So, last month I made a short clip of my car’s speedometer accelerating from 15 – 105-ish mph on an empty stretch of highway late at night. After I watched it again I noticed the car seemed a little slow and one thing I noticed was that at the end of 4th gear I was only around 105mph, at 6,500 rpm the factory gearing on a 6-speed in 4th gear should take a stock Z/G to 116 mph, somewhere 10 mph got lost. I’m pretty sure it’s the clutch holding me back.

After I got the car together with the single turbo and tuned I made 360 whp, but when I went to the track I only trapped 102 mph.

So, it’s got to be the clutch right? I’ve made an appointment to swap it out next week, just want a second opinion.

 

What are the clutch specs? If your running stock then off course its holding you back.

 

What size tires do you have on the car. If they're not the same height as stock your speedometer will be off.

 

Haha, yeah…stock clutch... the only thing that had me a little puzzled was that it wasn’t slipping in the normal manner I’ve experience with other cars, where the RPM’s shoot up and the speedometer goes little to nowhere. The car was moving, just not as fast as I think it should have been and it seemed to hold on the dyno recently too.

OEM wheels and tire sizes too though.