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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 05-14-2010, 04:35 PM   #21
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For track/autocross guys, logging tire temps in three spots across the tire face in real time on all 4 tires has HUGE value. Would need 12 channels sampling and 12 IR sensors, yikes.

Also, logging suspension movements. Linear transducers are expensive, I've heard, so some are using rotary transducers and converting into linear measurements.

I know it's not engine stuff, but cool, anyway...
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Old 05-14-2010, 04:37 PM   #22
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The boost leak detector algorithm is a great idea, I hadn't thought of that. I'm curious how the wheel speed would improve a boost control algorithm, aside from being a failsafe. Please elaborate...
I typed a long response last night and lost it...

Basically the control loop will be a nested or "cascaded" loop. The main, outer, boost error loop, will control shaft speed. The shaft speed will be the inner, faster loop. Cascaded control loops are higher performance (faster response) when the inner loop is a variable that changes faster than the controlled variable.
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Old 05-14-2010, 05:03 PM   #23
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I just measured my blowby flowrate.
A "good" engine will have 1.2 cfh per hp.
At 5500 rpm / 10 psi or est 200 hp I get 100 cfh. (good is 240 cfh)
At redline or est 240 hp I get 150 cfh. (good is 290)

I'll say my 600-mile Supertech rings are seated.
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Old 05-14-2010, 08:17 PM   #24
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Quote:
Originally Posted by JasonC SBB View Post
I typed a long response last night and lost it...

Basically the control loop will be a nested or "cascaded" loop. The main, outer, boost error loop, will control shaft speed. The shaft speed will be the inner, faster loop. Cascaded control loops are higher performance (faster response) when the inner loop is a variable that changes faster than the controlled variable.
Interesting. If you feel inspired to retype it sometime, please do. My control theory background is pretty shallow. I'll do some googling.
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Old 05-14-2010, 08:42 PM   #25
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?? I measured TIP (turbine inlet pressure) and posted the numbers above.

1:1 pressure ratio seems unachievable with most streetable turbos (e.g. those that make say 8 psi by 3000 RPM). Streetable track cars, perhaps.

Do you know of any turbo setups that have that magical 1:1?
Sorry, I just skimmed the post. I didn't note TIP as Exhaust manifold pressure.

Either way, yeah, it's not that uncommon to find something roughly 1:1. Assuming you use a turbo with a compressor wheel and turbine wheel with similar limitations, most of the work is done by the exhaust manifold to achieve the 1:1 ratio. Adding volume does hurt spool 200-300rpm typically, but the gains in the midrange and top end are typically significant enough to warrant the change. Once you get to that 1:1 ratio, using NA cams allow you to make stupid increases in power. I'm not suggesting using aggressive NA cams, but a mildly aggressive cam really does make power.

The company that I know of that has done the most testing for this is Full-Race and Jeff Evans. In the end, it's all about using an exhaust manifold with a higher volume without going extreme and killing midrange power(unless that is your desire).
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Old 05-14-2010, 09:11 PM   #26
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Thinking about this some more...

A standard electronic boost controller takes as input a setpoint (target pressure) and current manifold pressure. The difference between the manifold pressure and the target pressure is the error. The top level table in the ECU might be target pressure vs RPM (ideally with one table per gear), but the control algorithm just takes the current setpoint. The output of this process is a duty cycle for the wastegate control solenoid ("Wastegate Frequency Valve" in Bosch parlance.)

With the nested algorithm, the outer loop still takes a target pressure setpoint, and current manifold pressure, but outputs a shaft speed instead of a duty cycle. The inner loop takes as input the target shaft speed from the outer loop and the current shaft speed, and outputs a solenoid duty cycle to bleed off more or less pressure from the wastegate actuator.

I wonder if the outer loop even needs feedback. It can take the setpoint and look up a target shaft speed based on the compressor map for the turbo. Given a target pressure ratio, if you can get estimated kg/s air flow from the VE table calculation, you can determine what the shaft speed should be. Then you can use an inner PID loop to control shaft speed error.

I'm not sure what this buys you compared to the conventional approach, but it'd be fun to play with. Most of it could be simulated offline once the compressor speed data was available in the main data stream.
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Old 05-14-2010, 10:05 PM   #27
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Quote:
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...
The company that I know of that has done the most testing for this is Full-Race and Jeff Evans. In the end, it's all about using an exhaust manifold with a higher volume without going extreme and killing midrange power(unless that is your desire).
I don't think it's simply a matter of runner sizing. It's more a matter of turbo selection. And such a selection would mean a turbo that would be laggy on the street.

Have you seen any data of such a 1:1 turbo setup and its spoolup?
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Old 05-14-2010, 10:14 PM   #28
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kday,

you'd still need an outer loop because external factors (e.g. ambient temp) would cause a loss of 1:1 correspondence between shaft speed and boost (at a given RPM and say throttle position).

What it would definitely buy you is reduced overshoot due to the phase lag between shaft speed and final boost caused by having to pressurize the intercooler piping.
It probably takes ~100 ms to pressurize the piping from 0 to 15 psi when the turbo is spinning at the boost target's shaft speed.

However I think the more significant phase lag is between duty cycle, and wastegate position. It takes time to fill up or empty that wastegate can. Maybe the inner loop can be the wastegate position lol.
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