• General Notes on Boost Controllers

• Boost Controllers Part I (The Risks)

• Boost Controllers Part II (The Rewards)

• Boost Controllers Part III (More Concerns)

• Boost Controllers Part IV (The Greddy Profec B)

General Notes on Boost Controllers:

     Boost controllers, long popular with Japanese-auto performance enthusiasts, are starting to find a following with UrS enthusiasts, as well.  Boost controllers take the place of the Wastegate Frequency Valve (WGFV), and control the wastegate, and therefore, the boost level of the turbo.

     There is some debate, as to the safety of using boost controllers, because their use circumvents the safety features built into the ECU, that are designed to protect the engine in cases of overboost and knocking.

     The best information on boost controllers, as they pertain to UrS-Cars, can be found here:

HKS EVC IV Boost Controller Installation by Geoff Jenkins
A’pexi AVC-R Boost Controller Installation by Kevin Pearson

Boost Controllers Part I (The Risks)

Since the boost controller thread started, I've received a large number of questions as to the safety and effectivenes of these devices. In order to answer some of these, I've put together two posts (the other should be going out simultaneously) which reflect my interpretation and opinions of the risks and returns which these devices offer.

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How Risky Is It?
================

Three significant concerns have been raised over the use of boost controllers on our cars (though they may not be _real_ problems, or indeed there may be other issues which have not yet been brought up). The issues are Altitude, Heat and the ECU's response to Knocking.

Altitude:
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Problem: At higher altitudes, where the air pressure is lower, there is a risk that a "dumb" boost controller will attempt to make up for the lack of ambient air pressure by piling on the boost (i.e. it will try to maintain a pressure reading without considering the drop in _outside_ pressure). This, naturally, will lead to risks of running unacceptably high boost, or of overspinning the turbo.

Resolution: The straight HKS "EVC IV" _doesn't_ deal with this issue. The "EVC IV atm" allegedly _will_, but I am informed that it is not yet on sale. If I was living in CO, I suspect I would wait for it to be available. Here in Michigan, it doesn't seem like a worry.

Heat:
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Problem: If you're running high boost under high load in a hot climate, the air intake temperature may become "too high" (note: this is a value which remains unknown at this time), at which point the ECU will attempt to dial back the boost. The EVC, however, will ignore this and keep responding to the driver's right foot. The consequences of overly hot air entering the engine include detonation, with all its expensive consequences.

Resolution: So far, _in_my_environment_ and _with_my_driving_style_ and having maintained a relatively low boost level (+ 1.25 bar), this does not appear to be a problem. The car has been taken to the track (prior to the EVC) and after 45 minutes of lapping in 80+ degree weather, boost had not been perceptibly reduced by the conventional ECU. That would indicate that the "too high" temperature is _very_ high.

Further methods of clarifying this could involve an intercooler-exit air sensor, warning the driver to lift off when the temperature exceeded X degrees. IMO, this is either: (a) not very relevant, if the "X" temperature is drastically high or (b) a very sensible mod for all high-boost cars, if the "X" temperature is easily reached.

An alternative might perhaps involve a larger intercooler, hence delivering cooler air for any given boost level. My own solution is somewhat simpler. Because of the EVC's effect on the car's reflexes, a boost level which was previously merely "OK" now supplies ample response, so I simply keep the boost lower than I otherwise would have wanted. Lower boost -> lower heat,
all things being equal.

Knocking:
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Problem: When the engine knocks, the ECU attempts to both retard timing and cut the boost. The boost cutting signal will be ignored by the EVC. If the driver attempts to maintain full throttle with the turbo delivering high boost while the engine is fighting against knocking, at the very least, temperatures will climb dramatically.

Resolution: Currently, there seems to no technical fix to this. (a) You have to use good gas and (b) if you hear knocking, back off.

In the longer term, there are two additional answers. In the near future, a rework of the ECU code may be available (according to Scott Mo.) which would allow the "Check Engine" light to come on as a warning that the ECU was attempting to back off. Secondly, it _should_ be possible to isolate the signal which the ECU sends to the WGFV to ask it to open up the wastegate in
an emergency, and use that signal to switch the EVC automatically from its "high" boost mode to "low" boost. A driver who ignored such warnings would have nobody but himself to blame.

For myself, I'm _concerned_ but not worried about this issue. However, I probably _will_ obtain the reworked ECU code when it's available, and _would_ be interested in the signal-switching solution, though it lies far beyond my technical scope to implement.

So... How Risky Is It?
======================

If you encounter situations where the ECU would be attempting to dial back the boost: High Altitude, Overheating, Knocking, then the EVC's failure to adjust will pose a risk. To answer Frank Amoroso's original question: No, it does not retain all of the factory safeguards.

If you use good gas, if you don't reach the "magic temperature" and if you live in the flatlands, the odds are that you aren't going to encounter enough risky situations to make it a serious threat, but that's ONLY if you don't run excessive boost, and even then, a _somewhat_ higher risk potential will now exist.

To my mind, the moment I start to tweak a car at all, I have to consider the balance of risk vs. reward (which I'll come to in an accompanying post). Given my driving and my estimation of the risks, I view the rewards to be more than sufficient to justify installing an EVC in my car.

Going up the Rockies in a fully laden car at max boost on a hot day with dodgy gas, the EVC will add to the risk, but there's no good in pretending that under those circumstances the EVC is responsible for all of the risks that are present.

Geoff Jenkins

Boost Controllers Part II (The Rewards)

After the recent tome on risks, I'll keep this brief. A few people asked about the effects of the EVC on performance. To reiterate from the first post, the key qualitative benefits are:

- Much quicker response on-boost
- Better sustained power at the high end
- Controllability of boost and overboost

In more quantitative terms, Graydon and I have run a number of tests in the car with a GTechPro, yielding the following data:

Note:
A) All of launches of my car were at 3000-3500 rpm, near sea level, temperatures c. 40-45 F. What improvements/losses would occur with a different technique/different environment are speculative.

B) I don't want to get into a bragging match, so if you disbelieve the data, that's your prerogative. All of the post-EVC measurements were taken with a second driver either at the wheel or in the car with me.
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0-60:

S4 (Stock): 6.2 sec
My S4 (EVC, K&N, Scorpion exhaust): 5.2 sec

*** Notes:

1) prior to the EVC, my best 0-60s for this car with a TAP chip, WG spring, K&N and exhaust were about 5.6 sec.
2) by comparison, in European Car (March 1998), a 360 HP Hoppen S6 claimed 0-60 in 4.9 sec.
=====================

1/4 Mile:

S4 (Stock): 14.9 @ 94
My S4: 14.09 @ 102.5

*** Note:

1) previous best runs with my car (pre-EVC) resulted in times in the high 14s or low 15s (blame poor technique on my part) and trap speeds of c. 99 mph.
=====================

Power:

Stock: 227 HP @ engine
Pre-EVC: c.250 HP @ wheels
w/. EVC: c.270 HP @ wheels w/. + 1.25 bar boost

*** Notes:

1) Later, I will test what HP figures I get if I dial back the boost incrementally
2) If there's any interest, I may videotape the GTechPro and tach simultaneously, to get a pseudo power curve.

Geoff Jenkins

Boost Controllers Part III (More Concerns)

A couple of thoughts regarding the use of a separate boost controller and the factory safeguards.

Here is some info from the Service Training Book. WSP 521-218-00 "Motronic Engine Management System for the Audi S4 and the 4.2 liter Audi V8"

Regarding the air temp sensor. "The  temperature signal is used to adjust injection quantity, ignition timing, knock regulation and charge pressure control. The ignition timing adapts to the current intake air temperature. If the intake air temperature exceeds a predetermined level, the charge pressure is reduced to prevent detonation."

Question: How will the HKS EVC know when the intake air temp is too high and reduce the boost pressure?

The other area of concern is the Knock Sensor information:

"Signals from the knock sensors are used by the Motronic control module for cylinder selective knock control. The ignition timing of an individual cylinder can be retarded if knock is detected. If knock continues, a richer fuel mixture will be used and the charge pressure is reduced."

Question 2:
How will the HKS EVC boost controller know the engine is knocking so it can reduce the boost pressure?

Most pinging can NOT be heard by the driver until it gets pretty bad. If the timing is retarded by the Motronic system but the boost level is maintained by the HKS EVC, the exhaust temperature will climb.

The Motronic system also has a separate altitude sensor to reduce boost pressure above 3200 feet to prevent over spinning the turbo (assuming stock K24). If the HKS EVC atm can also do this, that is a plus.

It would interesting to do some testing on the stock Waste Gate solenoid (freq valve) and see how well it can hold the waste gate closed versus using another solenoid (like the HKS unit) which then could be controlled by the Motronic system. If it were my car I would try this approach instead of using an expensive boost controller that has no idea if the engine is knocking or what the air temp inside the manifold is.

The Waste Gate spring tension can also be increased a little to help keep the WG closed but IMHO , you don't want to over ride the Motronic's ability to reduce the boost to 1.5-1.6 bar if a problem occurs.

If you decide to use the RS2 injectors, the Motronic ECU should be using fuel maps that were designed for these higher flowing injectors. During light cruise the O2 sensor would be able to tweak the mixture slightly and adapt to these new injectors, but at mid to full throttle I would be concerned that the stock ECU would provide too much fuel.

Scott Mockry
SJM Auto-Technik

Boost Controllers Part IV (The Greddy Profec B)

Geoff,

    Excellent post concerning the boost controllers. I was at Steamboat again this weekend, this time with the NW quattro club so I couldn't write of my experience to the list with the Greddy Profec B boost controller in my modified 10v turbo motor.

     Let me first clarify a few things regarding my decision for the boost controller. With any of the modified computers that I have run before (TAP, IA, Home brew) I was consistently getting boost spikes which, depending on outside temps, would cause pinging (pre-detonation) at anything above 15psi boost. Without a trained ear, the ping was barely audible, but if you didn't get your right foot out of it pretty quick like, you "may" be counting the seconds before you're looking at a rebuild. I was also running a massive wastegate spring to get quicker spoolup. This made me feel uncomfortable and since I have just had my motor rebuilt for the second time in 5000 miles, I wanted a few safeguards to prolong the longevity/reliability of the new motor, hence my decision.

     A few of the mods to the new motor include: Rebuild from the bottom up including a modified baffled S4 oil pan, 200q flywheel, adjustable cam gear, 268* camshaft, port and polish head and matched port intake manifold, Dialynx exhaust manifold-already larger ports, fuel mods, k-24 turbo, bypass valve setup, cone filter conversion, 2 5/8" Stromung exhaust (similar to Scorpion) and no cat. This all entailed quite a bit of readjustment of the fuel system but once we got it, the car runs really well.

     Just as Geoff stated, my Greddy Profec B spec replaces the wastegate frequency valve with a much quicker actuator that must be mounted somewhere cool. Yeah right, find me a cool place in any Audi turbo bay. So we went with a mount below the black plenum that covers the heater box and some A/C components. I mounted the boost controller itself just to the left of the steering wheel and right above your left knee. It has four main knobs which include a low boost, high boost, balance and select knob. The balance knob was the only one that took some playing with to get it right but I still don't know if it makes a whole lot of difference. Anyway, what this controller does is eliminates the oem WGFV and pulls boost only from the bottom of the wastegate itself now. The boost response is much quicker (also due to the k-24) and is dead consistent with your pre-set boost limits. I can now pull 8-10 psi in third gear at 2000rpms and rapidly see 16 psi by 3100rpms. Another plus is the boost attainable in 1st and 2nd gear. The pull is downright fun off the line now where in the past, I had to really rev the motor to get any kind of jump. So I too feel that the boost comes on sooner, feels stronger and stays much more consistent at the limit. Not having to lift your right foot and then get back on the gas once ping occurs is very nice.

     I've now set my high boost at 19psi which most of the time works well with no ping except on warm/hot days. If this occurs, I just dial it back to 15-16 psi. The low boost is set at 10 psi. The balance knob has what is labeled a "mild" and a "sharp" side. I have left the knob in the middle or balanced between these two areas. It is supposed to be adjusted to the mild side when unstable or hunching boost occurs also known as falling off. The sharp side is for when over-boosting occurs. Turn the knob toward the mild side if over-boosting does occur. I have found that the middle selector works best for my application.

     Bottom line, I think it's a very cost effective mod for my peace of mind.

Chad Clark '87 5ktq