largely due to the pavement rather than the cars' performance. What is interesting is the straight line performance of the two cars is very similar - this could be due to the taller 225/50-15 rear tires on the 2003 car, but is honestly somewhat surprising.

Sebring

1997 Miata in green, 2003 Miata in red:

There is a big difference in tires between the cars. 1997 car was on 245/40-15 RC-1, 2003 car was on 225/45-15 full tread NT01 RC-1s offered more grip which was particularly obvious through turns 17 and 15. 2003 car liked to oversteer through both of these corners which was not helpful for lap time. 2003 car also struggled to enter turn 7 with good rotation - something that gear selection may have played a part in.

The 1997 car was equipped with the stock 4.1 open differential, while the 2003 car was equipped with the stock 4.3 factory LSD.

The 1997 car was about half a second faster overall, making up the time primarily in the corners, while the 2003 car did have more power and higher straighaway speeds.

I'm not sure why 2003 car is slower through turn 14 - perhaps there was a short shift involved. The fact that the speed trace is noisy is also suspicious.

From what I recall, I had a much easier time driving 1997 car around Sebring, specifically in turns 15 and 17, than I did with the 2003 car. I'm thinking that removing weight, and specifically nose weight, from 2003 car will help as it is significantly raked right now. The rear end of the car really likes to jack up in corner entries, I imagine this doesn't help with stability at all.