mdynna and myself have created house rules for vehicle modification. They can be viewed on my website. We haven't finished the tests needed to put in the modifications but those should be done soon.

http://www.geocities.com/tbrminsanity/
under my shadowrun page
under vehicle modification rules

Enjoy

Seems fair enough. Have you considered other things like NOS? Only one of my runners is keen to get something like.

We have also house ruled for cosmetic modifications, fast and the furious style, 1,000 for each level of cosmetics (spoiler, vents, neon etc.) each level give +1 social tests in the right circles. (-1 per level for executive type situations of course).

I should also clarify that the symbol there means "Base Vechicle Cost." Also, these are only a start to the vehicle modification rules. We will be continuing with converting the additional accessories (like NOS) that can be purchased in the Rigger book. As well, we have rules sketched out for adding weapon mounts, and we are working on converting the much-loved "big V" vehicle weapons (Vindicator, Vanquisher, Vigilant, and Victory)

The idea of these rules is alos a blanket modification. So a boost to your top end acceleration could very well be a nitro system installed. That is up to the player to describ what was done.