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(Post Link) post #1 of 10 Old 26-02-13 Thread Starter
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Boost pressure sensor values & larger intercooler

Hello guys,

correct me if i'm wrong pls

lowering intake T (larger intercooler / water injection) reduces intake pressure / boost pressure. This reduction in boost is then registered by the boost sensor which in turn results in an adjusted vnt setting to re-establish the pre-determined boost pressure.

As a result the turbo's output is increased (more air mass displacement) which will be detected by the ecu via the mass air meter and corrected for by longer injection times.

Basically what i'm wondering is would the 'initial' reduction in intake pressures due to a larger volume intercooler be corrected for by adjusted vnt settings?

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Hi, you are right, in closed loop control stage, the turbocharger is controlled by the boost pressure request. So you will get more airflow at the same pressure with bigger intercooler. And for the higher airflow the turbo has to work harder, thus there will be noticeable change in VNT settings.

In open loop control stage (basicaly idling, spool up, low throttle cruising) the turbocharger is controlled directly by VNT settings request, so there you shouldn't notice any change.
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Thanks yan.ko

I was thinking about a larger intercooler but wanted to make 'sure' it would have an positive effect, i guess so then!

Do you think it would be worth the investment?
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Yes, especially if you plan further performance tuning
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Hi yan.ko

it is already chipped but that would not be a problem do you agree?

Thanks again
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if it helps I tried to directly compare original smic and fmic
as you can see I was suffering a bit of boost creep on smic as boxed and overfuelling causing higher boost than requested, but compare to fmic we have lower temp difference maf intake temp to map temp, higher airflow seen by maf from denser air even though fmic has lower boost pressure(less airflow mid point but not supprised for 200mbar less)
cant remember if there was a slight boost leak on hoses on intercooler pipes after fmic so when cured airflow higher again.
Attachment 163127
will help run cooler inlet temps and therefore cooler egt, raise afr and run cleaner. but will work turbo harder.
ps this was a small to med size fmic (approx twice size of smic) and fmic and pipework not much over 150.(similar size to joels stuff here
JS-Tuning.nl)

Last edited by sussexa; 02-12-15 at 20:02.
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(Post Link) post #7 of 10 Old 04-03-13 Thread Starter
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Sussexe thanks

up to 3k it seems ligit but after that there seems to be no gain.
Why is that? Could it be that the turbo simply cannot keep the desired boost pressure up because of the higher rpm's?
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File Type: pdf fes smic vs fmic.pdf (167.5 KB, 31 views)
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You will need VNT maps adjusted for better boost control + raise fuel limiters... otherwise no gain.
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as said there may have been a slight boost leak = mass airflow is similar from 3000 revs but has equalled it with much lower boost pressure. with equal boost to smic id imagine mass air would have been much higher.
I had a test log still with original turbo and a digiboost device that gave me around 27psi boost or so on gauge.
saw some nice maf readings but not sure how long turbo would have lasted like that, and I was testing in preparation to fitting larger turbo anyway.
and ill dig out some recent logs also.
i have seen much bigger fmic fitted but I fitted max size that would physically see direct airflow through grill orifice.i think its quite small but I see nice cool temps maf to map temps
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here was one from still original turbo and fmic but with digibooster so real boost more like 27psi+(1850mbar boost) ignore act boost in data.
also looking at temps here may have been with water methanol on also?
Attachment 163590
this one is recent and is hybrid turbo so cant really compare and currently ecomap not performance, but boost is real actual here
Attachment 163591
I have loads of logs over the last few years, anything in particular you want to see I will see if I have one?
also joel or yanko had much better graphs showing increased airmass from fmic ill try to find.
edit
here post 84 shows nice gain from lower temps and increased mass air
https://www.alfaowner.com/Forum/tunin...16v-gtb-4.html

and apologies I may have gone off topic here.
as coolbits said if your inlet temps are currently not reducing fuelling you will see little difference less smoke most likely. I have seen the ecu is capable of adjusting vnt for differences upto a point as I run w/m, then no w/m ,then w/m then no w/m at various boosts (21,23,25,27psi)and saw approx 3% difference in vnt% readings between w/m and no w/m to keep boost close to desired.

Last edited by sussexa; 02-12-15 at 20:02.
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