Specifically in a 1983 Spider, I'd go with headers - hands-down! The manifold of the series 3 is purposely restrictive, and this will have a positive effect on performance and power efficiency. If the car still has the OEM cat, I would also suggest that when the time comes (that could very well be now) you replace it with a modern unit.
I would also encourage you to do a search... There are several threads about perfromance covering this subject, and some are pretty long, so take your time. For starters, and rather than trying to repeat some of what I've written, I'll point you to this post and this thread.
Best regards,
I would also encourage you to do a search... There are several threads about perfromance covering this subject, and some are pretty long, so take your time. For starters, and rather than trying to repeat some of what I've written, I'll point you to this post and this thread.
Best regards,