<?php
$str = 'SI_NurbsCurve Edge1 {
        1,
        0,
        0,
        4,
        0,0,1,1,
        2,
        870.243,1229.35,143.395,1
        927.537,1323.53,103.842,1
        }

        SI_NurbsCurve Edge2 {
        1,
        0,
        0,
        4,
        0,0,1,1,
        2,
        899.54,1217.88,116.255,1
        870.243,1229.35,143.395,1
        }';
$reg = '#(\}\s+)?SI_NurbsCurve Edge[0-9]* \{
        1,
        0,
        0,
        4,
        0,0,1,1,
        2,#';  
$rep=""; 
$str=preg_replace($reg,$rep,$str);

var_dump($str);

string(160) "
        870.243,1229.35,143.395,1
        927.537,1323.53,103.842,1
        
        899.54,1217.88,116.255,1
        870.243,1229.35,143.395,1
        }"