Keep the 528 stock, buy the 535 to go faster. I HAVE 2 OPTIONS I CAN BUY A 535 WITH A 3.5 ALREADY IN IT AND REPLACE THE CYLINDER HEAD FOR 300 ITS GOT RECARO SEATS ALL KINDA SUSPENSION UPGRADES BUT WITH A 4 SPEED MANUAL TRANNY OR I HAVE MY 80 528I THATS BONE STOCK WITH ALL KINDA NEW PARTS IN VERY GOOD RUNNING CONDITION SO WHAT DO U THINK I CAN DO TO MY 528 CUS I THINK I AM GONNA BUY MY ONE 535 FOR 300 AND FIX IT