I don't think they would nessacarily run bad on a smaller engine than 600CID... it just might not run to it's max potential. Sort of like how I have heads that flow 340 CFM on a 410 horse 392, yes I could easily bump it up to 440 CID a couple more points of compression a huge cam and make 700 HP but it runs just fine on a lesser engine. I really don't think my engine will run any better with a 200 CFM head even though that's all you need to make 410HP.