club.liberty.asn.au

Hey gents this question is coming up so I thought I'd post new topic..

So as topic says what is safe S# boost levels without engine failure is 18 psi to much ?

Depends on a million other factors.

18psi is the best efficiency for a VF46.
More than that and the charge is over heated or the pressure too great for the stock headstuds which lift at 22psi (if hitting that regularly).

40psi sounds good.

Just keep upping it til its not safe anymore.

Interesting... what psi do they usually tune the vf52 to?

afaik similar, the VF52 will drop off a little less due to the slightly larger compressor, afaik

You just keep increasing boost until the engine blows, then back it off a bit.


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coyote wrote:You just keep increasing boost until the engine blows, then back it off a bit.

bigBADbenny wrote:afaik similar, the VF52 will drop off a little less due to the slightly larger compressor, afaik

Sorry Benny but can a tuner set to say 18psi and have it not over boost more than that ?

coyote wrote:You just keep increasing boost until the engine blows, then back it off a bit.


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Makes sense

I guess ill find out in a couple weeks. MSR doesnt actually ask me what boost pressure I want, he just does it. Hes tuned so many subarus I guess he knows what works best.

Newbie GT wrote:

bigBADbenny wrote:afaik similar, the VF52 will drop off a little less due to the slightly larger compressor, afaik

Sorry Benny but can a tuner set to say 18psi and have it not over boost more than that ?

In theory, yes. That's what boost control and the wastegate on the turbo are for.

One thing to be aware of though are boost spikes - when boost increases sharply, and potentially goes beyond the boost limit the tune has set before the ECU realises what's going on and operates the wastegate. In general, boost spikes shouldn't happen with a good tune.

28 psi

24+

Newbie GT wrote:

bigBADbenny wrote:afaik similar, the VF52 will drop off a little less due to the slightly larger compressor, afaik

Sorry Benny but can a tuner set to say 18psi and have it not over boost more than that ?

Our ECU's run a PI controller (https://en.wikipedia.org/wiki/PID_controller) for boost, you set boost targets and the control loop tries to hit those targets, but input disturbances upset the system (shit happens and can cause boost spikes. The closer you set your targets to mechanical limits (clamping force of head studs) or closer to running your actuators at full saturation (wastegate duty cycle close to 100%) the higher the risk.

In more general terms, you have a requirement - more power. Let your tuner arrive at the best practice way to meet this requirement. Don't specify a solution to your requirement (some aspirational boost target for whatever reason).

Doesn't the stock BOV start leaking pressure at around 15psi (my thoughts would be that it would save damaging the engine, but it looks like this isn't the case).