You can just do this to them.

Stock 420's= 67mph

Mild Thunder modified 420's= 90mph.

Great engines! I did this to mine..[ATTACH=CONFIG]531117[/ATTACH]

NICE! Tell me...what all did you do? Dyno test? I was "told" mine were 496's by the previous owner....of course, he wont return calls or e-mail Same boat I have! Mine is the red/black version

Good looking mill, Joe!

if i remember correctly the only thing 420 on your engines would be the block&crank.

anychance you could have the 496 425hp motor?? which would be a completely different animal. are you carbed or fuel injection??

I don't think so? These have rec port iron heads, 800 Holley, say 420 on the finned alum valve covers. Will have to tear into one to figure it out, or "try" to get the Build Sheet from CK Motorsports, the port motor has NEW Crank, etc....If they are indeed just 454's...they WILL go back in as 496! Hyd Roller cam, etc...

I did a roller cam and aluminum heads, there's a nice write up in the formula section. I documented everything with photos along the way so might be beneficial for you to check that out.

AWESOME! Im new here...Formula Section?

Dummy me....just had to scroll down farther...lol What is the Title of the Thread? would LOVE to read it!