They {meaning Mazda}. Coment coming from an engineer and thats why i stay off this site lots of punks trash fitting against each other. Some RX fans we are!

 

well, you did basically make yourself sound like you think you are smarter than the mazda engineers who built the turbo system. the system does work fine, when it is all working correctly.

arrogance usually is rewarded with arrogance.

 

This is a good thread and dont mean to clutter However just want the rx owners to understand why the twins are a little eratic and get surges. Simple to understand put some twins on the table follow the air flow pattern and see how your air crashes even if you have a prespool in the secondary. done with my comments....peace

 

My friend and I reviewed the diagnostic setup and to our naked eye on video playback it appeared as if the charge control and charge relief solenoids switch at the exact same time. This was a 2nd gear run, however, so everything is happening relatively quickly engine speed wise, and since we have no clue how long this potential surge condition can last, we could have easily missed it.

We're going to try it again in a higher gear and see if we can see it.

 

^ are you logging from the factory diagnostic protocol? Because that has a very slow sample rate

It is interesting that two different SAE papers talk about this surge condition (on the 13B-REW and the 20B) but the workshop manual and service highlights say nothing about it. I am inclined to believe the SAE papers.

 

This thread is after all a technical discussion about the technical challenges of sequential twin turbo transition. Sweeping generalizations that defy convention and are supported with neither fact nor theory might get attention but not consideration.

You have two turbos generating 10psi of pressure. You have an engine drawing vacuum if not for the turbos. The air coming off the compressor(s) goes right into the engine. Since both turbos are equal size and efficiency, the 10psi of air coming from the other compessor has no more effect than if a wall was there instead. I've monitored boost pressure on both sides of the charge control valve and they are both 10psi when it opens. It's no different than an exhaust manifold that joins and exits in one tailpipe.

Boost spikes are caused by poor boost control. The stock Mazda design does not spike boost and the engine does not blow up. Poorly modified cars might do those things, but it's not because the flow is going backwards, and it's certainly not a fault in Mazda's design.

You could do all of that and if that's the only change to the stock design you've added restriction. No benefit. It will be slower and hotter.

 

No, my friend could not get his board to read the factory diagnostic protocol so we used his diagnostic LED board. It displays exactly everything going into and out of the ECU in realtime, albeit in LED form.

 

The only way to know for sure would be for someone to disassemble the sequential turbo control logic in the factory computer.

 

Do you know the publishing date of these documents?

I wonder if this system was being developed and later scratched for some reason.


John

 

How can I not know for sure when I can see everything the ECU is switching and controlling in realtime?

 

Or, as I had already mentioned, you just monitor the output of the factory computer. Watch the TCA, CCA, CRV, WG, PC, etc. That's easy to do and no matter what's going inside the ECU the electrical output to the solenoids is the bottom line.

 

As someone earlier pointed out, it may be that the research was done after the first FDs (series 6) were released. It may be that Series 7 (96-99) or Series 8 (99+) models have this new control technique.

Either way, it's pretty simple to check using a portable oscilloscope or logic analyser. I'd do it myself except I only have access to mains powered o'scopes.

 

The first paper:



The second paper:




It is conceivable, although not likely, that it only happens rarely or under very specific conditions, and we would only be able to find out if we understood how the ECU was programmed. But if you can't observe it during normal driving, for all intents and purposes the service manual is correct and for whatever reason there is a significant difference between all of Mazda's test engines and their production engines. That in itself would be a fascinating mystery.