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3.
An 80's Nissan, made from the front of a Silvia S13 and the ass end of a 180SX. This was done because when someone fucked up the front of their 180SX, Silvia S13 fronts were lighter and cheaper. When this style began to grow popular, Nissan factory produced it, but only for a few years.
Guy: "Hey, I like your Sil'Eighty. You make it?"
Jim: "Yea I had a nasty reck a few weeks back, replaced the front."
by Guy, P August 08, 2007
 
1.
Sileighty is a Nissan 180SX (240sx in the states) with a Nissan Silvia's headlights and front bumper installed, hence the 'Sil' in front and the 'eighty' rear. The car is popular because it's less costly to replace a Silvia's front than a 180SX's front.
Dam that sileighty's front looks hot drifting around those corners.
by 95S14 January 07, 2006
 
2.
A Nissan Car that is the hatchback 240SX in the US (180SX in Japan) with a Silvia front clip installed on the front of the car, it was made bacause in japan the 180sx front ends are to high in cost to replace after a crash, but the Silvia front clips are cheaper and easier to find.

Hints the Name Sil-Eighty, Sil fron Silvia and Eighty from 180sx

Also note that Nissan made 500 offical Sil-Eightys.
That Sil-Eighty just flew by us like we are sitting still!
by Kyle January 11, 2004