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Discussion and questions related to the course Boost Control
Hey Andre/Fellow tuners,
I will be undertaking re-flash tune on an evo x that has been fitted with forged pistons and rods and a bigger turbo charger.
One of the areas I'd be addressing is the boost control area. I've attached a PDF file that basically explains what tables are available in the stock ecu for tuning boost control. I'm a bit confused on a couple areas since the reactive base waste gate duty cycle, engine boost target and boost correction tables are all related to each other. I am not sure how to approach the tuning since I have no experience flashing evo's but to anyone that does.....do I need to tune each of these tables separately or if I tune 1 will the other 2 automatically adjust them selves? For instance, if I simply change the boost target table, would the base waste gate table stay the same and the ecu automatically update the boost correction table with the relevant values to achieve the boost target? Or do you need to manually go in and tune each separate table?
Also in terms of my initial tune approach on the car, my plan was to zero out the base waste gate tables so that the engine runs only on waste gate spring pressure before adding more boost. I think this would be safe since I have no idea how this new turbo will reach with the current tuning parameters. Does this seem feasible?
Lastly, in the boost control course Andre addresses boost control as it pertains to WOT.....if you look at the PDF i've attached many of the evo tables are RPM vs TPS with load values in the table. I understand what you've taught in the course Andre but when it comes to the other areas of these maps how do you suggest I approach that?
Your approach regarding zeroing the wastgate duty to see what the base line boost is a sensible one, what you might find that you will hit an error situation as the target boost level is not reached, I've never mapped an Evo X so I'm not sure how it will react.
If you are changing one table you need to adjust the other tables to match, this is an area to make a method and stick to it as missing one adjustment can cause possible drive-ability issues or sporadic fault situations.
I have noticed most of modern the ECU's I've dealt with use a calculated load in their tables rather than actual values, some even use target torque, load is a calculated value from the sensors, usually boost and AFM, from the look of your PDF it is just using MAP. As you make adjustments to the boost control check back on the MAP based load Calc incase you need to re-scale it for the extra load generated by the bigger turbo.
When your running a bigger turbo than stock you'll find that on most of the partial throttle areas you'll not be able to increase the boost, even with 100% duty cycle, these areas should have their targets adjusted to suit, once the engine is flowing enough to generate any real boost then you can increase the duty cycles to achieve a consistent boost level throughout the throttle range, just be careful as too much duty in the lower areas can cause over boost in a transient situation so be sensible with your targets.
Thanks a lot for the feedback bro.
As for the suspected error situation, you think this can be combated by zeroing out the target table as well?
I guess what I am getting a bit confused with is the fact that since all the tables are inter-related then how do you tune one without the others having an effect on the current one you're trying to dial in. It's not like a stand alone where you can turn a function off. But guess my approach to zeroing maps out may be the way to go?
As for the load values, I believe they use the MAF and MAP values together to derive this "load" value. I have seen there is a patch available to convert the boost maps to psi based so you don't need to cater for atmospheric changes varying the calculated load value.
On another note chris, since this car is now fitted with forged rods and pistons, do you think this will require the knock threshold table to be adjusted?
The general approach I use when adjusting the boost on an OE ECU is to log, make a small change to a table, test and log again to see the effect of the change. OE ECUs are often a lot more complex than aftermarket and they can be fiddly to tune, particularly when you are finding which tables need to be adjusted.
Yes, zeroing the wastegate duty cycle would be a reasonable idea to start with minimum boost. Alternatively you could do this by just unplugging the wastegate solenoid though too if you just want to do a quick run to see where you are with regard to boost.
When you're adjusting the boost tables you will need to manually adjust each table - As you increase the boost target you also need to increase the wastegate duty cycle to match. This is very much like tuning the open loop boost control part of this course.
If you have the ability to control the boost target relative to TPS then this can be used to reduce the boost at mid throttle and achieve a more linear relationship between throttle opening and engine torque. Generally I will try and reduce the boost target as the throttle is closed from 100% to reduce engine torque.
you'll need to see how the engine behaves before thinking about adjusting the factory threshold for knock, monitoring and listening to it yourself.
Thanks for the reply Andre,
Can you touch on that RPM vs TPS area some more though?
Are you suggesting smoothly increasing the target boost as you go from part throttle to full throttle? Another thing I saw from the maps I've seen online is that the evo x maps all come configured to only 80% TPS.....did you notice this Andre?
There's no right or wrong way of dealing with boost vs TPS. It's up to your own preference and will also depend on turbo size. in general a turbo is exceptionally good at making boost and what you will find is that perhaps you see 20 psi at 100% TPS, but if you hold the rpm constant (on a dyno) and reduce the throttle, the boost might stay at 20 psi until you get the throttle down to perhaps 50% or thereabouts. The result is a very non linear relationship between engine torque and throttle position. Purposely reducing the boost target at lower throttle openings can make the car a little easier to drive, particularly if the car is very powerful or the track/road is wet.
Ok Andre, understood.
The turbo the car is fitted supposedly has a 18psi waste gate spring in it. To me I am foreseeing issues tuning this car especially on 95 RON since theoretically 18psi would be the minimum boost we can target correct? I was planning on running a maximum of 20psi of boost which makes the window only 2psi. This may make boost control much more difficult do you think? I am not sure if I'm thinking of this the wrong way.
It's not going to make it more difficult, it just makes the numbers required for you duty cycle to be extremely low. Standard ECU's don't trim the duty cycle dead zones so you may reach 30 or even 40% before the boost increases but once it does you won't need to ad much.
18 psi is the theoretical minimum pressure but if you are using a turbo outlet pressure source you may only see 16 or 17 psi manifold pressure if you have a good intercooler.
Personally I would like more head room from base to target pressure, a minimum of 5-10 psi, that way if things are going wrong you can pull the boost back.
Thanks a lot chris,
I understand what you're saying. I'll zero the duty table out, richen the entire boosted area of the fuel table and take about 5 degrees out of the ignition map as well as set my boost cut out to 21psi or so then do my first pull and see where everything is at. Does this seem adequate? Any other suggestions ?
Your precautions are sensible but particularly if you're doing your tuning on a dyno it's very easy to just abort the run if anything isn't how you wanted it - Too much boost, lean AFR, knock etc. When I'm setting up boost control I'm always hovering over the clutch pedal ready to abort the run if I'm not happy with something.
All things being equal you should find the engine will take more timing with a larger turbo at the same boost level. Pulling some timing initially is smart but just be prepared to pile it back in once you start dialling the tune in.
For me, an 18 psi spring would be a pretty good place to start and I doubt you'll have trouble. As Chris has mentioned though you may not strictly end up with exactly 18 psi as a base boost pressure anyway but there's only one way to find out.
Ok guys, thanks for all the guidance I will let you all know how it goes.
Just two more things Andre, one is with regard to the TPS upper scale limit on the stock evo x map only going out to 80%.......I've seen this on the net from more than one source. I find this a bit strange, do you see any reason why it would be set up this way?
And on a side note with regard to tuning variable cam control on the exhaust cam of the evo x. I understand from the webinars how to tune the intake cam but you never went into too much detail with the exhaust cam. Is it just the opposite? Retard the exhaust cam at low rpms and at higher rpms advance the cam?
Curious are You still running the stock boost control solenoid or have you swapped it for a 3 port solenoid
good option would be to use 3 port solenoid for evo x. (like grimspeed)
and zero out one of solenoids maps - you can find info in evolution forums.
If this is stock rom file from original mitsubishi ecu (not tephra mod, not racerom etc)
Stock rom files adjust boost regarding of load - MAF checking air mass. More load requested more boost etc...
And I think map sensor more is for safety features, for some speed density rom files it works like main load source. (maybe i am wrong and someone could correct)
I would do like this:
Make run with spring pressure and check what boost level and load it makes. (with wgdc corrections set to 0 and base wgdc to 0)
Start to raise up boost levels and log all the time
get desired boost levels and correct base wgdc and than, check what is the load value at necessary boost level. Than adjust ENGINE DESIRED LOAD table - after logged data.
Finally set back wgdc correction table, that boost control works.
maybe here is some pro with evo ix and evo x OE ECU tuning and could give some good guideline for best boost setting aproach.