How to Tune Boost Maps

by **juice** » Thu Oct 23, 2014 7:57 pm

Hey guys, i have a question regarding boost maps(request, limiter and svbl) because i saw a lot of styles to tune these maps, but especially i`m asking here because on my bmw is different than all VW and other bmw files which ive seen.
Boost target 2100 from 2000 to 4000 rpm, Boost limit by Patm = 2250 in that zone and SVBL the same , 2250.
I saw that all VW/audi cars have for example 2100 request, 2150 Patm limiter and the biggest value is SVBL.
In some maps i saw SVBL lower than Patm Limiter.
What's the correct approach ?

by **DavidRUCABITS** » Mon Nov 03, 2014 11:21 pm

The correct order should be:

Requested
Limiter
Svbl

SVBL is the safety for your boost tune, turbos with stuck geometries will spike or over-boost. SBVL is there so that if something goes out of what you tune it will stop everything and the car enters in limp mode (Safe).

Hope it help

by **juice** » Tue Nov 04, 2014 7:55 am

What should be the difference between these numbers? Its strange that bmw put atm and svbl the same. I know that svbl is for limp mode and i thinkl that ATM limiter is for PID control to correct the boost

by **DavidRUCABITS** » Wed Nov 05, 2014 10:11 pm

I dont know the reason for that in my Tune's i put SVBL over the atm limiter by 50mbar or a little more. Look @ your turbo performance map and look for a good value for boost cut.

For ex. i am running the stock Gt1749VA on my car, and tune it to do 1,5Bar, i set my Svbl to 2680mbar (1,68Bar of boost) and sometimes it "limps" cause i didn't touch n75 map so it probably is over-boosting (spiking).

Use a 200Mbar limit over the requestes and a 250mbar on Svbl it will be a good safe position for your turbo.

Cheers

by **juice** » Thu Nov 06, 2014 7:47 am

Yea..that's a good idea, maybe that's why i feel sometimes spikes. I made some graphic logs and i see the pressure increases to 2300..2350..2450 and goes automatically down to ~2200. I request 2300 and Patm = 2400 and SVBL = 2400..well i think that the difference is too small and when ecu is seeing spikes , goes down. I opened pretty much N75 vanes but i think the actuator is old and responds with lag...or maybe the difference is too small.
I checked compressor map, my turbo has maximum surge line up to 2450 - 2500 mbar, there is maximum limit...i request 2300 and i limit to 2400 for safety..maybe i should try to put limit to 2450 or to request only 2250(maybe too little air for 65 mg of fuel on 2.0liter engine = ~2.3 bar = 1150 mg air) . What do you think ?

by **juice** » Thu Nov 06, 2014 7:49 am

juice wrote:Yea..that's a good idea, maybe that's why i feel sometimes spikes. I made some graphic logs and i see the pressure increases to 2300..2350..2450 and goes automatically down to ~2200. I request 2300 and Patm = 2400 and SVBL = 2400..well i think that the difference is too small and when ecu is seeing spikes , goes down. Original difference is 150..2100 request and 2250 limit.
I opened pretty much N75 vanes but i think the actuator is old and responds with lag...or maybe the difference is too small.
I checked compressor map, my turbo has maximum surge line up to 2450 - 2500 mbar, there is maximum limit...i request 2300 and i limit to 2400 for safety..maybe i should try to put limit to 2450 or to request only 2250(maybe too little air for 65 mg of fuel on 2.0liter engine = ~2.3 bar = 1150 mg air) . What do you think ?

by **DavidRUCABITS** » Thu Nov 06, 2014 5:03 pm

Log the car and try to see if the requested and the actual boost are to different. Try to put the limiter @ 2450mbar and the Svbl @2500mbar and run the same boost. See what it happens.

I think that your actuator are actually getting stuck by the geometry (carbon @vanes). Try to log and match the requested to the actual boost.

In relation to the AFR, use this: AFR = (Boost * cylinder capacities) / IQ, so in your case.

AFR = (2,3*500)/65, your AFR = 17,69, you can put more fuel on it. I run a afr of 15,83 and is smoking just a bit.

Where 500cc^3 is "equal" to 500mg of air (without boost).

by **juice** » Thu Nov 06, 2014 9:47 pm

My turbo goes max to 2.45..its a GT1549V i dont want to pass too much 2400 for safety..
Well for 65 mg i think i should go with 2250 request, maybe 2400 Patm limiter and 2450 SVBL.
I know all this theory about AFR and fuelling , the only problem is that in full load the boost goes too much above requested..even if i longered actuator ROD..i lost some power in middle area..i opened n75 vanes on last 2 columns and still sometimes the boost is lower than requested and sometimes too much.
I removed both CATs, its a reason for more flow and overboost...I took out the actuator from the turbo and that little thing from VNT is moving free with the hand, i can handle it pretty easy..maybe the spring from actuator is too weak and doesnt open fast to avoid overboost.

by **mladenke** » Fri Nov 07, 2014 5:24 pm

without a diagnostic log, we can't help you

by **juice** » Fri Nov 07, 2014 6:04 pm

See the print screens. that looks like a spike, i have opened n75 so much in last 2 columns, still there, vanes are clean...i think its related to the boost settings.