zenrx8

iTrader: (4)

I found this trolling YT for information on different aspects of forced induction; comments on what this guy has done?


http://www.youtube.com/watch?v=yJbQRhtagvM

arghx7

I don't agree with many of his critcisms. At 1:30 he basically says all 3 port boost control solenoids (same as AEM Tru Boost or newer Greddy Profec) are noisy and constantly cycling on and off. This is simply untrue. The solenoid does whatever the controller tells it to do. If you have an aftermarket external controller then they are usually too dumb to keep the solenoid off to prevent noise. He also doesn't have a filter or a recirculation hose installed on his solenoid so that causes additional noise. He criticizes the spoolup time with 3 port solenoid but that is completely a matter of the tuning.

At 3:20 he argues that you should get your pressure signal from the manifold. There are arguments for and against that. It depends on the plumbing, the spring pressure and target boost, and in the case of EBC's the control logic and type of solenoid. Lots of methods can be made to work if you know what you're doing. His argument is that the manifold pressure is the "true" amount of pressure seen after all the pressure drop. Well yeah that's true but a wastegate is pneumatically actuated and there are sometimes good reasons to want the higher pressure off the compressor housing.

arghx7

At 4:50 he warns that your wastegate needs to flow enough and be mechanically set (spring pressure and possibly preload) in order to keep boost under control. This is a good reminder but still common knowledge.

When he starts doing the pulls, he claims that his boost isn't falling off but the shot fades quickly. Also, he is reading off a gauge rather than logging a MAP sensor which would be a much more accurate indication.

Final verdict: it's just an ebay ball-and-spring manual boost controller built with hardware store parts. I had a similar one that I got for $22 a couple years ago. All the pros and cons associated with that kind of design also apply to this. They're simple to use and inexpensive. They fluctuate with the weather. Depending on your wastegate spring pressure and a number of other mechanical factors you can still get some spiking. He was running this MBC to the side port of an external wastegate with 11psi spring. That's not the same mechanically as running an MBC to an internal gate with 6psi spring.

Frosty288

I have a lot of thoughts on this style of getting wastegate pressure, but I would advise highly against it, especially in systems utilizing 'drive by wire' throttle such as the RX8 and almost every other car made after 2000. While getting the signal from a source after the intercooler and most 'restrictions' (Usually, you just tune the EBC or spring pressure on your boost controller) is usually close to what you're seeing at the outlet of the turbo, it doesn't make too much sense either, and isn't a true accuracy. What if you had a small boost leak after the intercooler, but before the wastegate signal? The turbo would constantly be trying to keep up.

At least with mechanical throttle bodys, pedal to the floor (Or at least maximum throttle position) is usually, 100% open. Drive by wire throttles can adjust the throttle plate on varying conditions, changing the amount of air that really gets into your engine. An extreme example (This is from experience) when increasing the boost on a factory turbocharged vehicle with a drive by wire throttle, when the ECU started seeing anything over 12.5psi via the MAP sensor, it would start closing the throttle plate to manage the boost if it had no other means of doing so. So long story short, your wastegate is seeing ~12.5psi because it's being controlled by the PCM, but your turbo doesn't know that, and is constantly trying to create more and more pressure to compensate. Aka, 25+ psi at the turbo. I blew off a lot of charge piping in my learning days.

There are others much more informed on tuning the RX8 then myself, but I wouldn't be surprised that based on certain conditions the throttle plate isn't always 100% open when applying 100% throttle. Either way, best to get your boost source as true as you can, which means right after the outlet of the turbo.

note: I didn't actually watch the video

arghx7

Almost every gas engine with factory electronic boost control uses at least one restricter pill in-line from the pressure source for the wastegate. So factory engineers design the system so that the wastegate doesn't see "true" manifold pressure. That doesn't mean it's automatically a good or bad design... it depends on your goals and what you're trying to do. What matters most with boost control are the final results over time as conditions change... you can still make all sorts of plumbing work.

From the factory the Evo X uses two bleed-type boost control solenoids and three pills.



The boost control system in the computer has gear-based target load tables. These engineers took the pressure source from the compressor outlet and they engineered a system that peaks at 23psi and intentionally tapers down. On cars without a factory boost control system you just have to make do with rigged up aftermarket systems. You don't see R35 GTR, Evo X, or STi owners running aftermarket boost control very often.

Brettus

iTrader: (2)

The other thing about connecting it direct to the manifold the way he did is that it wont control boost under part throttle . Something that I've found is essential on a smaller turbo if you want to stay on the road .....

zenrx8

iTrader: (4)

I'm struggling to keep up here. I didn't realize turbo management was so complex/refined. What are the "pills" in the diagram? Some sort of flow restrictor?

Brettus

iTrader: (2)

/\ just little restrictors - not sure but I'm guessing they would be around 1mm diameter .

And BTW it's not as hard as some people make out . You just need to understand what is going on and then use that knowledge to make the right choices ...

zenrx8

iTrader: (4)

Well, it's challenging to me at the moment. Working my way through it. Take this one: my sister is a trucker.

Yep. You don't want to cross her. She's as likely to shoot your *** as put a tire iron upside your head, but that's another story.

Anyway, right now she's hauling for a contractor, making runs to GA, FL, and SC a couple times a week. She takes whatever rig is available. One run, she had the oldest rig in the fleet, some 750K mi. She said it ran like stink but it sounded like "an angry guinea pig" on boost and made 40 lbs on a setup rated for 32 lbs. Turns out there was a nut missing on the turbo housing (not sure which side, but I'm guessing the hot side) letting exhaust pressure leak; her explanation it allowed the turbo to build more boost. When the nut was replaced before the next run, it would barely make 30 lbs boost and ran like a pig. I'm guessing the leak out of the turbo housing was just enough to keep the internal wastegate from opening...

I'm guessing.

So the method of boost control is only part of the equation for turbos, right? Along with turbo size and drive ratio of turbine to compressor; wastegate actuation helps with powerband distribution within the confines of the physical setup of the turbo and wastegate setup (internal/external). Just thinking out loud; makes sense to have an boost controller linked to the ECU with mapping dependent on gear, rpm, throttle postion, MAF, and other parameters I don't understand yet, vs. just a physical valve that bleeds pressure off the wastegate actuator to vary maximum boost.

????

Brettus

iTrader: (2)

The advantage of boost control tied to the stock ecu is that the manufacturer has control over how much boost is made under many different conditions . That can give them more confidence in giving a warranty on the drivetrain etc.
For an aftermarket setup that is less of a consideration and good boost control can be had quite simply . The problem is that you only need to push a button to get more boost and that is just too much of a temptation .

Interesting sig BTW ......

zenrx8

iTrader: (4)

Wondering when you'd catch it.

Brettus

iTrader: (2)

I know how to bring out his best/worst

zenrx8

iTrader: (4)

Yes, you are truly a god - that was an all time classic

arghx7

The truck you sister drove probably didn't have a wastegate. Lots of diesel trucks don't have wastegates at all, especially older ones. My buddy's 89 Ram doesn't have one. It's just a Holset H1C turbo bolted right to the exhaust manifold.

Just about every OEM boost control system with traditional wastegates (not electric or vacuum operated wastegates as some newer cars have) use two port solenoids to bleed pressure out of the wastegate actuator. The old Rx-7's worked that way from the factory as well.





The size of the restricter pill(s) is very important. They work with the solenoid to raise or lower the overall range of possible boost levels. There are multiple plumbing arrangements for restricter pills. The Evo X is one of the most complicated. Depending on the location of the pill, a larger pill will raise boost or it could actually lower boost. This is assuming all other things are held equal in the system.

Lots of OEM's use target load tables for boost control, but some use target boost tables. The newest OEM systems integrate the boost control into the torque control system. So you will have a target engine torque vs rpm and accelerator pedal position map. And then to achieve the calculated target engine torque the computer manipulates both the wastegate and the electronic throttle. The OEM boost control systems are also integrated into the knock protection system so that if too much knock is detected the boost will decrease.

arghx7

So check this out. Here are three methods of ECU based boost control.



The top one is target boost vs rpm & throttle plate opening angle (car has electronic throttle). The ECU looks up how much boost it should run at a given rpm with the throttle plates open a specific amount. That's a reactive type of system. It reacts to other stuff it sees going on in the car.

The middle table, for an Evo X, uses target load only. Boost control is done without even measuring boost. This is a common Mitsu strategy that goes all the way back to the early 90s. At a particular throttle angle the ECU tries to achieve the load % in the table (in most cells take that % and add an additional 80% to it). It does this by manipulating the two wastegate solenoids to relieve pressure from the actuator.

The bottom strategy is used on the latest Subarus and increasingly on other manufacturers (Saab for example uses a variation of this). The ECU reads the position of the accelerator pedal and has a map to tell it how much torque the driver wants in newton-meters (map not shown here). By knowing how much torque the driver wants it then uses a series of other tables to help it determine the requisite opening angle of the throttle plates and the duty cycle for the wastegate solenoid. It then commands the electronic throttle motor and the wastegate solenoid to achieve these target positions using closed loop logic. The torque control system (request torque) can also be implemented into traction control calculations.

If enough knock is detected then boost is cut to protect the motor, while the target AFR richens up and the ignition timing retards. It's a much better (but more complicated) system then turning a couple ***** on a Greddy EBC or a ball-and-spring valve. The wastegate and electronic throttle can also be manipulated when wheelspin is detected through the requested torque calculation.

zenrx8

iTrader: (4)

I think you're right, she mentioned the truck originally having an "automatic" wastegate, but the turbo was replaced with a turbo having a "manual" wastegate - am I right in assuming a small leak (missing nut) on the turbine side would allow the turbo to continue to build boost, wastegate or no?

This is really twisting my brain but I'm starting to see a little glimmer here.

The tables for the different boost control strategies are interesting. The EVO strategy is interesting; boost control without a direct measurement of boost based on a set of static tables. That would seem to lend itself to easy manipulation of boost with a manual controller like the guy in the YT video was showing. And yes, I can see where the WRX method attempts real-time control based on multiple variable while at the same time introducing exponential complexity; the boost control version of going from carbs with floats and jets to EFI with and ECU. It seems there is no absolute right or absolute wrong; manual controllers or static table electronic controls are simple but contribute to boost spikes/creep/overboost; active electronic boost controls manage boost better and may arguably mitigate engine damage risk, but are much more complex and difficult to alter.

Thanks, BTW, for taking the time to post those tables, I appreciate it. Getting ready to bury my nose in "Basic Electronic Engine Tuning" (or something like that). This is a lot easier on motorcycles than cars, or at least it seems that way to me. I don't know why cars intimidate me so much when I'm not afraid to tear into a motorcycle engine.

arghx7

I find it unlikely that an exhaust leak would increase boost. I don't have the truck in front of me so who knows what the full situation was.

They're target load tables but they actually do have closed loop control (proportional only, as in PID without the I or D). The fuel cut on most Mitsu applications is based on maxing out the airflow sensor, not on hitting a particular boost level. So it's easier to throw an MBC on there and play around with it without pissing off the computer. This was common in the days of the DSM especially.

In modern vehicles with traction/stability control and electronic throttles the boost control is increasingly integrated into all the other systems of the car.

Some lower end EBC's use open loop control only. The AEM Tru Boost is one example. It's a lot easier to turn a **** on an MBC but they are especially sensitive to the weather.

There's not much debate about mitigating engine damage risk. If you overboost on a modern factory turbo car, you throw a check engine light. If you overboost on a car that wasn't engineered for a turbo you will probably blow your motor. But there's no doubt that OEM based boost control is trickier to get dialed in. You have the control tables in the computer plus the plumbing aspect.

Don't jump into buying a book yet. Read articles from Toyota's EFI training program. http://www.autoshop101.com/autoshop31.html Look through "Engine performance OBD" and "Engine performance OBD II" section.