performance curve

[redmist]

I'm new to the M42. Bought a 91 IS with 113k on it. Didn't even drive it before I spent a couple of weeks sorting it out, suspension brakes etc. Bought the Mark D. chip.
Car is alot of fun, great torque and throttle response up to 4000 rpm. After that the revs don't climb very fast.
Is this a characteristic of the motor? I did change to an aftermarket header but maintained the 2.25 inch diameter pipe, free flow cat and magnaflow muffler. The only reason I mention this is that the engine just seems "bottled up" after 4k rpms.
Thanks!

[batsbats]

The first thing I noticed was the lack of throttle response and torque before 4k RPM or thereabouts.  I attribute this to the heavy dual mass flywheel setup the car came stock.

Anyone else want to chime in?