Hi,
Not sure if this has been discussed before...did a search but to no avail.

Why does our car have two boost solenoids??

My best guess is that the ECU has 2 different boost settings....and activates the appropriate solenoid for the job.

 

here ya go, this may help

http://www.roadraceengineering.com/e...lsolenoids.htm

 

interesting, good write up and/or find.

 

^^^ : Wow, way over my head... can somebody break this down to newbie terms for me?

 

Basically, boost pressure is constantly pressing against the wastegate and the boost control solenoids contantly and simultaneously. When boost pressure opens the wastegate, boost drops because exhaust gas (what spools the turbo) escapes out of the wastegate port and is diverted away from the turbo. When the solenoids open, they let this boost pressure (that would otherwise open the wastegate and cause boost to drop) escape out of a vent port on the solenoid thus maintaining boost.

The ecu has programmed tables called "wastegate duty cycles" that control how long and how rapidly the solenoids open and stay open. ECU tuning can increase boost, imparticular taper (fancy term for the boost curve as the rpms rise) by raising the wastegate duty cycle tables to cause the solenoids to stay open for longer (again causing less pressure to press on the wastegate and thus maintain boost for longer). I hope that this helps to explain this without getting too technical.

 

Second solenoid duty cycle is based only on rpm and is not subject to feedback loops in the ecu, Primary solenoid duty cycle is based on feedback from the ecu.

Think of the secondary solenoid as a course adjustment (set it and forget it for the most part) and the primary solenoid as the fine adjustment.

 

I have twin solenoids in my car (jdm evo IX) never knew why.... I guess it's the same as the twins in the X...

 

That's funny since the primary solenoid that is based by load and RPM is at 100% WGDC stock at WOT and the secondary solenoid that is base by RPM only has much more room stock.

 

^Interesting. So if the primary solenoid is already at 100% WGDC stock then why does boost taper so much? Is it the secondary solenoid that, once ecu tuning is done, allows for the much improved taper and not the primary then?

 

Yes that is correct from what I have experienced.

 

wow, thanks for the info guys. So much to learn... good thing I have no life and plenty of time to figure this stuff out.

 

From my experience also, upping the duty cycle on the secondary wgdc map is what will help since it is at 0% from 6500 on. LOL

 

here is the main solenoid table stock:



Here is the secondary solenoid table stock:

 

Well that explains a lot. There clearly is a lot of room to bump up the duty cycles in the secondary solenoid map. Interesting that from 4000 rpms, the secondary solenoid only hits about a 55 % duty cycle and only goes down as rpms rise. This would explain why the boost taper is so bad on the stock tune. Just out of curiosity though, why is the main solenoid incapable of producing a better taper when the duty cycles are at 100 % in stock form?

The ony thing that I can think of is that the orfice in the solenoid vent port (or the pill near the solenoid, if there is one there like the evo 9) is smaller then the one in the secondary solenoid. This might explain why even at 100 % duty cycles the first solenoid isn't able to vent out enough pressure quickly enough to prevent the wastegate from opening. Perhaps the orfices in both solenoids are the same, but are both small so only when combined at high duty cycles can they vent out pressure fast enough to allow the turbo to produce it's maximum efficient boost level. Thoughts anyone?

 

I am sure it is by design. The Evo 8 and 9 single solenoid was at 100% WGDC from the factory as well.

It didn't stop us from doing things to bring the boost up for the same WGDC % though.

I'm going to be experimenting with pills very soon. For pump gas (at least the 91 we get here), it seems like the stock system will work pretty well, but for the race gas and E85 guys a pill might help a bit.