Overboosting in 5th

[CalMac]

While doing a few top-end pulls in 5th on track over the weekend (maybe 70/80 - 120mph) I was really happy with how it was pulling on low boost (0.9 bar).

This was on a Blitz Dual SBC - since I bought the car 2 weeks ago the 2 boost settings have remained pretty consistent. High boost is set to about 1.1 bar, but sometimes hits 1.15 bar peak if driving at night.

ANYWAY, there I was testing out the high gear pulls when I hear *beep beep* - looking around the car wondering where the hell the noise came from then I looked down at the SBC and it was flashing red saying 1.47 bar

I slowed straight down to 50mph for about 10 minutes as the turbo timer had crept up to nearly 2 minutes, even though my oil and water temp were both at about 90 degrees C.

Fiddled with the SBC and managed to turn the red light off, now it seems to be ok pulling as normal in lower gears hitting 0.94 bar on low boost at the same parameters I initially had it on.

Could it be that the turbo was just going nuts and over-reaching itself in the top end? I didn't hear any new noises, and it was still pulling the same.

Rev 3 import - Greddy SMIC, Berk DP and HKS Hi Silent Power, ARC air box, Dual SBC, uprated oil cooler, chipped/remapped/fiddled with ECU.

ANy suggestions would be much appreciated, don't want to drive it now in case I blow something up

[Nic]

You will always see higher boost levels in higher gears when the engine is under more load. Same as you see no boost when in neutral when the engine is under no load.

[Odin_S]

Simple... turn down the duty or gain. This always happens when the weather gets colder. Plus you'll always get over boost with your setup

[CalMac]

But if I turn down the gain I'll make crap boost in the lower gears which I use more often?

Can't I fit something to stop it from overboosting? And why will my setup overboost?

[Odin_S]

Creep in my experience happens mostly in lower gears. Especially when changing down

[CalMac]

So is it normal for my boost to peak at 0.5 bar more than normal in 5th then?

[2mad]

No that is an odd one, if you overboost it should happen in all gears not just 5th .. I cured my overboosting (all gears) by porting my wastegate . but that is abit extreme for now .

Never owned a blitz ebc so cant help you with settings.. hope you sort it



Kev.

[jon]

Check the ignition timing is spot on, if it's retarded the exhaust gases will be hotter at the turbo, making more boost.

A Rev 3 turbo with downpipe, free flowing exhaust and SMIC or chargecooler is right on the limit of what the CT20b wastegate can handle.

My MR2 with a chargecooler, downpipe and exhaust will hit fuel cut on stock boost control with a UK ST205 ECU but not on a JDM ST205 ECU. The difference is purely down to the slightly retarded ignition timing map in the UK ECU.

Crap fuel can also provoke overboost, if the ECU detects knock it will also retard ignition.

[nickg07]

Also with the blitz you can set a max boost level like 1.2 and it won't boost any higher so protect your engine till you sort it out