Inconsistent boost with external wastegate?
 

How much should boost fluctuate given the same wastegate spring pressure?

Just yesterday it seemed to fluctuate from 0.6 bar to 0.8 bar. Is this normal, given temperature and atmospheric pressure fluctuations?

All of my temperatures are very stable, and intake temperature is usually quite low (less than 105 degrees Fahrenheit).

This is with my boost controller off, for the record. The spring is set of 0.8 to the best of my knowledge.

Depends on factors including boost control and boost creep in my experience.

If you have MBC and the bleed orifice behind the check ball is too small you will get a boost spike as boost comes on and then it will settle.

If you have boost creep then the boost will be higher when there is maximum load on the engine and the air temps are coolest.

Once I sorted both of the above issues then boost was VERY constant on the boost gauge though data logs would show ~1psi fluctuations in MAP (taken from TB location).

3psi changes I would check diligently for a small boost leak once a hose is soft and hot.

It has an external wastegate. A boost controller is only an issue when you want to *increase* boost.

It should be running at 0.8 bar constantly, theoretically. I've seen it as low as 0.55 or so...

I have a HKS external wastegate that sees a fair bit of boost taper. On spring pressure it'll peak at 0.7bar at 4500rpm then taper to as low as 0.6bar at redline.

My HKS EVC currently doesn't have rpm correction turned on, so it'll see 0.9bar at 4500rpm and tapers to 0.8bar.

It always peaks low and tapers though. Never see boost creep.

I am in the process of setting up ECU boost control via MAC 3 port, which should allow me to tune duty cycle against rpm, then use closed loop to deal with any other fluctuations.
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I mention my experience with boost controller as you haven't said how your boost reference is set-up.

Are you boost running boost reference straight from compressor housing to external wastegate?

When I have run like that only boost creep and boost leaks have affected peak boost the way you are having it.

I was running my electronic boost controller off, so effectively it was purely running on wastegate spring pressure.

Where is the pressure source for the side port of the gate? Take it after the intercooler and it apply less pressure to the diaphragm.