Ok, the TL;DR is lack of aero, and weight, and we couldn't really fix it, and keep our class.
As I mentioned, we took an SR20 and destroked it to get it under 1500cc. We loving (sometimes) referred to is at the SR15VET or the 150SX. The class also limited aero. We were able to take some of the JDM body pieces off of the Type X Silvia, but we couldn't add any other aero components, and keep our class.
Our best guess, since it happened religiously at the same speed, was that it was an aero issue (mostly). Air would get under it, the car would get light and then spin. Land speed racing is counterintuitive to EVERYTHING you know about racing. Typically, you want a light as possible, and the biggest fattest tires, with relatively low tire pressure, amongst other things. You also typically want a linear power band, with progressive power over the whole range. Land speed racing is it's own beast. You want the skinniest tires you can get to work, and I swear, you overinflate them. You want the car to be heavy too. Our power band was also, basically, nothing, nothing, nothing, nothing ALL OF IT. I can't find the dyno right now, but it really couldn't get out of it's own way, and then when like 6k rpm hit, and the turbo started to get happy there was a MASSIVE power/torque increase.
Some of the old timers came by our pit, in their golf cart, and started chatting with us. They seemed fascinated by our little import, and what we were doing. So they start asking questions. "How much does the car weigh?" "2800lb", or whatever it was. "bullshit, you need to add xxx more pounds" "what kind of tire pressure you running?" we reply "xxxpsi" "bullshit you need to be over 70psi". "did you add ballast?" "no....." "bullshit. you need to talk to xxx guy, he'll tell you where to get some cement" This was really our first foray into land speed racing, and it was definitely a learning experience.
Our next course of action was to add ballast, but the thing about land speed racing is that it takes place on "dry" lake beds (typically). Here is an iconic pic of Challenger II in 2014, when Speed Week got rained out (happens a lot). They had dragged the car all the way to Boneville only for the weekend to ultimately be cancelled. And they had to take pics of the car on the "salt" of course.
The year that we went out, and set the record (same year Challenger II did) a massive storm blew in over the mountain range, as our car was in tech, making sure we could make another pass, on our last day. Well, it was lingering over the mountain range, and heading for us. I've seen what that amount of water can do, and how fast it can do it, so we decided to get the pit packed up and head out, before we were submerged. There were EZ-Ups blowing away, shut flying everywhere, raining, windy, and salt was already getting more soggy (there is only a patch in the middle of the lake that's dry enough to drive on typically. The edges are usually still lake-ish. The day we arrived, I drove the "borrowed" SUV off the end of the road, and onto the salt, but I had to drive through water to get to the pits. The water was up to about the side skirts of a big chevy SUV. When we left the salt on the last day, the water was basically trying to come in the cabin, it was that high, at that point. The whole point of that is that we didn't have time to play with any changes, and the team captain and driver weren't able to continue with the car the following seasons, so it go mothballed.