My 421 is just about done. Right now I have the hawks 1 3/4 long tubes with 2 1/2 collector. Im thinking the collector is about 1/2 to small. Been reading alot into primary size and it seems the 1 3/4 inch should be fine considering my rpm redline is in the lower 6000s. They do offer the same header with a 3 inch collector. Hp should be around 600 crank. Nitrous is an option. Thanks

 

hooker makes them with 3" outlets you shouldn't have 2 1/2 on those 1 3/4 that's gonna be the choke point on your exhaust

 

You need 3".

Could sell urs and buy new set. Or cut collectors off and weld new ones on that have 3".

 

Have doug's long tube 1.75" and 3" collectors ceramic coated on mine. From jegs I believe

 

Dougs make them for our years?

 

Yes they do

 

my guess would be that 1-3/4 primary tubes will be to small for that size engine to start with. If or when you add nitrous, it will get much worse. try a stepped header 1-7/8-2.0 primary with at least a 3" collector. Oh bring lots of $$ for headers if you decide to change up in size.