I have a 2005 RX-8 with the mods listed below just recently at about 4000 rpm the car seems to "fall on its ***" for a couple of secounds the pick right back up the car only has 38k on it any ideas o and just for a mention i let my brother drive it and he flodded it 2 mounths ago if that has anything to do with it but has ran fine since other than what i entioned earlier

 

Does the car trips a CEL; when were the last time you had the ignition coils, plug wires, spark plugs replaced?

 

Ive never thrown a cel as far as i know but i bought the car when it had 30000 on it about 6 mounths ago not sure if its had plugs or wires coils or anything i change oil religiously every 2500-3000 miles and take it over 6000rpm at least once during my 22 mile drive to work. Not sure if this has anything to do with it but i live in ohio it was 8 degrees when i left work last night and yes it acted up around 4000 rpm it seems like something is sticking then it opens up and run normal. Also it wont do it in 1st 2nd or 3rd its only 4th 5th and 6th.

 

i just recieved my bhr ignition system upgrade and no difference other than smoother operaton but i still have the odd "pause or shudder at 4000RPM.

 

https://www.rx8club.com/do-yourself-...-video-184663/

Sounds like this.

 

If it's SSV, it should happen in all gears around 4k rpm.
If it only happens in certain gears, you might wanna looking into something else.
Dunno what could be, hopefully someones else can chime in.