gear vs rpm

[zoomx2]

Just did alot of engine tune type work on the beast..plus lower 60k..now she feels like she is going way to fast to easy..the question is how fast (kph or mph) should you be going if say 4000rpm in 5th gear..i have a feeling either my tach or speedo is off.
Mike

 

[sdpatt]

The speedometer is calibrated within a given range for the OEM tire size. What size are yoru tires? The tachometer is more like a voltmeter that is not a calibrated device. The tach is also affected by the temperature of the DIS module: the lower the temp, the higher the reading. The tach is not calibrated. Go by your speedometer.

 

[zoomx2]

okay..tach appears to be correct..tested with another unit..both are close enough to say they are the same..tires are the original size..still have the basket weaves on her..its just 4000 is giving me just shy of 180 kph..and its reving up there way quick..a tune and belt change should not make that much of a power change, or should it?
mike

 

[olympic]

Your speedo may be slightly off. Mine reads about 160kph(100mph) at 4000RPM. That's with an aftermarket VDO tach but I have no idea if my speedo is accurate either. But I do recall other SHO owners saying theirs reads 100mph at 4000RPM also.