He's back at it.

[Bluezone]

I was looking at my YouTube channel list. This came up.

I thought it was kind of interesting what he found with the boost levels.

 

[stripSHO]

I'm only saying it because he asked me to, but this guy is an idiot. Manifold boost is controlled first and foremost by the throttle body. The wastegates then work to try and maintain a set pressure differential across the throttle. All that disconnecting the wastegate will do is make the throttle close up, and throw your turbos into surge territory forcing the BOVs to open. They're opening to stop his turbos from blowing up, not to maintain boost pressure. If he had TIP up on the screen you would have seen a much different story. I would also assume doing this robs horsepower due to unneccessary added exhaust backpressure due to both flow resistance and increased EGR (without proper cam phasing more boost actually means less airflow and just more exhaust reversion).

The solution for gaining more boost is pretty damn simple: ask your tuner for more boost. Stock turbos can do 20 psi up to around 4000 rpm or so. But they'll never make more than ~16 psi at top end no matter what you do.

 

[yaycandy]

I'm only saying it because he asked me to, but this guy is an idiot. Manifold boost is controlled first and foremost by the throttle body. The wastegates then work to try and maintain a set pressure differential across the throttle. All that disconnecting the wastegate will do is make the throttle close up, and throw your turbos into surge territory forcing the BOVs to open. They're opening to stop his turbos from blowing up, not to maintain boost pressure. If he had TIP up on the screen you would have seen a much different story. I would also assume doing this robs horsepower due to unneccessary added exhaust backpressure due to both flow resistance and increased EGR (without proper cam phasing more boost actually means less airflow and just more exhaust reversion).

The solution for gaining more boost is pretty damn simple: ask your tuner for more boost. Stock turbos can do 20 psi up to around 4000 rpm or so. But they'll never make more than ~16 psi at top end no matter what you do.

I didn't think these engines had EGR, or do you just mean that in general?

I guess you could simulate an egr with valve overlap. I have one vehicle purposely setup like that

 

[stripSHO]

I didn't think these engines had EGR, or do you just mean that in general?

I guess you could simulate an egr with valve overlap. I have one vehicle purposely setup like that

Exactly. Exhaust pressure is far greater than boost pressure, so EGR is achieved with cam timing. Need for an external valve was eliminated.

 

[yaycandy]

Exactly. Exhaust pressure is far greater than boost pressure, so EGR is achieved with cam timing. Need for an external valve was eliminated.

Question for you as I'm still learning. I did my intercooler setup and it dropped iat2 pretty good. My tuner says my fuel pressure is beyond maxed out now at 93 octane. I have slight fuel pressure dips in the mid range because of the lower air temps. He said he added throttle control instead of dropping boost pressure as it was just a slight fuel pressure dip. Is that what you mean by throttle control boost?

Time for an xdi pump...

 

[stripSHO]

Question for you as I'm still learning. I did my intercooler setup and it dropped iat2 pretty good. My tuner says my fuel pressure is beyond maxed out now at 93 octane. I have slight fuel pressure dips in the mid range because of the lower air temps. He said he added throttle control instead of dropping boost pressure as it was just a slight fuel pressure dip. Is that what you mean by throttle control boost?

Time for an xdi pump...

Not sure really. I have to assume they previously had the ETC torque control tuned out of the equation and reintroduced it for you? Maybe load targets were set unrealistically high? I don't really know for a fact but I do get the impression that most tuners believe that keeping the throttle wide open at all times is necessary for good power production.

The way it's supposed to work (cliffnotes edition) is that your pedal position and engine speed determines a torque request. The ECU then determines how much load (airmass) is required to achieve that torque target. Using the ideal gas law, it then compensates for IAT2 to determine what MAP it takes to supply that load. The wastegate control then tries to keep TIP slightly above MAP so the throttle body always has enough pressure available to meet demand.

Honestly though I highly doubt you have anything to actually worry about with fuel pressure. Everyone is overly sensitive about it. How low does it go?

 

[yaycandy]

Not sure really. I have to assume they previously had the ETC torque control tuned out of the equation and reintroduced it for you? Maybe load targets were set unrealistically high? I don't really know for a fact but I do get the impression that most tuners believe that keeping the throttle wide open at all times is necessary for good power production.

The way it's supposed to work (cliffnotes edition) is that your pedal position and engine speed determines a torque request. The ECU then determines how much load (airmass) is required to achieve that torque target. Using the ideal gas law, it then compensates for IAT2 to determine what MAP it takes to supply that load. The wastegate control then tries to keep TIP slightly above MAP so the throttle body always has enough pressure available to meet demand.

Honestly though I highly doubt you have anything to actually worry about with fuel pressure. Everyone is overly sensitive about it. How low does it go?

Copy pasta from my email.

"You are still getting some fuel pressure dips in the midrange so the only alternative is to drop boost and pull a pound or so out. But I'm thinking you don't want to do that. You have a nice flat boost curve so boost is well controlled so the fuel pressure won't get worse than it is now. I would just warm the motor before going crazy WOT but you should be doing that anyway. If you were getting closer and or below 1000 psi that's getting pretty bad, you drop to about 1300 and only briefly then towards the top end it starts to recover. And your knock sensors are happy where the spark is. The intercooler is working well enough to cool the charge and get the air more dense so your fuel pump is not liking that so much. "

"Ok that is great spark for 93 oct. I'm leaving that but the cooler charge temps now are making the fuel pressure take a hit.....I'm going to leave the boost alone but dial in some throttle control. Nothing you should really feel."

Thanks buddy I'm just trying to learn how these engines work with boost. When I turbod my miata is was more easy with megasquirt and a boost controller...

 

[stripSHO]

Yeah I personally wouldn't even bat an eye at a rare 1300 psi dip, at least not on my own vehicle. But trimming back load limits just a little bit in that area isn't a bad idea at all. I logged a drop to 900 psi a couple weeks ago lol. That's definitely something that needs to be addressed but at the same time it doesn't worry me in the least. There's more to it, like what pressure provides optimum delivery and combustion efficiency. But speaking strictly in terms of running out of fuel, rail pressure is of secondary relevance. What's most important is that you don't run out of injector timing. And as long as you don't screw up injector limits the ECU will shut the throttle waaaaayyyyy before you get into any serious trouble.

Check out the screenshots below. The first one is a hot summer heatsoaked run at 20.2 psi, and the 2nd one is a cold winter run at 18.5 psi (sorry I log in kpa because that's the native unit for most of the tuning tables). Note that the calculated Load is identical at quite different boost levels due to the difference in density. Once you also factor fuel trims the cold weather air actual load is a bit higher. Also take note that the throttle angle is only 57% on one log, vs 100% on the the other. This is illustration of the electronic throttle doing its job as described before! You'll see that I log injector maximum pulsewidth, which is just a math parameter I made up based on my max available injection angle with respect to engine speed. I also log actual injector pulsewidth from the ECU. When a 6% difference in airmass makes your injector pulsewidth jump 24% that's when you know you're running on the ragged edge of your fuel system. Actual vs. max injector pulsewidth lines touching each other provides confirmation that it's time for me to back off a bit. Any more air at all and the throttle will close itself to avoid leaning out. But at less RPM the concern goes away because there's more time available for the injectors to spray.





Hope this helps a little