vgt base duty

hi,

i wanted to know if increasing the vgt too much could cause damage to the turbo?or would it help to increase low end response and spool time?

and if i make most of the table 100% without exceeding let say 23psi, would it be ok?or does the desired boost has to match the vgt duty cycle

and which table effect spool more desired boost or base vgt

thanks

Fahad,

Increasing your VGT % significantly above the factory settings will usually cause a 'choke' situation where turbo drive pressure will rise as a multiple to boost pressure (example 3:1). Usually when modifying the feed forward vgt position table it's wise to work in 5% increments. On our most common platforms bumping the feed forward VGT in the upper left hand quadrant from 80% up to 85% will improve response but going to 90% will cause choke.

Do not under any circumstance make 'most of the table 100%'. You're likely to at least cause blow out an exhaust gasket or worse.

FWIW: Most platforms use the table you've posted as a starting point and then work a closed loop vane control to adjust vgt position to hone in on a target boost number.

Hope this is helpful,

Nick

hi nick,

i have made changes to the desired boost and now the truck makes turbo spool noise in light acceleration and cruise and hits 24.5 at wot but drops down to 22 when heatsoaked

does the table look too optimistic what is the down side of having higher value in the desired boost table than the actual boost,is it important to datalog actual boost and copy it to the desired boost table

one time i had 12psi at 2000rpm wot but most of the time my boost is 5-8psi in the same rpm and throttle, does the vgt learn overtime and i need to increase base duty? or could it be fuel as i tried to limit smoke in maf limit table,but my afr is 14.5 during spool,

im having trouble finding maf total mg when i can only datalog maf g/s,is the a way to calculate the total mg

when increasing vgt base and max what are the things to look for?is it the actual vgt position? at wot my vgt is at 59% do i copy that to vgt base or max(my max is 46% right now just as the base)

thanks

I have made changes to the desired boost and now the truck makes turbo spool noise in light acceleration and cruise and hits 24.5 at wot but drops down to 22 when heatsoaked.

-The changes to your desired boost table look pretty ambitious. For instance you're asking for 3-4 more psi even at very low fuel rates like 30mm3. Generally you shouldn't need to add boost unless you've modified the pulsewidth at the same corresponding fuel rate. Asking for extra boost out of the turbo under light load like described isn't the worst thing but it can cause excessive fuel consumption. Reading your VGT numbers at 59%/WOT I would say you're pushing the turbocharging system to its maximum output. Any time the duty cycle is higher than 50% at WOT you're likely pushing the compressor out of it's map and driving a lot of heat into the system.

does the table look too optimistic what is the down side of having higher value in the desired boost table than the actual boost,is it important to datalog actual boost and copy it to the desired boost table.

For the most part I've answered this above. The A/F log should drive any desired boost adjustment, not actual boost. Remember the goal of the boost table is to target the correct airmass for the engine to maintain A/F ratio at a given RPM and fuel rate. The boost table should not be used to enhance throttle response unless the engine response is specially lambda limited in those conditions. Most of the time the factory boost table is adequate so long as the fuel rate hasn't been skewed by artificially inflating the pulsewidth table.

one time i had 12psi at 2000rpm wot but most of the time my boost is 5-8psi in the same rpm and throttle, does the vgt learn overtime and i need to increase base duty? or could it be fuel as i tried to limit smoke in maf limit table,but my afr is 14.5 during spool,

There is often some learning trim built into the VGT duty cycle PID so that as the vehicle is driven it more effectively targets VGT position instead of over/undershooting. What might have happened in the 12 psi scenario is that the vehicle was able to achieve a higher load than usual, possibly on a hill or manually holding a gear.

im having trouble finding maf total mg when i can only datalog maf g/s,is the a way to calculate the total mg

I'm not sure which software or platform you're tuning with. It may be possible to custom define a PID or request your software provider add dynamic cylinder air.

when increasing vgt base and max what are the things to look for?is it the actual vgt position? at wot my vgt is at 59% do i copy that to vgt base or max(my max is 46% right now just as the base)

It can make the boost control system more effective to build a histogram of actual VGT during a long drive cycle and paste the average of it into the feedforward VGT map. Usually we do this if we're seeing excessive hunting of the VGT PID while driving. Generally this is unnecessary unless the turbocharger config has been altered from stock (larger turbine, comp wheel, vanes, etc. ).

Hope this helps,

Nick

thanks

hi nick,

i just watched intro to vnt turbo webinar, and i wanted to make sure my understanding of vnt is right

100% vnt is closed 0% is opened

on toyota ecu 18psi is 72% duty cycle and 24psi is 58%?

open vnt is higher boost than closed?

open vnt more horsepower? closed vnt more backpressure

what makes it more confusing for me the base duty cycle is 33% for 18psi and i increased it to 46% for 24psi, is it the opposite in this table than the datalog?

thanks

Fahad,

I can only share with you that in my experience with the ECU's I've seen they've all been 0%-Open and 100%-shut. The easiest way to verify would be to listen to the pitch of the exhaust at idle. Target the vanes to 97% and target them to zero. The open setting should sound more like a Naturally aspirated exhaust note, the closed setting should sound like a jet.

Hope this is helpful,

Nick