Turbo motor continues to build Boost wile Lifting

[whittlebeast]

We are in process of tuning a Turbo Rotary motor installed in a Miata. This car is built for autocross and road racing so throttle response and control is very important. The install has fairly large ITBs. Here is a pic of the install. We are just getting started on the tuning of the motor.

http://www.nbs-stl.com/miata/MiataMotor2013_01.jpg

The problem we are having is that when on boost, it is requiring the driver to pull the throttle all the way back to about 10% throttle to get the motor to stop accelerating (hard). Has anyone else run into this issue and have they found a way to make the throttle control more linear. This motor will build near full boost any time the throttle is at about 16% or more. I realize that going to throttle angle based boost control would at best get the boost back to "on the spring". I think we need to get even farther out of the out of the power band to control this motor.

http://www.nbs-stl.com/miata/AccelWhenLifting.png

We ran into this on a previous install but that was a drag car. In that case, we found it difficult for the driver to control wheelies.

Andy

[duxthe1]

I have similar looking datalogs because I have a small turbo (.42 /.48) on a 3.0L engine. Anything over 20% throttle and I'm in boost. I would think you'd have to go to a bigger turbine or possibly intergrate some sort of progressive throttle linkage to lessen this behavior.

EDIT: Another thing that may help is adjusting the blow off valve to pop off sooner/easier (assuming it is adjustable)

[Peter Florance]

When you say 10% throttle, is that based on throttle sensor or driver's foot?

[whittlebeast]

The throttle is about 1 to 1. There is no rising rate bell crank involved.

[mUnky]

Seems really strange... O_O

Are you sure it's not something simple like the throttle springs being too soft?

[HidRo]

I had something like this when I used Closed Loop Boost control. For some reason, sometimes it would spike turbo pressure even without being at WOT.

[Peter Florance]

The throttle is about 1 to 1. There is no rising rate bell crank involved.

15% could be 40% power or more on some setups. Especially if the ITB's are really big.

[whittlebeast]

Just thinking out loud here...

Would it be possible to have a screen created in TS

We could call this Electronic Horsepower Modulation EHM or possibly Electronic Acceleration Override EAO. What to do when TPSdot is negative by some adjustable degree and Rpmdot is positive by some degree. Clearly, what to do when the driver has had enough but the motor wants to keep developing more power.

Override Waist Gate PWM Note that this is only capable of taking the HP down to the spring. I may have too much HP even if we go all the way back to NA.
Dump the blow off valve. It may take a valve like we use for boost control and a vacuum accumulator to do this. I already have a boost accumulator in the car. I may have too much HP even if we go all the way back to NA.
Activate rev limiter fuel cut
Activate rev limiter ignition cut
Pull timing X degrees

All based on the dagree of the problem

Andy

[Peter Florance]

Just thinking out loud here...

Would it be possible to have a screen created in TS

We could call this Electronic Horsepower Modulation EHM or possibly Electronic Acceleration Override EAO. What to do when TPSdot is negative by some adjustable degree and Rpmdot is positive by some degree. Clearly, what to do when the driver has had enough but the motor wants to keep developing more power.

1 Override Waist Gate PWM Note that this is only capable of taking the HP down to the spring. I may have too much HP even if we go all the way back to NA.
2 Dump the blow off valve. It may take a valve like we use for boost control and a vacuum accumulator to do this. I already have a boost accumulator in the car. I may have too much HP even if we go all the way back to NA.
3 Activate rev limiter fuel cut
4 Activate rev limiter ignition cut
5 Pull timing X degrees

All based on the dagree of the problem

Andy

If you were using Closed Loop Boost Control (CLBC), #1 would be handled by that. Also try a smaller spring combined with CLBC.

[whittlebeast]

Even with a 3 lb spring, this motor would still be making like 250 HP. The BOV dump may get me down to 225 HP.

The car I was last messing with this issue was pulling 1000 HP. When the situation came up , the owner scratched the rear bumper real bad.

Andy

[Peter Florance]

Even with a 3 lb spring, this motor would still be making like 250 HP. The BOV dump may get me down to 225 HP.

The car I was last messing with this issue was pulling 1000 HP. When the situation came up , the owner scratched the rear bumper real bad.

Andy

sounds like throttles are way too big on this car if it's making that much power at 15%

Check graph on Page 6

http://www.vanderbilt.edu/dces/PDF/pape ... _final.pdf

[dieselgeek]

Sounds like the exhaust turbine is way way too small?

[whittlebeast]

The turbo is about 30" down stream of the exhaust port. That would be very challenging to change at this point.

In MLV, this formula finds when he pressure in the intake needs to be blown off fairly well.

[Field.MAP]>110 && ([TPS]-[TPS-3])/([Field.Time]-[Time-3]) <(-125) && ([Field.RPM]-[RPM-3])/([Field.Time]-[Time-3]) >75?1:0

I have the parts collected to try this real soon. A friend of mine that builds drift cars told me that this is a fairly common problem.

Andy

[whittlebeast]

Here is what I am going to try for creating a Pressure Dump / BOV. The arrow looking thing in the hose is a one way valve. The large box in the center on the drawing is a vacuum accumulator. It recharges on downshifts when the intake is at a huge vacuum.

The valve will be triggered only when the RPMdot is positive and the TPSdot is fairly negative. I will use the MS3 on/off trick.



Andy

[whittlebeast]

This is how the Boost controller is set up right now. It is working just fine as it was designed to develop as much boost as possible as until the boost limit is reached.

[jsmcortina]

As Peter posted, I really think you need to use the actual closed loop boost control. That would start pulling boost on the throttle lift - your home-brewed setup is still trying to build boost regardless.

James

[Peter Florance]

As Peter posted, I really think you need to use the actual closed loop boost control. That would start pulling boost on the throttle lift - your home-brewed setup is still trying to build boost regardless.

James

MS3 boost control works very well. That coupled with better throttle ratio (progressive linkage) would probably make a huge difference in driveability of this car.

[muythaibxr]

I agree with everyone else... just use closed loop boost control and have it pull boost linearly with throttle position.

Ken

[whittlebeast]

Does anyone have a log off an autrocross/hillclimb/drift car running a turbo motor on closed loop boost control? Something that has enough power to haze/fry the tires at will. I am curious to see the data logs from one on course.

The logs coming of our car running last years setup (about 300 HP) generally only runs 4 power requests. No power (braking), about 90 KPA (hold the car at the current speed wile cornering), all you can get till the rear tires give up, and back pedaling to regain traction. You almost never need 90 percent of the available power. Things are simply happening way too quick.

Most power applications happen in under 2 sec and the RPM will climb about 2000 to 3000 RPM in this 2 sec from about 4500 to 6500 RPM. The MAP will go from about 100 KPA at the exit of the corner to about 200 KPA in this 2 sec. The trick is saving your life and the run when the tires blow off.

Keep in mind we also run in the rain with the same setup.

Andy

[Peter Florance]

Does anyone have a log off an autrocross/hillclimb/drift car running a turbo motor on closed loop boost control?

Andy

No I don't, but you could. Just turn on closed loop control.

I can send you some settings to try.