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 Post subject: How to determine maximum boost
PostPosted: Mon Aug 15, 2016 9:44 pm 
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Vehicle: MY11 S-Edition - SWP

Posts: 1090
Location: Sydney
I see some people set a maximum boost of around 16 PSI, others 17 or more and some less. I did some searching but can't determine how maximum boost is determined. I assume there would be something in the tune readings which would indicate a maximum boost has been reached. Thanks for any advice.

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 Post subject: Re: How to determine maximum boost
PostPosted: Mon Aug 15, 2016 11:03 pm 
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Vehicle: MY06 XT - Black

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Location: Canberra
Not exactly sure what you're asking.

The ECU map has a table where desired boost is set and will attempt to control the wastegate in order to hit that desired boost.

The ECU also has a MAP (manifold absolute pressure) sensor connected to it, and so it knows what boost pressure is in the engine. This can be logged or displayed in various ways.

You can also fit an aftermarket boost gauge to read what's happening.

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 Post subject: Re: How to determine maximum boost
PostPosted: Tue Aug 16, 2016 4:59 am 
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Vehicle: MY11 S-Edition - SWP

Posts: 1090
Location: Sydney
Trying to understand why some tunes are done with a specific boost eg 15 and others tunes are done at a higher boost. For example the tune on my car has a max boost of about 17. Why 17 and not 16 or 18? Does that make sense?

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 Post subject: Re: How to determine maximum boost
PostPosted: Tue Aug 16, 2016 8:12 am 
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It depends on the tuners preference to some degree , also it would depend on how much boost it can flow ( restriction ) as in exhaust - headers etc etc and how much boost it can handle and use efficiently - type of turbo - heads , intercooler , piston type , head studs etc , at least that's my understanding of it .


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 Post subject: Re: How to determine maximum boost
PostPosted: Tue Aug 16, 2016 7:13 pm 
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Vehicle: MY06 XT - Black

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Location: Canberra
Yeah I get ya now. And yeah what cam99 said. Stock internal engines of the various flavours tend to have a max boost pressure where people have learnt over time that they maintain some level of reliability. This of course varies by tuner to some extent.

Then you start reinforcing and using stronger components that can handle more and more.

My tuner went with 19psi on 98 octane and 21psi on E85. Stock EJ255 from an 06 XT.

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 Post subject: Re: How to determine maximum boost
PostPosted: Tue Aug 16, 2016 7:32 pm 
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Thanks for the info. I assume there are specific measures such as exhaust pressure or other reading that would indicate maximum boost has been reached.

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 Post subject: Re: How to determine maximum boost
PostPosted: Tue Aug 16, 2016 7:39 pm 
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S2-13BT wrote:

The ECU also has a MAP (manifold absolute pressure) sensor connected to it, and so it knows what boost pressure is in the engine.


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 Post subject: Re: How to determine maximum boost
PostPosted: Tue Aug 16, 2016 9:02 pm 
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While there is a MAP sensor, the readings don't control how much boost it will run. Ultimatey it is controlled by the wastegate duty cycle tables under the boost control section in the tune.

How much boost you want to run is up to you or the tuner but is limited by the size of the turbo and strength of the motor to withstand detonation events (knock) occuring under high boost situations. You want enough boost to provide the power where you want it but too much boost and you risk causing detonation. There is also the relationship between timing advance and boost pressure and sometimes you want more boost and less timing where as other times maybe less boost and more timing. It's not quite as simple as I want x or y boost level and why tuning is an artform. The articles below may help you to understand a little but it's not exacly light reading.


http://www.cobbtuning.com/support/how-s ... rks-v1-09/

https://cobbtuning.atlassian.net/wiki/d ... ning+Guide

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 Post subject: Re: How to determine maximum boost
PostPosted: Tue Aug 16, 2016 9:24 pm 
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jonp wrote:
Thanks for the info. I assume there are specific measures such as exhaust pressure or other reading that would indicate maximum boost has been reached.

Most cases the turbo probably ' could ' run more boost , I would say its more the tuners preference where adding more boost is no longer beneficial to the overall tune or long term drivability of the car .
Some people ask for conservative tunes so that's a another reason why it will vary a bit for similar mods / turbos as well the tuners method for getting more power .


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