What does APC stand
for and what does it do?
APC is an acronym for Automatic Performance Control. The APC system is used by Saab (Also Swedish) on all of their turbo cars since '83. The APC adjusts the charge air pressure automatically to the maximum possible for the grade of fuel used at any given time. Fuel available to the pumps has been quite irregular in quality for some time now. The APC system enables the engine to achieve ideal performance regardless of the grade of fuel in the tank.
Under heavy engine loads, knocking and pinging can occur. Knocking is caused by pre-ignition of the air fuel mixture. Pre-ignition causes high heat and stress loads on an engine which can cause serious damage if allowed to continue. There is another type of knocking that occurs at high engine speeds which is inaudible to the human ear. This inaudible knocking is the most damaging to the engine.
In most cases, manufacturers (Volvo included) restrict the performance to allow for fuel quality variations. Unfortunately, not all of the full energy potential can be extracted from the fuel, and is lost in the form of heat. The APC system is a mostly transistorized system with only one moving part. This makes the system very reliable and unlikely to give any trouble.
After initial installation, the performance gain was quite noticeable. I hooked up a graduated pressure gauge to get some exact numbers. The stock boost setting on the '87 740 is supposed to be 10 psi, but is often lower than that in real life, in my case it was about 8 psi which corresponds to about 2:30 on the stock Volvo gauge.
The needle on the stock gauge is currently reading right to the end of the gauge on the dash which I confirmed to be 14psi with an accurate graduated gauge. This is after adjusting the maximum boost setting in the control unit. The turbo also spools up faster to the max pressure. After a year of running with the APC system, I have seen a bit of what I will call "overswing" to 16 psi on cold mornings, I suspect that this can be reduced by shortening the lengths of the hoses on the solenoid valve. The APC also has a minor annoyance which I am trying to find a solution to -- Boost taper. When the APC reaches it's set boost level, it starts to taper back by 1.5 to 2 psi based on RPM and other factors. Supposedly most of the modified APC control units sold by the major Saab tuners have dealt with this problem although I have no empirical evidence to back this up.
According to the brochure for Volvo's turbo + kit, 14 psi should be an increase in horsepower from 160hp to 190hp with 207lb/ft of torque. This is a very nice increase in power with no reduction in normal drivability. I recently gained a ton of extra power using a big bore throttle body, rising rate fuel pressure regulator, 3" mandrel bent exhaust (turbo to tail), VX3 cam and adjustable cam gear (all parts were purchased from Maximum Vehicle Performance), Some day, I'll have enough money to install a hybrid T-03/T-04 turbo.
Where do I get it and How much
does it cost?
The parts for this system can be purchased from a wrecking yard. I recommend U-Pull-It type yards that aren't familiar with Saabs since they will have the best prices. Expect to pay $25-$200 for all of the parts depending on your location and what sort of wrecking yards are available to you (It's probably not worth it to spend more than $200). The author of the web site does not sell parts for this project. It's up to you. You will find a list of parts needed on this web site as well as a complete description of what the parts do and what they look like as well as where they are located on the donor car.
How difficult is it to install
an APC system?
This not a modification for the novice. If you tend to fix things with epoxy and bailing wire, forget it, you will already have your hands full just trying to keep you car on the road. I would only recommend this modification for someone who has a considerable knowledge of electrical and mechanical concepts as well as the ability to execute quality repair work. I would also expect that you have done your homework and understand how engines and turbos work. I highly recommend you read the book "Maximum Boost" by Corky Bell before considering any increase in performance on a turbocharged engine.