Afterburners in FSDS1 are done with actual parts, rather than effects.
Several parts are made (the afterburner shock diamonds), with special "tags" that mean they only appear within a certain engine RPM range.
For example, between 0RPM and 10,000RPM, no shock diamonds can be seen.
Between 10,001 RPM and 15,000 RPM a small shock diamond appears.
Between 15,001 RPM and 20,000 RPM a larger shock diamond appears.
And so on. You simply keep adding shock diamonds until there is a smooth range of motion.
It can be quite a pain to figure out what's going on, so I have uploaded an example I did for you. You can get it here:
http://uk.geocities.com/happymulletuk/SR71_BURNERS.ZIP Right-click and "save target as".
Of course - you could just do this the way everyone else does it, and use ".fx" files.
Ric B.