I made a reaper-boosted helicopter with near-minimal weight, and got this image right before crashing in bedlam:
Check the speedometer: 910 km/h. I have yet to get over 1,000 km/h, but I feel like if it had more space to fly it could be doable. I might have to take off the 2 small fused ammo packs, but I’m not sure yet. If I can screenshot a 1,000+ km/h speedometer I will let you all know (if it goes up that high), but right now this is the best screenshot so far.
Someone claimed to reach 4,000 km/h on the “Way to the Top” map by driving in circles then diving straight down, although I doubt the validity. I have only ever gotten to about 700, and that was on “Ravager’s Foothold”, a fairly circular and large map. I’d suggest you try that one next.
i think it might be possible to get to 1000 maybe a little over on the way to the top map. if you take a nose dive and fire reapers on the way down it may be possible due to gravity and the reapers boosting you.
So I modified the previous heli to have 1 small ammo pack instead of 2, and replaced a buggy floor with that ammo pack, instead of having the ammo slapped on the outside. I also tried changing the maple/impeller combo into a petrel, but that was slower for some reason. In the new bedlam map rn (Crater) I got this:
That is 26 km/h away from my goal of 1k, it’s so close.
Also:
I tried this in a custom battle with a friend of mine, but a bug prevented my from using my heli (I made another topic for that, and a bug report). So until they get that fixed imma have to wait for the actual bedlam map to be way to the top to try this. 
…So the over the top map didn’t work too well, the heli had issues going straight down with it’s rotor, and detaching the rotor wouldn’t show the speed. I added some wheels to show speed but the heli didn’t fly straight without a rotor. But it turns out I didn’t even need any of that. I actually did it!! 
How you may ask?? (JK lol ya’ll probably don’t really care, but imma tell you anyway) It turns out the “Harpy” Cabin I was using was 1000 Kg (not much for a cabin, but it could be better). I just happened to have a “Kronos” cabin from the red light brawl a while back due to it’s speed, and it was 420 Kg, less than half of the mass of Harpy. It also had a higher max speed with rotors/wheels (idk if that helped or not). So I put an asymmetrical cabin on my build for speed and hoped it wouldn’t cause issues in the mass distribution. After the first test, it was noticeably better, and I broke 1,000 km/h easily with the new cabin!!
Congratulations Fuzz!!! 
You’ve made it further than I have…
Kronos is best light cabin, you can’t change my mind.
You should test out my “built for speed”, I think you have most of the parts. Really fun in next step
