1991 Celica Gti

[Deejay]

I have a 91 celica gti - Now according to parkers stats it should be capable of around 135mph top end. I can only seem to muster 125mph and 5th gear is almost pointless. Despite having a mongoose can from the down pipe back and a K&N cold air intake and filter.

My questions to anyone out there:

Is the topspeed wrong or is my car a little ill?

Also I found what looks to be a pointless box on the air-intake pipe, after removing it and putting a blank over the hole, it seemed to make a louder intake noise, would this box have another point other than to silence the air flow?

I am currently looking at dastek engine management and NOS each

costing around £500 to fit. So I can get some proper use out of fifth gear also I think it could use a bit of weight loss

Any help would be appreaciated!

Just needed to add that obviously I have never done these speeds on a public highway. Only at track days!