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For both the 16V and 8V classic turbos, Saab sets the timing maps based on low octane gas, from light load / high vacuum conditions, through initiation of boost at around 1 - 3 psi. The timing is adjusted through the distributor by either a module or internal mechanism. This strategy is too much retard for high octane gas use. Then, at 1 - 3 psi, Saab dumps in an extra 5 degrees of retard all at once, now excessive retard for even low octane, and way too much retard for high octane. This is what I call the max slug point. This sudden step change in timing reduces power at that point and creates a flat spot in the power curve, especially for the 8V-T.

As boost then rises through the 'basic boost' level ( 4-6 psi, based on model), the timing is about right for low octane, but still too retarded for high octane gas. Finally, from a few psi higher than 'basic' boost, up to max stock boost, timing is NOT retarded enough for low octane and about right for high octane. This is the upper pressure range where the knock sensor can cut back boost that is likely to occur with low octane.


So for those filling up with high octane and looking for max performance from high stock or tweaked boost levels, timing is too retarded up through about 2/3 of max stock boost. Retard is most excessive at around 1-3 psi. This makes response/power less than optimized with high octane. But if you are dipping well into the red, more retard may be needed than the stock system can provide.

For a strict diet of high octane gas, what is needed is:

1) more advance up through the 2/3 max stock boost point
2) about stock timing from the 2/3 point through to max stock boost
3) if boost is tweaked much higher vs stock, a little more max retard
4) more gradual application of 'boost retard'.

The stock retard actuator, at the distributor, can be 'bent' to increase the retard kick at 2-3 psi from 5 to up to 9 degrees or so. This allows some of these issues to be solved, but not all. And it makes the flat spot at 2-3 psi (and a bit above) worse. It is very difficult to change it to bring retard in more gradually.


The BTM reads boost and after 1 psi to settle things, it retards timing in proportion to boost, based on an adjustable gain knob that can be installed near the driver (in my glove box). If set at .5, it retards timing by 2 deg at 5 psi [ (5-1)x.5=2 ], 4 deg at 9 psi, 6 deg at 13 psi, and so on to a max of 15 deg retard.

I made plots of boost vs retard, for several settings in the .3 to .8 range, up to 13 psi, and it was exactly as MSD predicted. I have had a BTM in my 88T for over 8 years..................


1. Adjust actuator yourself for increased retard.

This will give you more boost at the top end, but this option will increase the hole at very low boost levels. This is because the actuator will activate at 1 psi of boost and will retard the timing way back.
2. Install AID module for the distributor.

I'm not sure you can still buy these, but they can probably be found on Ebay. It basically is a mechanical unit that works similar to the MSD BTM. The main drawback is that it is mechanical and is not 100% accurate like the MSD.

3. Install MSD BTM.

This is one of the best options for the C900. You will need to instal a pressure relief valve on the vacuum line going to the actuator and a pressure relief valve on the BTM. The first valve prevent the stock actuator from retarding the timing, and the second one sets a max retard for the BTM unit. This option gives you a smooth retard of timing up to a set max.

4. Aftermarket fuel and ignition ECU

This is obviously for the super serious about engine power. The stock system can only go so far with band-aids, and this is the only way out!
There are many aftermarket ECU options out there and plenty have been installed into C900's.


The stock retard is accomplished by the actuator screwed to the side of the distributor. It also controls vacuum advance. Suck on the nipple :) to be sure it does not leak. Remove the 2 screws and wiggle the actuator toward the cap. The arm that passes into the side of the dist'r has a hole in the end of it, that must be eased off a pin inside (the pin is on a plate that rotates a bit about the central distributor shaft ). Some may find it easiest to remove the distributor from the engine, esp the 8V-T's.

Notice the arm has a notch, where a rivited cylinder 'stop' on the bracket limits the arm motion. On one side of this stop is a gap of about .04" or so. This is the movement for about 5 deg retard at 2 psi boost.

For option #1 above you need to increase the amount of gap to about 0.08". This will give you about 10 deg of retard.


Another feature of the MSD is that it has a built in redline limiter. With the 6000 RPM chip installed, the MSD will avoid the stock 6200 rpm, windsheild in your face, fuel cutout. The stock cutout is very bad for the engine as it causes massive lean out. This can cook the piston rings with the amount of heat a lean out creates! The MSD cutout at 6,000 rpm will simply only fire 3 cylinders to keep the revs down and you will be able to stay at redline all day without eating the windshield. It chooses a different cylinder each time so that it will burn the fuel in the next cycle.


Before you install the unit you must first set the unit to 4 cylinders and insert the rpm limiter chip. You just pick the RPM you want and plug it into the box.

Installation is just as easy. Find a spot on the fender and screw it down. Check to make sure your hood closes properly before screwing it down! Also, do not use really long screws because your tires are down there! I think mine extrude 1/4".

I installed a T in the vacuum line going to the vacuum canister in the fender and plugged the line into the MSD.

To wire up the MSD, you intercept the stock ignition wires from the coil and connect the MSD wires back to the coil. You then hook the MSD to battery and group and fire up the car!

In the picture you can see the stock blue trigger wire being connected to the white MSD wire. The green/white striped wire is the power wire.
Then the Orange MSD wire goes to the + side of the coil and the black MSD wire goes to the minus side of the coil.
To power the MSD you run the bigger red and black wires right to the battery. As you can see I need to get better terminal connectors to the battery!

The next thing to do is to hook up the Boost Timing Master. This involves running the dial inside the car somewhere and then connecting it to the MSD. I choose to run it into the glove box.


To give full potential to the MSD. I'm using a High Vibration Blaster coil and Magnecor 8.5mm ignition wires. The reason for the high vibration coil is because MSD does not recommend the blaster 2 coil be mounted horizontally. Some kind of cooling problems. Some people have done this anyways and I have not heard anything bad.

Once the car starts up you want to set your initial timing to something like 18-20 deg BTDC.

Now you need to eliminate the stock boost retard system. The easiest way to do this is to put a bleeder valve on the vacuum line going to the distributor actuator. The bleeder valve allows the vacuum to advance the timing for good highway cruising and MPG, but doesn't allow it to retard the timing during boost. This retard is handled by the MSD.
Click here to see how to make a bleeder valve yourself.

The last addition I made to the system was to add another bleeder valve on the vacuum line going to the MSD box. I set the valve to bleed boost past 15 psi. This prevents the MSD box from retarding the timing too much. Otherwise, the MSD could reduce the timing all the way back to 0 degrees which would drastically cut power.

To see how the timing works out, I've created an excel document where you can put in different parameters and see the changes it makes in your overall engine timing.

Good luck with yours and have fun!

The total cost of the project is as follows:
MSD High Vibration Coil - $40
Magnecor 8.5 Wires - $100
MSD 6BTM - $320
2 pressure relief valves - $50

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