Boost demand is influenced by the torque model, so the target moves with operating conditions. That makes Boost Target Error the useful measure: how closely actual pressure follows what the ECU is requesting.

A steady target makes diagnosis easier, but the car needs to track changing demand properly too.

How the target is built, and the PID tables as they stood before this work, are in Boost Control on the Emtron KV12: Where the Target Really Comes From. That post describes refining the initial position table by no more than 3 percent at a time. The changes here are much larger, and they are provisional.

What the original logs showed

The earlier logs contained periods where boost remained around 10–25 kPa below target, alongside substantial changes in wastegate duty.

Three features of the original calibration stood out:

• An isolated 10.00 proportional-gain cell, at −25 kPa error with manifold pressure rising at 5 %/second, compared with 0.50 in every other cell at that error.
• Integral gain dropping to zero at ±10 kPa error, limiting its ability to correct a sustained deficit outside the narrow near-target region.
• Derivative output making sizeable contributions to duty during some transients.

Those observations justified investigating the tables, but they didn’t establish a complete replacement calibration. Some logs also had gaps exceeding a second and channels updating at different rates. That limits how confidently individual output changes can be tied to events happening a few hundredths of a second apart.

The first PID revision

The first revision removed the isolated proportional-gain spike, extended modest integral action further from target and reduced the positive-error derivative gains.

These were trial values, not a finished calibration.

Proportional gain

The only change from the original was the 10.00 cell. With it gone, proportional gain no longer depends on how fast pressure is rising.

That made the gain surface consistent. It did not establish that overshoot would improve. That cell was the overboost catch: boost well above target and still climbing was the one situation where the controller was allowed to hit hard. Removing it removes that correction too.

The table is also asymmetric, which was inherited rather than introduced. Gain is 0.20 at −5 and −10 kPa, against 0.50 at +5 and +10 kPa. Proportional correction is weaker when boost is above target than when it is below.

Integral gain

The near-target values stayed unchanged. Adding 0.010 at ±10 kPa allowed integral action to extend beyond the original narrow region, tapering towards zero at ±50 kPa.

The integral limits remained ±5 duty percentage points.

Derivative gain

The gains at +10, +20 and +25 kPa were halved from 3.00 to 1.50. The negative-error end was retained.

The output limits remained 5–80% duty, and the initial-position table was initially left unchanged.

That last decision became important.

Why boost status mattered

Some of the earlier duty changes coincided with changes between Emtron boost status 15: ON–Mass Flow Limit and 1: ON.

Those transitions could change both the final boost target and the initial duty selected from the table. A sharp duty change therefore wasn’t automatically evidence of a PID problem.

The distinction matters on this car because the final boost request is influenced by the torque model. Looking only at the base target, or only at the PID outputs, misses part of the control sequence.

Boost system status and boost PID status are also separate channels. Their numbers cannot be interpreted interchangeably.

Status names are from Emtron’s Boost Status reference.

The sixth-gear log below shows how large those transitions are. Between about 3,000 and 3,100 rpm, the status flipped between 1: ON and 15: ON–Mass Flow Limit four times. Each flip moved the target between 290 kPa and roughly 190–200 kPa, and moved commanded duty between 80% and about 31%. None of that was the PID.

At a target near 190 kPa the initial position also read zero, because the table holds zero at 200 kPa and below. From about 3,100 rpm the status stayed at 15 for the rest of the pull, so the whole overshoot happened with the mass flow limit setting the target.

The run that exposed the overshoot

The next useful log contained a sixth-gear pull from approximately 3,000 to 4,300 rpm, with no shift recorded during the pull.

It showed a clear overshoot:

Positive error means actual pressure is below target. Negative error means it is above target.

This wasn’t simply an apparent overshoot caused by the target suddenly falling. During the initial pressure rise above target, the target itself increased from approximately 261 to 271 kPa absolute.

Actual pressure climbed much faster.

The maximum logged error and maximum manifold pressure occurred at slightly different timestamps. With independently updating channels, those figures should not be forced into an exact same-row calculation.

The initial-duty table explained much of it

At approximately 3,680 rpm, boost was almost on target:

• Boost Target Error: +3.3 kPa
• Initial duty: 75.5%
• Final commanded duty: 74.6%

The engine was already reaching the requested pressure while the controller was still commanding substantial spool duty.

The original initial-position table held 100% duty through 3,500 rpm for target rows from 220 to 340 kPa. It then dropped sharply towards the values at 4,000 rpm.

For the 260 kPa target row, interpolation produced this curve:

The table tapered spool assistance according to engine speed, without directly accounting for how close actual boost had come to target.

In this sixth-gear pull, boost reached target before RPM had advanced far enough through that taper. Feedback then had to remove a large amount of duty while pressure was already rising rapidly.

Between target crossing and the pressure peak, about half a second, the taper itself took initial duty from 75.5% to about 51%, and P removed roughly another 26 points. Pressure kept rising anyway.

That strongly implicated the feedforward transition. It did not prove that every aspect of the overshoot came from that table.

What P, I and D were doing

The individual outputs helped separate the causes.

P was correcting the overshoot. It eventually removed approximately 27 duty percentage points. That correction arrived as negative error developed, but it did not prevent the pressure peak.

It was also starting from its weakest settings. Between −2 and −10 kPa the gain was 0.10 to 0.20, reaching 0.50 only at −25 kPa. This overshoot passed −25 kPa with pressure still rising, which is the region the removed 10.00 cell used to cover. The log can’t show what that cell would have done, but this run went through the conditions it was there for.

I was not winding up and driving the event. Integral output was approximately zero at target crossing and slightly negative at the peak. Increasing integral correction would not address the main cause shown here.

D had a gap around target crossing. The revised table had zero derivative gain from +5 to −40 kPa error, as the original did.

As error approached zero from the positive side, derivative gain tapered away. It then remained zero through the first 40 kPa of overboost, approximately 5.8 psi. Gain only returns beyond −40 kPa, reaching 3.00 at −50. With a worst logged error of −57.6 kPa, derivative gain was available only over the last 18 kPa or so of the overshoot.

The log shows what that did. Above target, derivative output was zero from about −13 kPa to beyond −50 kPa. Its only negative contribution there was −2.1 points, at the peak. As pressure began to fall it switched to +6 and then +12 points, with boost still 30 to 50 kPa over target.

That is derivative doing its job, resisting the rate of change. Here, though, it was adding duty to an engine that was still overboosting, and final commanded duty briefly climbed from 17% back to 46% in that window. On this run, the −50 kPa end of the D table added more duty during recovery than it removed at the peak.

The combination was the problem: high initial duty approaching target, with weak proportional and no derivative correction through target crossing.

The first D revision had retained that gap. The later log showed why it could not be treated as a validated overshoot-control calibration.

Adding resolution where the problem occurred

Seven engine-speed breakpoints were added to the initial-position table: 3,250, 3,600, 3,700, 3,800, 3,900, 4,100 and 4,250 rpm.

The existing 3,500 and 4,000 rpm breakpoints were kept. The 4,000 rpm values stayed as they were. The 3,500 rpm values did not: for the 220–280 kPa rows they came down from 100% to between 50 and 57%.

Adding columns alone changes nothing if the new values simply reproduce the old interpolation. The purpose was to create enough resolution to reshape the transition deliberately.

The revision reduced duty earlier and brought it closer to the existing 4,000 rpm values before the previous target-crossing point. It covers the 220–280 kPa rows from 3,250 to 3,900 rpm.

These are provisional trial values, chosen to reduce the excessive duty carried into target crossing. They were not calculated from measured equilibrium wastegate requirements.

At 3,700 rpm and a 260 kPa target, initial duty falls from approximately 72% to 38%. That is a substantial change, with a possible cost in spool response.

The 80% at 3,250 rpm changes less than it looks. It matches the 80% output limit, so while boost is still below target the commanded duty there is the same as before. The real reduction starts at 3,500 rpm.

The 4,100 and 4,250 rpm columns are there for later shaping. For now they hold interpolated values only.

Checking the entries mattered

The first screenshot of the edited table showed that the 280 kPa row had been missed.

That would have affected operation below 280 kPa too, because the ECU interpolates between target rows. EMtune had filled the new 3,700 rpm cell in that row with 72.5%, the original interpolation rounded to the nearest 0.5. At 270 kPa and 3,700 rpm, that would have produced approximately 55.25% initial duty, rather than the intended 39%.

The row was corrected before considering the revision complete.

A separate limitation remains above it. The 300–340 kPa rows retain the original aggressive spool profile, and the step into them is steepest at 3,500 rpm:

That matters in sixth gear. With the 10 kPa sixth-gear target offset, 290 kPa is the full-demand target in that gear, and this log requested exactly that whenever the status returned to 1: ON. The revised 220–280 kPa region does not establish that the rest of the table is suitable.

Where the calibration stands

The revised initial-position values have been checked in the calibration screenshots. There is not yet a subsequent log demonstrating their effect.

P, I and D are being held unchanged for the first comparison so the effect of the feedforward change can be assessed separately. Three closed-loop issues remain open: the derivative gap from +5 to −40 kPa, the weaker proportional gain above target now that the 10.00 cell has gone, and a −50 kPa derivative gain that adds duty during recovery from overboost.

The next assessment centres on Boost Target Error:

• Peak negative error during boost arrival.
• Time spent above target.
• Recovery after the peak.
• Any additional positive error or slower spool introduced by the reduced duty.
• Behaviour when the torque model changes the target or boost-control state.

The useful result will be a smaller, shorter overshoot without creating an excessive boost deficit elsewhere. Until that is demonstrated, this remains a calibration under development.

The lesson from this stage is specific: before asking PID to correct a boost error, examine the initial duty it is correcting around. In this run, boost was arriving on target with roughly three-quarters duty still commanded. That was the first problem to address.

More to come.

The post Tuning the Supra’s Boost Control: PID Gains Were Only Part of the Problem first appeared on BlownByTwins.

The post Tuning the Supra’s Boost Control: PID Gains Were Only Part of the Problem appeared first on BlownByTwins.

Saturday, 27th July 2024, what a long day, but totally worth it. I had to drop the R34 GTR at The Exhibition Centre in Liverpool for The Ultimate Show, then my mate Big Paul (ironic name) came to collect me and take me down to Nottingham to collect the Supra. We arranged a collection time of 4pm, and then I head south to Watford Gap to meet an old friend for a coffee and give the car a run before heading home for 10pm. 220 miles of blissful driving in my new toy. I forgot just how good they are, and how much stronger it pulls above 4000rpm. I can’t wait to start the modification route with SRD Tuning.

When I arrived at the previous owners house, I was immediately greeted with the extensive history, and the receipts for pretty much anything that has been done to the car in the UK ownership. We went through this when I went to view it anyway, but it’s reassuring to see. Although the sight of a certain “respected” tuners name in the file sent a shudder – although it was from the import and not for work. And it was a long time ago. Even though, their name is on the license plate. Suffice to say, a new plate was ordered immediately and is in the post as we speak. Wye aye, I’d not let that place tune my piano, pet. And I don’t have a piano.

Once we’d done the paperwork, and had a look around the old owners new car, it was time to leave. Or was it? No. Battery. He’d had it on trickle charge and forgot to turn the plug on! Mortified, but we got a laugh out of it. Jump leads to the rescue. 5 mins and it started first time. We left it running, shook hands and both agreed it was a pleasure to deal with each other – see, I can be nice!

I head off to Watford Gap to meet Peter, and found a Shell petrol station around 30 miles away. Plenty of distance to put a good charge in it. The fuel was low when I arrived at the Shell, and I totally forgot about the 70 litre tank. That was an expensive, but equally brilliant stop.

The 56000th mile clicked over on this journey and all was going well until the traffic built up just before the Watford Gap services turn off. That gave me 5 mins to play with the stereo. Yep. Definitely upgrading that.

After leaving Watford Gap, leaving the car there for just under 2 hours, chewing the fat, it was time to go home. Two words: very smooth. The car is only a 4 speed auto for now, with 390bhp. But it can delivery it nicely and it makes it a really nice motorway car, albeit quick and relatively thirsty. But it drives well, no noises, very few squeaks and rattles – nothing that some soundproofing won’t cure.

As night fell, the lights came on, I think. The stock bulbs in the Supra are ferociously crap. That’s already been remedied, with LED bulbs on order all around – thanks to Auto Bulbs Direct for relieving me of £295. But, I remember from my last car, just how much better night time driving became. And this will be the same – but it says a lot when I ordered the license plates first!

I got home and I was still giddy.

Isn’t she lovely. Side view, no license plate!

The post Mk4 Supra – It’s Home! first appeared on BlownByTwins.

The post Mk4 Supra – It’s Home! appeared first on BlownByTwins.

Compressor Side:

• Compressor Wheel: The G30-770 is equipped with a high-performance compressor wheel designed for maximum airflow. The exact specifications of the wheel may vary, but it typically features an inducer diameter of around 58mm.
• Trim: The compressor wheel trim is usually specified as 84 or similar, indicating its size and design characteristics.
• Housing: The compressor housing is meticulously engineered to provide efficient and unrestricted airflow, optimizing the performance potential of the compressor wheel.

Turbine Side:

• Turbine Wheel: The turbine wheel of the G30-770 is designed for high-performance applications, typically featuring a diameter of approximately 68mm. This larger wheel size allows for increased exhaust gas flow and higher power potential.
• Trim: The turbine wheel trim is typically specified as 84 or similar, highlighting its size and design for efficient exhaust gas flow.
• Housing: The turbine housing is designed to handle high exhaust gas temperatures while maintaining optimal flow characteristics. The 1.01 A/R (Area/Radius) turbine housing is commonly used with the G30-770 to achieve a balance between low-end response and top-end power.

Specifications:

• Boost Pressure: The G30-770 turbocharger is known for generating substantial boost pressure. With proper supporting modifications and engine tuning, it can produce boost levels of approximately 2.5 bar (36.25 psi) or more, depending on specific application and setup.
• Power Output: The G30-770 is designed to support high-horsepower applications. It is capable of producing power outputs ranging from 700 to 800+ horsepower at the wheels, depending on supporting modifications, fuelling, and tuning.
• Response and Spool: The larger size of the G30-770 turbo and the 1.01 A/R turbine housing may result in a slightly slower spool compared to smaller turbos. However, the combination of a larger compressor and turbine wheel provides excellent top-end power and performance.

Here’s the table with the approximate maximum airflow in pounds per minute (lb/min) for the pair of HKS 2530 turbochargers and a single G30-770 turbocharger at a pressure ratio of 2.5 bar absolute:

From this, the G30-770 should be able to provide an extra 10lb/min over the 2530s, which is nearly 100bhp.

Here’s a comparison table with approximate RPM ranges for the G30-770 turbocharger alongside the HKS 2530 turbochargers:

So, the G30-770 should be spooling anything up to 1000rpm earlier. Hopefully more when you take into consideration the upgraded cams that I’ve gone for. With no additional peak power, I’ll have more power in more places, more of the time, resulting in a quicker car point to point. Ready for the next slap! Adventures trip to Scotland

The post The G30-770 first appeared on BlownByTwins.

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Compressor Side:

• Compressor Wheel: The HKS 2530 features a high-performance compressor wheel with an inducer diameter of approximately 46.5mm.
• Trim: The compressor wheel trim is typically specified as 56T, which indicates its size and design characteristics.
• Housing: The compressor housing is engineered to provide efficient airflow and features a compact design suitable for various engine bay configurations.

Turbine Side:

• Turbine Wheel: The turbine wheel has a diameter of approximately 53.8mm, optimized for quick spooling and strong mid-range torque.
• Trim: The turbine wheel trim is often specified as 62T, indicating its size and design for efficient exhaust gas flow.
• Housing: The turbine housing is designed to handle high exhaust gas temperatures and provide optimal flow characteristics. It commonly utilizes a T25 flange, compatible with many aftermarket exhaust manifolds.

Specifications:

• Boost Pressure: The HKS 2530 turbos are known for delivering impressive boost pressure levels. They are capable of producing around 1.5 bar (21.75 psi) of boost, depending on supporting modifications and engine setup.
• Power Output: With their efficient design and moderate-sized compressor and turbine wheels, the HKS 2530 turbos can support power levels of approximately 400-450 horsepower at the wheels. However, it’s important to note that power output will vary depending on other factors such as engine modifications, fuelling, and tuning.
• Response and Spool: One of the standout features of the HKS 2530 turbos is their quick spool and excellent response characteristics. These turbos are designed to minimize lag, providing strong mid-range torque and responsive acceleration.

The post HKS 2530 Twin Turbos first appeared on BlownByTwins.

The post HKS 2530 Twin Turbos appeared first on BlownByTwins.