Intermittent Gtt boost spike?

[cedwards]

Sorry to re-ask a previous question. I'm sure this has been covered but can't seem to find it again.
I have a Blitz dual turbo timer how accurate are the boost readings off this? The reason I ask is it stores peak boost which I have seen up at 1.2 bar before, every time I tried watching the boost it reliably boostsup to a max of 1bar then drops back to 0.8. Today however i looked down and to my horror saw a reading of 1.33 (foot quickly retracted from accelerator).
I read about the wastegate being a potential issue although this was disputed by some and also the boost controller being an issue. I don't think it is a case of a hose being popped off somewhere as it seems to rectify itself.
Any suggestions?
Also how easy is it to test the wastegate and boost controller?
Only mods to engine is exhaust.

[sergei]

How far is the exhaust goes?
I've seen plenty cars to spike to 1.4Bars (STIs, EVOs etc) and drop down to 1Bar... Very common with bleed of type of boost "control" and exhaust.

[fivebob]

The wastegate itself is not an issue, there is plenty of capacity to control boost. However the actuator has been know to fail in the past, though that would usually mean uncontrolled boost.

By far the biggest cause of boost spikes is poor boost controllers, if you are still relying on stock boost control, or worse still have a mechanical or cheap electronic boost controller then that is far more likely to be an issue.

I have a HKS EVC IV controlling the boost on my GTT and it has absolutely no problems controlling the boost to where I set it, at most it may exceed the set level by <0.25psi and only for a fraction of a second.

[sergei]

Stock boost control is complete rubbish,
with my ST205, first issue is boost fluctuating, second issue in very cold night at about 3500rpm in 3rd gear I get mild cut.
The only "mod" is that I have K&N panel replacement filter, stock every thing else...
Saving money on some closed loop electronic boost controller....

[fivebob]

Stock boost control is complete rubbish,
with my ST205, first issue is boost fluctuating, second issue in very cold night at about 3500rpm in 3rd gear I get mild cut.
The only "mod" is that I have K&N panel replacement filter, stock every thing else...

Whilst I agree it is rubbish, it's not the same as the earlier models like the ST205, which are passive systems that rely on the size of the bleed hole in the VSV to regulate boost. The ST215 system at least makes an attempt at being an active system as uses PWM to control the VSV. It's up to the job of controlling a stock engine, but any mods will render it useless.

[cedwards]

How far is the exhaust goes?
I've seen plenty cars to spike to 1.4Bars (STIs, EVOs etc) and drop down to 1Bar... Very common with bleed of type of boost "control" and exhaust.

Exhaust starts after cat.
"bleed off type of boost "control" " are you referring to the factory boost control vsv unit? As all apart from exhaust is standard. Definitely no bleed valve or el cheepo boost control that I can see.

[cedwards]

The wastegate itself is not an issue, there is plenty of capacity to control boost. However the actuator has been know to fail in the past, though that would usually mean uncontrolled boost.

When you say fail does it get stuck shut, ie diaphram breaking and not opening or jam in some way. Is it possible the actuator is working but not to the full degree of travel ie getting maxed out at higher revs with more air being generated? doesn't really explain the intermittency tho..[/quote]

[gttNICK]

hmmm so it may be worth checking this if I'm running a turbo-back exhaust set up? Best to diagnose with a boost guage first?

[cedwards]

The ST215 system at least makes an attempt at being an active system as uses PWM to control the VSV. It's up to the job of controlling a stock engine, but any mods will render it useless.

When you say any mods does this include the exhaust?
Also not sure I fully understand the factory controller
But here's what I have hope i'm not too far off.
PWM pulse wave modulation this I assume opens and closes a solenoid valve rapidly at varying rates to selectively "bleed" air from the wastegate at an attempted controlled rate? Depending on factors like air/engine temp?

Is it possible this solenoid is intermittently getting stuck open while boosting? If so could I test it by blocking off this valve and effectively running low, safe boost

Where does one get a decent boost controller from and how much should I expect to pay..