My car is slower after mods

[eTiMaGo]

Hmmmm when you are at 180km/h you are in 5th gear right, at what kind of RPMs? I don't remember the dyno specifics of your car but maybe it is producing a lil less power at that point, meaning that it has less power to overcome wind resistance and thus cannot reach a higher speed?

I myself have experienced a similar problem, when I first got the car and the first round of mods (wheels, intake, HKS exhaust), I was able to reach 200km/h according tot he speedo (didn't know GPS would be more accurate at that point)

Couple years later I had the opportunity to really floor it again but could also only reach 180ish, acording to the speedo again. Could have gotten a bit more but ran out of road, so I did not hold this as a conclusive result. At this point I had changed the exhaust for the full Nitto piping, and I might have also installed the NST lightweight pulley (which should have no effect on power output if the engine speed is relatively stable)

So, as I never dynoed the car before and after, I suspect I may have lost some high-end power (the car pulls well at low-mid RPMs), or it might just be an effect of the engine aging, who knows, really.

What I did notice though, and maybe this is related, as I have a basic AFR gauge, at WOT the AFR goes very very rich, if the gauge is to be trusted I would see as rich as 10:1 AFR (on the second run, didn't look the first time around), which would have a negative effect on power output. So another possibility is that the stock open loop fuel map is not adapted for the intake and exhaust mods. Anybody wanna sponsor an AFC Neo or similar?