Boost spike on dyno but not on street test

[Cullen]

I got my spec b legacy tuned recently to 191kw 356wnm at 16psi. On the dyno the boost spiked to 21 psi! Apparently this never happened on the street run which was done afterwards.

 

It seemed weird because the clutch was slipping at 17psi, hence the boost being limited to 16psi. The clutch never slips when I drive it hard. Should I be concerned at all?

 

A few months later the cambelt snapped, I'm not blaming this on the tuner, could a poor timing belt cause this?

 

This is my first time ever getting a car tuned 😁

Edited February 24 by Cullen

[boon]

The dyno will load your car in ways that it's unlikely to ever see on the road, but also... no, it shouldn't do that.

 

Clutch is on the way out, if it slipped on the dyno it will start slipping on the street, but presumably you have the motor out anyway due to snapping a cambelt so you may as well do it.

Timing belt isn't going to cause boost spikes, it's either a crap tune, inadequate parts, or something was faulty or installed incorrectly.

[Gripless]

How old was the belt and how many kms on the motor?

cambelts mostly snap as worn or something seized up. Eg camshaft stop but crank still running.
Well missing plastic covering and small stones getting in like to shred things as well.

[Loren]

A bad tune can't snap the cambelt or make the clutch slip.