I just had a b18a1 put in my car with a b18c1 gsr head i know the gsr redlines at 8100 and the stock b18a1 redlines at 6500 but if you put the gsr head on the b18a1 does the 6500 redline go up or does it still redline at 6500 if so that sucks cuz my vtec barley kicks in at 4500

 

Get it tuned and find out where power falls, redline there. 4500 is way to low for your crossover that's why it feels weak

 

You should have installed arp rod bolts and headstuds when you rebuilt it. That is almost the golden rule when building a reliable ls vtec setup. I wouldn't take it past 7500-8000 as it sits just to be on the safe side.